Abstract
It is very important aspect to understand & determine the circumferential yield strength of pipe products which actually required in service condition. A limited number of paper has been published in public domain to understand & determine the circumferential yield strength through ring expansion test.
Determination of circumferential yield strength have its own importance in respect to actual service condition of pipe lines. It helps to know the sustainability of pipe lines with different pressure gradient at inner and outer radius of the pipe lines. When it comes to the actual service condition of pipe lines, the accuracy, precise & minimum standard deviation values of yield strength have the great impact for pipe line integrity.
Ring expansion test is carried out on ERW pipe samples of API 5L grade L360M (X52M), pipe diameter 355.6mm & 12.7mm and 8.6mm wall thickness.
It was observed that ring expansion test gives a highly accurate results of hoop stress than a flattened pipe sample. Ring expansion test explained the sensitivity to the metallurgical condition of steel.
In resemblance to flattened tensile test sample, ring expansion test provide 1) higher yield strength; and 2) narrow standard deviation. The major role played in higher yield strength of ring expansion test due to minimize the Bauschinger effect. Bauschinger effect significantly reduce the yield strength of flattened sample. The narrow standard deviation is the results of nullification of flatness and machining alteration that done on a flattened samples.
After several ring expansion sample test and correlation with flattened test, it is observed the ring expansion testing gives the accurate and precise values of pipe circumferential yield strength.
