Enhanced Lifetime for Internal Pressure Fatigue of DSAW Pipes
Pipes are used as construction elements, to transport liquids and gas in pipelines and as storage containment’s for gas and liquids. A very cost efficient method to fabricate larger diameter pipes with heavier wall thickness is the DSAW process. In many applications in the above listed fields the pipes are exposed to fatigue loads. Several design codes and standards exist which consider SAW pipes for the different applications. Depending on the loading conditions the stress concentration resulting from the weld of the DSAW steel pipe but also from the connecting welds in the structure leads to a significant reduction in lifetime. This reduction is accounted in the different design codes. To utilize the cost efficient DSAW pipe also for applications which so far could economically only be served by seamless pipes a method was developed to reduce the stress concentration in the area of the long seam. This method provides pipes with a lifetime similar to a seamless pipe by still maintaining the competitiveness of the welded steel pipe manufacturing process. A test program to qualify this method for Cargo Tank Cylinders for Compressed Natural Gas Transportation on vessels was accomplished in order to proof that the measures taken are effective.