According to DNV-RP-D101, Appendix G, the occasional cases representing the wind and motion accelerations, are given only in one direction. for instance W+P+T1+WIN1 is there but, the case consisting -WIN1 doesn't exist. I just want to confirm whether this would be a sufficiently conservative approach or not.
my next question is: would it make any difference if I made separate stress cases for occasional conditions for hot and cold temperatures? suppose the load cases are as follows:

1- W+T1+P1 hot temperature
2- W+T2+P1 cold temperature
3- W+T1+P1+WIN1
4- W+T2+P1+WIN1
5- W+P1
6- L3-L1
7- L4-L2 * is this case necessary to make?
8- L5+L6 (scalar)
9- L5+L7 (scalar) *

thanks

1) It is only an example. It is you that have to determine the required load cases.
2) If the system is nonlinear, yes, you need L4-L2 and the successive L9.

Regards,

Dan,

thanks for your reply, how could I tell if a system is linear or non linear? would it be enough to know if all supports functioned equally effective in both cases?(no gap, no one way restriction) theoretically sounds easy but, practically hell of a job especially when the piping system is enormous with so many supports in it.

regards,

Exactly. It is not easy.

Try to determine if T2 is relevant for WIN and / or accelerations case. If yes, then you need to add also these load cases. If not, you may skip. The reality is that the system is subject to WIN/U loads also when in stand-by therefore in theory you have to consider also for W+P1+WIN1, but for convenience we skip this part.

Regards,

In fact, due to the usually non-linear nature of systems, I somehow disagree with the DNV approach because the way it constructs the load cases is partly for non-linear systems and partly for linear systems. But I guess is not so important for DNV what I think.

Also I would rather apply the wind and the accelerations over the system at operating temperature instead of design temperature, because many (?) times the supports with gaps that are active in design condition are not in the normal operating condition.

Dan,

thanks for the point by bringing up such a delicate matter when you said that you would check the OCC stress in OPE temp. since sometimes some supports would act differently in OPE temp. than DES temp. I had never thought about it before!
I will take care of it from now on.

cheers