Weld on Weld in offshore structures

By sachin Date 08-01-2019 08:58

Dear all,

Design codes and standards often do not provide technical justification for avoidance of weld-on-weld nor do they specifically address conditions by which code compliance is ensured. However probable underlying factors affecting the in-service performance of weld-on-weld in an offshore structure can be as the following:
 Possibility of altering the microstructure of existing weld and HAZ by application of the second weld. The hardened microstructure may reduce the toughness and strength properties of the joint. It may also reduce ductile to brittle fracture transition temperature resulting in pre-mature brittle fracture failure.
 Need for a new weld procedure specification (WPS) and associated procedure qualification records (PQR), as the original WPS is for base metal weld material rather than to another weld.
 Possibility of defect generation during the application of the second weld on the surface of the first weld in case of weld-on-weld. It is possible that the first weld might contain defects where the application of second weld on top of first one may concentrate defects in a limited volume. This can be more concern in repair welding of an aged offshore structure, which may contain defect or residues of aging artifact as a result of exposure to service environment.
 Welding if no PWHT is applied leaves behind residual stress and flaws, which are known to reduce fatigue life of the joint during service life. Separating welds with minimum required distance will prevent adverse effect of welding residual stress in fatigue performance (hot spots) when the structure is under cyclic loads.
 The welding residual stress coupled with hardened microstructure in offshore environment especially in the presence of generated hydrogen from CP may reduce the environmentally assisted cracking performance of the joint.

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By zeki.kasap (*)

Date 08-20-2019 08:37

There is something you have to understand, before and while the welding progress, you or your welder clean the surface with brush and see the result all passes. And also choose the right consumable wire, I know it is a very expensive method, but, in long term it is very useful. Afterthat, acc. to material, you prefer to choose pre-heat temperature and interpass temperature. This application is for Heat affected zone area, when the welding progress continues, form of the sheet metal stays to stabilize toughness and material features.
Choose and prepare the rightful pWPS, and See the result in PQR requirements.
Best Regards.

By TimGary (****)

Date 08-20-2019 13:22

Design Codes and Standards detail minimum requirements.
Weld on weld is a common practice in welding that is not detrimental in all but extreme cases.
Standard Code requirements for controlling how much weld may be placed in a single joint or connection are weld size tolerances, heat input limits when impact requirements apply, and requirements for WPS controlled repair procedures.
At any time "The Engineer" wishes to exceed minimum Code requirements, they may do so, in any way they choose, through additional project specifications. However, these requirements are to be detailed at the beginning of a project, or before the job bidding process.
Additional requirements may be applied to a project that is already underway, but this means the Contractor(s) can submit Change Orders to cover unplanned expenses, or internal changes need to provide increased cost justifications.
Many Contractors rely on this to profit from jobs, as they submit an initial low bid to get the work, then charge a premium for change orders.

Tim