[Joe K]

Torque is a matter of "stretch." Stretch is proportional to torque (roughly.) That is until you stretch beyond the "yield point" of the bolt.

Most torque values of torque-tensioned bolts are designed to be within this yield point. Some modern bolting systems (My TDI VW fer instance) uses "stretch bolts" as a way to establish a more consistent amount of "residual stretch" (stretch remaining after yield)and compensate somewhat for different amounts of stretch found resulting from different degrees of lubrication for the torque-tensioned bolt system.

Stretch bolts are of course supposed to be stretched only once. Bolts torque-tensioned supposedly can theoretically be re-torqued many times, although most restorers prefer important bolts be torque-tensioned only once.

I have done both. I have repeated torque-tensioned bolting with success, and also had my failures. And new bolting is not a guarantee of torque-tensioned success.

One thing is pretty certain: success in torquing is an almost foolproof guarantee against failure in service. Most tensioning is done WAY beyond the tensioning required of actual gasket compression or strength of joint against shear or tension.

If the tensioned bolting survives tensioning action, it will survive to end of life.

Joe K