Dents in an oil and gas pipeline can be detected by In-line-Inspection (ILI), and structure integrity analysis of the pipe with theses reported dents is important for the safe operation. Strain analysis of the dented pipe is a way of fine assessment and ASME B31.8 has established the strain assessment code and its acceptable range. However, the method of strain assessment is rarely used due to the difficulty of strain calculation for a buried pipe. In this study, features of ILI data are investigated to elaborate the necessary of filtering analysis for strain analysis of the dent with ILI data. Then typical filtering methods are used to smooth the ILI data, and strain analysis are carried out with the smoothed data to study the practicability of strain assessment. Profile and strain of a dent in D813 pipe were obtained by Finite Element Method (FEM). Then different filtering methods were used to smooth the simulated ILI data of the dent which were selected from FEM profile. Strain of the dent were also calculated by smoothed data with the latest ASME B31.8 code, and compared with it from FEM at last to prove the feasibility and validity of the filtering methods with ASME B31.8 code.

The girth weld defect is one of the most common types of defects on oil and gas pipelines, which can have a strong impact on the operation safety. Several girth weld failure accidents have occurred on PetroChina’s pipelines in recent years. In this paper, PetroChina’s current work on inspection and fitness for purpose assessment of girth weld defects is summarized. The in-line inspection has been proved to be the best practice for oil and gas pipeline defect inspection, but there are still some technical issues such as defect characterization and parameter selection. Fitness for purpose assessment methods for girth weld defects include strength assessment method based on plastic collapse, FAD method based on both plastic collapse and fracture, simplified factor method and numerical analysis method based on finite element. It is critical to identify the actual type of defects detected in in-line inspection to select an appropriate assessment method. The identification of various loads and the selection of appropriate material parameters are also important issues in assessment procedure. The key techniques to be developed include defect characterization, load identification, assessment of defects on high grade steel pipes, reliability-based assessment, etc.