HOW TO INCREASE COLLAPSE RESISTANCE OF LARGE DIAMETER OIL & GAS PIPE
Traditional manufacturing processes for large diameter pipe can result in reduced collapse pressure compared to seamless alternatives. However this can be avoided by finishing longitudinally welded pipe by compression rather than expansion, which can improve the performance over seamless pipe.
A unique cold sizing press called Impander® has been developed by Eisenbau Krämer to produce pipe with reduced ovality, reduced residual stresses and increased compressive yield strength to significantly increases collapse pressure.
Pipes larger than 16 inches in diameter are mainly produced by cold forming using the UOE or JCO processes. After the seam is welded, the pipe is finished by expansion or outside calibration, but its collapse pressure can be up to 30 percent lower than that of seamless pipe with the same diameter, thickness and steel grade.
However, replacing cold expansion with cold compression can avoid compressive strength degradation and increase collapse pressure. This process is known as impansion.
Eisenbau Krämer pioneered this process several years ago. Our unique Impander® compression press reduces ovality and straightens the pipe while contracting the pipe's circumference, inducing compression which increases yield strength.
Pipe with diameters ranging from 14 to 60 inches can be compressed to a pre-chosen value that can exceed 1.0%. This calibration and compression process produces pipes with internal diameter tolerances of less than 0.5 mm and ovalities smaller than 0.5% over the whole length of the pipe.
To prove the benefits of Impander® we carried out tests with X-65 grade steel, which found that impansion significantly improved the circularity of pipe, reduced residual stresses and improved straightness. More importantly, it improved significantly the compressive stress-strain response of the pipe by increasing yield strength.
We also found that the significant increase in collapse pressure could be enhanced if the impanded pipe was heat-treated at a temperature range typical for pipe coating processes.
Eisenbau Krämer's Impander® press is a manufacturing innovation that has enhanced the capabilities of welded pipe to not only match, but improve on the performance of seamless alternatives and is changing industry perceptions of pipe tolerances.