Opinions on "Heat to Fit" Piping Practices

[dtn6770]

The engineering group I’m in recently became aware of a fairly common practice performed by our production/manufacturing group that spurred an ongoing debate. When needed to make (B31.1/B31.3) piping runs fit, they use a torch to heat the pipe, usually at an elbow, and apply enough force to deflect/deform it to achieve the desired alignment. There has been no follow up testing or inspections.

When they weren’t able to produce any type of procedure for this practice the we were tasked to create an engineering specification/procedure which basically took the form of, “don’t do it.” Recognizing the potential for it to happen any way, we included a list of follow up tests and inspections that included dye penetrate testing, mag partical testing, and 30-minute 1.5xMAWP hydro-testing. Their counter to those requirements was to perform just a low pressure leak test which we find unacceptable.

I’m curious as to other perspectives on this matter.

 

[gr2vessels]

dtn6770,
I think that the lack of answers to your post, is an answer on it's own. I hate to think of the consequences of such practice. I would first carefully (and without many waves) investigate the chances I've got to keep the guarantees for the piping material. The supplier will void the guarantees immediately.
It is very likely the bends are ruined by local overheating and uncontrolled deformation of the most sensitive areas of piping bends. You could definitelly expect some crack initiation on inside or outsiede of those bends, depending on the degree of bends deformation, the depth of those cracks is your job to determine, at worst you'll have to determine the remaining life of those bends... If you're lucky, perhaps no aparent damage of the bends has been sustained, hence a thorough NDE of those areas would support the continuing use of the bends.
Good luck,
gr2vessels

 

[metengr]

When needed to make (B31.1/B31.3) piping runs fit, they use a torch to heat the pipe, usually at an elbow, and apply enough force to deflect/deform it to achieve the desired alignment. There has been no follow up testing or inspections....I’m curious as to other perspectives on this matter.

My perspective is that this practice can be performed if one has a technical understanding of the pipe material properties, behavior of these properties and requires nondestructive testing (NDT). For carbon steel and low alloy steel (less than 3% Cr), one can get by using heat and force provided it is under controlled conditions AND there is NDT (surface and/or volumetric) performed to assure no defects were introduced as a result of this process.

Some materials are forgiving as indicated above while other materials are not. You certainly need some type of guideline for others to follow with regards to heating, cooling and forces applied that is only used for certain materials.

 

[dtn6770]

I'm pleased that our [engineering] position on the practice isn't unique. We're a bit annoyed with the entire affair and somewhat diappointed in how easily the risks are dismissed...by some.

I'm intentionally not mentioning what service the piping is in since I don’t believe that matters. I will say this; it’s more than just cooling water service.

 

[pmover]

To supplement other responses . . . and yes, I would be annoyed as well. Such activities tells me of mfg imperfections or mis-alignment of pipe-to-pipe fittings (something to think about . . .).

Conducting such activities for "proper alignment/fit" to rotating equipment connections can be detrimental to the rotating equipment. Certainly, the nozzles for rotating equipment are designed to withstand some stress/loads, but placing excessive/additional stress/loads on these connections (i.e. force fit piping) is generally not practiced (my observations). The additional stress placed on rotating equipment housing/casing can cause operational problems (i.e. premature bearing failure, etc.).

For fixed/static equipment, this is a different matter, but there are limitations as well at the connections.

Good Luck!
-pmover

 

[Sid7]

As emphasized by metengr, some materials are forgiving and same time the service was cooling water, so probably the service conditions of the line are also forgiving. I doubt if anyone fabricator doing business long time would risk doing the same thing to hot service piping or other service critical lines!

If these practices are there, then it must be working too(if done by experienced crew!). I believe there were, are and will always be cost effective practices as such contradicting the code effective practices, as long as its not going to hurt anyone.
regards,
Siddharth

Siddharth
These are my personal views/opinions and not of my employer's.

 

[jcurfew]

We recently had a similar "heat to fit" request from a compressor fabricator. We experienced piping and scrubber inlet connection failures due to piping mis-alignment stress. The fabricator proposed to use "thermal stress relief" rather than re-fabricating the piping. The biggest problem has been in 2" 600 series piping. In one case, we found approximately 1" misalignment in a three foot piping run. We politely refused to allow thermal stress relief and requested that the piping be re-fabricated to meet piping codes. Question - for compressor discharge piping (1200 psig)is anyone comfortable with "thermal stress relief" to correct misalingment or should we continue to demand re-fabrication. Thanks for your input.

 

[BigInch]

Besides the hot spot material issues, the stress runs (what a waste of time in this case) had probably assumed a tie-in temp of 70F, so you can toss those. On pipeline tie-ins I always give a max and minimum ambient temperature (assumed = pipe temp) for which tie-ins can be made.

http://virtualpipeline.spaces.msn.com

"We can't solve problems by using the same kind of thinking we used when we created them." -Albert Einstein

 

[hydtools]

My first reaction is to ask 'Who the hell is in charge?'.

If you are tasked with writing a procedure for an unacceptable pratice because the practice will go on, then whoever ordered you to write the test procedure ought to insist or, if high enough on the staff, order that the procedure you wrote be followed. Failure to follow the test procedure should have loss of employment consequences.

Who will hang if there is ever a failure due to 'them' preforming the heat-to-fit process?

Responsibility and accountability..

Ted

 

[IFRs]

I have seen this done on 8" to 16" relatively low pressure (100 psi) A53B piping where field fit up is critical (for instance to a pump flange +/- 0.005") but it is unreasonable to expect the shop spools to fit exactly considering the rest of the large construction work associated with the assemblies. Sometimes a single source of heat is used (perhaps called a "Rose Bud") and sometimes a complete ring of ceramic heaters is used. The pipe temperature is monitored and after the pipe is bent, the area is re-heat treated to relive any residual stresses. I had been informed that this was a pretty standard practice around the oil patch.

 

[justinwest]

I feel that tolerances in alignment and temperature would have to be clearly defined and closely followed.
Also, it would probably be good idea to define the differences between "heat to fit" and heat treatment for stress relief.

 

[rmw]

Why bother with "heat to fit" when you can just go get Bubba and his big hammer and "beat to fit?"

As a young engineer while working at a manufacturing company I designed a process that consisted of several skids that had to be butted up together in the field and the piping connections made up. I was pretty amazed when we went to the field and the piping connections fit without any modification AT ALL. We just put the bolts and gaskets in the flanges and tightened. It can be done. Why aren't these people doing it.

One reason it might have worked so well in that case which was steel pipe was that the production bay that made these skids normally worked with sil-brazed CU/NI pipe that wasn't forgiving so they were accoustomed to getting it right in the first place. I think that what is going on in your place is that since they are allowed to "heat to fit" or "beat to fit" as the case might be they don't need to do it right the first time.

I've used the rose bud to get out of a bind on several occasions throughout my career, but it was as a last resort and not as normal course of action.

Something doesn't sound right here.

rmw

 

[justinwest]

RMW,
I agree completely.
It can be done right the first time. I'm currently building skidded packages myself, and when there are competent installers in the field, everything will bolt up without rosebuds or hammers. When something doesn't align properly, our normal course of action is to re-fabricate on site. No "heat to fit"!

 

[dtn6770]

Thanks for all the comments. Fortunately, sanity has prevailed.

Earlier, Hydtools posed the question, “Who’s in charge?” Our Engineering and Manufacturing groups have a common manager who wants everyone to get along which is something I can appreciate, to a point. Some topics just aren’t (or shouldn’t be) open to negation and common grounds can’t always be reached.

Again, the engineering group’s position is against the practice but for convenience the manufacturing group embraces it with minimal follow up inspection and testing. One aspect to the procedure we (engineering) were told to write (for the manufacturing group) imposes enough (appropriate) inspection and testing that “heating to fit” was no longer the path of least resistance.

Okay, so what cleared the log jam? The companies QC group from an entirely different department weighted in fully supporting the testing and inspection we prescribed. I wasn’t there but I’m told the manufacturing lead and some foremen were, “We gotta do all that…well that sucks.”

I don’t want to offer the impression that a lot of this goes on. We’re a good company and produce good products. Like everyone else, we have our internal battles.

 

[hydtools]

Glad this was resolved. There is always common ground. It just may be farther from one position than another.

Ted

 

[moltenmetal]

I've seen stainless pipe given a "diamond heat" (ie. heating on one side in a diamond pattern then allowing it to shrink back) to straighten it. This approach is often necessary due to the tendency of stainless to distort during welding.

I've never seen pipe heated and then mechanically distorted to make it fit, but then again I'm pretty glad I've never seen it. Sounds like a process that would be tough to control. Mind you, it's better than just straining the pipe to make it fit cold...seen that plenty of times...Bubba's got a great big "paip wrainch" and teeny little brain...

RMW: yes, you can fit pipe precisely if you know what you're doing. What you can't do is shop fabricate pipe in one shop to an iso, and mount vessels in another shop to a matching layout drawing, and expect everything to fit when they finally meet one another- without providing field welds or doing templating or dummying of the equipment. The combination of angular and positional tolerances while fabricating the piping make such "blind fitting" to drawings alone impractical- the positional and angular control, measurement and QC you'd need to make that work precisely enough are actually more expensive than the field welds in the end, unless the field welds are impossible.

The best you can do without field welds and/or templating is to get it reasonably close- and angular tolerances bedevil that approach. 1/2 degree over ten feet is a pretty big distance, and I've yet to see a pipefitter ACTUALLY work to +/- 1/2 degree regardless what they say on the iso. It's often when we engineers think that the field welds are unnecessary and the drawings are king that the "beat it to fit" or "heat it to fit" approaches get applied in the field. They're done in an attempt to avoid chopping up "finished" pipe to make it truly fit, rather than doing it right in the first place.

BTW: thanks for stealing the "beat it to fit" line- but you forgot to add, "...and paint it to match!"