Radiographic examination of socketweld 2

[MisterDonut]

Is radiographic examination (RT) applicable to socketwelds on piping? I have found sources on both sides.
Specifically, I'm concerned about a carbon steel (A106B, sch 80) piping system with class 3000 forged steel (A105) socketweld fittings, 1.5" NPS, handling high-pressure steam condensate. Design pressure is 250 psig, design temperature is 500ºF.
Owner requested 100% RT as well as a pressure test on the portion of the system that will be underground. Contractor claims socketwelds can't be examined by RT.

 

[Zapster]

Owner requested 100% RT as well as a pressure test on the portion of the system that will be underground. Contractor claims socketwelds can't be examined by RT

Yes socketwelds can be examined by RT, and specifications are routinely written with the RT requirement to ensure that the gap between the pipe and fitting is correct. See

http://www.eng-tips.com/viewthread.cfm?qid=141113&page=1

for some interesting discussion.

 

[eliebl]

In my experience socket welds can be radiographed. The radiograph only tells you whether there is appropriate root gap, not much on the quality of the weld.

With a temperature of 500F I would be concerned about the root gap.

EJL

 

[unclesyd]

You can see anything internally you want to see on RT of a socket weld and coupled with a good VT of a clean weld you can wee everything you need to see. Most contractors do not understand or want to understand the capability of an RT inspection. They will have a hundred arguments why RT is going to cost you money and slow them down.

All contractors will claim to have gobs of experienced welders that are capable of correctly welding sockets and there is no need to RT as it want show nothing. One will find this is not the case 99% of the time. As one looks at enough socket weld radiographs one gets to know the welder and how good or bad they are.

In the same process area of my post in the referenced thread recent modifications resulted in approximately 500 new socket welds on new and existing piping that were only going to have RT at 25% to save money again. The construction group went through the whole song and dance again. There was a clause in the contract that anything over 5% rejects would trigger 100% RT. This happened on the first pass of RT and Visual. The initial problem stemmed from not cleaning the existing pipe and trying to use 7018 in lieu of 6010. This coupled with single pass welding was trouble.
My experience over the years has been that contractors see sockets as a money maker by initially agreeing to the contractual requirements and then trying worm out of same when fabrication starts.

Just remind them that bad welds are what slows a project down.

 

[moltenmetal]

unclesyd: I rarely disagree with anything you say, but in this case I'd respectfully suggest that if you're going to do 25% RT on socket welds, what you really wanted up front was butt welded construction and that's what you should have insisted on- and paid for.

Socket welding isn't a license to print money unless butt welding has been bid and socket welding has been swapped in as "equivalent"- if that happens, whoever prepared the bid spec AND the project manager both need some teaching! When properly specified, SW is a fitting/welding practice used for small sized lines where (internal) corrosion and thermal stress concerns are minimum. The technique takes less labour and skill to do correctly than butt welding does, and this more than offsets the greater cost of the fittings. Like every other method it has its strengths and weaknesses.

Random RT of sockets will help you find excessive gap due to poor fitting practice. That's far better than finding a systematic problem with the fitters the first time you have to cut a joint. Nobody can reasonably claim that spot RT causes excessive cost or delay.

To my knowledge there is no code requirement for a gap of a certain size in the as-welded condition unless you (the owner) stipulate one. There IS a requirement that the pipe not be bottomed out in the fitting PRIOR to welding, but that ain't the same thing! In my experience, shooting RT to ENSURE a gap in the as-welded condition is just a recipie to force the fitters to exaggerate the gap so they pass the test.

What you should do if you're worried about gap is to specify gap-a-lets. Then you can shoot for the presence of the gap-a-let. A random RT sampling will tell you whether they're using them or not.

 

[unclesyd]

moltenmetal,
We don't want nor is there is a desire or need to have a butt welded system in this process area though about 20-30% of the welds are butt welds. As stated before this system is for a heating media, Vaporized Therminol @ 70 psig and up to 700F. This vapor system where we essentially use on the latent heat is a legacy system that started with mainly 1/2" and 3/4" piping and has now been replaced by 3/4" through 1-1/4" piping due to increase in throughput. For a total of 17 process lines where conservatively there are over a 100,000 socket welds. This system was conceived in 40's by people a hell of lot smarter than me and the decision was to go with sockets instead of Acetylene welded butt joints. Socket welds have served us well since plant start-up in 1952. There has been one major spill/leak of vaporized Therminol, 22 gals, from a piping failure and that was where a welder made an ill conceived correction to correct a mistake.

It is only in the last fifteen years or so that we have trouble with pipe fabrication when using socket welds by project contractors. Our own welders and welders from the on-site maintenance group have no trouble at all with socket welds. All our piping specifications for the Therminol system are very specific as to our requirements and have stood a test in court. We have on-site radiographs and sectioned fittings, aside from the drawings, that are available for inspection prior, during, and after one starts fabrication. We have data, time studies, showing that it takes no more time to do it right including RT than to screw up. These samples show the gap and insertion, fusion, porosity, 2 pass welding and appearance requirements.
One reason for such strict requirements is that the majority of the system is in building where a one time 2000 people were working and any leak could result in catastrophic vapor cloud explosion(detonation). This is a real possibility that has been looked at by two international experts on same, the loss prevention departments of two major chemical companies, and the insurance people. Another reason was that for several years a recordable spill was 2 ounces, whether liquid or vapor, and the exposure limit was also very low. Both exposure limits and reportable limits have been raised to a more achievable level, we still don't like leaks.
To mitigate the above hazards the system the piping specification for Therminol also requires the use of RTJ flanges, double globe valves(reversed) and new ring gaskets anytime a flange is made up.

All we have ever asked is that one bids on the job as specified and get it right the first time without trying any shenanigans. It's not the question of what might be better, cheaper, quicker, or faster it's doing the job as specified with competent people at which point we will inspect and make the call, good or bad. If you need to know any fabricators excuses just let me know as I have book full.

PS:
Our original 1950's fabrications have about 1/2 the number of fittings that a comparable system of today would have as a great number of pipe spools were bent on slab with only a flange at each end.

 

[MisterDonut]

To minimize risk for the owner on this system (see original post,) what NDT should be specified/performed? Since the system will be buried, a failure would be expensive to fix, which is whay the owner wants to be over-cautious with NDT.

 

[unclesyd]

The best you can do is make sure you have competent and willing fabricators.

Have a inspector not only to test the finished weld but one who is capable of monitoring the fabrication.

We require a two or three pass weld using 6010 for all passes but have achieved acceptable results while using other rods.

For your size it will require at least two passes of whatever the filler metal your procedure requires.

I would do a VT for surface breaking porosity, undercut of the pipe, filler volume based on your requirements, and general appearance. Watch for filing of the weld edge on the pipe side.

Follow the VT with RT and look for fit, lack of fusion, porosity. Lack of fusion is somewhat a judgement call as one has to determine how the fitting/pipe intersection is fused. All the other are self-evident.

In short get a good VT and RT then proceed to the required hydrotest.