Weld Inlays

Weld Inlays Improve Integrity of Bellows-to-Chrome Moly Attachment Welds

Certain materials such as Chrome Moly steel can experience significant loss of ductility in the heat-affected zone of welds. Depending on weld size and the specifi cation, post weld heat treatment is used to improve the ductility of Chrome Moly welds.

However, tests have shown that even a very small fi llet weld such as a bellows attachment weld can result in high hardness and signifi cant loss of ductility in the heat-affected zone of Chrome Moly materials. The results of microhardness tests performed on bellows attachment welds made on Chrome Moly base metals are shown below.

The common practice is to weld a bellows directly to Chrome Moly without post weld heat treatment or inlays. There is abundant evidence that this typical approach results in successful performance in spite of the increase in micro hardness in the heat-affected zone. However, there are instances in which loss of ductility has resulted in crack propagation through the heat-affected zone of the weld.

To insure against leakage through the heat-affected zone, an inlay is recommended for bellows attachment welds on Chrome Moly materials. The inlay spreads the heat-affected zone over a large area and the geometry of the inlay discourages separation such that crack propagation through the heat-affected zone is virtually eliminated. The inlay also provides an excellent surface for bellows attachment by making the metallurgy of the bellows material and the base metal very similar.

To insure good performance of the inlay, the inlay fi ller metal should be compatible with the bellows material and base metal. The fi nished inlay should receive 100% dye penetrant examination. The inlay can be post weld heat treated if the Chrome Moly base metal is to be heat treated in accordance with the fabrication specifi cation. However, the inlay itself is adequate insurance against leakage through the heat-affected zone. An additional heat treatment specifi cally for the inlay is not considered necessary for reliable bellows attachment weld performance.