Decades ago, its introduction to the world only entrusted it with the simple, yet dependable, role of temporarily repairing damaged steel-hulled vessels, but today, underwater welding has grown and expanded into an advanced and widely-practiced method of construction and repair for numerous structures. Finding rigorous applications in the repair of submerged marine pipelines, offshore structures, and nuclear power plant components, underwater welding positions welders into locations where the environment stands in direct opposition to the completion of their tasks, necessitating the need to displace water and alter pressure. The complicated nature of underwater welding lends importance to standardization in assuring the best practices in hyperbaric welding methods. For this purpose, the underwater welding code can be looked to for guidance.
The underwater welding code traces its origins back to the mid-1970s, when the AWS Committee on Marine Construction requested the Subcommittee on Underwater Welding in the pursuit of establishing a standard that reflected the state-of-the-art technology for underwater welding. Their efforts culminated in the initial publication of the code in 1983, followed by five subsequent revisions. The sixth and current edition of the standard, AWS D3.6M:2017 – Underwater Welding Code, has recently been released.
AWS D3.6M:2017, amidst the assortment of variables and inspection procedures it details, ultimately is driven towards one clear goal: to conveniently specify underwater welding work of a known quality level.
In general, the standard addresses welding in both dry and wet environments, being applicable to five specific hyperbaric environments, each facing different underwater conditions. These are welding: in a pressure vessel in which the pressure is reduced to approximately one atmosphere (dry welding at one atmosphere), at ambient pressure in a large chamber from which water has been displaced so that the worker does not need diving equipment (dry welding in a habitat), at ambient pressure in a simple open-bottomed dry chamber that accommodates at least the head and shoulders of the welder (dry chamber welding), at ambient pressure in a small, transparent, gas-filled enclosure, with the welder outside in the water (dry-spot welding), and at ambient pressure, with the welder or diver in the water and without any barrier between the water and the welding arc (wet welding).
Clauses 1 through 8 of AWS D3.6M:2017 apply to all types of welds, addressing their workmanship and technique, as well as the qualification of the welders. 9, 10, and 11, however, are each devoted to a different weld class, specifying a level of serviceability and properties to which each class must conform. The weld classes featured in the underwater welding code are:
Class A Welds – intended to be suitable for applications and design stresses underwater that are comparable to their conventional surface welding counterparts.
Class B Welds – intended for less critical underwater applications where limited discontinuities can be tolerated.
Class O Welds – must conform to another designated code or standard and additional guidelines to cope with the underwater welding environment.
As the latest revision of the underwater welding code, AWS D3.6M:2017 contains many alterations from the 2010 version of the standard. Some major changes include:
- Cleaning requirements have been better defined
- Acceptance of qualification to earlier editions of D3.6M is incorporated
- Ultrasonic Examination Clause 8, Part IV, has been updated to better align with the UT technique described in AWS D1.1/D1.1M, Structural Welding Code—Steel
- Sample Forms have been revised
- An informative annex has been added to address the qualification of marine welding inspectors
- There is a restructuring of the clause numbers
- Ultrasonic Stress Relieving has been added to the document
Any change within the AWS D3.6M:2017 document from the previous version of the underwater welding code is marked by either a vertical line in the margin or underlined text.
AWS D3.6M:2017 – Underwater Welding Code is available on the ANSI Webstore.