Page 178 - MY STORY
P. 178
pressurized tank grew because of sustained or cyclic
stress, the flaw was to grow until it penetrated the
opposite surface and leaked. What was not permitted was
the flaw growing to a critical size at operating pressure
and failing before penetration of the opposite surface and
causing catastrophic failure (explosion).
This was of critical importance to the relatively thick
walled helium storage vessels that operated at 3000 psi
pressure. Lots of stored energy in the compressed
helium.
Our strength people knew from experience that the
stronger a material, the lighter the component – it could
just be made thinner. They selected a high strength, heat
treated, titanium alloy for these 3,000 psi pressure vessels.
When I performed a fracture mechanics analysis, I
pointed out to the responsible strength engineer that their
design was not leak-before-burst, and that they would
have to switch to a lower strength, but higher fracture
resistant titanium alloy to meet leak-before burst criteria
at this operating pressure. In fact, to meet the failure
criteria, the stronger alloy would be heavier than the
lower-strength alloy. This was well beyond their
experience and they wondered aloud, and not nicely:
