Keeping Weld Root Leaks at Bay with Computed Radiography

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Figure caption – CR pixel value radiograph on 14-inch line

The IRISNDT UK group is using a pixel value routine and CR (computed radiography) to monitor weld root losses.  The piping is in-service at 90–130°C, and we monitor the uninsulated welds every three months.  The pixel value technique is a good option considering the location of the wall loss under the weld reinforcement and the customer not allowing any weld cleaning/grinding.  The estimation of the remaining wall thickness under the weld cap is done by comparing the known parent wall thickness of the pipe with calibrated 5 mm by 10 mm wedges.

Preferential weld attack/localized attack is a common problem for many industries.  This insidious attack leaves entire large cross-sections untouched while causing a highly localized leak often due to miniscule differences in chemical composition between the deposited weld metal and the parts it joins.  Refinery alkylation units are prone to this damage (see IRISNDT article  Off shore and onshore pipelines are prone to this damage as well (often in the presence of CO2).  The steam assisted gravity drainage (SAGD) industry and chemical processing industry are also plagued by this.