Expertise in the welding qualification of large pipes

Welding qualification of large pipes

Applying the API-RP-2Z standard of the American Petroleum Institute (API), we performed comprehensive girth weld inspections for our customers on longitudinally welded high-strength X80 grade steel pipes. This placed particularly high demands on the geometric arrangement of the weld and the mechanical-technological properties in the heat-affected zone (HAZ). Welds were technically qualified on large pipes with thicknesses ranging from 32 to 51 mm and with a maximum outer diameter of more than 900 mm. Weldability was combined by means of multi-layer welds using a variety of processes and heat inputs per unit length of weld and analyzed with specific preheat and intermediate layer temperature conditions. This permitted broad weld processing simulation windows and enabled verification of the material properties required for this parameter range. Low heat inputs per unit length were achieved with the gas metal arc method and high heat inputs per unit length were achieved with the submerged arc method.

One of the main features of the destructive testing was prevalence of certain microstructures in the HAZ. We had to take great care in the arrangement and adjustment of welding components and of the monitoring of processes and parameters as well as the documentation. Installed guidance systems helped significantly increase welding precision. The HAZ properties obtained with the girth welds were also more than satisfactory after simulated stress relief annealing.