Cái này cop trên mạng share cho anh em.
Shahid Rafiq: Dear all,
In our company, stress analyis engineers have been taking Xmas Tree vertical displacements (for oil and gas wellheads in onshore installations) in doing analysis. The value taken is normally 50mm upwards. Due to this movement, we have to give spring support at very first support near the wellhead. What is the source of this 50mm displacement, nobody knows.
Recently a question was raised, why this vertical movement? What is the basis? How can we calculate the Wellhead Christmas Tree displacement? And should we consider any displacement at all?
One of my seniors who has very good experience in off-shore piping, says it is not required at all. Please give your opinion or share your experience with us on this.
MoverZ : The oil / gas well is not just a hole in the ground, it's a tubular, cemented into the strata way down below. The upward movement is due to thermal and pressure expansion of the well string. Dependent on the depth of the well, expansion can be around 300mm. Ignore this at your peril. Note that in certain circumstances there can be a net downward
Shahid Rafiq: MoverZ,
Thanks for reply and noted that it should NOT be ignored!
But what exact displacement should I take? Should the source for this infomration be client only? Can I calculate this displacement myself? If yes, what is the method? Or should I give "SOME" value based on judgement? Unfortunately, on this we cant apply our "ENGINEERING JUDGEMENT"! Or can we?