High Pressure Valve Body Fatigue Cracking | Causes & Prevention Methods

High-pressure valves serving in petrochemical refining, hydrogen energy projects, power plant boiler systems and long-distance fluid transmission pipelines work in extremely harsh cyclic working environments. Frequent pipeline pressure fluctuations, alternating cold and hot temperature stress, and periodic water hammer impact will cause cumulative fatigue damage to the valve body. Among all structural defects, fatigue cracking is the most concealed and dangerous fault, which may lead to equipment shutdown and safety accidents. Fatigue cracks mostly occur at stress concentration positions of the valve body, including flange transition fillets, valve body arc corners, wall thickness mutation areas and valve stem boss roots. Different from sudden burst failure caused by excessive pressure, fatigue cracking is a slow and cumulative damage process. Micro internal cracks inside the valve body will expand gradually after thousands of cyclic pressure impacts. When the cracks penetrate the valve body wall completely, it will cause medium leakage and equipment system failure. Valve body manufacturing process directly determines the anti-fatigue performance. Cast valve bodies have inherent defects such as internal porosity, shrinkage cavities and discontinuous metal grain flow, resulting in poor fatigue resistance and easy cracking under cyclic load. In contrast, die-forged valve bodies feature dense and continuous metal grain streamline, uniform internal structure and stronger structural stability, which can effectively resist fatigue damage under long-term alternating pressure working conditions. In actual production, the main inducements of valve fatigue cracking include incomplete heat treatment process, unresolved forging residual stress, irregular pipeline operation, frequent pressure surges and repeated water hammer impact. To effectively prevent fatigue cracking, targeted control measures shall be implemented from both manufacturing and operation maintenance links. Manufacturers must strictly carry out standardized normalizing and tempering heat treatment to completely eliminate forging residual stress and optimize internal metal structure. On the user side, pipeline operation should avoid rapid pressure rise and sudden valve opening and closing actions to reduce water hammer impact. For key high-pressure process valves in core production links, regular UT ultrasonic testing and MT magnetic particle testing are essential. Timely detection of micro fatigue cracks can eliminate hidden structural dangers in advance and ensure the long-term safe operation of pipeline equipment.