How to support the pipe 3

[srm7584]

Hi

I feel piping and piping support is an art, which comes from a rich work experience and sharing the learning so as others can avoid the mistake and can deliver good and safe design to customer an ultimately to the people.



I am a budding piping engineer involved mostly in the pipe stress analysis. I was analyzing the system and got jumbled in some questions. So just posting here, request all the members throw some light on the issues.



My doubt is how to appropriately support the pipe. There are NO strict rule written but when I gone through some technical articles I found some guidelines, which I am deriving in steps so as to focus in the problem. I request the forum member to correct if I am wrong



1. First follow the standard spacing spans from ASME B31.1 power piping code to limit the sagging. The support is only the vertical to take gravity loads.

2. The second step is to find the thermal movements and then adjust the guide gaps so as to allow the thermal movements, this will produces very optimal loads and thus support will not experience much loads in the thermal and will produce optimal loads.

3. If the support is required to divert or stop the pipe growth then the zero gaps should be allowed and see the ASME code stresses. These may or may not reduce the anchor loads.



Now the problem is if we allow the support gaps as per the thermal movements then each support will be a special support and has to design Whether this will be an economical solutions?

Should we restrict to standard available support and make the layout changed till it reduces to permissible loads? The layout changes also depend upon the possibilities.

Giving large gaps may tend to increase the vibration of the piping, which may not be a good?

Is there any guideline, which gives any relation with the diameter to support loads?



I shared my thought; please let me know the views.

 

[BigInch]

That's about it in a nutshell.

The trick is to design the piping configuration so you can use normal pipe shoe supports, except for those few places where you NEED adjustable or other special supports. The fewer you need, the better pipe stress engineer you are. Same goes for anchors. Both while keeping the pipe from overloading your tie-in points and nozzles by providing flexibility, but limiting excessive movement and snaking into the adjacent pipes.

Unsupported gaps (I think you mean "support lift off") are not ideal and should be avoided whenever possible.

You need to calculate support loads and hand those over to the support design engineers whenever they are more than the dead + live load + weight of contents, and the friction of same.

"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics

http://virtualpipeline.spaces.msn.com

 

[khardy]

We could probably guide you better if you told us what type of piping it is. For example, the requiremnts for a high pressure steam pipe arent the same as those for bulk product transfer.

 

[pennpiper]

srm7584,
I suggest that you go to:

http://www.pipingdesigner.com

"Training" (button)
"Pipe Supports"

There are two articles here that I think will help you.

 

[MJCronin]

If you can get your hands on:

http://www.amazon.com/Piping-Pipe-Support-Systems-Engineering/dp/0070589313

It will address most of these issues

-MJC

 

[srm7584]

Thank all of you for your inputs.
As per Khardy’s suggestion. I am providing some more details about the piping I am doing. The pressure and temperature are 250 psig and 85 0 F .The flowing media is gas. My main question is whether I should design special supports at each support location or use the available applicable standard U-bolt . I am not sure, how much these U bolts will be able to handle the side-loads and whether their use will effect the vibration of piping?

 

[BigInch]

What code are you using?
What gas?
What pipe diameter, wall thickness and material?

U-bolts should probably not be used for anything other than very light gravity loads and providing some lateral stability. Check bolt shear and tension allowables and you'll see why they won't hold much in the way of typically large pipe expansion forces.

Since your case is 85ºF, maybe your expansion is not significant, so you might have a chance to use u-bolts.

Why do you think you need special supports?
Be sure you can easily inspect contacting surfaces.
Vulcanized rubber pads are often placed between supports and pipe and between the U-bolts and pipe for natural gas lines.


"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics

http://virtualpipeline.spaces.msn.com

 

[srm7584]

BIGINCH
Let me put the question again:

The pressure and temperature are 250 psig and 85 0 F on 4" NPS Pipe .The flowing media is natural gas.

When I design the piping layout , I required to give 0.5" gaps in the support so as to allow thermal displacement , other wise stresses are too high. My main question is whether I should design special supports at this support location or use the available applicable standard U-bolt of higher size to accommodate the Gap of 0.5"and suitable for the loads. For 4" NPS can we use 5" U-Bolt. I am attaching the Support Sketch. I n normal cases the pipe is resting on the support.

I am not sure, how much these U bolts will be able to handle the side-loads with the gaps provided and whether their use will effect the vibration of piping?

 

[BigInch]

You have to check the pipe loads vs the U-bolt allowables. If the pipe will not move more than your 1/2" gap, you don't need u-bolts. If it does, u-bolts probably won't work.

"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics

http://virtualpipeline.spaces.msn.com

 

[JohnBreen]

srm7584

1. To WHAT PIPING CODE is this system being designed?
2. Have you completed the flexibility ad stress analysis with (I hope you have modeled the 0.5 inch gaps in the U-bolt guides) and what information do you have from the analysis (does the analysis tell you that you need a spring hanger anywhere)?

Regards, John

 

[JohnBreen]

srm7584

1. To WHAT PIPING CODE is this system being designed?
2. Have you completed the flexibility and stress analysis (I hope you have modeled the 0.5 inch gaps in the U-bolt guides) and what information do you have from the analysis (does the analysis tell you that you need a spring hanger anywhere)?

Regards, John

 

[srm7584]

Thanks JohnBreen for your input.

The system is designed to ASMEB31.3
I have completed the flexibility and stress analysis with 0.5" gaps in the u-bolt guides.And the system results are with in limits.
Analysis doest not ask for use of spring hangers
I am just worried how the use of u-bolts will effet the vibration in piping and whether U-bolts are designed to take the side loads.

 

[StressGuy]

If you're putting in 1/2" gaps to allow thermal movement, just what is the purpose of the u-bolts, anyway?

What's your install temperature, anyway? If you're based on the typical 70°F, and thus only have a 15°F temperature change, I'm curious what the justification is for even running Caesar on such a system. 250psig, 85°F, 4" pipe with natural gas?

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

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

 

[srm7584]

Thanks StressGuy,

Actually the temperature is 850 F. If I am not providing the U Bolts there, the forces at anchors are too high. I want to use the standard U blt than special support to be economical.

 

[ApC2Kp]

srm7584,

The 850 deg F temperature should require a CR-Mo pipe material, so what U-bolt material were you planning to use?

Hot piping would typically be elevated on steel pipe shoes of T-shape or WF-shape structural section to keep the pipe insulation clear of the supporting structural steel. Typically U-bolts are used on un-insulated piping, since the U-bolts do not provide for a thermal barrier to the structural steel, if the pipe is running on a pipe rack or other pipe alley. Some U-bolt supports might include a wood spacer to keep U-bolt clear of the insulation. The 850 deg F temperature won't allow a wood spacer to survive.

The thermal expansion of temperature 850 deg F must be generating some sizable forces at restraints. I would choose something more robust to guide the pipe shoes, like steel angle clips on the structural steel. Some gap for clearance to the angle clips would be included to allow for normal piping movements. If the gaps are established for the thermal expansion of the piping, and the gaps are closed when normal operating temperture is achieved, then it should effectively restrain the piping against vibration. The spacing of the restraints will need to be short enough to eliminate mode shapes less than or equal to vibration or gas flow pulsation frequencies (particularly < 20Hz.) If the anchor restraint loads are too high, then some revision of the pipe layout might be in order, even when the piping stresses are within allowables.

 

[StressGuy]

Indeed - 850°F is no small deal. You can certainly forget about U-bolts for that kind of temperature. I generally agree with Apc2Kp. With that kind of temperature, I would expect your line to be heavily insulated and supported on pipe shoes. You are not going to sit that on galvanized structural steel.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

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

 

[BigInch]

SRM7584!!!

I was analyzing the system and got jumbled in some questions.

Well it certainly does seem so. What IS the temperature? It was 85ºF up to now? Are you changing that to 850ºF? 10 X???

"I'm all in favor of keeping dangerous weapons out of the hands of fools. Let's start with typewriters."
- Frank Lloyd Wright (1868-1959)

 

[doberdorks]

What IS the temperature? It was 85ºF up to now? Are you changing that to 850ºF? 10 X???

Well, 10x depends on your frame of reference

1. deltaT (assume 70degF install) 52x
2. Absolute approx 2.5x...

(sorry, couldn't resist, hope no one takes it as sarcasm)


SLH

 

[BigInch]

Scarcasm??? No.

"I'm all in favor of keeping dangerous weapons out of the hands of fools. Let's start with typewriters."
- Frank Lloyd Wright (1868-1959)

 

[KevinNZ]

What about earthquake loads? You will need all the little gaps then.