Hoop VS Combined Stress - Steel Pipeline

[LearnerN]

Newbie question here. I'm considering a calculation where a vehicle load will be crossing directly over a steel pipeline (5' soil cover). I'm using the Spangler equations for vehicle loads.

I'm assuming max operating pressure in the pipeline so have 72% capacity for hoop stress. Following ASME B31.4, I'm doing the equation for Combined Stress and coming up with a 43% SMYS capacity [subtracting hoop pressure from longitudinal pressure...don't have to account for thermal].

Intuitively, I think this makes sense. If the pipe had full operating pressure AND a vehicle crossing at the same time, while the hoop pressure would be 72% capacity, the combined effect including longitudinal would only be at like 43% capacity. Since neither of those values are over the allowable capacity for the associated stress category, it all checks fine.

Am I understanding correctly?

 

[LittleInch]

I think so yes. At 5 feet deep you could probably run anything you like over the top of it providing the ground doesn't compact and you get shear on the pipe ( the pipe trying to hold the earth and load up).

Hoop with no thermal load will put some tension on the pipe due to Poissons effect so end cap forces will reduce that.

Is this bare earth?

Also check out API RP 1102.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[LearnerN]

Thanks, LittleInch. It's actually over a concrete drive, so that does help spread the loads out even more.

Conceptually, I believe this all makes sense in that there's only a tiny part of the pipe resisting hoop stress, but a lot larger area of the pipe resisting longitudinal stress. So combined stress capacity will be a lot greater than hoop stress capacity.