PWHT

there are two methods that I am aware of

1- Drilling a small hole and measuring the strain by strain gauges.

2- X ray diffractography. The second method is usually commonly used being non-destructive.

However if you follow the code, the residual stress is not likely to be significant.

Errata (Add to the above (sorry went out and the edit window got closed)

1- Drilling a small hole and measuring the strain by strain gauges.(ASTM E837-08)

2- X ray diffractography. (ASTM E1426) This is usually commonly used by us being non-destructive.

A few other methods are available (like magnetoelastic, Barkhausen effect, Ultrasonic etc) but have no familiarity with them.

you may go through these papers for these

http://www.ndt.net/article/wcndt00/papers/idn030/idn030.htm

http://www.ndt.net/article/wcndt00/papers/idn430/idn430.htm

And now the mechanical resonance peak of the structures are also being used as a check for the residual stress (check any vibration stress relief site)- Quite a few vendors are trying to sell the eqipments and submitted the literature, and we are planning to buy a few after ensuring the effectiveness by the X ray method.

you can do harness testing of the weld and HAZ, a pretty common method. also your

PWHT provider should be able to give you temperature vs time charts which will show up ramp rate, soak time, and down ramp rate