the combination of occasional load cases and sustained case to be considered as occasion load or sustained load. my friend is saying that it should be sustained case for more conservative. so even both are correct, which one normally to be referred?...

WW+HP HYD
W+T1+P1 OPE
W+T2+P1 OPE
W+T3+P1 OPE
W+P1 SUS
W+T2+P1+U1+WIN1 OPE
W+T2+P1+U2+WIN1 OPE
W+T2+P1+U3+WIN1 OPE
W+T2+P1+U1+WIN2 OPE
W+T2+P1+U2+WIN2 OPE
W+T2+P1+U3+WIN2 OPE
L6-L3 OCC
L7-L3 OCC
L8-L3 OCC
L9-L3 OCC
L10-L3 OCC
L11-L3 OCC
L18+L5 SUS or OCC
L19+L5 SUS or OCC
L20+L5 SUS or OCC
L21+L5 SUS or OCC
L22+L5 SUS or OCC
L23+L5 SUS or OCC

Santrokumar,
Why would you select SUS? These are occasional cases and shall be compared with occasional allowable stress (1.33 times Sh).
There is no question of being conservative. Just follow the code requirements.

Some people consider some occasional load (as wind, psv reaction force and so on) as sustained, because B31.3 makes explicit reference only to wind and earthquake as occasional loads.
So they say it is better to consider some occasional load as sus.

But in your case you are talking about earthquake and wind: so I agree with Rajinder "there is no question of being conservative. Just follow the code requirements".

Just some notes, if you don't mind:
1) calculating earthquake + wind in the same occ case is again very conservative (especially if your wind is the extreme wind), but possible.
2) Check your load cases because in L6 you have T2 and in L3 you have T1.
3) for your 1.33 times Sh, it depend on the code. We should say which code are we using...

Further to Vannella's point number 1. As per B31.3, 2010 edition, para 302.3.6 (a), wind and earthquake forces need not be considered acting together.

Wind at few geographical locations (areas near ocean) blow continuously. There, it is prudent to take wind as NON occasional case. However, earthquake is considered as occasional case.

We have all sorts of protection systems before PSV. Popping PSV is the last phenomenon that can occur. In other words PSV pops up occasionally. Analyzing it as SUS case could be really conservative. Also, it will not result in the gross distortion of the piping system.

@ rajinder and vannella,

Thanks for your reply.. but i havenot used earthquake and wind together. but W+T2+P1+U1+WIN1 (OPE) is motion load + windload..

Depend on your return period.

100 years return period is OCC

Regards,