hi

i would like clarify few doubts regarding earth settlement

1)As per ASME B 31.3 "319.2.1 C" earth settlement is considered under secondary stress,and its also stating
"since it is a single cycle effect, will not significantly influence fatigue life"
then the equation for the allowable stress range ie f(1.25Sc+.25Sh) is valid here? or i can take more allowable for this particular case ie 1.5 Sc+1.5 Sh?

2)im doing a tank farm where we have 20 mm earth settlement for all support structure, when iam designing spring shall i include 20 mm settlement in the Spring travel load cases ie(W+D1+T1+P1 -HGR)?or we need to consider only the relative movement of pipe and support?


Regards
SB

any comments?

1) The next sentence in B31.3 says that you may exceed the allowable stress range when considering earth settlement. I guess using the old Appendix P limit (1.5*(Sc+Sh)) is a good comparison but I would include the sustained stresses as well.
2) If the pipe AND the structure both settle the same amount, then the spring selection will NOT be affected.

Thanks Mr dave for your response

Regarding Spring selection i still have some doubts,
my pipe is lifting 3 mm ,When iam including the Settlement in Spring travel load cases ie(W+D1+T1+P1 -HGR),spring hanger table showing vertical movement as 23mm (20 settlement+3 thermal) and cold load is calculating accordingly.(iam following hot load based design).

if iam not including the Settlement in Spring travel load cases ie(W+T1+P1 -HGR) spring hanger table showing vertical movement as 3mm and cold load is less compared to first one

here which is the best option to be followed,?

Regards
SB

If you are expecting the spring to settle along with all the other pipe support points in the area, then the spring can be selected without regard for settlement. (But the system may require evaluation considering differential settlement with other sections.)
If there is a possibility that the spring may settle differently compared to other supports in the area, then proper selection should account for any added travel. This spring should accommodate both the unsettled position and the settled position.