Marine Technical Limits Water-backed Welding Procedures Gains Class Approval

After extensive research, and in-house trials, into the development of a water-backed welding procedure, Marine Technical Limits has had its process qualified by two Classification Societies.

In previous years, MTL experts have carried out significant in-house trials to establish water-backed welding procedures suitable for specific projects. However, the latest qualification by DNV and Lloyds Register has given the organisation endorsement to carry-out bottom-shell pit welding projects – without having to seek case-by-case approval, and without the introduction of any preheating arrangements. 

Not a Commonly Used Process

Welding afloat with a water backing (water-backed welding) is not a commonly used or well-established process. This is because of the cooling effects the water has on the welds. Typically this causes the welds to cool quickly resulting in high hardness and often with surface breaking and/or volumetric defects.  

There is limited Class guidance on this subject. Water-backed welding is not often required for in-service tankers this is because hotwork repairs to trading tanker hull structures are typically undertaken within dry-docks.  With FPSO (floating, production, storage, and offloading) and FSO (floating, storage and offloading) vessels often remaining at sea for in excess of 10 years, the need to undertake hotwork repairs whilst vessels remain on-station is far greater.  

As a result, MTL’s team of naval architects and marine engineers undertook extensive research to better understand water-backed welding and its associated challenges.

Significant Investment and Research

Senior Project Engineer, Adam Westwell, said, “Throughout the last few years MTL has invested heavily in the research and development of robust water-backed welding procedures. Our team designed and manufactured a bespoke welding test tank connected to an industrial water chiller unit, allowing us to simulate the flowrate and seawater temperatures found offshore. By creating the same conditions, we were able to strategically experiment with welding variables and techniques to establish the best process to achieve repeatable results.”   

“After carrying out numerous welding trials, along with undertaking the necessary non-destructive and mechanical testing of each weld to provide certainty of weld quality, we gained extensive knowledge and understanding of the key variables and the effects these variables have on the water-backed welding process.”

By completing the research and trials in-house, the MTL team has gained a wealth of specialist knowledge for water-backed welding, allowing the development of procedures that are more suited to its client’s offshore repair requirements.