Ultrasonic peening and residual stresses

Post-weld heat treatment (PWHT) is carried out to improve the brittle fracture resistance of welded joints by relieving residual stresses and in most cases also to improve the toughness of the weld metal and heat affected zone (HAZ).

Ultrasonic Peening can effectively replace conventional PWHT. The HSE Guidance Notes require PWHT for highly stressed nodal welds greater than 40 mm thick and other welds greater than 50 mm thick unless fracture mechanics calculations show that the joint posses adequate toughness in the as-welded condition. Consequentely, there is interest for an alternative way to relieve residual stresses. The replacement of conventional PWHT can be done by  ultrasonic peening.

CTOD increased values by ultrasonic peening treatment

The treatment has demonstrated its contribution to the reduction of tensile residual stresses and the introduction of compressive stresses. Clear improvement on CTOD values, which is a measure of brittle fracture resistance, has been achieved as a result of ultrasonic peening treatment of the weld and HAZ.

The increased CTOD values due to the application of ultrasonic peening after every weld layer in thick welds have a wide field of applications in the arctic offshore industry, where increased toughness and/or resistance to brittle fracture in welds including HAZ is of great importance.

Advantages of Ultrasonic Peening Treatment when replacing conventional PWHT;

  •     Ultrasonic peening systems are small and versatile even for places of difficult access.
  •     Less energy used
  •     Much less time required for treatment
  •     Treatment can be applied locally
  •     Environment friendly due to saving of energy
  •     Residual stresses are relieved and fatigue resistance is improved during  the same working operation.
  •     Fatigue life increased fourfold.

 

Ultrasonic peening treatment and weld reshape

Ultrasonic peening treatment and weld reshape