Given: 7 in. P-110 casing (D/t = 7/0.59) with axial tension of 50M & internal pressure of 11M psi. Collapse pressure (psi)?
Combined tension and pressure? Complex. Use 6 DTC 4:
1) (σz + pi)/σyield = (50M + 11M)/110M = 0.554
2) Chart: --> 0.544 ---> -0.60 = (pi - pcrr)/pcr (note negative sign for collapse)
3) pcrr = pi - (-0.60)pcr) = pi + 0.6(pcr) = 11M + 0.6(pcr)
We're here in less than 2 minutes but still need pcr. The Redbook shows 7 in. P-110 casing's collapse rating is 16,990 psi. Of course you can calculate it (from D & t; see the formula on 6 DTC 2) but it's faster to use the Redbook. This allows us to calculate collapse pressure in this situation:
pcrr = pi - (-0.60)pcr) = pi + 0.6(16,990) = 11M + 10.1M = 21.1M.
3 minutes. Not bad! We've lost at least half our engineers by now on an exam. Last but not least: do a quick mental check; does internal pressure strengthen or weaken collapse? Clearly strengthen, and that's what the equation shows. Just be careful; it's easy to make a sign mistake.
where is this exam?
ReplyDeleteIf you mean the 2005 SPE Exam, you can buy it from SPE, or get it from various sources on the web. It's often called 2004, 2005, 2009, etc.
DeleteNote I'm just showing how to solve similar problems to this exam using the Guidebook because I get so many questions about how to do this. I think Bing gives the test and solutions away in his class as well.
Is there a way to solve this problem not using the table provided in the Guidebook 6 DTC 4? I am trying to prepare for this problem only using the RG?
ReplyDeleteThanks in advance!
Sure, check out around P50 in the RG. I'm not at home right now so can't look but I think it's between 50-60 in Drilling.
DeleteMake sure you know the RG very, very well, because you won't want to keep looking in there during the exam. You really need to roughly know where each item is before even looking, since speed is everything. Let me know if you can get it and what pages you used.
Hi David. I'm currently studying for the 2021 exam and am working through this same problem as the user above. For this problem, using the RG (2020 Update edition), I'm working with equations "Effective Yield Strength in the Presence of Significant Axial Stress" on page 55 and "Yield Collapse" on page 56 (I think these are the correct two? Ha). But, using these, I arrive at an answer of 22,749 psi, which is close to answer choice C, but not exact. Perhaps I'm doing something incorrectly.
DeleteAnonymous I must be having some calculational errors here. What are you coming up with for effective yield strength and what values are you using for the d/t?
ReplyDelete