| Pressurized pipe is the special equipment in the oil and gas industry. In the pipeline installation, due to welding conditions, it is difficult to avoid welding defects in the weld among which unfitness and misalignment are the common defects. Existence of defects will influence the safety operation of pipes and may have potential danger to human life and properties. Therefore, it has both theoretical significance and practical value to analyze the load-carrying capability of the pressurized pipes with defects.In this paper, finite element model using ANSYS was established for the pressurized pipes with circumferential welds having unfitness or misalignment defects. Non-linear stress analysis under internal pressure was performed and limit loads based on two-time initial slope as well as double slope methods were calculated.Results show that under pressure loading, stress concentration occurs at the site where defect presents with the magnitude increasing with the defect size. As a result, the limit load decreases with increasing the defect size. The limit load based on double slope method is relatively smaller, or in other words, strength design or safety assessment with this method is more conservative.Based on finite element results, formulas for computing the limit loads were fitted as the functions of pipe diameter, wall thickness and defect size. Numerical tests revealed that the formulas are accurate enough in the range of pressurized pipes with diameter from 500mm to 900mm, wall thickness from 6mm to 10mm and unfitness defect from 1mm to 5mm or misalignment defect from 1°to 10°.Finally, a software for computing the limit loads for the pressurized pipes with circumferential welds having unfitness or misalignment defects has been developed which can be used to calculate the pipe load-carrying capability easily and, thus, is helpful for the engineering design or safety assessment of the pressurized pipes with these kinds of defects. |
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