625 is not strengthened by a specific heat treatment. Heating at 700 deg C may result in slightly higher mechanical properties as a result of precipitation of certain phases. However, this does not embrittle the material nor seriously impact corrosion resistance.
Read the seamless tube spec, B166, you will see that the final mechanical properties depend on the specific annealing temp.
If there has been any welding or cold work then this temp is clearly too low.
I don't know why you would bother with this temp, you will not even get good stress relief until you heat to 850C or so.
If your service temp is below 550C then don't bother with a heat treatment unless you can go hotter.
the heat treatment (at 700°) is not intended for the item in 625 but for the item to which it is welded to;
my concern was related to the fact that the item in 625 could be adversely affected because of this heat treatment.
Welded Low alloy Cr, Mo; for this it is required PWHT @ 700°C.
It is forseen a buttering between Cr,Mo and 625 if we want to avoid treat them together, but I was in doubt about the possibility to do it.
