What is the typical inspection rate for pressure testing of valves in steam power pipelines in power plants?

Analysis of the inspection ratio for pressure testing of valves in steam power pipelines in power plants. In the steam power systems of power plants, pipeline valves serve as critical control and safety components, and their reliability is directly related to the safe and stable operation of the entire system. To ensure the sealing performance, strength, and operational efficiency of the valve under high-temperature and high-pressure conditions, it must undergo pressure testing. Pressure testing is an essential quality control step before valve installation or after major repairs, and the determination of the inspection ratio requires comprehensive consideration based on relevant **standards, industry regulations, and actual project requirements. I. Types of pressure tests Valve pressure tests usually include: 1. Shell strength test (pressure resistance test): To evaluate the strength and sealing performance of the valve shell and its connections under pressures higher than those encountered in normal operation. 2. Sealing test (closed-seal test): To examine the sealing performance between the valve seat and the valve disc when the valve is in the closed position. II. General provisions for inspection ratios According to the current relevant standards in China, such as \"GB/T 13927-2008 Industrial Valves – Pressure Testing\", \"DL/T 641-2015 Test Procedures for Power Station Valves\", and \"ASME B16.34\", the pressure testing inspection ratios for valves in power plant steam power pipelines are as follows: 1. Factory testing: ○ All valves must undergo 100% shell strength testing and sealing tests before leaving the factory. ○ These are the basic quality assurance measures of the manufacturing plant, applicable to valves of all nominal pressure classes. 2. Random inspections before on-site installation: ○ For valves that already have valid factory test reports, re-inspections can be carried out at a certain rate before on-site installation. ○ General provisions: ■ For key systems such as main steam pipes, reheat steam pipes, and high-pressure feedwater pipes, valves must undergo 100% on-site pressure testing, especially for important valves with a nominal pressure of ≥4.0 MPa and an operating temperature of ≥400°C. ■ Non-critical systems or low-pressure pipelines: Sampling inspection can be conducted on a batch basis. The sampling ratio is usually 10%–20%, but it must include at least one unit. ■ If non-conformities are found during sampling, the sampling rate should be increased to 50% or 100% full inspection. 3. Requirements for special operating conditions: ○ For nuclear power plants, supercritical/supersupercritical units, and other power plants with high operating parameters, safety considerations require that 100% on-site pressure testing be carried out on all main system valves. ○ For critical valves such as important control valves, safety valves, electric gate valves, and globe valves, it is recommended to conduct 100% inspection regardless of the system classification. III. Basis for adjusting the inspection ratio The inspection ratio is not fixed; it should be adjusted dynamically based on the following factors: ● Historical record of valve manufacturing quality (such as supplier reputation, past failure rate) ； ● Valve type (such as globe valve, gate valve, ball valve, control valve, etc.) ； ● System importance (main steam, bypass, blowdown, etc.) ； ● Operating parameters (pressure, temperature, medium properties) ； ● Whether it is an imported valve or the first domestically produced set of equipment. IV. Conclusions and Recommendations In summary, the inspection ratios for pressure testing of valves in steam power pipelines in power plants are as follows: ● At the factory stage: 100% full inspection, which is a mandatory requirement ； ● On-site installation phase: ○ Critical system valves: 100% re-inspection ； ○ General system valves: 10%–20% sampling rate, but not less than 1 unit ； ○ When defects are detected, random inspections or full inspections should be increased. It is recommended that, in engineering practice, a detailed \"Valve Testing Plan\" be developed based on the project design documents, supervision requirements, and plant operation procedures, specifying the scope of testing, standards, methods, and inspection ratios to ensure the safe and reliable operation of the system.