Patent ID: 11965819
Assignee: SAUDI ARABIAN OIL COMPANY
Field: Measurement (Instruments)
Classification: CPC G  B  C | IPC B  G

Claim 0:
1. A method for determining whether a post weld heat treatment process is required to avoid stress corrosion failure of an external weld joint on a subject pipe having a wall thickness, comprising the steps of:
preparing a first group of test samples, each of the test samples in the first group having a different wall thickness;
welding each of the test samples in the first group at a first welding heat input;
preparing a second group test samples, each of the test samples in the second group having a different wall thickness;
welding each of the test samples in the second group at a second welding heat input, the second welding heat input being lower than the first welding heat input;
measuring the residual stress in each of the test samples of different thicknesses in the first and second groups;
determining an upper heat input stress trendline across a plurality of wall thicknesses for the first welding heat input based upon residual stress measured in the first group of test samples versus wall thickness;
determining a lower heat input stress trendline across a plurality of wall thicknesses for the second welding heat input based upon residual stress measured in the second group of test samples versus wall thickness;
determining a residual stress threshold based upon a measured residual stress in a longitudinal seam weld of a selected pipe;
determining an upper intersection point between the upper heat input stress trendline and the residual stress threshold;
determining a lower intersection point between the lower heat input stress trendline and the residual stress threshold; and
determining whether post weld heat treatment is required for the external weld joint based upon the wall thickness of the subject pipe compared to the corresponding wall thickness of the upper intersection point and the lower intersection point,
wherein if the subject pipe wall thickness is less than the corresponding wall thickness of the lower intersection point, then post weld treatment is required, and if the subject pipe wall thickness is greater than the corresponding wall thickness of the upper intersection point, then post weld treatment is not required.