Would any members know if there are external loadings on tees, which can initiate fatigue cracks on the inside surface of the tee wall?

Review of some of the papers by Markl, and by Rodabaugh that I have access to indicate to me that fatigue cracks from external loadings initiate on the exterior surface of the tee only.

I have not seen a report where inside cracks would have been caused by external forces. Look if there is some rapid inner surface cooling possibility. Cooling can be happening often. I would think that could result in fatigue type cracks.

I saw pictures of the inside of a 110"+ pipe with small inside cracks due to the constuction crew pulling on the line for fit-up with numerous come alongs etc. It seems to me cracks can initiate anywhere depending on hard spots or the like on large diameter cylinders.