The selection of the WPS is hard to judge based on the information you give however as far as what is required to qualifiy the wps and what range of variables the wps is qualified for goes, thats all in the code.

I have seen Carbon Steel to 2 1/4" Chrome procedures qualified with Carbon Steel Filler, 1 1/4 chrome 1/2 moly filler, and 2 1/4 chrome 1 moly. So the selection of filler metal may be based on any number of things. The Most common I have seen is the use of Exxx-B3L materials.

One thing that I would be concerned with is why did it crack. Was it in service long? Have the operating conditions changed in the last 50 years (increase in pressure or temp). Are piping supports still functioning ?

This in my opinion is a very serious situation if there is any significant pressure/temperature and the selection of a WPS, though important doesn't carry the weight of discovering the cause and eliminating the possibility of a future failure at that location. Maybe a radiograph or UT of the joint and any adjacent joints would be prudent.

The requirement for PWHT would be based on the material thickness in most cases however in emergency repair situations someone may have made the decision to not perform PWHT. With an isolation valve leaking by that could cause some issues with PWHT. Buildup of pressure, difficulty in getting to temp. Who knows.

In answer to your question, there is not enough information to say whether the WPS was "qualified" for the joint. Repair procedures are somewhat more complicated than new materials or joints. Selection of a WPS for MOST situations is more of an engineering decision than an inspection decision. There is a BIG difference between being able to verify a WPS is qualified properly as compared to its suitability for a specifi task involving a repair.

All of the above is an opinion. I have repaired a 10 sch 160 superheater outlet before in which a large amount of the circumference was cracked. I didn't question the welding as much as the materials / service. After indicating to the mill and my employer that I would not weld on it until they verified the actual material, they called in an engineer from the paper companies main office, he looked at the joint surface and said the same thing I did. Wrong material for the service. However me saying things had little to no bearing until the engineer looked at it. He sent the piece of and it was plain carbon steel in a 1200 ??? (I think ) Psi superheated steam line. Up to the point I balked, the local plant engineer and maint people wanted me to just vee it out and weld it up. It probably would have failed in the near future. And that failure would have been serious. That plant had just had 2 or 3 people die when a digester blew its top, which flew a considerable distance, and then killed people.

Of the 10 or so "pinhole leaks" I have repaired on steam lines maybe 1 or two have been pinholes or small isolated discontinuites . Most have been cracked haz's, or large area of non fusion etc. That is only MY experience though.

Have a good day.

Gerald Austin