Underwater Welding in the North Sea

 

Underwater Welding for Offshore Operations in the North Sea: Scientific Principles, Modern Technology, Education, Field Engineering and Logistics

Technical essay | Offshore engineering, subsea construction, inspection and repair | North Sea focus | October 2026

Abstract

Underwater welding is one of the most demanding specialist activities in offshore engineering. It combines welding metallurgy, materials science, hyperbaric physics, marine construction, diving medicine, structural integrity, subsea inspection and complex offshore logistics. Its purpose is to restore, modify or construct metallic structures that are submerged in water, including pipelines, jackets, conductors, risers, piles, mooring components, subsea manifolds and other offshore installations.

For the North Sea, underwater welding has particular significance because the region contains mature oil and gas infrastructure, operating subsea production systems, offshore wind developments, interconnecting pipelines and structures exposed to severe marine conditions. These installations must remain structurally sound despite corrosion, fatigue, hydrodynamic loading, pressure cycling, accidental impact and decades of operation.

The engineering challenge is not simply to produce a weld beneath the water. It is to demonstrate that the resulting joint has the required strength, toughness, fatigue resistance, corrosion performance and reliability under the actual service conditions. A weld that appears visually acceptable may still contain hydrogen-induced cracking, lack of fusion, unacceptable porosity or other defects that threaten structural integrity.

Modern underwater welding therefore depends on a complete system of engineering controls: qualified procedures, appropriate materials, competent divers and welding personnel, reliable surface support, carefully planned diving operations, non-destructive examination, environmental monitoring, emergency preparedness and auditable quality assurance.

This essay examines the scientific foundations of underwater welding, its established and emerging technologies, the education and competence required, lessons that can reasonably be drawn from experienced offshore engineering practice, and the detailed logistical arrangements needed for safe and effective operations in the North Sea.

A critical distinction throughout the discussion is made between established industrial practice, promising research and technologies that still require project-specific qualification. The discussion is intended as an engineering and educational reference, not as a substitute for an approved welding procedure specification, diving project plan, structural assessment or site-specific safety case.

1. The North Sea offshore environment

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The North Sea is a demanding environment in which to conduct underwater welding. Its engineering constraints differ from those of a sheltered harbour, an inland fabrication basin or a controlled laboratory tank.

1.1 Environmental conditions

The North Sea is characterised by cold water, limited visibility in many locations, strong currents, tidal variation, changing wave conditions and frequent weather deterioration. Winter operations may be particularly challenging because vessel access, crane operations, diving support and emergency recovery can all be affected by sea state and weather.

Water temperature varies by location, season and depth. Temperatures of approximately 5–15°C are a useful broad planning range for many North Sea conditions, but the actual water temperature must be obtained for the worksite and planned depth. Local extremes and seasonal variation matter.

Important environmental parameters include:

• Water depth and hydrostatic pressure: determine the diving method, equipment requirements and pressure conditions affecting the weld.

• Current velocity and direction: influence diver stability, umbilical management, debris movement and the ability to maintain the required welding position.

• Visibility and turbidity: affect navigation, joint preparation, inspection and communication.

• Temperature: affects diver thermal protection, dexterity, heat transfer and post-weld cooling.

• Wave and vessel motion: affect the availability of a stable work platform, particularly for surface-supplied diving and lifting operations.

• Marine growth and corrosion products: may conceal defects, obstruct access and complicate surface preparation.

• Water chemistry: influences corrosion behaviour and may affect the local electrochemical environment during welding.

These parameters must be treated as measured engineering inputs rather than assumed conditions.

1.2 The infrastructure requiring underwater intervention

Underwater welding may be considered for several categories of offshore asset, although welding is not necessarily the preferred repair method in every case.

Offshore asset	Potential engineering application
Fixed steel platforms	Repair of selected braces, nodes, secondary steelwork and attachments
Subsea pipelines	Specially engineered repair or tie-in operations where welding is technically justified
Risers and conductors	Localised structural repairs or modifications subject to detailed assessment
Offshore wind foundations	Inspection-led repair of selected submerged steel components
Subsea manifolds and frames	Repair or modification of suitable structural members and attachments
Piles and marine structures	Repair of selected structural connections and corrosion-damaged areas
Mooring and support structures	Specialised repair where access, loading and material conditions permit

The feasibility of welding depends on the function of the component, its material, wall thickness, stress state, defect type, internal pressure, fatigue exposure and consequences of failure.

For example, welding a non-pressure-retaining support bracket is fundamentally different from welding a pressurised hydrocarbon pipeline. The latter can introduce substantial risks associated with burn-through, hydrogen cracking, ignition, fluid release and loss of containment.

Consequently, an offshore engineer must first determine whether a weld repair is necessary and permissible at all. Clamps, mechanical connectors, engineered sleeves, composite repairs and component replacement may provide safer or more reliable alternatives in some circumstances.

2. Fundamental scientific principles of underwater welding

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2.1 Electric arc formation underwater

Conventional fusion welding uses an electric arc to generate the heat required to melt the parent material and consumable electrode or filler material. Underwater welding applies the same fundamental principle, but the surrounding water changes the thermal, electrical and chemical conditions.

In shielded metal arc wet welding, an electrode is connected to an appropriate welding power source. When the electrode contacts and separates from the workpiece, an arc is established. The arc produces high temperatures that melt the electrode and local base metal, creating a molten weld pool.

The surrounding water is not a stable gas-shielding environment. Instead, the arc generates a rapidly changing cavity containing vapour, gases and reaction products. The electrode coating helps establish and stabilise the arc and contributes gases and slag that influence protection of the molten metal.

The local environment changes continuously as the electrode moves. The arc cavity expands and contracts, gas bubbles detach, water approaches the hot region and the molten metal solidifies.

This unstable environment is a major reason why underwater welding requires specialised procedures and highly controlled execution.

2.2 Hydrostatic pressure

Hydrostatic pressure increases with depth according to:

\[ P_{\mathrm{abs}}=P_{\mathrm{atm}}+\rho gh \]

where:

• \(P_{\mathrm{abs}}\) is absolute pressure at depth;

• \(P_{\mathrm{atm}}\) is atmospheric pressure at the water surface;

• \(\rho\) is the water density;

• \(g\) is gravitational acceleration;

• \(h\) is depth below the water surface.

For seawater, a useful approximation is an additional 0.1 MPa of pressure for every 10 metres of depth. At 100 metres, the absolute pressure is approximately 1.1 MPa, or about 11 bar, depending on the assumed atmospheric pressure and water density.

This pressure affects the welding process in several ways.

First, it changes the physical behaviour of gas bubbles and the arc cavity. Second, it influences gas density and the properties of the local shielding environment. Third, it changes the conditions under which heat, mass transfer and chemical reactions occur. Finally, it directly affects the diver's breathing environment and the design and operation of any hyperbaric habitat.

It is important to distinguish two situations: the pressure experienced by a wet weld in surrounding water, and the pressure experienced by a dry weld inside a habitat maintained at the pressure appropriate to its surroundings. Dry hyperbaric welding removes direct contact between the arc and the surrounding water, but it does not eliminate the influence of pressure.

2.3 Heat transfer and rapid cooling

Water has a much greater heat-transfer capacity than air. Consequently, heat is removed rapidly from the workpiece, and the weld region may cool more quickly than a comparable weld made in air.

The actual cooling rate depends on water temperature, local flow, depth, plate thickness, heat input, joint geometry, pre-existing temperature and the thermal properties of the material.

Rapid cooling can produce hard microstructures in the heat-affected zone (HAZ), particularly in susceptible steels. In some carbon and low-alloy steels, the formation of hard martensitic or other brittle microstructures can increase the risk of hydrogen-assisted cracking.

A simplified expression for arc energy per unit weld length is:

\[ E=\frac{VI}{v} \]

where \(V\) is arc voltage, \(I\) is welding current and \(v\) is travel speed. This expression gives energy per unit length when consistent units are used; effective heat input also depends on process efficiency.

The equation is useful for understanding the relationship between electrical settings and energy delivered along a weld. However, underwater welding cannot be controlled through arc energy alone. The water environment, electrode behaviour, welding position, joint configuration and pressure-dependent phenomena also matter.

Increasing heat input may reduce some cooling-related risks, but it can also cause excessive penetration, undesirable microstructures, greater distortion or other defects. Appropriate settings must therefore come from a qualified procedure rather than a universal rule.

2.4 Hydrogen and metallurgical cracking

Hydrogen-assisted cold cracking is one of the principal metallurgical concerns in wet welding of susceptible steels.

During welding, hydrogen-containing species may be generated through reactions involving moisture and the welding environment. Some hydrogen can enter the molten metal and remain dissolved in the weld metal. As the weld cools, hydrogen may diffuse into the weld metal and heat-affected zone.

Cracking risk depends on several interacting conditions:

1. A susceptible microstructure, often associated with high hardness.

2. Sufficient diffusible hydrogen.

3. Tensile stress or restraint.

4. Appropriate temperature and time conditions for crack formation.

These factors explain why a weld may initially appear sound yet develop cracks later. Immediate visual inspection alone is therefore insufficient to establish integrity.

Hydrogen control requires qualified consumables, appropriate storage and handling, controlled welding conditions, suitable joint preparation, material-specific procedure qualification and the required delayed examination where applicable.

Wet welding presents particular difficulties because the surrounding water is an inherent source of hydrogen-bearing species and a major influence on cooling. Specialized electrodes and procedures can improve performance, but they do not eliminate the need for metallurgical assessment.

2.5 Microstructure, toughness and fatigue

Underwater weld integrity must be assessed at several scales.

At the microscopic level, the weld metal and HAZ contain microstructures determined by chemistry, thermal history and cooling rate. These microstructures influence hardness, strength, ductility and fracture toughness.

At the component level, weld geometry, penetration, undercut, residual stress and defect size influence the local stress field. At the structural level, loading cycles, corrosion, vibration and wave-induced stresses determine fatigue performance.

A weld that satisfies a tensile-strength requirement may still have inadequate fracture toughness or fatigue resistance. This distinction is particularly important for North Sea structures subjected to long-term cyclic loading.

For offshore fatigue-sensitive structures, the engineering assessment should consider the applicable structural design basis, fatigue detail category, weld profile, inspection method, defect acceptance criteria and remaining service life.

2.6 Electrochemistry and corrosion

Welding modifies the surface condition, microstructure and local electrochemical behaviour of steel. After welding, the exposed area may contain weld metal, heat-affected material, residual oxides, coating damage and regions with different electrochemical properties.

In seawater, corrosion is influenced by dissolved oxygen, salinity, temperature, flow, deposits, biological activity and the electrical characteristics of the structure.

Cathodic protection may reduce corrosion on suitable submerged structures, but it must be considered as part of the overall integrity system. Welding can affect coatings and protective arrangements, while temporary electrical configurations during welding can introduce additional hazards.

For carbon-steel structures, the long-term repair strategy should address coating restoration, cathodic protection compatibility, inspection access and any material-specific corrosion mechanisms. For duplex and other corrosion-resistant alloys, material selection and welding procedure qualification become even more important because the required microstructure and corrosion performance can be sensitive to thermal history.

3. The principal types of underwater welding

The two most important categories for offshore work are wet welding and dry hyperbaric welding. They solve different engineering problems and should not be treated as interchangeable.

3.1 Wet underwater welding

tradecolleges.org

Wet welding is performed directly in the surrounding water, without a dry enclosure around the weld. The most established process is shielded metal arc welding (SMAW), also known as manual metal arc welding (MMA).

The electrode has a waterproofed flux coating. During welding, the arc creates a local gas and vapour cavity, while the flux produces shielding products and slag. The diver manipulates the electrode and controls the weld pool under conditions of restricted visibility and movement.

Advantages

• Equipment is comparatively compact and portable.

• Mobilisation can be simpler than for a large hyperbaric welding spread.

• Selected structural repairs may be completed without enclosing the entire joint in a pressure-controlled habitat.

• It can be useful for certain non-critical attachments, temporary repairs and applications specifically qualified for wet welding.

Limitations

• Rapid cooling and hydrogen uptake can make cracking control difficult.

• Arc stability and metal transfer are influenced by water depth and local conditions.

• Weld inspection and repair access can be challenging.

• The diver faces direct electrical, entanglement, thermal and environmental hazards.

• Fatigue-sensitive, fracture-critical and pressure-retaining applications require particularly careful justification and qualification.

Wet welding is not inherently incapable of producing sound welds. Research and industrial experience demonstrate that acceptable weld properties can be achieved under appropriate conditions. However, the range of acceptable applications depends on the procedure, material, weld quality requirements and service conditions. TWI discusses both the achievable quality and the limitations of the process in its technical guidance.

TWI

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3.2 Dry hyperbaric welding

maritimeoffshore.nl

Dry hyperbaric welding takes place inside a sealed habitat or chamber that excludes surrounding water from the welding zone. The habitat is maintained at a pressure compatible with the surrounding water and the operating design.

The welder or welding equipment operates within a controlled gas environment. Depending on the system, the process may be manually operated, remotely controlled or fully mechanised.

Dry welding provides better control over shielding, weld-pool behaviour and joint preparation than direct wet welding. It is therefore particularly important for critical subsea pipeline connections and other high-integrity applications.

However, a dry habitat is not a simple underwater workshop. It must withstand external pressure, maintain its gas atmosphere, control contamination, accommodate the equipment and joint geometry, and provide reliable interfaces with the surrounding structure. Habitat installation, sealing, pressure management and emergency recovery are substantial engineering tasks.

The principal benefits are improved control of weld quality, access to mechanised welding processes and the possibility of qualifying highly demanding joints. The principal disadvantages are cost, deployment complexity, dependence on specialist equipment and limitations imposed by depth, geometry and available access.

3.3 Comparison of the principal methods

Characteristic	Wet welding	Dry hyperbaric welding
Welding environment	Directly in water	Enclosed, controlled gas environment
Typical process	SMAW/MMA	Mechanised GMAW/MIG, TIG/GTAW and other qualified processes
Setup complexity	Usually lower	Usually substantially higher
Metallurgical control	More difficult	Generally better
Inspection and joint preparation	Often constrained	Better controlled within the habitat
Suitable applications	Selected qualified repairs	High-integrity repairs and subsea connections
Main constraints	Hydrogen, rapid cooling, visibility, diver exposure	Habitat integrity, pressure, gas management, equipment complexity
Suitability for critical pipelines	Exceptional and application-specific	Established technology for suitably qualified applications

The choice should be based on a formal engineering assessment rather than on depth alone. A shallow weld can still be highly critical, while a deeper intervention may be more appropriate for a remotely operated dry-welding system than for a diver.

4. Latest technology and scientific developments

The most important developments in underwater welding are not limited to new electrodes or more powerful welding machines. They include remote operation, improved process monitoring, better metallurgical modelling, automated inspection and the integration of welding into wider subsea intervention systems.

Research published in 2026 reviews advances in wet-welding heat-transfer modelling, bubble behaviour, metal deposition, microstructure prediction and machine-learning-assisted monitoring. The review also emphasises that several emerging methods still face significant technical and deployment limitations.

ScienceDirect

4.1 Remote-controlled hyperbaric welding

oedigital.com

Remote-controlled hyperbaric welding is among the most significant developments for North Sea pipeline intervention.

In this arrangement, specialised tooling and a dry habitat are deployed around the subsea joint. Welding equipment performs the joining operation, while personnel on the surface supervise the process, monitor parameters and evaluate the recorded data.

The system may integrate:

• Precision pipe-end preparation and alignment.

• Mechanised welding heads.

• Controlled delivery of filler wire and shielding gas.

• Welding-current and voltage monitoring.

• Travel-speed and position measurement.

• Habitat pressure and gas monitoring.

• Automated recording of welding parameters.

• Inspection and verification systems.

This approach reduces or eliminates the need for a diver to perform the actual welding, although divers or remotely operated vehicles may still be needed to position, connect, inspect or recover equipment.

A notable example is the Norwegian Pipeline Repair and Subsea Intervention Pool, or PRSI Pool. A paper presented at the Offshore Technology Conference in April 2025 describes remote-controlled hyperbaric welding for subsea pipeline tie-ins and repairs, including reported operational experience from four successful subsea tie-ins. The paper describes an inert, dry habitat, gas metal arc welding, engineered weld profiles and process monitoring. It also discusses ambitions to extend operating depth and qualify additional material combinations. These future ambitions should not be confused with already demonstrated capability.

OnePetro

The broader engineering significance is substantial: welding quality can be controlled through a repeatable mechanised process, with a permanent record of key parameters, rather than relying solely on manual execution under difficult conditions.

4.2 Advanced hyperbaric welding processes

Research and industrial development include several welding processes that may be used in specialised underwater or hyperbaric environments.

Gas tungsten arc welding (GTAW/TIG)

Offers precise control of the arc and filler addition. It is valuable for qualified root passes and specialised pipe-joint procedures. Its productivity and automation requirements must be evaluated for the particular joint.

Gas metal arc welding (GMAW/MIG/MAG)

Supports mechanisation, continuous wire feeding and repeatable parameter control. It is central to many remote hyperbaric welding concepts, subject to qualified shielding-gas and pressure conditions.

Flux-cored arc welding (FCAW)

Offers useful deposition characteristics and may be applicable to particular wet or controlled-environment procedures. Consumable design, gas generation, slag behaviour and depth-dependent performance require qualification.

Friction stir and other solid-state joining

These methods avoid conventional fusion of the joint and may reduce certain fusion-welding problems. Underwater deployment is constrained by tool forces, access, materials, fixture stiffness and equipment scale. They are not general-purpose replacements for subsea pipeline fusion welding.

The important point is that no welding process is universally superior. Process selection must consider the actual material, design, wall thickness, weld position, habitat conditions, required inspection and service environment.

4.3 Cold metal transfer and controlled metal deposition

Cold metal transfer (CMT) is a controlled short-circuit metal-transfer process designed to reduce heat input relative to many conventional arc-welding modes.

Research facilities in Norway have developed hyperbaric welding capabilities using CMT, alongside established TIG-based systems. SINTEF reports equipment capable of simulating pressures corresponding to substantial water depths and describes work on procedure development, qualification and pipe repairs. These laboratory pressure ratings are not, by themselves, evidence that a complete offshore welding system is qualified for deployment at those depths.

SINTEF

Potential benefits include improved control of deposition and thermal input. However, suitability for a particular offshore application still depends on mechanical properties, weld geometry, productivity and procedure qualification under the required conditions.

4.4 Artificial intelligence and digital welding records

Machine learning is attracting attention for analysing welding signals and identifying relationships between process conditions and weld quality.

Potential applications include:

• Detecting abnormal arc behaviour from current and voltage signals.

• Identifying deviations in travel speed and wire-feed behaviour.

• Analysing images of the weld region and arc cavity.

• Predicting the likelihood of particular defect types.

• Comparing production records against qualified parameter ranges.

• Supporting inspection planning through risk-based prioritisation.

A digital welding record can combine the weld identification, procedure revision, material certificates, consumable batch, recorded parameters, environmental conditions, operator information, inspection reports and final acceptance status.

Such records can improve traceability and make it easier to investigate anomalies.

Nevertheless, machine learning does not prove weld integrity by itself. An algorithm trained on a limited set of test welds may not generalise to different steel grades, depths, geometries or habitat conditions. AI-based defect prediction should therefore supplement, not replace, validated inspection and acceptance procedures.

The strongest practical use of AI is likely to be as an additional monitoring and decision-support layer within an already qualified welding system.

4.5 Underwater robotics, ROVs and automated inspection

geomatics-expert.com

Remotely operated vehicles (ROVs) are increasingly important to underwater welding operations, even when they do not perform the weld themselves.

ROVs can support pre-job surveys, confirm the location of a defect, measure the structure, inspect the worksite, observe equipment deployment and assist with post-weld visual examination.

Work-class ROVs may carry cameras, sonar, laser measurement systems, manipulator arms and specialised inspection tools. Their use can reduce unnecessary diver exposure and improve access to areas with limited visibility or hazardous geometry.

However, an ROV is not a universal replacement for a commercial diver. Fine joint preparation, some mechanical operations, complex tool positioning and specific inspection tasks may still require divers or dedicated intervention equipment.

A sound offshore strategy combines ROVs, divers, surface personnel and engineering controls according to the task, rather than assuming that one technology can perform every function.

4.6 Other emerging developments

Other areas of research include laser-based processes, advanced flux and electrode formulations, underwater additive manufacturing, digital twins and improved computational modelling of weld-pool behaviour.

Their potential benefits vary:

• Laser systems may offer precise energy delivery but face challenges in optical access, shielding, power transmission and subsea deployment.

• Underwater additive manufacturing may enable local deposition of material, but producing a qualified structural repair is more demanding than demonstrating material deposition.

• Digital twins can combine inspection data, structural models and operating history to improve repair planning.

• Computational fluid dynamics and coupled thermal-metallurgical models can help explain bubble dynamics, heat transfer and defect formation.

These methods should be classified as established, application-specific or emerging according to their demonstrated qualification and operational history. A successful laboratory experiment is not equivalent to an accepted offshore repair method.

5. Scientific findings and the evidence required for engineering acceptance

Scientific research explains why underwater welding can succeed, why it sometimes fails and which parameters require the most careful control. Offshore engineering must then translate that evidence into measurable acceptance criteria.

5.1 The principal findings

Scientific finding	Engineering implication
Water promotes rapid heat extraction	Cooling rate and HAZ properties must be assessed
Wet welding can introduce substantial hydrogen	Hydrogen-assisted cracking requires explicit control
Depth changes pressure and the local arc environment	Procedures must be qualified for the relevant conditions
Weld quality depends on position and operator/process control	Qualification must represent the production application
Weld defects can affect fatigue and fracture behaviour	Acceptance must reflect structural criticality
Mechanised processes improve repeatability	Process records can strengthen quality assurance
Inspection has method-specific detection limitations	No single NDT method should be assumed to detect every defect

The technical literature supports the conclusion that acceptable underwater welds are possible, but the achievable properties depend heavily on the process and application. TWI notes that some wet welds have achieved demanding quality levels, while also warning about hydrogen cracking and the difficulties associated with certain welding positions.

TWI

5.2 Why weld testing must be comprehensive

A complete qualification and acceptance programme may include several different examinations.

Visual examination identifies surface imperfections, weld-profile problems and visible evidence of poor workmanship.

Magnetic particle testing can reveal surface and near-surface discontinuities in suitable ferromagnetic materials, provided the method is properly adapted to the work environment.

Ultrasonic testing can detect and characterise internal discontinuities when the procedure, geometry, material and access conditions support reliable examination. Phased-array ultrasonic testing may provide improved coverage and imaging in appropriate applications.

Radiographic testing may be useful for selected joints and geometries, but offshore deployment, access, radiation safety and the requirements for underwater use can limit its practicality.

Metallographic examination and destructive testing are particularly important during procedure qualification, when representative test welds can be sectioned and examined.

Mechanical testing may include tensile, bend, impact and hardness tests, as required by the qualification standard and application.

The final acceptance strategy must be specified before production begins. It should identify the required inspection methods, coverage, acceptance criteria, reporting requirements and the treatment of rejected welds.

6. International standards, qualification and North Sea compliance

Underwater welding for the North Sea must be governed by a project-specific standards register. The applicable requirements depend on the country, operator, asset, component, welding method and regulatory regime.

The fact that a welding procedure complies with an international standard does not automatically establish that it is acceptable for every offshore structure. The operator's design basis and project specifications determine the required level of quality and integrity.

6.1 Important standards and guidance

The following documents are particularly relevant starting points for an engineering review.

ISO 15614-9:2025 — Procedure qualification for underwater hyperbaric wet welding

Published standard

Specifies how a preliminary welding procedure is qualified by testing for the steel groups and processes within its scope. It addresses production and repair welding in hyperbaric wet conditions. The standard identifies quality levels A, B and Z; selecting the appropriate level remains an application-specific engineering responsibility.

Source: ISO official standard page. Published November 2025.

Part 9: Underwater hyperbaric wet welding

ISO 15618-1:2016 — Qualification of underwater welders

Specifies qualification testing for welders working with hyperbaric wet welding on steel. It covers the relevant qualification conditions, test requirements and certification.

Source: ISO official standard page. Confirmed current in 2021 according to ISO's published record.

Part 1: Hyperbaric wet welding

ISO 15614-10:2005 — Procedure qualification for hyperbaric dry welding

A relevant reference for dry hyperbaric welding. The ISO committee catalogue records this edition at status 90.93, meaning confirmed, so the current applicable national or adopted edition should be verified when preparing a project standards register.

Source: ISO underwater welding committee catalogue.

Underwater welding

DNV-RP-B204 — Welding of subsea production system equipment

Covers technical requirements for welding subsea equipment, including quality assurance, procedure qualification, NDT and personnel. DNV lists the 2020 edition, amended in September 2021.

Source: DNV official recommended practice.

DNV

IMCA D 014 — International Code of Practice for Offshore Diving

Establishes an important framework for diving responsibilities, personnel, equipment, medical requirements, operational planning, emergency arrangements and documentation. IMCA identifies Revision 3.3, March 2025, in its technical library.

Source: IMCA official code of practice.

imca-int.com

Other standards may govern offshore structural design, fabrication, materials, pipeline integrity, inspection, welding coordination and quality management. Depending on the asset and contract, relevant documents may include the applicable DNV offshore standards, NORSOK requirements, ISO welding and NDT standards, ASME pipeline codes or AWS underwater welding specifications.

A competent engineer should confirm the current editions, amendments, contractual hierarchy and jurisdictional requirements directly with the relevant standards bodies and project authorities. A document appearing on a technical reference list is not, by itself, evidence that it is the controlling document for a particular job.

6.2 The North Sea regulatory context

A North Sea operation may fall under Norwegian, UK, Danish or other national offshore requirements, depending on its location and asset.

For a Norwegian Continental Shelf project, the team must identify the applicable offshore safety and petroleum regulations, relevant Norwegian offshore standards, operator requirements and accepted diving practices. UK-sector projects require the corresponding UK legal and offshore safety framework.

The diving contractor's management system and the welding contractor's quality system must interface correctly. Diving competence alone does not qualify someone to perform an underwater weld, and a welding certificate alone does not qualify someone to undertake commercial diving.

6.3 Procedure qualification and the production weld

A project should distinguish four different things:

1. Welder qualification: demonstrates that an individual can weld within a defined qualification range.

2. Welding procedure qualification: demonstrates that a defined combination of materials, process, parameters and conditions can produce acceptable weld properties.

3. Production welding controls: establish how the qualified procedure is applied and recorded in the field.

4. Inspection and acceptance: determine whether the actual completed weld meets the specified criteria.

For critical offshore work, these controls should be linked to a traceable weld identification and an approved quality plan. Deviations require assessment and authorisation through the project's defined technical control process.

7. Education and professional development for underwater welding

Underwater welding is a multidisciplinary career. A person may enter the industry through commercial diving, conventional welding, materials engineering or offshore engineering, but each route develops different competencies.

It is important to distinguish between becoming a qualified welder-diver and becoming a senior underwater welding engineer. The former requires specific diving and welding qualifications. The latter normally requires additional engineering education, extensive industrial experience and responsibility for technical decisions.

7.1 Educational pathways

Path A: Commercial diver progressing to welder-diver

Complete recognised commercial-diving training accepted for the intended offshore jurisdiction. Develop underwater work skills, qualify in conventional welding and then undertake specialist underwater welding training and procedure-specific performance testing.

Best suited to people whose primary occupation will be offshore diving and hands-on underwater work.

Path B: Professional welder progressing to underwater welding

Build a strong foundation in conventional welding processes, metallurgy, weld preparation, quality control and fabrication. Obtain the relevant commercial-diving qualifications and subsequently train for the required underwater welding methods.

Best suited to people who already have strong practical welding experience.

Path C: Welding or materials engineer specialising in subsea repairs

Study mechanical, materials, welding or offshore engineering. Develop expertise in welding procedures, structural integrity, fracture mechanics, fatigue, corrosion and inspection. Obtain suitable offshore exposure and specialist competence in hyperbaric welding systems.

Best suited to technical authority, welding engineering, repair design and quality-assurance roles.

7.2 Core technical subjects

A serious education programme should cover the following subjects.

Welding metallurgy. The student must understand weld-metal chemistry, phase transformations, heat-affected zones, hardenability, hydrogen diffusion, fracture toughness, residual stress and the consequences of rapid cooling.

Welding processes and consumables. This includes SMAW/MMA, TIG/GTAW, MIG/MAG, flux-cored processes and mechanised systems where relevant. Students should understand the limitations of each process rather than merely memorising equipment settings.

Materials engineering. Offshore structures may use carbon-manganese steels, low-alloy steels, corrosion-resistant alloys, duplex stainless steels and clad or lined materials. Material selection, compatibility, weldability and service conditions must be understood.

Structural mechanics. Welding engineers need to interpret loads, stress concentrations, fatigue, fracture, buckling, restraint and load transfer. They must know when a repair requires a specialist structural assessment.

Inspection and NDT. Training should include the purpose, capabilities and limitations of visual examination, ultrasonic testing, magnetic particle testing, radiography and relevant subsea inspection techniques.

Corrosion engineering. The curriculum should cover seawater corrosion, galvanic effects, cathodic protection, coatings, erosion-corrosion and the integrity of repaired structures over their remaining service life.

Commercial diving and hyperbaric systems. For anyone who will dive, training must include the appropriate diving procedures, equipment, communications, decompression requirements, emergency arrangements and medical fitness. Engineering personnel who do not dive still need to understand how their decisions affect the diving operation.

Offshore operations and logistics. Students should learn marine operations, lifting engineering, dynamic positioning interfaces, weather constraints, equipment certification, risk assessment, permits and work-pack preparation.

Quality assurance and documentation. Competence includes interpreting specifications, managing revisions, maintaining traceability, recording production parameters, resolving non-conformances and producing defensible technical reports.

7.3 Practical qualification requirements

A welder-diver must hold the diving qualifications and medical fitness required for the planned operation and the relevant jurisdiction. They must also hold the applicable welding qualification and demonstrate competence for the specific underwater process.

For hyperbaric wet welding, ISO 15618-1 is an important qualification reference. For a procedure within its scope, ISO 15614-9:2025 provides the procedure qualification framework. The two serve different purposes and should not be confused.

Part 1: Hyperbaric wet welding

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A typical training progression may involve:

• Conventional welding practice and qualification.

• Commercial-diving education and required medical certification.

• Supervised subsea work and familiarisation with offshore procedures.

• Specialist underwater welding training.

• Procedure-specific practical qualification.

• NDT and inspection awareness, with formal certification where the role requires it.

• Recurrent assessment and project-specific familiarisation.

There is no single universal number of training hours that guarantees competence for all underwater welding work. The qualification required depends on the process, position, material, depth, joint type and job specification.

7.4 Education for a senior underwater welding engineer

A senior engineer needs more than excellent welding technique. The role demands the ability to make and document decisions that balance structural integrity, metallurgical performance, diving risk, operational feasibility, time and cost.

A suitable professional development plan should include:

Development area	Expected capability
Materials and welding engineering	Assess weldability, select or review procedures and interpret qualification data
Offshore structural engineering	Understand load paths, fatigue, fracture and repair implications
Diving operations	Understand the limits of the diving system and the consequences of work-pack decisions
Inspection engineering	Define inspection scope and evaluate results within the engineer's competence
Project engineering	Coordinate contractor interfaces, equipment, vessel time and technical approvals
Risk and safety management	Identify hazards, evaluate barriers and control changes
Leadership	Brief teams clearly, challenge unsafe assumptions and stop work when necessary

Professional qualifications such as an International Welding Engineer (IWE), or an appropriate national equivalent, may be useful depending on the role and employer. They do not replace offshore experience or the specific qualifications required for commercial diving and underwater welding.

7.5 A practical career development plan

Stage 1

Foundation

Education and basic competence

Establish a foundation in welding, metallurgy, materials, occupational safety and the chosen entry pathway. Obtain the required formal training before undertaking operational work.

Stage 2

Qualification

Specialist competence

Acquire the relevant commercial-diving and underwater welding qualifications, practical training, supervised work experience and procedure-specific assessment.

Stage 3

Experience

Offshore project exposure

Work with experienced supervisors and engineers. Learn how permits, vessel schedules, weather windows, equipment failures and inspection findings affect real offshore operations.

Stage 4

Leadership

Technical responsibility

Progress into procedure development, repair engineering, quality assurance, project planning and technical authority roles, under appropriate supervision until formally competent.

The pathway is not necessarily linear. A welding engineer can become highly experienced in hyperbaric repair design without being a diver, while a commercial diver can become a highly skilled welder-diver without taking on the responsibilities of a welding engineer.

The essential principle is that each person must work within their actual competence and authorisation.

8. Field experience: lessons from senior underwater welding engineers

The following section presents realistic engineering scenarios and lessons consistent with established offshore practice. These are illustrative composite case studies, not claimed first-hand accounts or quotations from a named senior engineer. They demonstrate the kinds of decisions experienced North Sea teams must make.

8.1 Case study A: A fatigue crack in a jacket brace

magazine.boskalis.com

Imagine an ageing fixed steel platform where an inspection identifies a suspected crack near a tubular brace connection.

A junior engineer may initially focus on how the crack could be welded. A more experienced engineer starts by asking why the crack occurred and whether welding is the correct intervention.

The engineering team would first establish the defect's location, size, orientation and likely cause. The assessment would examine cyclic loading, the joint's geometry, local stresses, corrosion, historical inspection records and the structural significance of the member.

The team would then determine whether the structure can remain in service while a repair is planned. Depending on the findings, the operator might need additional monitoring, operational restrictions or temporary structural support.

Only after the structural assessment would the repair method be selected. Options could include underwater welding under an appropriately qualified procedure, a mechanical repair, a clamp, a structural modification or replacement of the affected component.

The senior engineer's lesson: a crack is evidence of a failure mechanism, not merely a gap to be filled with weld metal. A repair that does not address the underlying stress concentration or fatigue mechanism may fail again.

8.2 Case study B: A subsea pipeline tie-in

wermac.org

Consider a subsea development requiring two pipeline sections to be connected. The connection may be planned during a new field development or required following a failure or modification.

A senior engineer would first confirm the pipeline design, material grades, wall thicknesses, operating conditions, connection geometry and applicable qualification requirements.

The intervention plan must then address pipeline isolation, internal fluid management, depressurisation or other approved pressure-control measures, pipe-end preparation, alignment, habitat installation, welding, inspection and return to service.

Remote-controlled hyperbaric welding can be especially attractive where high-integrity welds are required and direct diver welding would be unsuitable.

Norway's PRSI Pool provides a useful real-world reference. A 2025 Offshore Technology Conference paper describes its remote-controlled hyperbaric pipeline welding capability, operational experience with four successful subsea tie-ins and a development roadmap for additional applications. This is a specific documented industrial example, not evidence that every pipeline geometry or material combination is already qualified.

OnePetro

The senior engineer's lesson: the weld is only one part of the tie-in. Alignment tolerances, pipe-end condition, habitat reliability, process records, inspection and pressure-system integrity must all be managed as one engineering system.

8.3 Case study C: Deteriorating weather during an offshore campaign

Imagine that a diving support vessel is conducting an inspection and repair campaign. Weather forecasts indicate that the sea state may deteriorate before the planned work is complete.

A less experienced planner may try to preserve the original schedule by compressing the work programme. A senior offshore engineer instead reviews the critical path, the vessel's operating limits, the diving supervisor's assessment, the availability of safe recovery arrangements and the consequences of an incomplete repair.

The team may decide to finish only those activities that can be completed safely, secure tools and equipment, recover the diver or ROV, and suspend the remaining work.

The resulting delay may be expensive, but it is usually less consequential than forcing an operation beyond its approved limits.

The senior engineer's lesson: weather downtime is a design input to the logistics plan, not an unexpected administrative inconvenience. A robust campaign includes contingency days, safe stopping points and clear criteria for suspension.

8.4 Case study D: An apparently acceptable weld fails inspection

Consider a weld that appears satisfactory during the initial visual examination, but subsequent ultrasonic testing identifies an indication requiring evaluation.

The correct response is not to assume that the indication is harmless or to begin grinding and rewelding without a plan. The team must identify the indication, confirm the inspection method's limitations, compare the result with the applicable acceptance criteria and determine the required disposition.

Depending on the findings, the weld may be accepted, subjected to additional examination, repaired under an approved procedure or rejected.

A repair can introduce further metallurgical and structural concerns, especially if the same region is reheated or the component is highly restrained.

The senior engineer's lesson: inspection is part of the repair design, not simply a final administrative check. The inspection plan must be defined before welding starts, and the team must agree how unexpected findings will be handled.

8.5 Case study E: Equipment failure offshore

Imagine that a critical welding control unit or habitat gas-monitoring instrument develops a fault during mobilisation.

The immediate temptation may be to use a substitute instrument or modify the setup. An experienced engineer first determines whether the equipment is safety-critical, whether the substitute is approved for the intended service, whether calibration and certification remain valid, and whether the change affects the qualified process or the diving system.

If the required assurance cannot be demonstrated, the operation must not proceed merely because the vessel and personnel are already offshore.

The senior engineer's lesson: equipment redundancy is valuable only when the alternative equipment is compatible, tested, available and authorised for the task.

8.6 What distinguishes a strong senior engineer?

Across these scenarios, the most valuable characteristics are consistent:

• The engineer verifies the problem before choosing a solution.

• The engineer understands when welding is inappropriate.

• The engineer uses measured data and qualified procedures rather than intuition alone.

• The engineer respects the authority of the diving supervisor and other designated safety-critical roles.

• The engineer plans for failure, weather deterioration and incomplete work.

• The engineer maintains traceable records of decisions, changes and acceptance.

• The engineer understands that technical confidence must never replace evidence.

The best field engineers are not those who promise that everything will proceed according to plan. They are those who recognise when conditions have changed and know how to respond without compromising integrity or safety.

9. Detailed offshore logistics for underwater welding in the North Sea

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Offshore logistics can determine whether an underwater welding campaign succeeds. A technically excellent welding procedure is of limited value if the correct equipment, consumables, qualified personnel, inspection capability or vessel support are unavailable at the worksite.

Logistics must therefore be designed around the complete intervention: engineering preparation, mobilisation, transit, installation, execution, inspection, demobilisation and the possibility of aborting or recovering from an unexpected event.

9.1 Establishing the logistics basis

The first stage is to define the operation accurately enough to calculate resources and constraints.

The project team needs to establish:

• The asset's precise location and water depth.

• The component, material, wall thickness and joint geometry.

• The defect type and proposed repair method.

• The required welding process and procedure qualification.

• The diving method, if diving is required.

• The expected inspection and acceptance requirements.

• The vessel and intervention equipment needed.

• The environmental and operational limits.

• The required permits, approvals and emergency arrangements.

The scope should define the work that is included and excluded. For example, a pipeline repair may include isolation and inspection but exclude upstream process shutdown activities, which must be separately coordinated with the operator.

The logistics plan must also define the criteria for declaring the job complete. A weld deposited but not inspected or formally accepted is not a completed repair.

9.2 Selecting the offshore vessel

The vessel is a major logistical and safety decision.

A project may require a dedicated diving support vessel, a construction support vessel or another suitably equipped offshore vessel. Selection depends on water depth, the intervention system, environmental conditions, lifting requirements and the need for saturation diving.

A vessel assessment should cover the following areas.

Station keeping and marine capability

Dynamic positioning, where required, must be suitable for the operation and supported by an appropriate operational and failure-response philosophy. Thruster performance, redundancy, power generation and environmental limits must be assessed.

Lifting and deployment

Cranes, A-frames, winches, moonpools and handling systems must be compatible with the weight, geometry and dynamic loads of the diving bell, ROV, habitat or welding equipment.

Diving and life-support facilities

The diving spread must be suitable for the intended mode of diving, with the necessary control stations, gas supplies, life-support systems, communications and emergency arrangements.

Deck layout and services

The vessel must accommodate the welding spread, consumables, test equipment, power distribution, lifting routes, storage and maintenance areas without compromising safe access or emergency escape.

Vessel selection must also consider endurance, fuel, accommodation, crew changes, medical support, communications and the availability of specialist technicians.

The lowest day rate is not necessarily the lowest total cost. A vessel that cannot support the required intervention efficiently may incur additional offshore days, repeated mobilisation or an unacceptable reduction in operational capability.

9.3 Mobilisation and equipment preparation

Mobilisation is the process of transforming a collection of equipment and personnel into a verified operational system.

The welding contractor, diving contractor, vessel operator and client must coordinate their activities before departure.

A mobilisation register should identify every critical item, its owner, inspection status, certification status, required location, test requirements and contingency arrangements.

Typical equipment includes:

Equipment group	Typical contents and purpose
Welding system	Qualified power source, welding head or holder, control system, cables and approved consumables
Habitat system	Chamber, seals, gas controls, pressure monitoring and associated tooling where required
Diving system	Bell, umbilicals, gas supplies, communications, life-support and recovery equipment
Subsea intervention	ROV, cameras, manipulators, hydraulic tools, survey equipment and deployment frames
Inspection	Qualified NDT equipment, calibration references, data acquisition and reporting systems
Electrical distribution	Approved supplies, isolation equipment, protective systems and relevant monitoring
Lifting equipment	Certified slings, shackles, spreader beams, lifting points and handling equipment
Consumables and spares	Electrodes or wire, gas supplies, seals, filters, hoses, connectors and critical replacement parts
Emergency equipment	Required medical, rescue, evacuation and contingency equipment

The actual equipment list must be tailored to the intervention. A wet-welding job will not require the same habitat equipment as a remote hyperbaric pipeline tie-in.

9.4 Equipment certification and functional testing

Equipment must not be treated as ready merely because it is physically present on the vessel.

Before offshore use, the responsible personnel should verify:

• Inspection and examination status.

• Required certification and traceability.

• Calibration of relevant measurement instruments.

• Correct configuration and compatibility.

• Functional testing under the intended operating conditions.

• Availability of operating manuals and approved procedures.

• Completion of interface and communication checks.

• The status of critical spares and backup arrangements.

For hyperbaric welding, particular attention is required for seals, gas-control equipment, pressure monitoring, welding controls and any system whose failure could affect the habitat atmosphere or the quality of the weld.

For wet welding, the integrity of electrical insulation, power-control arrangements, approved consumables and communication systems is essential.

The project should use a formal pre-departure readiness review to identify outstanding items. Any unresolved critical defect must be assessed and closed before the operation is authorised to proceed.

9.5 Personnel logistics and competence

An offshore welding campaign may involve the following roles:

• Client representative or offshore installation representative.

• Project manager and offshore construction manager.

• Welding engineer or responsible welding coordinator.

• Welding supervisor and qualified welder or welder-diver.

• Diving superintendent and diving supervisor.

• Commercial divers and life-support personnel, as required.

• ROV supervisor and ROV pilots or technicians.

• NDT personnel and inspection engineer.

• Structural integrity or pipeline engineer.

• Vessel master, marine crew and dynamic-positioning personnel.

• Lifting supervisor and rigging personnel.

• Electrical, hydraulic and mechanical technicians.

• Offshore medic and other designated emergency-response personnel.

Not every job requires every role. The organisation must match the actual scope and risk.

The key is to define decision authority clearly. The welding engineer is responsible for the relevant technical welding decisions; the diving supervisor controls the diving operation within the established management system; the vessel master retains the relevant marine responsibilities; and the client or operator controls the applicable asset and work authorisations.

A competent offshore organisation prevents gaps between these responsibilities.

9.6 Weather forecasting and the operational window

North Sea weather planning requires more than checking the forecast on the morning of the job.

The project should identify environmental limits for vessel station keeping, lifting, diving, ROV deployment, habitat installation and recovery. These limits may differ between activities.

The planning process should include:

1. Reviewing the forecast before mobilisation.

2. Updating forecasts during transit.

3. Assessing the expected weather window against the critical path.

4. Identifying the latest safe start time for critical activities.

5. Allowing sufficient time for recovery and securing equipment.

6. Establishing clear suspension and restart criteria.

7. Planning for the possibility that weather deterioration will prevent immediate resumption.

The limiting condition may be the capability of a particular piece of equipment rather than the vessel itself. For example, a vessel may be capable of maintaining station while a specific subsea deployment system is outside its approved operating envelope.

A sound plan recognises these differences.

9.7 Diving mode selection

For North Sea work, the choice between surface-supplied diving and saturation diving depends on depth, duration, task complexity, exposure and the applicable rules.

Surface-supplied diving may be appropriate for certain shallower tasks within the permitted operating envelope. Saturation diving may be appropriate for longer-duration work at greater depths, where repeated compression and decompression for each working period would be impractical.

The selection must be made by competent diving specialists using the relevant operational and regulatory requirements. It cannot be determined by a universal depth threshold alone.

Saturation diving also introduces significant logistical obligations: chamber occupancy, life-support operation, bell runs, diver rotation, gas management, medical monitoring and decompression or emergency evacuation planning.

Where a remotely controlled welding system removes the need for a diver to perform the weld itself, it may reduce diver exposure and change the required diving scope. It does not eliminate the need to assess any remaining diving tasks.

9.8 Welding consumables and material traceability

Welding consumables require specific planning because the correct product must be available in the required quantity and in a condition suitable for use.

The logistics team should verify:

• Consumable classification and approval.

• Compatibility with the qualified welding procedure.

• Batch or lot identification.

• Storage and handling requirements.

• Quantity required, including a justified contingency allowance.

• Availability of approved replacement batches.

• Traceability from the consumable used to the completed weld.

Wet-welding electrodes require particular attention to the manufacturer's storage, waterproofing and handling requirements. Hyperbaric dry-welding systems require appropriate wire, gas and consumable arrangements for the qualified process.

The project must not assume that an electrode or wire with a similar commercial designation can replace the approved consumable without technical assessment.

9.9 Logistics for a hyperbaric welding habitat

dcndiving.com

A habitat-based repair has additional interfaces that must be engineered and managed.

The equipment must be transported to the site, deployed, positioned, aligned, secured and verified before the welding phase. Habitat sealing and pressure management must then be established in accordance with the approved system design.

The operation may require:

• Survey and measurement of the joint.

• Confirmation of seabed and structural clearances.

• Habitat and tooling deployment.

• Pipe-end or component preparation.

• Verification of joint alignment and fit-up.

• Confirmation of the required internal environment.

• Welding-system checks and process readiness.

• Execution of the qualified welding sequence.

• Examination and review of the completed joint.

• Controlled recovery of the equipment.

The exact sequence depends on the habitat design and the repair method. A project must use the approved operating procedures for the specific system rather than generalised assumptions about pressure, gas composition or chamber operation.

Particular attention should be paid to equipment recovery. The habitat, lifting interfaces and subsea tooling must be recoverable within the limits of the vessel and marine operation. A system that can be installed but cannot be safely recovered under foreseeable conditions is not an acceptable logistics solution.

9.10 Detailed operational sequence

The following sequence illustrates how an offshore welding intervention may be organised. It is a planning framework, not an executable diving or welding procedure.

Phase 1 — Engineering and preparation

Complete the defect assessment, repair design, welding procedure review, risk assessment, permits, inspection plan, equipment register and mobilisation schedule.

Phase 2 — Mobilisation and transit

Load equipment, verify certification, perform functional tests, brief the team and transit to the site with adequate time and resources for the planned intervention.

Phase 3 — Site verification

Confirm the worksite, locate the defect, check access, verify isolation and operating conditions, and confirm that the repair method remains suitable.

Phase 4 — Intervention setup

Deploy the required diving, ROV or habitat systems; prepare the joint or repair location; confirm tooling and measurement results; and complete the authorised readiness checks.

Phase 5 — Welding execution

Apply the qualified procedure, monitor required parameters, record deviations and maintain communication between the offshore worksite, welding supervision and the relevant control stations.

Phase 6 — Inspection and acceptance

Complete the specified examination, evaluate findings, resolve non-conformances and obtain the required technical acceptance before proceeding to any return-to-service activities.

Phase 7 — Recovery and close-out

Recover equipment, secure the vessel spread, reconcile consumables, complete the weld records, report deviations, issue inspection documentation and hand over the repair information to the asset owner.

9.11 Power, communications and control systems

Underwater welding requires reliable control of the electrical and communications systems.

For wet welding, the system must use approved equipment and protective arrangements designed for the specific underwater process. Electrical isolation, power control, insulation, cable condition and communication between the diver and surface control are safety-critical.

For hyperbaric dry welding, the control architecture must integrate the welding power source, mechanised equipment, monitoring instruments, habitat services and the surface control station. Faults must be identifiable, and the operating procedures must define the response to abnormal conditions.

The system design should specify which parameters are continuously monitored, which require periodic verification, which alarms demand immediate suspension and which records must be retained.

The surface team should not improvise electrical modifications offshore. Any change affecting the qualified welding system or diving safety must be reviewed and authorised through the appropriate technical and safety processes.

9.12 Inspection logistics and quality documentation

Inspection resources must be mobilised with the same care as welding resources.

The project should confirm that suitable NDT equipment, trained personnel, reference standards, calibration arrangements, data storage and reporting facilities are available.

Where a method requires access to the weld surface or a particular inspection geometry, that access must be designed into the intervention. It is inefficient to complete a repair and then discover that the required examination cannot be performed.

The inspection plan should define the required coverage, the acceptance criteria, the reporting format and the process for resolving uncertain indications.

At the end of the job, the quality dossier should include the applicable records, such as:

• Approved repair design and applicable drawings.

• Welding procedure specification and qualification record.

• Welder or operator qualification records.

• Material and consumable traceability.

• Relevant equipment and calibration records.

• Production welding parameter logs.

• Inspection reports and acceptance decisions.

• Records of deviations and approved dispositions.

• Relevant photographic, ROV and survey records.

• Final repair and asset handover documentation.

The exact dossier is determined by the contract, asset requirements and applicable standards. It must be sufficient to reconstruct what was done, which procedure was used, what was inspected and why the repair was accepted.

9.13 Contingency planning and emergency logistics

Contingency planning should be based on credible failure scenarios, not merely on the presence of emergency equipment.

Potential scenarios include loss of station keeping, deterioration in weather, failure of critical welding controls, loss of communications, habitat-system faults, ROV failure, unexpected structural conditions, unsuccessful inspection and the need to abandon the planned repair.

The project should identify:

• Which activities can be safely suspended.

• How equipment will be secured or recovered.

• What conditions require diver recovery or emergency response.

• Which alternative systems are approved for use.

• Who has authority to suspend or restart the operation.

• How the asset will be left if the repair cannot be completed.

• Which additional resources may be required for a second mobilisation.

Saturation diving requires additional planning for life support, emergency response and hyperbaric evacuation, consistent with the applicable diving management system and guidance. IMCA publishes dedicated guidance on these matters.

imca-int.com

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The project should also consider the consequence of an incomplete repair. For a non-critical structural attachment, the asset may be left under an approved temporary arrangement. For a damaged pressure-retaining pipeline, the acceptable interim state may be much more restrictive.

The engineer must determine the technical limits of any temporary condition before the offshore campaign begins.

10. Logistics planning: schedule, cost and resource management

The total cost of an underwater welding campaign is determined by much more than the welding itself. Vessel day rates, mobilisation, diving-system availability, engineering, inspection, weather downtime and the consequences of unsuccessful work can dominate the budget.

A useful planning model is:

\[ C_{\mathrm{total}} = C_{\mathrm{engineering}}+ C_{\mathrm{mobilisation}}+ C_{\mathrm{vessel}}+ C_{\mathrm{diving}}+ C_{\mathrm{welding}}+ C_{\mathrm{inspection}}+ C_{\mathrm{contingency}} \]

This is a conceptual cost structure. The individual categories must be defined to avoid double-counting costs already included in contractor or vessel rates.

10.1 Illustrative campaign schedule

The following is an example of how a project manager might organise the work. It is not a prediction for a particular North Sea asset, and actual durations may differ considerably.

Work package	Illustrative planning allowance	Main dependencies
Engineering, repair design and approvals	2–6 weeks	Defect data, materials, operator approval
Procedure and equipment readiness	1–4 weeks, potentially overlapping	Qualified procedures, equipment availability
Mobilisation and testing	2–5 days	Vessel and contractor readiness
Transit and site setup	1–3 days or longer	Port, distance, vessel and weather
Survey and intervention setup	1–3 days or longer	Access, depth, seabed and equipment
Welding and inspection	1–5 days or longer	Repair complexity, inspection results
Recovery and demobilisation	1–3 days	Weather, lifting and equipment recovery
Engineering close-out	Several days to weeks	Inspection records and acceptance

The schedule should be developed from a task-based estimate, not from the allowances above alone. A critical pipeline repair may require extensive preparation and qualification, while a simple, previously qualified structural repair may need much less engineering effort.

10.2 Cost drivers

The major cost drivers include:

• Vessel and specialist intervention-system day rates.

• The duration of the offshore campaign.

• Saturation-diving and life-support requirements, where applicable.

• Hyperbaric habitat deployment and operation.

• Engineering, procedure qualification and materials testing.

• NDT and specialist inspection.

• Spare parts, consumables and logistics support.

• Weather delays and additional vessel time.

• The risk of rework, repeated mobilisation or an unsuccessful repair.

A useful commercial measure is the expected total intervention cost rather than the quoted welding price.

For example, a lower-cost repair technique may require more divers, longer offshore exposure and greater inspection uncertainty. A more expensive mechanised system may offer better repeatability or reduce some of those costs. The comparison must be based on the actual repair scope and risk profile.

10.3 Spare parts and supply-chain resilience

For remote North Sea operations, a missing seal, cable, connector, sensor or approved consumable can delay the entire campaign.

The logistics team should classify equipment according to its criticality and lead time. Critical items should have an appropriate backup strategy, whether that means carrying spares offshore, securing a tested replacement at a nearby base or maintaining an agreed emergency supply arrangement.

A spare is useful only if it is compatible, certified where required, and available within the time needed to prevent a critical delay.

For consumables, the project must preserve traceability and the approved material specification. Unauthorised substitutions are not acceptable merely because the correct item is unavailable.

10.4 A practical readiness checklist

Offshore readiness review

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Use this interactive list to organise a planning review. Checking every item is not formal authorisation to commence work.

Engineering

Repair design and technical basis approved

Welding procedure and qualifications verified

Inspection plan and acceptance criteria agreed

Isolation and return-to-service requirements confirmed

Vessel and marine operations

Vessel suitability and operating limits confirmed

Lifting and deployment plans approved

Weather window and recovery arrangements reviewed

Personnel and equipment

Required personnel qualifications verified

Critical equipment inspected and function-tested

Consumables, spares and calibration records available

Communications and emergency arrangements checked

Quality and close-out

Weld traceability and recording system ready

NDT resources and reporting arrangements confirmed

Non-conformance and stop-work processes agreed

Reset checklistCopy checklist

11. Environmental responsibility and long-term asset integrity

Underwater welding must be evaluated as an intervention in a sensitive marine environment. The welding process, habitat operation, cleaning activities, coating removal and recovery of waste materials may all have environmental implications.

A responsible project should consider the following.

Material and consumable waste. Electrodes, wire ends, slag, abrasive material, packaging and other debris must be controlled and recovered where required. The work method should minimise uncontrolled release to the seabed.

Water quality. Cleaning, surface preparation and the use of chemicals must be assessed for their potential environmental impact. Any discharge or containment requirements should be identified in the project environmental plan.

Noise and disturbance. Vessel operations, ROV activity, lifting and other offshore work may generate noise or disturb marine habitats. Relevant restrictions must be incorporated into planning.

Corrosion protection. Repair coatings, cathodic protection and material compatibility should be considered together. A structurally acceptable weld that creates an unresolved corrosion problem is not a complete long-term repair.

Inspection and monitoring. The repaired component should be incorporated into the asset's inspection programme, with an appropriate basis for assessing its future condition.

For an ageing North Sea installation, the repair strategy should be linked to the remaining service life of the asset. The objective is not simply to restore the component to its previous state, but to establish that the repaired system can meet its required performance over the intended period of operation.

12. Future direction of underwater welding in the North Sea

The future of underwater welding is likely to be shaped by five related developments.

First, remote-controlled hyperbaric welding will continue to be important for applications where a highly controlled, repeatable weld is required. Norway's experience with subsea pipeline tie-ins provides a concrete industrial foundation for further development.

OnePetro

Second, advanced sensing and digital records will improve the ability to detect process deviations and establish traceability. Machine learning may contribute to monitoring and defect assessment, provided its predictions are validated against appropriate experimental and inspection evidence.

Third, inspection and repair systems will become more integrated. ROVs, automated measurement, digital asset models and specialist intervention tooling can reduce uncertainty before work begins and help target repairs more precisely.

Fourth, research into alternative welding and joining methods may expand the available options. Solid-state joining, controlled metal transfer, improved consumables and underwater additive manufacturing are promising research areas, but each must demonstrate suitable mechanical properties, repeatability, inspection capability and offshore deployability before being accepted for a specific structural application.

Fifth, offshore wind and ageing oil and gas infrastructure will create different repair requirements. Wind foundations may involve fatigue-sensitive structural details and coating systems, while subsea pipelines may require high-integrity pressure-retaining connections. These applications demand different engineering criteria even when the same broad welding technology is used.

The most important future development may therefore be not a single new welding process, but a more integrated approach to inspection, engineering, intervention, qualification and long-term monitoring.

13. Final conclusions

Underwater welding is a specialised engineering discipline in which metallurgical science, subsea technology, commercial diving and offshore project management must work together.

Wet welding offers portability and relatively simple deployment, but presents substantial challenges involving hydrogen, cooling rates, weld-pool stability and diver exposure. Dry hyperbaric welding provides a more controlled environment and is particularly important for high-integrity subsea pipeline connections and other critical applications, although it requires more complex equipment and logistics.

The scientific evidence demonstrates that acceptable underwater welds can be produced, but it does not support the assumption that any underwater weld is automatically fit for service. Material selection, procedure qualification, process control, inspection and structural assessment remain fundamental.

For the North Sea, the engineering requirements are particularly demanding because operations must account for severe marine conditions, ageing assets, fatigue, corrosion, vessel limitations and potentially substantial consequences of failure. The latest developments in remote-controlled hyperbaric welding, automated monitoring, ROV-supported inspection and digital traceability offer meaningful improvements, but their use must remain grounded in demonstrated capability and application-specific qualification.

Education must be equally multidisciplinary. A welder-diver needs recognised diving and underwater welding qualifications, while a senior underwater welding engineer must additionally understand metallurgy, structural integrity, inspection, offshore operations, risk management and technical governance.

Finally, logistics should be regarded as part of the engineering design itself. Vessel selection, equipment readiness, personnel competence, weather planning, consumable traceability, inspection resources and contingency arrangements determine whether the repair can be completed safely and accepted technically.

The defining principle of good North Sea underwater welding is therefore straightforward: the objective is not merely to deposit a weld underwater, but to deliver a verified, structurally appropriate and durable repair within a safe and controlled offshore operation.

Selected references and further reading

The following sources provide a starting point for deeper study. The official standards and guidance should be consulted directly for their complete requirements.

1. ISO — Underwater welding standards and committee information. ISO/TC 44/SC 15: Underwater welding. Includes the relevant standards for underwater welder qualification and welding procedure qualification.

Underwater welding

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2. ISO 15614-9:2025. Specification and qualification of welding procedures for metallic materials — Underwater hyperbaric wet welding. Particularly relevant to the qualification of procedures within its scope.

Part 9: Underwater hyperbaric wet welding

3. ISO 15618-1:2016. Qualification testing of welders for underwater welding — Hyperbaric wet welding. A key reference for welder-diver qualification.

Part 1: Hyperbaric wet welding

4. DNV-RP-B204. Welding of subsea production system equipment. Relevant to subsea equipment welding, qualification, inspection and quality assurance.

DNV

5. IMCA D 014. International Code of Practice for Offshore Diving. A key source for offshore diving organisation and safety management.

imca-int.com

6. TWI — Underwater welding technical guidance. Can sound welds be made by wet underwater welding?. Useful for understanding weld quality, hydrogen cracking and process limitations.

TWI

7. Offshore Technology Conference, 2025. Prepared for the Unplanned — Subsea Pipeline Tie-Ins and Repairs by Remote Controlled Robotic Welding. An industry reference for remote hyperbaric welding and subsea pipeline repair.

OnePetro

8. SINTEF — Welding laboratory. Hyperbaric welding and weldability research. Information on hyperbaric welding, welding procedure development and laboratory capabilities.

SINTEF

9. Journal of Manufacturing Processes, January 2026. Review on advances in wet underwater arc welding: Thermo-mechanical aspects and emerging machine learning approach. A recent review of underwater welding physics, modelling and emerging computational methods.

ScienceDirect

10. Discover Applied Sciences, 2026. A comprehensive review of emerging underwater repair techniques for offshore structures. A broader review of subsea repair strategies, including robotics, hyperbaric welding and emerging techniques.

Springer Nature Link

Practical recommendation: For a real North Sea project, begin with the asset owner's repair specification, the applicable jurisdictional requirements, the current diving code and the relevant welding qualification standards. Have the welding engineer, structural integrity engineer and diving contractor jointly confirm the repair basis before mobilising personnel or equipment.