Posted by: Ltorrado
Swivel Elbow Expansion Loop - 10/19/10 07:35 AM
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.
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.