Evaluation of Weld Misalignment in Pressure Vessels and Pipelines Based on Fitness-for-Service Assessments in Accordance with API ۵۷۹- ۱/ASME FFS-۱

This research investigates and evaluates Fitness-For-Service (FFS) assessments to achieve a comprehensive understanding of the re-serviceability of damaged equipment in the oil, gas, and petrochemical industries. One of the challenges faced by these industries is the occurrence and development of weld misalignment, which leads to fatigue damage in pressure equipment. Pressure vessels, storage tanks, and piping systems degrade over long service periods, ultimately affecting the system's integrity. Under such conditions, implementing FFS assessments to evaluate structural integrity, extend the life of defective equipment, and estimate remaining service life becomes essential. If equipment exhibits weld misalignment or shell distortion, particularly when accompanied by gouges or crack-like flaws, conducting a Level ۳ assessment is necessary to confirm its fitness for continued operation. In these scenarios, in-service monitoring is typically mandatory. For equipment suffering from weld misalignment, loss of circularity (out-of-roundness), or local bulges, stiffening plates and lap patches can be used to reinforce the structure. The choice of reinforcement depends on the equipment's geometry, temperature conditions, and loading state. Reinforcement must be designed based on the principles and allowable stresses defined in the equipment's original construction code. Adhering to these requirements ensures the reinforcement is compatible with the original structure and that the equipment's safe operational capability is maintained. In sections of cylindrical shells that have lost their circular shape, mechanical methods can be used to restore them within the original fabrication tolerances or to a geometry that reduces local stresses to acceptable limits. The use of hydraulic jacks for reshaping stiffened cylindrical shells has yielded successful results. The reshaping process must be carried out under careful monitoring and control to minimize the risk of damage to the shell or adjacent connections. This method enables the restoration of the structure's geometry to an acceptable condition and can serve as a practical solution for extending remaining life and reducing failure risk. In-service monitoring is a key tool for ensuring the safety, operability, and remaining life of pressure equipment. This process involves a set of activities and methods for continuously or periodically inspecting the equipment's condition under real operational circumstances. The conducted FFS assessments have resulted in cost savings, prevention of unnecessary component repairs, reduction in the likelihood of sudden system shutdowns, and enhanced safety for industrial personnel.

کلیدواژه ها:

Weld Misalignment ، Pressure Vessels and Piping ، Fatigue ، FFS Assessments