Hi,

I am currently designing a "special" expansion loop for the well kill line of an offshore platform. Well kill line comes off wellhead and is about 30' away from platform. According to a wind load analysis made by our civil department, we can expect wellhead displacements of up to 2.5" and 1" (laterally, X and Y axis). We can also expect 9" growth(vertically, +Z axis). The vertical growth is due to high temepratures coming off the well (400ºF at the wellhead). I am operating in extremely high pressures (30,000 psi).
I've been asked to design an expansion loop using a combination of swiveling elbows to allow for the vertical growth AND the lateral movements. I came up with a "scissor style" arrangement of elbows. Now, here are my questions:

1) Material to be used is AISI 4340 (120 ksi yield) which is a forged steel rod that is drilled through. Material is not listed in Caesar's database, that's all the information I have. But I looked for several equivalent ASTM numbers and I came up with A322, A331, A752. The problem is that none of these are listed in B31.3. So can I use a material that is not listed by B31.3 and still use the B31.3 calculation method?

2) Has anyone ever dealt with these swiveling elbows? I suggested using an expansion loop but manager wants to stick to these. Should I be worried about leaks developing as time goes by? Thermal growth will put most stresses, but we only expect it during start-ups.

3) Pipe is 4.625" OD and 2.698" ID. Caesar gives me a 4E error stating that: "Wall thickness is greater than 1/2 the diameter". How do I deal with this error?


I would appreciate any help.

Sorry if I'm not giving much help here, but when I hear swivel, I don't look to CAESAR II. CAESAR II is a beam bending model. I think of a swivel as a geometrically constrained system - a linkage.
Our stiffness matrix is based on the original (input) layout of all these beam elements. They do not take large rotation well. If you swivel angulates more than a few degrees, CAESAR II will not properly predict the loads.
The expansion joint manufacturers deal with hinged piping systems. Perhaps they can help.