Reuired clarification in Specification

The welding rod strength must at least be equal to the strength of the welded parts at the heat treatment temperature. It appears to also make the same requirement at the in service temperature, although that is not entirely clear. In general what the spec wants is for you to be sure that the welding rod has at least the same strength as the base metal strength has at any and all temperatures, including the heat treatment temperature, if the assembly will be subject to heat treatment.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

It's a bit odd and maybe was left in by accident.

My interpretation is that this if the Pipe itself or the weld is subject to heat treatment, either pre or post weld then the weld filler needs to be as strong or better than the heat treated material or weld.

I suggest you talk to a welding and /or materials engineer to see if this clause is still relevant for your particular pipeline.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.