Full radiography of joints for lethal service

[vpkhati]

Hello everyone,

Can anyone provide me the basis of radiography level for lethal service, like why do we give full radiography for the lethal service job. (UW-2(a) and UW-11(a)(1) - All butt welds shall be 100% radiographed, agreed but why ).

Also in some specification it is given that above 50 mm category “D” joint shall be butt joint. Why ?

Regards

 

[vesselfab]

I will answer your question with a question/

If you were out in a unit that handles, say, phosgene. Would you feel more comfortable working around vessels that were fully 100% xrayed esuring good welds or around vessels with one 6" spot every 50 feet of weld...thats 1% of welding checked.

 

[deckie]

You may wish to consider 100% UT as an anternative. I understand that Section VIII Div 1 allows UT as a volumetric examination method in lieu of RT without having to use a Code Case as of 1 July.

 

[EdStainless]

I am not sure that they use of UT is allowed in UW.
The last two UW jobs that I saw were cyanide and HF.
Both were speced this way for good reasons.

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Plymouth Tube

 

[racookpe1978]

Ask the former residents of Bhopal India if they wanted less NDE on lethal service, high pressure gas pipelines and tanks.

 

[moltenmetal]

Bhopal gives a good example of what happens when things to horribly wrong with plants handling lethal substances, but the incident had NOTHING to do with a lack of radiography or other NDE.

As to the OP's original questions:

1) Why 100% RT for lethal service? Because it's an appropriate response to the risk involved with this piping- that's why 100% RT is CODE MINIMUM NDE for welded joints in lethal service. However, it remains the owner's call as to whether or not a particular service is considered lethal or not, so the owner's judgment is still called for.

2) "Some specifications" ask for all sorts of stuff, without giving reasons as to why. Why only butt welds beyond 2" NPS? Socket welding is rarely used beyond 2" NPS because the fittings are hard to come by and expensive. Unlike your "some specifications", we do permit slip-on flanges beyond 2", even in normal fluid service much less category D- but both the inner and outer weld are completed regardless of the service. We are not relying on a single fillet weld anywhere beyond 2" NPS.