Tensile Deformation and Fracture Behavior of API-5L X70 Line Pipe Steel

Thermo-mechanical controlled processing (TMCP) is employed to obtain the required level of mechanical properties of contemporary HSLA steel plates utilized for gas and oil pipeline production. The strength and crack resistance of pipeline steels are mainly determined by its microstructure and crystallographic texture. In this study, the influence of the structural and textural states of industrially produced API-5L X70-X80 pipeline steels on tensile mechanical properties was analyzed. TMCP routes with different hot rolling temperatures and cooling rates were employed. The texture of steel was assessed using the Taylor factor, which was calculated based on electron backscatter diffraction (EBSD). The decrease in rolling temperature resulted in the sharper texture characterized by {001} planes banding (cleavage planes in the bcc lattice) parallel to rolling direction. The tensile deformation behavior at the stage of necking was determined by the crystallographic and morphological texture of the material and demonstrated significant anisotropy. Rupture of all investigated samples was accompanied by the development of splitting on the fracture surface. The splitting was localized in the rolling plane similar to the splitting in standard Charpy tests of pipeline steels.

Carbon Steel X65QS Pipeline Qualification for Extreme Sour Service a Global Approach: Line Pipe, Welding, Eca Methodology and Diyab Pipeline Case Study

In the wake of failures of large diameter pipelines made from plates using the Thermo-Mechanically Controlled Process (TMCP), the suitability of carbon steel material for sour environments where the H2S partial pressure is largely over 1 bar has been questioned. Understanding that seamless quench and tempered material are not prone to the same phenomenon as large diameter TMCP pipes, it has been decided to ensure the integrity of the DIYAB pipeline by qualification using the actual production environment pH=3.5 at 24°C and 6.84 bar H2S plus 6.84 bar CO2. The global approach includes the qualification to sour service resistance under 6.84bar H2S of the base material and the welds without post weld heat treatment. Fracture toughness tests under 6.84bar H2S were also conducted, and the results fed into an Engineering Criticality Assessment (ECA) to define the Non-Destructive Testing (NDT) acceptance criteria. The NDT tools were selected for their ability to detect the critical flaws and validated. The global approach methodology and results are presented.

Investigation of Ultrasonic Testing Failure in ERW Line Pipe of API 5L X52M Grade

Electric resistance welding (ERW) is conventional manufacturing technology for production of linepipe. ERW is known for its low cost, high efficiency & reliability. Investigation was performed on Electric Resistance Welded (ERW) pipes having Ultrasonic Test (UT) indication observed during in-process inspection. The location of indication was adjacent to weld fusion line. The study was done on pipe size 168 mm (6.6 inch) outside diameter and 6.4 mm wall thickness of API 5L X52M grade to verify the cause of UT failure related to pipe manufacturing process and/or steel making process. The samples were drawn from UT indicated area and analysis is carried out by chemical testing, optical microscopy and scanning electron microscopy with energy dispersive spectroscopy. From systematical research by Why-Why analysis, it is clear that the reason of sub-surface defects on ERW pipe is due to presence of non-metallic inclusions. On the basis of the composition of observed non metallic inclusion, possible sources are identified. The countermeasures for each source cause were verified and successfully implemented the affected one.