Effects of Aging on the Mechanical Properties of Pipeline Steels

Abstract

The intelligent design of a given pipeline system intended for operation beyond the elastic limit should incorporate specific features into both the base material (line pipe) and girth weld that enable the affected system to deform safely into the plastic regime within the intended strain demand limits. The current paper focuses on the mechanical properties known to influence the strain capacity of the base material (i.e., line pipe steel independent of the girth weld). Line pipe mechanical properties of interest include: longitudinal yield strength, tensile strength, yield to tensile strength ratio, reduction of area, elongation and uniform elongation. Of particular interest (in consideration of the conventional thermally applied corrosion protection coating systems to be employed), are the longitudinal mechanical properties in the “aged” condition. The present study investigates six (6) different pipeline steels encompassing grades X60 (415 MPa) to X100 (690 MPa), and includes both UOE Submerged Arc Welded - Longitudinal (SAW-L) and seamless (SMLS) forming methods.

Effects of Finish Cooling Temperature on Tensile Properties After Thermal Aging of Strain-Based API X60 Linepipe Steels

“…[1,2] In particular, the uniform elongation of the linepipe steels are reduced during the coating process to prevent corrosion after the piping processes. [3,4] The epoxy coating temperature range of linepipe steels is 473 K to 573 K (200°C to 300°C), at which the Cottrell atmosphere occurs. [5] In the Cottrell atmosphere, the decrease in uniform elongation is caused by the interactions between the carbon atoms in ferrite and dislocations, which results in yield point phenomena during the tensile tests.…”