PR15283 September 2010

High Integrity Underwater Repair Welding Technologies

For: A Group of Sponsors

Contents Executive Summary Background Objectives Benefits Approach Deliverables Price and Duration

1 Introduction 1 1.1 Wet welding 1 1.2 Hyperbaric welding 2 1.3 Dry localized welding 2 1.4 Underwater Laser Beam Welding 2

2 Objectives 3

3 Approach 3

4 Deliverables 3

5 Price and Duration 4

6 References 4 Figures 1-4

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Executive Summary 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. Whilst wet underwater welding, hyperbaric welding, and underwater friction welding were each first used many years ago, there have been more recent technology developments, including dry localised welding - welding at ambient pressure in a small, transparent, gas-filled habitat with the welder/diver outside in the water (NEPSYS system by Neptune Marine Services referred to as Neptune from here on). In addition, underwater laser beam welding (ULBW) offers potential for transfer of technology and experience from the nuclear industry as a future viable approach for repairs in the oil and gas industry. TWI proposes to carry out a work programme, as a Group Sponsored Project, on underwater welding for participation by interested organisations, in which several underwater welding processes will be investigated/ developed. Objectives

To identify and define technological boundaries or limitations for wet underwater welding through a state-of-art review. The state-of-art review will be extended to include experience with the NEPSYS system, where data can be made available by Sponsors.

To determine feasibility of laser-assisted TIG hyperbaric welding through trials. To establish applicability of the NEPSYS system and Ni-based electrodes through trials at

varying water depths and carry out procedure qualifications, if suitable. To demonstrate use of the ULBW process at water depths up to 30m/40m water depth depending

on limitations of ULBW head on butt, fillet and weld overlay configurations. To establish whether the welds produced meet the requirements of Class A of AWS D3.6 (1999)

through weld procedure qualification tests. Benefits

The state-of-art review will be essential in establishing the knowledge and experience available to contractors considering wet underwater welding and NEPSYS based weld repairs. The information will be presented in the form of a matrix which 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 welding procedures will provide Sponsors with recommended approaches to repair primary and secondary members of offshore platforms and also identify potential technologies for further development in the future, such as ULBW. Approach

Recent project work including a state-of-art review carried out for BP by TWI will be drawn upon to improve the potential and quality of wet welding techniques including repair of high carbon equivalent structural materials. Since the review was based on BP experience; information from other Sponsors in terms of their experience including qualified procedures and test data will be collated and incorporated in the review. The state-of-art review will also be extended to include experience with the NEPSYS system, where data can be made available by Sponsors.

Trials on wet underwater welding to further develop the approaches identified for BP including buttering with oxidising electrodes and controlled deposition techniques. We will be working with Hydroweld.

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Trials for laser-assisted hyperbaric Tungsten Inert Gas (TIG) and Metal Inert Gas (MIG) welding processes at Cranfield University.

Trials with the ULBW system by Westinghouse Electric Corp. (referred to as Westinghouse from here on) Welding and Machining (WEC-WAM) on structural steels used offshore simulating butt weld and fillet weld configurations - to demonstrate viability and capability of the technology for further development.

Trials with the NEPSYS system and Ni- based electrodes by Neptune/TWI. For all the successful techniques, full welding procedure qualification tests will be carried out to

the Class A criteria of AWS D3.6 (1999).

Deliverables

A final report with results from: A paper based state-of-art review of the four technologies identified in this proposal. Further development of three identified wet MMA techniques up to 40m water depth. It should be

noted that current experience with Ni-based weld metal is limited to

1 Introduction 1.1 Current Status

Underwater welding is used in various applications that range from repair of offshore structures and pipelines to ships and submarines: current techniques that are generally used are wet underwater welding and hyperbaric welding. Whilst wet underwater welding, hyperbaric welding, and underwater friction welding were each first used many years ago, there have been more recent technology developments, including dry localised welding - welding at ambient pressure in a small, transparent, gas-filled habitat with the welder/diver outside in the water (NEPSYS system). In addition, underwater Laser Beam Welding (ULBW) offers potential for transfer of technology and experience from the nuclear industry as a future viable technology for repairs in the oil and gas industry. Each technology has its limitations in terms of weld quality, costs, water depth limits and materials that can be welded. Some critical issues associated with underwater welding 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.

1.2 Wet welding

In wet welding (Figure 1), the arc is in direct contact with the water. In Phase 1 of a recently concluded confidential TWI project for BP Plc (BP), a state of the art review was prepared in order to assess the potential of underwater wet welding for the repair of offshore platforms. As part of Phase 2 of the same project, a practical programme of work was carried out aimed at establishing guidelines for underwater wet welding repairs for steels with high carbon equivalent (CE) up to 0.40. Steels with high CE will produce high heat affected zone (HAZ) hardness which makes them more susceptible to cracking. Consequently, it was necessary to investigate special techniques for preventing hydrogen cracking in high CE steels. The techniques investigated in this phase of the project included the use of special electrodes and techniques which are claimed to reduce the susceptibility to hydrogen cracking. Table 1 presents the relative suitability for wet welding of different electrode types in relation to water depth and CE. Welding trials were carried out at ~4m water depths on low CE (0.31) and high CE (0.38) steel. The test groove welds were carried out as butt joints with permanent backing and with strongbacks simulating restraint during actual production welding. For the high CE steel, three candidate special techniques were used for the welding trials. The techniques used included: Standard technique with ferritic steel electrodes. Controlled weld bead deposition techniques using ferritic steel electrodes. Buttering on bevel faces with ferritic electrodes and oxidising flux followed by groove

weld using ferritic steel electrodes. Standard technique with nickel electrodes. These welds were evaluated for ease of welding in the vertical position (PG/3G vertical down) against a control trial weld made in the 0.31CE material using standard ferritic electrodes and a standard welding technique. The welds were tested by radiographic inspection and macroscopic examination as specified in AWS D3.6M and hardness tests as specified in AWS D3.6M /ISO9015-2. In addition to these standard tests, the welds were also subjected to additional hardness testing of the HAZ (parallel to the FL on both sides of the weld), magnetic and ultrasonic inspection and micro examination up to 1000x. Additionally, the weld metals with the three different types of electrodes used in the trials were tested for the diffusible hydrogen contents.

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1.3 Hyperbaric welding

Dry hyperbaric welding processes, Figure 2 and Kononenko V Ya (2008), may be water depth limited, with TIG currently used up to 180 metres sea water (msw). The Welding Engineering Research Centre at Cranfield University has a unique hyperbaric welding facility. The 1m diameter chamber enables all position welding process research and development to be carried out at pressures up to 250 bar (2,500msw equivalent depth). Using this facility, fully automated MIG welding has been proven to be successful at up to 250 bar for operations such as repair and hot tapping of pipelines. The key enabling technologies are welding power source technology and optimised metal cored wire composition. It has been found that with increasing depth and pressure cooling rate becomes high and weld metal cracking tendency increases substantially. Maintaining preheat is vital to avoid such hydrogen assisted cracking. However, given that heat input and metal deposition are coupled in the GMAW process there is little opportunity to increase the heat input. The proposed solution to be investigated in this project is laser assisted MIG welding. The multi kilowatt laser power will be delivered by fibre and will be applied in conduction mode for maximum weld quality. The study will investigate the role of moisture level, pressure and heat input on the cooling rate of the weld pool, the associated heat affected zone and cracking tendency. Additionally improved quality through minimisation of spatter using a reciprocating wire GMAW process (CMT) will be investigated.

1.4 Dry localized welding

The NEPSYS Dry Underwater Welding system, Figure 3 and Anon (2005), is claimed to be a low cost underwater welding system that produces an approved, permanent weld equal to dry weld standards. The system is also claimed to achieve good quality welds satisfying Class A, AWS D3.6:1999, although this is yet to be validated by review of existing data, qualification and through review of history of underwater repairs. The system incorporates a custom-built clear polymer housing that encloses and isolates the weld and HAZ from the surrounding environment. The enclosure is sufficiently large for the welding electrode to achieve complete run-out, or in cases where complex structures are involved it may be customised to surround the entire weld area, but it does not need to house all of the welding equipment or the diver. Heated inert gas, delivered at a pressure elevated above the ambient hydrostatic water pressure, is continuously delivered into the habitat to provide a completely controllable environment around the immediate weld area. The technology offers potential of using in-air Ni-based consumables at greater depths than wet MMA welding. The use of in-air Ni-based consumables at greater depth will need to be validated through a series of weld trials.

1.5 Underwater Laser Beam Welding

Underwater Laser Beam Welding (ULBW), is not a new technology (Szelagowski et al 1987), but it has not found wide acceptance. Toshiba has developed an ULBW, cladding technique for the nuclear industry, Figure 4. This technique involves the deposition of SCC-resistant Ni-based alloy 52M weld metal directly onto the surface of the aged components. In addition, Toshiba has carried out fillet weld trials and qualification for nuclear application. The technique has been demonstrated for water depths up to 30m and delivers cladding of an exceptional weld quality. Westinghouse Electric Company, Welding and Machining (WEC WAM) is working in parallel with Toshiba to develop this process for repair welding in both the US and Japan, as well as in other potential markets as reported by Tamura M et al (2008). Through the efforts of WAM and Toshiba, the US industry has included ULBW as an acceptable repair welding method for nuclear applications in ASME Boiler and Pressure Vessel Code Section XI. There is a need to demonstrate viability of the technology to be deployed for butt and fillet welds on structural steels with CE>0.38 and establish depth limitations of the technology.

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2 Objectives To identify and define technological boundaries or limitations for wet underwater

welding through a state-of-art review. The State-of-art review will be extended to include experience with the NEPSYS system, where data can be made available by Sponsors.

To determine feasibility of laser-assisted TIG hyperbaric welding through trials. To establish applicability of the NEPSYS system and Ni-based electrodes through

trials at varying water depths and carry out procedure qualifications, if suitable. To demonstrate use of the ULBW process at water depths up to 30m/40m water depth

depending on limitations of ULBW head on butt, fillet and weld overlay configurations. To establish whether the welds produced meet the requirements of Class A of AWS

D3.6 (1999) through weld procedure qualification tests.

3 Approach TWI proposes to carry out a work programme, as a Group Sponsored Project, on underwater welding repair technologies, as below (Figure 5). It is anticipated that the proposed project will be led by TWI, with support from leading academic and industrial partners, and be beneficial at the outset for Sponsors from system manufacturers, material suppliers, to marine and offshore contractors and operators. Recent project work including a state-of-art review carried out for BP by TWI will be drawn upon to improve the potential and quality of wet welding techniques including repair of high carbon equivalent structural materials. Since the review was based on BP experience; information from other Sponsors in terms of their experience including qualified procedures and test data will be collated and incorporated in the review. The state-of-art review will also be extended to include experience with the NEPSYS system, where data can be made available by Sponsors. Trials on wet underwater welding to further develop the approaches identified for BP including buttering with oxidising electrodes and controlled deposition techniques will be carried out at TWI and the National Hyperbaric Centre in the UK, in collaboration with Hydroweld. Trials for laser-assisted hyperbaric Tungsten Inert Gas (TIG) and Metal Inert Gas (MIG) welding processes are proposed at Cranfield University. Trials with the ULBW system are proposed to be carried out in partnership with Westinghouse Welding and Machining (WEC-WAM) on structural steels used offshore, simulating butt weld and fillet weld configurations - to demonstrate viability and capability of the technology for further development. Trials with the NEPSYS system and Ni- based electrodes are proposed to be carried out by TWI in partnership with Neptune. For all the successful techniques, full welding procedure qualification tests will be carried out to the Class A criteria of AWS D3.6 (1999) and a suite of welding procedure qualification records and welding procedure specifications will be written for use by the Sponsor group.

4 Deliverables

A final report with fully interpreted results and recommendations from: A paper based state-of-art review of the four technologies identified in this proposal. Further development of three identified wet MMA techniques up to 40m water depth. It

should be noted that current experience with Ni-based weld metal is limited to

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Trials with NEPSYS system and Ni- based electrodes and a review of potential benefits and limitations of this approach.

Welding procedure specifications and qualification records in accordance with AWS D3.6 (1999) for all the successful technique(s).

5 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. The data presented for wet welding is by courtesy of BP and will be used in the state of art review. Research will be carried out at TWI and Cranfield University. BP, Hydroweld, Neptune and Westinghouse will be in-kind contributors. It is anticipated that the project will commence with the support of three fully paying sponsors and that the work scope will be determined accordingly based on the final number of sponsors.

6 References Anon, 2005: Neptune underwater dry weld technology, Welding and Cutting, 2005, 4(5), 228-229. Anon 2008: 20,000 welds under the sea maintaining and repairing the worlds largest ships, Practical Welding Today, 2008, 12(4), 14-16. Kononenko V Ya 2008: Hyperbaric dry underwater welding (Review), Paton Welding Journal, 2008, 4. 36-40. Russian] (Translated from Avtomaticheskaya Svarka). Szelagowski P, Schafstall H G, Rothe R and Sepold G 1987: Wet underwater welding with high-power CO2 lasers, Proc, Int Conf on Power Beam Technology, 10-12 September 1986, Brighton, UK, Ed: J D Russell. Publ Abington, Cambridge CB1 6AL, UK; The Welding Institute; 1987. Tamura M, Kouno W 2008: Bringing Underwater Laser Beam Welding to Nuclear Plant Applications. Paper presented at 8th International EPRI Conference on Welding Repair and Technology for Power Plants, Sanibel Harbour, Fort Myers, Florida, USA.

Consumables for Steel CE Level

CE 0.40% AWS D3.6 Quality Depth Metres

Ferritic Rods

Ferritic FCA Wire

Ferritic Temper

Bead

Oxidising Buttering

Rods Nickel Rods

Stainless Rods

Stainless FCA Wire

Class A

Class B

Class C

0

10

20

30

40

50

100

150

200

Proven Proven Proven

Possible

Table 1 Suitability of electrode types for wet welding repairs.

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Figure 1 Illustration of Wet Underwater Welding.

Figure 2 Hyperbaric Welding (Courtesy: WEC-WAM) (Courtesy: Cranfield University / Isotek).

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Figure 3 NEPSYS system (Courtesy: Neptune Marine Services Ltd).

Figure 4 ULBW weld pad with ERNiCrFe-7.

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Water depth

Use of Ni based electrodes

Wet Welding Nepsys

Figure 5 Schematic showing the technologies that will be addressed in the GSP and the anticipated direction of progress. *ULBW capability currently demonstrated up to 30m (weld overlay) for nuclear industry.

ULBW* 40m

Hyperbaric 250m Laser assisted Welds

Feasibility of application

Increased depths

1 Introduction1.1 Current Status1.2 Wet welding1.3 Hyperbaric welding1.4 Dry localized welding1.5 Underwater Laser Beam Welding

2 Objectives3 Approach4 Deliverables5 Price and Duration 6 References