High pressure steam supporting? 4

[JacobsTim]

Hello

We have an high pressure line with Td= 510°c.
The material is P11.

In the piperack we want to install a horizontal dummy at an elbow to support the line?

Some stress engineers say that this is not allowed.
With this high temp the force are to high in the weld.

The dummy is only 1 meter long.


Tim

 

[BigInch]

Allowing flexibility is usually much better for both pipe and pipe supports than fixing a pipe and introducing stress into both. Pipe supports should only be located where needed.

Steps to resolve this problem.

#1.) Believe your stress engineers.
#2.) Believe your stress engineers.
#3.) Believe your stress engineers.

The stress engineer is usually responsible for locating supports, so if you don't like his design, its best to make an agreement for a solution acceptable to the both of you.



BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[pennpiper]

JacobsTim,
The answer to your question is "Yes" as long as it is done right.
You (and others) will ask "What is right?"
We would need a lot more information about your situation before we could answer that.
With that said you might try this.
Replace the elbow with a TEE. On the other (straight through) end of the TEE add a meter of pipe the same material and spec as the pipeline. This pipe extension becomes your "Dummy" support. Cap the end of the pipe.

 

[0707]

I suppose it will be a good idea to have a FEA (Finite Element Analisis)to see the stress force in the point where you want to install the support, after that you can chose the best support solution for your problem.

luis

 

[pennpiper]

JacobsTin (and others)

BigInch made the following statement:
"The stress engineer is usually responsible for locating supports, "

This statement is both true and not true. I believe it is true for "BigInch" because that was the way he was trained, the way his company operates and was what (all, most or some) the projects required that he has worked on. It is true and consistant with his experience. There is nothing wrong with this manner of operation. I would furthur recomment that you look at all of his responses, the ones to this question and other question as being very good advice.

However, his statement is not true and consistant with the training, experience, manner of operation and project types for all pipers and all companies. I am not speaking for all pipers but it was not true for me, my experiences and my company. Where I "grew-up" as a piper, I (and hundreds of others like me over the years) recieved training in the fundamentals of proper pipe routing and total system design. This included many classroom hours in the basics of stress, flexibility, forces, weight, support, expansion, etc.. This was classroom instruction conducted by the head of the stress department.
Why was this training done? Very simple! The ratio of piping designers to stress engineers was (and probably still is) 25:1. So this means there was a work load issue to be considered. Also, the head of the stress department and the manager of the total piping department did not want bad or unworkable designs submitted to the stress department. This would only increase the workload because of the recycle. We were required to submit what we considered a workable design. And we needed to be able to defend it. In this enviroment the piping designer located all the support points and the stress engineer checked the total line or system for complience to the codes and other factors as required by the project criteria.

 

[NozzleTwister]

I give you a star pennpiper. My sentiments exactly.

Back to JacobsTim's original question, I can speak for a Stress Engineer who has had this exact same problem.

I have the following comments and suggestions.
1) Adding a dummy leg would be my last choice. Try to add or relocate steel as required to avoid the dummy. If the dummy can't be avoided, moving or adding a support can reduce the force the dummy is required to support.
2) Sh is less than 1/2 Sc at 510 deg. C.
3) 1 meter is a very long dummy leg at this temp.
4) The Moment (force times length) is the problem with the local stresses.
5) If no other options, shorten the dummy as much as poosible.
6) Consider a heavier schedule elbow at the dummy attachment and taper bore elbow ends to match pipe.
7) If the pipe and dummy are large, consider inserting a plug of insulation inside the dummy against the pipe and insulate a portion of the dummy leg.

Since your Stress Engineer has already said your situation won't work, I hope you are working to give him some options that will.

NozzleTwister
Houston, Texas

 

[BigInch]

Since the OP didn't mention the forces or the design code, you guys can't say for sure that the dummy support is OK. Some codes even prohibit dummy supports when (as they usually are) welded directly to the pipe.

When I say "locating" I mean "has final responsibility for", which is pretty much the end of the story.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[rjstephens]

Hi All,

I am in agreement with BigInch, the codes that we deal with over here in the Power Gen industry are generally British or German. They warn against any attachments to pipe in the creep range as they are stress raisers and additional points of inspection during an outage, which is costly and time consuming. There is documented history on failure of attachments to piping in the creep range, and as such should be avoided if at all possible. Weld quality/heat treatment and inspection methods can contribute to the failure of the component if not performed correctly. The BS & DIN codes also give creep to rupture properties beyond those of the ASME B31.1 code, i.e. now BS 350 000hrs life, ASME 100 000hrs life. All components/fittings of highly stressed areas will need periodic inspection after 5-8 years and every few years there after, a metalurgist will need to be involved in the inspection schedules and the power station overall lifespan could be 50yrs or more with the correct maintanence. Failure of a pipe support can cause failure of the piping system and is just not worth the risk.

Cheers

Rob

 

[PhilEduard]

Hi Tim,

Let me say something here in my opinion. First of all supporting any pipe at elbows are often discourage by stress engineers simply becuase more often the method to locally analyze the stresses at this point is not readily available.There has been no module in Caesar II and perhaps any other pipe stress program that evaluates the localized stress effect of supporting pipe via elbows. If I understand it, you simply proposed and your stress guy simply says it's not allowed. I could tell anyone that even the recent big refinery projects still include dummy support at elbows both in horizontal and vertical fashion. In the actual design office though, this support type is evaluated in terms of local stress if acceptable. The best is of course by FEA. The length of dummy leg will dictate the displacement of your elbow which in turn will affect the load particularly at that point of weldment and finally that load is going to be used in the localized stress evaluation. If it pass, there is no problem using dumy leg in there. Your stress engineer perhaps has an idea on previous models where at such temperature and pressure such a dummy leg wont work. In most cases though, that support point simply is a vertical support and sometimes with a guide too but rarely a 3-way restraint - that point normally should slide axially (paralle to the longitudinal axiz of the pipe) and so if you can avoid it, place support off the elbow. Also in some cses this elbows has a high stress level and welding a trunnion in there would increase the stiffness of that elbow just like a flanged elbow has a stifness higher than without. So my opinion, if you can avoid it the better. Your stress guy should know it. Probably you need to communicate better in terms of the most prioritized requirement of this system. My opinion.

Phil