ASME B31.1 RT Access Hole Plugs

Date 02-09-2005 15:26

I am curious as to what others in the industry use for plugs on radiographic inspection openings on high energy piping constr. to B31.1. I have always seen something typical of 1" dia. hole drilled and tapped with a treaded plug installed, then seal welded. A contractor we have talked to says they will not use this design in supercritical boiler applications because of failures due to corrosion of the threads which will eventually deteriorate causing the seal weld to fail and pose a serious safety and reliability problem. They have proposed a partial penetration welded cap. FYI-We are going with the PP cap, because of their recommendation and engineering judgement.
So, a few questions:
1.) Has anyone experienced failures of threaded and seal welded RT access hole plugs?
2.) What are others currently using?
3.) According to B31.1-2004 (Para. 114.2.2), "A representative type of access hole and plug is shown in PFI ES-16." Would anyone have reference to this standard and what the "representative type" is?

Thanks,
Chris

By chall

Date 02-09-2005 15:57

We haven't worked on a supercritical boiler but we have done a number of high pressure boilers using P5B material for main steam that have used threaded and seal welded plugs.

I've never seen the kind of problem described by the contractor.

I don't have the standard, but for $20 you can get one here:

http://www.pfi-institute.org/Product.htm

Not much help.

Charles Hall

By gerold

Date 02-10-2005 14:49

Thanks, I have already ordered the book for my reference.

By MBSims

Date 02-09-2005 22:48

Response to your questions:
1) Yes, we have seen the seal welds crack on threaded RT plugs on supercritical units and some drum units. Typically, they have grossly oversized welds and fail due to creep cracking in the HAZ on the P22 pipe side. I have seen a few welded with E309 electrodes (for some unknown reason) that cracked due to thermal stress.

2) We have also used full-penetration welded caps. You can get them from Gibson Products in TX.

3) I don't have it here at home, but it shows the thread details, hole sizes, and plug details. "Representative" refers to a threaded plug and means the dimensions may be different than shown. But, it still has to be properly designed for the pressure since the threads carry the load.

By chall

Date 02-10-2005 12:52

Just an observation, but it seems to me that a supercritical unit would use materials other than P22. I thought the practical limit of P22 (temperature limit) was somewhere in the vicinity of 1050F.

Charles

By MBSims

Date 02-11-2005 03:08

Ours run at 1000 F main steam temp. Steam temps are controlled by atemperators on the pendant platen outlet.

By Jim Hughes (***)

Date 02-12-2005 02:45

I have seen it both ways. Just finished a Hitachi boiler back in Aug. and Hitachi had designed Gama-Plugs in the HP side of the boiler. I have seen them without Grama Plugs and in those cases you have to bring in a hot soarce (cobalt). Normal soarces of 100 curies+ can't go through 5" thick material without a very long shot time. We had P91 material that was 2.44 iches thick. Since you have to shoot through both sides of the pipe it comes to 2.44x2= almost 5". I have never seen a Gama plug fail after its been welded nor have I seen them in super critical boilers because of the pressures. 3000 to 5000 PSI.

JPH