The "best"? Perhaps but the "best" unit as described doesn't read bolt stress [3eyes]!! You cannnot use typical UT thickness guages or even UT flaw detectors for this specialised application. Attempts to do so have gotten more than one well-known NDE company into very hot water!
The other two...
@ Dan (TMoose)
Our Techs use these things in some pretty nasty conditions. However, speaking of "conditions", the Techs are also conditioned to have considerable respect for the devices! At approximately 7-8 K per instrument (including the necessary bits'n'pieces) we don't want them to get...
"With studs it is often not possible to measure stretch because one end of the fastener is not accessible"
Actually, this isn't the case. In fact, it's as easy to measure the relative elongation of studs as it is bolts. Furthermore, this is true regardless if either is in a blind hole or not...
This is a common issue. First solution is to throw away the damn impact wrench![mad]. Then, apply at least a modicum of "control" to your bolt tightening process. Although torque wrenches are notoriously inaccurate in terms of applied tightening force to bolt stress, perhaps in your situation...
Of course, both methods of tightening will eventualy get the job done. However, on large flanges such as this one, tensioning is advantageous not only because of the reason outlined above but also because it is a faster process. When tensioning, one is able to tighten at least 50% of the stud...
