Wet and Hyperbaric Underwater Welding

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1 PUBLISHABLE SUMMARY January 2013 Background Underwater welding is used in the repair of offshore structures and pipelines, ships, submarines and nuclear reactors. The difficulty of achieving high integrity repairs underwater has led to on-going efforts to improve the available technology, with varying approaches in the different industry sectors. Some critical issues associated with underwater repairs are: Depth limitations. The risk of hydrogen-assisted cracking in steels with high carbon equivalent. The risk of potential welding defects such as porosity, lack of fusion and cracking. The potential for inadequate weld metal mechanical properties (notch toughness and ductility) and weld joint integrity including fatigue. TWI proposes to carry out a work programme, as a Group Sponsored Project, on underwater welding for participation by interested organisations, in which several wet and dry hyperbaric underwater welding will be investigated/developed.

2 Objectives Underwater wet welding: Identify and define technological boundaries or limitations for wet underwater welding through a stateof-art review, including experience with the NEPSYS system and Underwater Laser Beam Welding (ULBW). Establish whether welds produced by underwater wet welding produced meet the requirements of Class A of AWS D3.6 through weld procedure qualification tests. Dry hyperbaric welding: Compare the traditional and state-of-the-art Gas Metal Arc Welding (GMAW) processes for heat input, spatter generation at different metal deposition rate under optimised condition Explore laser assisted CMT and Cold Arc processes to evaluate changes in cooling rate, metallurgical phases formation and optimisation of the process. Apply cold arc power source in a hyperbaric chamber Study of the effect of moisture on hydrogen content Benefits The state-of-art review will be essential in establishing the knowledge and experience available to contractors considering wet underwater welding. The information will also serve to highlight the gaps in the knowledge and experience which need to be covered before contractors would have the confidence to carry out repairs on offshore structures. The developed underwater wet welding procedures will provide Sponsors with recommended approaches to repair primary and secondary members of offshore platforms. The development work on dry hyperbaric welding will allow Sponsors to apply variation of standard arc welding processes to dry hyperbaric repairs and modifications of pipelines and offshore structures, with potential applications to diverless interventions. Participants The Sponsor Group currently comprises: BP Petrobras Scope of Work Underwater Wet Welding Previous work carried out by TWI (available to the GSP sponsors) showed that the underwater wet welding techniques listed below may be capable of achieving Class A to AWS D3.6. The work programme for underwater wet welding includes Options 1 and 2, which are considered the most promising. Options 3 and 4 are optional and subject to the available budget 1. Standard underwater wet welding procedures 2. Controlled bead deposition technique to further reduce HAZ hardness, particularly in the weld cap, and HAZ hydrogen cracking 3. Nickel electrode welding technique to reduce cap HAZ hardness (OPTIONAL) 4. Buttering and welding procedure to eliminate the minor hydrogen cracking observed and reduce cap HAZ hardness (OPTIONAL) The test material will be selected according to the likely maximum carbon equivalent values to be encountered in offshore structures.

3 Scope of Work continued Dry Hyperbaric Welding The work programme for dry hyperbaric welding is divided into four work packages, as follows: WP1: Compare the traditional and state-of-the-art Gas Metal Arc Welding (GMAW) processes for heat input, spatter generation at different metal deposition rate under optimised condition. Standard GMAW Cold Metal Transfer (CMT) and Cold Arc processes would be studied WP2: Explore laser assisted CMT and Cold Arc processes to evaluate: Changes in cooling rate Metallurgical phases formation and mechanical characterisation Optimisation of the process. WP3: Application of cold arc power source in a hyperbaric chamber; Metal deposition characteristics Dependence of the power source output characteristics on the pressure and related weld metal cooling behaviour Suitability of the process for application in hyperbaric condition. WP4: Study of the effect of moisture on hydrogen content; Characterise the hydrogen content in a weld metal under different level of moisture for a GMAW process Repeat the experiments with laser assisted GMAW process and characterise the hydrogen content to quantify the effect of laser power Deliverables A paper based state-of-art review of underwater wet welding for the repair of offshore structures, including Nepsys and ULBW. A report including results of previous work carried out by TWI on the following underwater wet welding MMA techniques: Standard underwater wet welding procedures Controlled bead deposition technique to further reduce HAZ hardness, particularly in the weld cap, and HAZ hydrogen cracking Nickel electrode welding technique to reduce cap HAZ hardness Buttering and welding procedure to eliminate the minor hydrogen cracking observed and reduce cap HAZ hardness A report on further development of the standard and temper bead wet MMA welding techniques for repairs on offshore structures. Wet welding procedure specifications and qualification records in accordance with AWS D3.6 (2011) for the successful technique(s). A report on the dry hyperbaric welding programme Copyright TWI Ltd 2013

4 Price and Duration It is anticipated that the estimated price per sponsor for the above programme of work is 100,000 and it will be performed over a duration of two years Further Information For further information on how a Group Sponsored Project (GSP) runs please visit: GSP Co-ordinator: Tracey Stocks Ref: 22870/3/13 gsp@twi.co.uk Project Leader: Marcello Consonni Marcello.consonni@twi.co.uk

5 Copyright TWI Ltd 2013