TWI Frequently asked questions
The fatigue strength of a butt weld can be increased by grinding the weld overfill flush with the parent material. However, in order to take advantage of the increased allowable stress range it is necessary also to prove by NDT thatthe joint is free of significant defects.
Fillet welded joints may be treated with a variety of techniques to increase the fatigue strength with respect to failure at the weld toe. The most common technique is weld toe grinding, preferably with a grinding burr rather than adisc. For joints in structural steels, the UK standard BS7608 states that the allowable stress range may be increased by 30% for fillet welds treated in this way. Other methods include peening, or remelting the toe by TIG or plasmadressing. All these techniques require definition of a detailed method statement and appropriate training for the operator - contact the Structural Integrity Department at TWI for assistance.
If fatigue failure occurs in the throat of a fillet weld, simply increasing the weld size or changing to a full penetration weld will give an improvement.
Further information can be found in:
'Fatigue Strength of Welded Structures', 2nd Edition by S J Maddox, Abington Publishing, 1991. (ISBN 1 85573 013 8)
'Improving the Fatigue Performance of Welded Joints', TWI, 1983, available from Abington Publishing. (ISBN 0 85300 164 2)
Copyright by TWI, 1999
