This brings up the question, which engines are eligible for extension of time, or exemption from the rules. SVRy #3 is a workhorse, but has hardly worked the last two seasons because of the unavailability of cheap firewood and restrictions on running during high fire danger. Should she be allowed an extension? I would hope so. She is well cared for and has many years left in her before removing the tubes and inspection.
So, who decides which locomotives are special cases. And, by what rules? Do new "exception" rules need to be composed? If so, by whom? Right now who at FRA is the judge on these matters and by what criteria?
I am neither a metalurgist or Mechanical Engineer. But it does seem to me metal under any kind of stress, due to welding, forming or casting, even if in a controlled environment will change over time. Although 15 years seems to me a short time for any solely stress related damage to occur. Maybe some knowledgeable person on this thread can address this issue of aging under low stress conditions.