Has anyone had problems with T23 boiler tube that has had failure caused by cracking and corrosion. Also problems welding new tubes to T23. T11,C.S etc...
Stress corrosion cracking has been reported on welds "too hard" exhibiting martensitic microstructures. Proper preheating will prevent the problem. There is also potential for reheat cracking.
Our welding problems with T23 tube have all been due to poor welder performance and lack of attention to proper ground placement.
We have had no problems with heavy wall, P23, pipe welds subject to PWHT.
we did have problems with grounding and tried different grounding areas (close to weld, jumpers etc..) any suggestions? we are done with the job X-rays were good and hydro was good. I am worried about long term.
Based on your statement above, I see no threat to failures in the short term. Long term, if the Grade T23 tubes are steam circuit tubes (and not upper furance wall tubes) you may have to resolve the concern of retained ferrite in the microstructure, and the impact of retained ferrite on creep rupture life (as I mentioned in the previous post).
Our grounding problems were more basic than just placement. The welders were welding with Miller 8-bank power supplies using improper grounding for both DC negative and DC positive simultaneous welding applications therefrom. Limited duty cycles of those units when all are being used further exacerbate arc voltage/amperage control. We never had problems using single Miller XMT power supplies or similar power supplies from Lincoln. There were reports of problems encountered when interpass temperature was high. Limiting interpass temperature between 450 F to 500 F max. mitigated those reported problems.
The real problem is lack of knowledge on the part of the welders and general foremen. Once finally brought to the attention of corporate Welding Engineers for review, rectification was easy. It is unfortunate that Welding Engineers (often considered expensive overhead)are not based on mega-project sites to the extent 20 to 30 years ago. Companies tend to rely on their CWIs to perform the tasks of a Welding Engineer; a task for which they are often not trained.
