Can you Disposition Laminations in Wrought A234 WPB Elbows?

[Bambie]

Phased Array inspection of a wrought A234 WPB, 18"nps sch 40, 90 degree, LR elbow has revealed laminations and inclusions.

The majority are located mid thickness along the cheeks of the elbow, not the extrados or intrados.

The majority lie parallel to the surface and do not break through either the OD or ID surfaces, however, some transition vertically through half the wall thickness.

Is there a sure-fire way of confirming that these are not cracks?

Perhaps someone familiar with A234 WPB wroughting techniques could comment on whether laminations with vertical transitions would form in the cheeks of large elbows.

 

[Bambie]

metengr,

ASME B31.1 Chapter VII and the Appendices provide guidance on maintenance and repairs.

My interest in solving the cracking conundrum shouldn't jeopardize structural integrity.

Cutting into and patching up an elbow that is suspected of cracking poses a greater concern to me.

 

[metengr]

I really don't understand your cracking conundrum - maybe after 40 years of supporting coal fired power plants in the US, working with this stuff day in and day out has become routine. Ok, let me go through and attempt to explain what you should consider;

1. You have performed PAUT and determined some type of sub-surface defects and/or non-injurious defects are present.
2. You have two course of actions - either go back into service and monitor again by PAUT (using the same NDT method) OR you remove a core sample to install an RT plug, thread and seal weld. RT plugs are installed in piping and elbows on a routine basis.
3. You send the core sample out for metallurgical examination and find these are all laminations with no crack extension or link-up. You are done with further evaluation and monitoring. Pipe and elbows with lamination defects are in piping systems today even after 50 years of service.
4. The lab results show crack extension beyond the existing defect or link-up of defects. This requires some level of future monitoring with PAUT. Perhaps on a 12 month basis for starters.
5. At some point in the future you either continue to monitor; if crack extension is un-recordable or non-existent stop monitoring or you replace the elbow.

ASME B31.1 code has been revised to believe it can be a repair code and frankly, it is not an in-service repair code. In most Jurisdictions across the US, B31.1 is not even regulated like boilers and pressure vessels so you have the freedom to use API, NBIC or PCC-2 for in-service repairs, period.

 

[Bambie]

metengr,

If I had any doubts;

that a fatiguing mechanism could not cause mid thickness radial cracking at the elbow crown, or

that laminations or inclusions with vertical orientation mid thickness at the elbow crown could occur during manufacture,

then I certainly could not justify core drilling to 'take a peek' with the intention of leaving the hapless elbow in service.

Monitor or replace are the only reasonable options.

 

[racookpe1978]

OK. Then do it your way.

You have heard our concerns and recommendations. It is your plant. 8<)