I just came off a job where there was some welding done on 30" SA-335 P91 pipe to B31.1. I was just there to observe for my client, not to act as an inspector. The first problem started when welding was done outside the parameters of the WPS. For instance the root opening was 3/32" plus or minus 1/32", the land was 1/16" plus or minus 1/32", torch gas 15-25 CFH, purge 5-25 CFH amperage for GTAW root pass using 1/8" filler was 70-130. From the fit the root opening was up to 1/4" the land was feathered the purge was set at 100 PSI (who knows how many CFH that is) the torch flow was 50 CFH with a gas lense, and the root went in around 160 amps. after the contractor was notified of these parameters he revised his WPS to pretty much allow them to weld any way they wanted to. the root opening was up to 5/16" the flow for the torch was 15-60 CFH and amperage was 50-200. now I know that there is a reason ASME allows changes to be made to Non-Essential Variables, but shouldnt there be a limit? the only thing the inspector could reject the pipe on was internal misalignment exceding 1/16"
You stated that the only thing on which the inspector could reject the joint was misalignment. It appears as though he was looking for a reason to reject the welds. If the weld was acceptable according to the acceptance requirements then the inspector should accept the welds. If it did not meet the acceptance requirements then he should reject it.
It would be bad form to change the WPS to fit the welding conditions rather than getting it right from the start, but as you pointed out, these are non-essential variables so it would only be the most hard-nosed inspector that would try to make a huge issue out of it.
Having said this, non-essential does not mean non-important! Details like the weld preperation is important and in some instances can mean the difference between a good weld and poor fusion etc.
Regarding the amps at which the welder was welding, I always prefer to let the welder sort this out him/herself unless heat input issues are a concern, because you generally end up with a better joint. This really is the issue at the end of the day. (As long as your welder was coded to perform the weld.)
What is important is to make sure that the welder has control of his equipment. With the gauge set as you say, it is possible that he does not actually know what the gas flow is. This would not be acceptable.
Regards
Niekie Jooste
Niekie,
I agree with you totally that a inspector should not just be on the look out to find a reason to reject. from my observations there were many things going wrong on this project because the contractor was in a rush. My personal opinion about the parameters for the welder (amperage, filer diameter, cup size, tungsten diameter) should be left up to the welders own judgement. (within reason)
As far as the gas flow on the purge I have never seen 70'-00" + of hose freeze and become so brittle that it breaks. the most I have ever seen freeze was maybe the first couple of feet from the tank. This hose had to be replaced twice. From the start the torch CFH was at 40 and the welders tacks were sugaring. I believe this was caused by turbulence fron the torch flow being too high. To fix this they increased the Purge flow (a flow meter could not supply enough flow so a PSI guage was used).
Dear Wildturkey,
In first place, let me say that I was amazed at your phrase "The contractor revised his WPS to allow the gang to weld any way they wanted to". I thought this happened only in our South American, third world, underdeveloped countries; I could have never imagined that it happened also in the United States.
In second place, I wholly agree with Niekie3 and will add just a couple of minor comments.
1. Construction contracts use to have a clause saying that the contractor must submit his methods and procedures to the owner approval before starting the job and that he can not change those procedures without the owner permit. Does your contract say that? If so, you're protected from a legal point of view.
2. You don't say what fluid the piping is intended to carry. However, from the large diameter, I'd say that it's low pressure, exhaust steam FROM the turbine. In this case, we must admit that the service isn't as much critical as it is high pressure steam TO the turbine, for example.
So, from an engineering point of view, we don't need to treat this piping as strictly and severely as we should do with the high pressure steam line.
3. Tell the contractor that measuring the gas flow isn't that difficult, or as we say in Brazil, "is not a monster of seven heads". A rotameter by the cost of a few dollars installed in the gas hose will do.
Giovanni S. Crisi
Sao Paulo - Brazil
Giovanni,
the pipe is the hot reheat pipe about 50'-00" from the steam turbine. I do not know what the pressure is but I know the temperature is >750 degrees.
I agree wholeheartedly with both Niekie and the Professor, especially Niekie’s comment about why the Inspector was looking for a reason to reject!
Throughout an Inspector’s career, there’ll be many times he’s forced out of his nice neat little box by some contractor who by his design (such as the example), perches precariously on the edge of his. Maybe one leg in and one leg out. I suggest to you that when this happens there are two things an Inspector needs to remember.
First is that he hasn’t “seen it all” in the welding world and of the very utmost importance, he has to maintain objectivity! How many times have we heard an Inspector say that he “didn’t like this/that” or “I didn’t like what he was doing”. It implies the same thing when an Inspector says, “the only thing I could reject”. The Inspector in Wildturkey’s example didn’t “like” what he saw and looked for reasons to quantify and qualify his subjectiveness in order to reject the weld through the stretched ranges of the WPS.
I’ve mentored many Inspectors on this particular issue and have always found it interesting that an Inspector is trained to be objective but it’s so easy for human nature to override it!
Seldom,
The reason the internal misalignment was mentioned is because it exceeded B31.1 1/16" max. Internal misalignment was up to 5/16"
it seemed that the inspector had no controll over the way this pipe was being installed so he rejected the pipe for internal misalignment. does anyone know why 1/16" is the maximum? and what can happen if it is exceeded?
I would imagine the welders had reasons for doing what they did.
If you fit me up a 30" diameter pipe with a 3/32" root opening I'm going to request 3/16" minimum. The gap will/may close up to nothing by the time the joint has half a root in it.
100 PSI on a regulator through a typical purge hose into a 30" pipe may not be excessive. If it works, weld it. A setup with a purge needle will develop 100 psi back pressure with very little flow if the needle had to be smashed to fit into some tight fitup.
I'd like to watch the 160 amp root pass though with a feather edge and 1/4" gap. But only so I could do it on the next job.
The contractor is responsible for welding in accordance with project specifications. If WPS approval was not specified by the contract and the welding was made in accordance with the WPS, seems OK to me provided the recommended practices for welding of the material were followed. If I were the inspector, I would worry more about what is detrimental. If I didn't know what was detrimental, I would ask.
I have sometimes caught myself thinking how dumb engineers are (to make myself feel better), but when I have a situation like you mention above they earn their well deserved money.
Many hours and much money is spent on code committee meetings and revising codes. Hopefully they didn't miss something when they allowed amperage to be a non-essential variable.
Just to clarify. I don't think engineers are "dumb".
However with me being human and with a group of peers, I have sometimes pointed out their missing of one of thousands of details they are responsible for.
How much greater than 1/16"? How round are the 2 pipes?
What did the inspector use to measure?
Is it an acceptable gage for this application?
How qualified is he with that instrument?
Does it require calibration?
Was it calibrated?
HI-LO was up to 5/16"....the pipe was out of round, there was enough thickness to counter bore the pipe and still matain minimum wall thickness , but this was not done.....a G.A.L. HI-LO guage was used to measure this.....yes the guage is acceptable
Was this a repair or new installation??
As an owner I like to keep my high energy piping as thick as I can, and not machine it to min. wall.
well its kinda both... the pipe was a new instalation but after start up they did a horn drop on the turbine and determined that the hot and cold reheat piping was putting the turbine out of tolerance... so the pipe was cut and the pup pieces were installed, one facing north and the other facing east..... the min wall thickness was .625 they had about .700 to work with for machining if they wanted to.
Some fit up problems that result in repairing high energy piping are that the pipe sizes specified aren't always standard pipe sizes. The ones that aren't are usually hollow forged, and in the past longitudinal seam welded pipe. Wall thickness of hollow forged pipe is seldom uniform around the circumference. Longitudinal seam welded, and I'm sure this P91 was not, usually has a flat spot on the seam welded side. So, sometime after installation you need to replace a piece of this off size pipe. Your options are to have a new forging made, very expensive, and likely the bore of the pipe won't be an exact match. Or buy an oversize piece of pipe and machine it to match the OD and ID of existing piece, in which case you try to match a perfectly round piece to an out of round piece. You could counter bore the pipe, but must be careful not to machine under min. wall, plus you now have a notch in the bore of the pipe. Which is worse a notch or a little mismatch? Since it's not a perfect world, I'd fit it up as well as possible, radiograph the joint after the root and a couple layers, and if it was acceptable go with it. You would think that in this case, new construction, pieces of the original pipe spool might still be available and you wouldn't have fit up problems.
P.S. It's problems like this that keep you and me out of the spring woods and turkeys safe from flying arrows, unless your handle has something to do with the bottled variety of wild turkey.
From the messages that have been posted and ASTM standard A- 335 which I have on hand, I've gathered enough information to express my opinion.
1. Wildturkey doesn't know what the working pressure is, but if the temperature is 750 F (400 C) and the piping carries reheated steam to the turbine's second section, I'd say that it isn't lower than 900 psig (60 bar). Consequently, this piping deserves high respect.
2. As DP Weber correctly assumes, this is a seamless pipe. I know that from the title of the specification: "Seamless ferritic alloy-steel pipe for high temperature".
3. Regarding fabrication tolerances, A 335 std. remits the reader to Standard ASTM A 530, which I also have on hand.
According to paragraph 10.2 of A 530, this is a "thin wall pipe" because the thickness is under 3% of the outside diameter. For thin wall pipe, paragraph 10.2.1 allows an "out of roundness" of 1.5% of the specified outside diameter (30 inches) which makes 0.45 inches, well in excess of the 5/16 found out in actual conditions. So, the pipe was within standard fabrication tolerances.
4. This being the case, the piping erector should have maintained the high - low dimensions within acceptable limits. To do this, he's got several means: strongbacks and wedges, pipe self-aligning devices etc. He could have also ground slightly the pipe wall by the inside, as Wildturkey correctly says, because the Code allows it. If he didn't do that, blame on him.
5. If the butt welding preparation (piping erector's responsibility) wasn't good, then the welder should have refused to weld it. If he welded it anyway, blame on him.
6. But now the piping is already welded and it's useless to blame anybody. What to do? Heroical decision: cut all the welds and reweld them again. Is it feasible from a practical point of view? I'd guess no. Reasonable decision: accept DP Welder suggestion and x-ray all the welds. If the radiographs are acceptable according to the Code, then accept them.
Giovanni S. Crisi
Sao Paulo - Brazil
Well put Professor, line six is exactly what happened. Thanks for the research and response.
Myself, I would reject the root weld. It's out of spec. The fact that you are not the engineer responsible for the design means you have to do your job the best you can to achieve what the engineer is asking for. Right or wrong, it's his call.
B31.1/127.4.11(B) may recognize and provide some relief for problems encountered during repairs.
Also, if this is a repair, what specification applies?? For new construction I believe B31.1 would, but not for a repair after the unit had been in service unless the owner and contractor agreed as to such, or either's QA Manual required using the original code of construction as the spec.
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