Session: 03-04-01 Environmental Effect on Materials Performance

Paper Number: 79322

79322 - Fracture Toughness Characterization of LSAW UOE Pipes in Sour Media and Implications on Burst Pressure 

Hydrogen sulfide may be present in processed materials in the oil and gas (O&G) industry and can cause Sulfide Stress Cracking (SSC) in different components. Additionally, the increasing interest on high grade pipelines, which may sustain higher pressures, make the SSC phenomenon an important issue in the assessment of safe operational conditions of O&G transportation facilities.

Although, a pipeline in service is submitted to different combination of loads, i.e.: internal pressures, tensile loads, bending loads, a basic assessment is the effect of longitudinal flaw in the maximum internal pressure the pipe can sustain. The Longitudinal Submerged Arc Weld (LSAW) is a potential source of flaws and undesirable microstructural features in the pipe. Therefore, it is important to assess the effect of the crack location on the material fracture behavior in aggressive media.

The adequate determination of fracture toughness value (i.e.: K-mat) is of fundamental importance for fitness for purpose evaluation. Particularly, the fracture toughness of materials in aggressive media is usually determined using Double Cantilever Beam (DCB) specimens and the obtained K-limit values are the employed for fracture assessment. Although, Method D of NACE using DCB specimens is the currently recognized testing methodology for pipe manufacturing QA/QC, its validity as a test to obtain the fracture resistance parameter for burst pressure estimation of flawed pipes remains uncertain and alternative methods are being evaluated.

In the present paper, a fracture mechanics experimental program in sour environment is presented. Parent pipe and weld material of large diameter LSAW UOE pipes in H₂S were studied. Fracture toughness parameters, such K-limit from standard DCB tests and K-threshold from Single Edge Notch Tension (SENT) specimens under constant loading, are compared and discussed. The fracture toughness values (K-mat) obtained from both testing techniques are used to calculate the burst pressure of flawed pipes using BS7910 equations.

Presenting Author: Sebastian Cravero Tenaris

Authors:

Sebastian Cravero Tenaris
Mariano Coloschi Tenaris
Martín Valdez Tenaris
Fabio Arroyo Tenaris
Philippe Darcis Tenaris