ASME B31.4 state as mainline pipelines: all in-line pipeline pipes, fittings, bends, elbows, check valves, and block valves between scraper traps.

So it is a good practice to install a check valve (swing check valve)in a pipeline when pigging is required?

No. But there is always some one that will come up with a reason.  For example, if you do not want a back flow up a leg of the pipeline, you could install one.

I think mectub was talking about whether it's good practice to install a swing check valve in the line to be pigged. I've not seen any used (lines didn't need them), but understand that you can procure swing check calves that can be pigged.

For us, check valves in the mainline is not something we do.  Reverse flow is controlled by components in compressor stations and meter stations, relieving the need for mainline check valves.

Thought I'd add that I've always used them in offshore gas pipelines, at the bottom of risers on platform export pipelines and at the tie-ins into other downstream pipelines; those places where you can't allow any backflow and don't necessarily want to complicate things by adding remote closing control to a ball valve.

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