If I have to calculate a line under Wind load or seismic load when I have to use SRSS method in case of algebraic method for combination?

Occasional stresses are to be combined with Sustained stresses using the "scalar" combination method.

thank you Richard

but isn't most practical when i combined occasional stresses with operating(W+P+T) case in place of sustained(W+P).

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The piping Codes require that the Occasional Stresses be combined with the Sustained Stresses as scalars, for "Code Compliance".

To combine these loads with the OPE loads (say for structural support design) I would recommend "algebraic".