Owing to the recent concerns regarding the pipeline field girth weld performance, particularly heat affected zone (HAZ) softening and toughness, EVRAZ North America has initiated a research program to evaluate the response of API grade line pipe to the current field girth welding procedures. In particular, this study aims to elucidate the role of steel alloy design as well as the welding procedure on the field girth weld and HAZ properties. This understanding is critical to balance the detrimental effects of HAZ softening on the joint overall strength against factors affecting the HAZ toughness.  

A selection of several different steels with varying alloying levels of C, Mn, Mo, Ni, Ti, N, Ceq and Pcm have been subjected to the welding trials to assess the effects of chemistry on joint performance.  Furthermore, an analysis of the effect of welding process parameters on the joint properties has been made. The welds, fabricated via a manual shielded metal arc welding (M-SMAW) process, were evaluated in terms of toughness, local vs global strain distribution using digital image correlation (DIC) technique, and hardness contour mapping of the weld and HAZ regions.

The results explicitly show that the extent of HAZ softening decreased as the amount of C, Mo, Mn and Ti/N ratio increased. However, this alloying addition resulted in a relatively detrimental effect on the HAZ toughness, particularly towards the cap and fill passes. The analysis of the HAZ properties as a function of the welding process parameters indicated that the HAZ softening increased as the interpass temperature and the welding heat input increased. In addition, the DIC strain distribution analysis along the weld and HAZ regions confirmed the weld passes towards the root, hot and first fill passes are more prone to the HAZ softening compared with the upper weld cap and fill passes.


Influence of Steel Chemistry and Field Girth Welding Procedure on Performance of Api X70 Pipelines

Division / Sponsors: 
Pipeline Systems Division

Paper Proceedings: https://asmedigitalcollection.asme.org/IPC/IPC2020/volume/84447

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