Steam piping expansion compensator 2

[sophyl]

For low preessue steam and condensate pipe risers in a 250 ft tall building what type of expansion compensator is best to absorb 4 inches of pipe expansion?

 

[JohnBreen]

Hello,

I brought this back to the head of the list for discussion because it sounds similar to

thread378-34510

Regards, John

 

[Mark31]

I agree with CRG, expansion joints in piping are bad news. Any torsion and they are likely to fail. My experiance with them is on steam piping. I understand your application is a little different but an expansion loop in the piping is simple and inexpensive.

 

[StressGuy]

I really hate blanket statements like "expansion joints are bad news" especially when it comes to so much misunderstanding about joints, both on the side of designers and end users. We're supposed to be engineers here.

There's no question that an improperly designed joint, or putting a joint into a situation that it cannot handle, is certainly going to lead to problems.

However, there are thousands of expansion joints working well in service all over the world. I would bet in most of those cases, the expansion joint is not only the best solution, but quite possibly the only practical solution.

Now, if a joint is not needed (i.e., and expansion loop can effectively be added to the design to handle the movements) then those options should be taken first.

But, it's clear there are large pockets of closed minds all around when it comes to expansion joints becuase one joint failed one time for someone, for reasons that were probably not fully investigated.

Perhaps groups like EJMA need to be more proactive in educating design companies and end users on the proper design and use of these joints.

Of course, joint companies are sometimes there own worst enemies. I remember one sales guy making a presentation trying to convince a room full of stress engineers that we should be using expansion joints instead of expansion loops for pipe racks. I don't think we've bought much from that company. Edward L. Klein
Pipe Stress Engineer
Houston, Texas

All opinions expressed here are my own and not my company's.

 

[CRG]

I never indicated that I thought all expansion joints are bad news; however, too many are used for the wrong reason. In contrast to StressGuy, I have seen expansion joint used in place of good engineering practices many times. Why design a good foundation when you can stick in a flexible joint to compensate for uneven settling? Why be careful when designing flexibility into a piping system when you can add a flex-joint at the end? Obviously, I am being facetious. In response to the original question, four inches of expansion in 250 feet of pipe should easily be controlled without an expansion joint. Without very specific information regarding routing constraints, I too would say that a expansion joint is unnecessary and might be bad new. That is, why couldn’t a engineer route and support a piping system to accommodate two inches of movement on each end?

 

[JohnBreen]

Hello all,

I kinda thought the discussion would go this way.

For the original question regarding risers in a building (where they often go up through the stair wells) I thought the approach I outlined in Thread378-34510 was OK. I really don't like to see EJ's in this (commercial or institutional buildings) application because they usually do not get proper surveillance and care (and they are in "harm's way&quot. I would much rather see welded pipe expansion "loops" (sometimes just a little offset will do) and it seems that y'all feel the same way.

It seems to be a good idea to remind readers of this thread that EJ's are one third of a "system". When you decide to install and EJ you need to remember that it is necessary to think about where to locate guides and where to locate "anchors" (the entire topic of what constitutes an anchor should be saved for another discussion). The EJMA Standards do a good job of explaining this concept but not enough "designers" (another topic for discussion) read and understand the EJMA Standards.

Expansion Joints fail either because the three-part "system" is ill designed in the engineering stage (or it is an incorrect application for the EJ specified) or they are improperly installed, or both. Often the "designer" calls the manufacturer's rep and asks him/her what to specify - bad idea. Or the "designer" picks the wrong EJ for the application. EJ's have a finite life like any piping component - if they are improperly applied or improperly installed, that fatigue life will be used-up in a sudden hurry (too often, less that one load application). If the "designer" does a creditable job of specifying the EJ system and the drafter (remember those? - NOW it is an insult to call a "designer" a drafter) gets it into the drawing correctly, someone still needs to get out and inspect the final installation - this is not done enough. Once the EJ is in service, it needs to be put on the maintenance list for routine checks of the joint, the guides and the "anchors". Sometimes the EJ is damaged later by adjacent construction projects - the bellows element is fragile, to form it the metal was formed and forced into the plastic regime of the material (by some definitions plastic deformation constitutes a "failure" in a piping component). If the bellows is not supplied with a protective cover it is open to damage (weld splatter, stuff between the convolutions, etc.). So we end up with many EJ "failures" (or are they "designer" failures?) and EJ's get a general bad (often undeserved) reputation.

I was hoping that Dr. Chuck Becht would wander into this discussion as he was the principal writer of B31.3 Appendix X, and this was the topic of his PhD dissertation.

Getting back to the original question, I still think designing the riser to include welded pipe offsets to accommodate the expansion/contraction is the most cost effective solution.

Best regards, John.