For the inspection of girth welds on newly constructed pipelines, traditional automated ultrasonic testing (AUT) technologies have proven to meet requirements from codes and standards as well as oil and gas company specific requirements. However, developments in oil and gas exploration have resulted in more stringent requirements for the pipeline and likewise for the inspection of the girth welds.
For pipelines which transport a corrosive product, the design can consist out of a carbon steel carrier pipe with a corrosive resistant alloy (CRA) clad layer on the inside which is sealed to the carrier pipe ends with a machined welded overlay area. Due to the presence of the CRA clad layer, the welding consumable must also consist out of an alloy. The combination of different material properties of the carrier pipe, the CRA layer and the weld poses significant challenges for traditional AUT techniques like phased array and zonal discrimination.
Recently, a novel technique (IWEX) was introduced for the inspection of welds with a CRA clad layer. This method is based on full matrix capture (FMC) ultrasonic imaging and it has been successfully subjected to a full-scale qualification program conform DNV ST-F101.
In this paper we will present the principles of CRA girth weld inspection with FMC ultrasonic imaging. We will present an application with additional project specific requirements together with the proposed validation program to demonstrate compliance. Examples of welds scans and comparisons with destructive testing of actual indications will be presented with a statistical analysis to determine the probability of detection and sizing accuracy. From experiences and observations during the validation program, lessons learned and opportunities for improvement were obtained. We will conclude this paper by sharing the lessons learned and discuss the potential future applications.
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