API 560 Furnace Tube 1

[fortmceng]

API 560 Section 7.1.4 does not allow furnace tubes to be circumferentially welded to make up for the effective tube length for example 15' of two length of pipe to make up for 30' effective tube length by circumferentially welding two pipe ends. Does anyone know why and what are the risk of doing so.

Thanks

 

[metengr]

For furnace tubes or piping for new construction of heat transfer equipment you are introducing a butt weld within a span that can result in failure in service. This is poor engineering design practice.

 

[fortmceng]

metengr

I understand that it is not a good practice but I am trying to find is what kind of failure mechanism could be expected on that butt joint. Is failure going to be in short term or long term.

Thanks

 

[metengr]

fortmceng;
The potential failure mechanisms are mechanical fatigue or creep/fatigue. If the weld is sound, you are probably looking at more of a longer term damage mechanism. If the weld quality is poor, you can have short term problems – leak from slag or IP or fatigue caused by weld undercut along the OD surface. If you need this butt weld, I would make sure you conduct a 100% volumetric examination of the weld, and blend grind the weld cap flush with the OD surface.