I would appreciate if anybody could advise me the most practical way to stress analyze a cladded pipe. As an example; 24" Sch. 20 Carbon Steel pipe with 1/8" thick Inconel 625 cladding at design temperature of 450 F.

My preliminary approach is to solve for the equivalent modulus of elasticity(Ee) and equivalent thickness(te) and use these value in the analysis. Is this approach acceptable?

Hello!

Cladded pipe is jacketed pipe?
In that case I suggest to model both traces - technological pipes and jacket pipes and connect one to the other with CNODE facility in their connecting points (supports, welds, etc.).
I am not sure if you have to analyze a jacketed piping system or a traced piping system (because of the big difference between the two diameters). In the case of traced piping system, at big difference of diameters between the technological pipe and the tracing pipe, you can take to account only about the weight of tracing pipe, its fluid, clamps for support, etc for adding it to the pipe weight. I usual calculate a thickness for insulation for including the weight of tracing pipe and fluid in insulation weight.

Of course the kind of modeling the ensemble depends from one case to other. There are cases when we have to model both technological and tracing pipes.
To obtain more information, please tell us more about your situation.

I hope this helps,
Dragos Aron

Hello Dragos,

Thank you for your reply. I just want to make it clear to you that cladded pipe is somehow different from a jacketed pipe.

Again, I would appreciate further response from those who have done the analysis of a cladded pipe.

Your composite section idea is valid assuming:

• Your cladding acts with the pipe, i.e. no slippage.
• The thermal expansion coefficient of both materials is the same. If they are not, differential thermal growth will cause slippage.

For these reasons, you may only want to consider the cladding for <em>"weight"</em> purposes, and assume system strength is due to your pipe wall only.

There are basically two types of clad pipe, metallurgical bonded or mechanically bonded. The metallurgical bonded is more expansive are better. I have come across research papers where the steel clading has been used for pressure containment but this is seldom used. As Richard has mentioned the clad thickness is usually ignored for stress calculation.

If your pipe is mechanically bonded be careful about production quality control. There have been cases where the contact surface are not properly cleaned and when exposed to high temperature, the cladding can boughs inwards due to steam trap between carbon steel and cladding contact surface.

Mechanically bonded clad pipes are restraint by a seal weld. Be careful about the differential expansion force (carbon steel vs cladding) acting on these seal welds. Get confirmation from vendor that 450 deg F is OK.

Others,

Be careful about upheavel buckling.
Be careful about temp derating properties of carbon steel (and cladding if you are considering its strength)
Be careful about your corrosion coating selection.
Be careful about your welding procedures, how to handle cutback etc.

That about all I can think of the time.