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Vertical Deflection of Steel Pipe

Vertical Deflection of Steel Pipe

Vertical Deflection of Steel Pipe

Dear All,

Can any one please tell me what is the maximum allowable vertical deflection of Carbon Steel Pipe (Ranging from 4" to 24") resulting in the Ovality of pipe cross section. Is there any standards which is mentioning % of vertical deflection. (I know in GRE/ FRP pipe it is 3%). But I need this for CS pipes. Kindly help me guys. Currently I have taken it as 5%.



RE: Vertical Deflection of Steel Pipe


If you are asking about piping systems "running horizontally" (or spanning between points of support and....

If you are concerned with the maximum deflection allowed at the center of the span, and.....

If you are interested in a "generally accepted rule of thumb", then..

Use 0.1 inches (center deflection)....ASME B31.1 Tables for suggested pipe spans have been based on this

There is no hard and fast rules here. The media transported (gas liquid or vapor ?), the schedule and materials of the piping all come into play here.

See ASME B31.1; in the section regarding pipe supports; Table 121.5


RE: Vertical Deflection of Steel Pipe

No rule, as along as it is under bending and combined stress allowables.  You may want to limit it at times to allow free draining and even increase the stiffness for minimizing vibrations.

We are more connected to everyone in the world than we've ever been before, except to the person sitting next to us.  Lisa Gansky

RE: Vertical Deflection of Steel Pipe

I used to use 1/2" at center span.  It depends on the slope of the steam line and how much of the sustained allowable stress you want to use..  

You don't want to trap condensate and slug it, of course.

Real world knowledge doesn't fall out of the sky on a parachute, but rather is gained in small increments during moments of panic or curiosity.  

RE: Vertical Deflection of Steel Pipe

BigInch has it, though some impose arbitrary limits.

Some claim their limit is in the interest of avoiding the "telephone wire" effect but I still haven't found anyone who has visually identified a 0.101" sag versus a 0.099" sag over a 20 foot span.  Another good excuse is avoiding pooling (and thus slugging), even though you can sag much more than 0.1" in a  20' span if your line is sloped 1/8" per foot.  And of course my favorite, "we've always done it this way" which is the hardest to defeat with logic or science.  But logic and science are forbidden fruit for many engineers nowadays!

Always ask why.  For GRP and FRP, why is it 3%?  (There may be a reason, but I'm not up to date on those materials.)

- Steve Perry
This post is designed to provide accurate and authoritative information in regard to the subject matter covered.  It is offered with the understanding that the author is not engaged in rendering engineering or other professional service.  If you need help, get help, and PAY FOR IT.

RE: Vertical Deflection of Steel Pipe

What is the service, and what are the linings and/or coatings involved?

RE: Vertical Deflection of Steel Pipe

Dear all,
I forgot to mention the vertical deflection under the "influence of external load" on the pipe?
i.e. "What is the % of permitted vertical deflection of steel pipe under external loads?" (live loads etc)

Hope I am more specific and clear now?  

RE: Vertical Deflection of Steel Pipe

No, you're not more clear.  

Yes, but you've really repeated the question:  What was asked above remains unanswered: What are your design conditions?  Sloped, draining, what dia pipe and what loads and what linings and coatings and insulation are involved?  

Why can you  not use the standard maximum lengths between supports recommended by the pipe support catalogs?     

RE: Vertical Deflection of Steel Pipe

Hope I can make it more clearer.

The pipe I am talking abt is buried. So when an external load is acting on them, live loads there will be a vertical deflection on the pipe.

For example if a pick up truck is parked right on top of it, the wheel load acting on the pipe will cause vertical deflection of the pipe. or ovaling. I just wanted to know what is the allowed percentage of vertical deflection for a "CS" pipe.

To be more clear if i can get that percentage, and can use it in the IOWA Deflection formula i can get the max. load that can be bored by the pipe!!!

Hope i am clear now.

Thanks & Regards,

ARp.. if anyone knows kindly help me...

RE: Vertical Deflection of Steel Pipe

I think that if corrosion is a major issue for your service, I would want to limit the deflection as much as is feasible, but usually I would think that if you are within the allowable stress and the line passes dynamic analyses, you are fine.

RE: Vertical Deflection of Steel Pipe

Guessing games with newbies are so much fun....!!!!!!


RE: Vertical Deflection of Steel Pipe

I think he needs to do a beam on an elastic foundation analysis here for the pipe.  bigsmile

Oh, and don't forget the impact factor.  banghead

Mike McCann
MMC Engineering


RE: Vertical Deflection of Steel Pipe

Thanks, Mike (you made my day, and have a star). If we can't get any more information to try to help, maybe that is a good way to end this thread and week!

[and epilogue to your perhaps quite fitting emoticon:  Q. Why do we do it?  A. Because it feels so good when we stop.]


RE: Vertical Deflection of Steel Pipe


Thanks for the advice everyone.


RE: Vertical Deflection of Steel Pipe

just to answer your post after 2 weeks and to end this week:
I understand that you are talking about the pipe cross section deflection not the pipe sag. Under AWWA standard, allowable pipe deflection for various lining and coatings are:
- 2% of pipe diameter for mortar lined and coated
- 3% of pipe d for mortar lined and coated
- 5% of d for flexible lined and coated

Have a nice weekend

RE: Vertical Deflection of Steel Pipe

Lest readers become even more confused (if that is possible?), I guess you probably meant to say "Mortar-lined and flexible coated" for your second bullet, and it might not hurt to also explain further that your first bullet actually refers literally "mortar lined and MORTAR coated".

Now if we just knew that the OP's service/appliocation was within scope of AWWA, I guess we would really have something (for some reason, however, I have unfortunately a sneaking suspicion it is not!)

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