T/CNS 5-2018 in English

Scope

In the process of drafting this standard, reference was made to national standards such as GB/T 10123-2001 "Basic Terms and Definitions for Corrosion of Metals and Alloys," GB/T 24196-2009 "Guide for Electrochemical Tests on Metal and Alloys - Polarization Measurements at Constant Potentiostatic and Cyclic Voltammetric Conditions," as well as ASTM standards such as ASTM G129-00 "Standard Practice for Slow Strain Rate Testing to Evaluate the Susceptibility of Metallic Materials to Environmentally Assisted Cracking," ASTM E647-11 "Standard Test Method for Measurement of Fatigue Crack Growth Rates," and ASTM E399-06 "Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness KIC of Metallic Materials." Relevant regulations on electrochemical tests and stress corrosion cracking growth measurement were also referenced from technical documents prepared by the Metal Research Institute of the Chinese Academy of Sciences regarding the electrochemical test methods and measurement of stress corrosion cracking growth for nuclear water reactor materials in high-temperature, high-pressure water. The standard was formulated based on experiences from the Metal Research Institute of the Chinese Academy of Sciences as well as relevant research institutions abroad concerning high-temperature, high-pressure water electrochemical tests and stress corrosion cracking growth measurements.

(1) To achieve loading of specimens under high-temperature, high-pressure water environments, the loading system should be connected with a dynamic seal to the high-pressure vessel to ensure long-term stable operation in such conditions.
(2) For convenient extraction of electrical signals from specimens in high-temperature, high-pressure water environments, it is recommended that metal wires made of the same or similar material as the sample be used as conductors. These should have an insulating layer of heat-shrink polytetrafluoroethylene tubing and be connected to the specimen via spot welding.
(3) To achieve real-time control and monitoring of water chemical parameters in high-temperature, high-pressure water solutions, the high-temperature, high-pressure water stress corrosion cracking sensitivity rapid evaluation test device must include a circulating water loop. This includes components such as storage tanks, circulation pumps, high-pressure pumps, heat exchangers, preheaters, condensers, back pressure valves, and ion exchange resins. The outlet of the storage tank is connected to the circulation pump via piping. The outlet of the circulation pump leads to both a water chemistry monitoring loop and a high-temperature, high-pressure water loop. The water chemistry monitoring loop includes conductivity probes, dissolved oxygen probes, pH probes, and ion exchange resins before returning to the storage tank. The high-temperature, high-pressure water loop has components such as high-pressure pumps, heat exchangers, specimen holders, high-pressure vessels, condensers, back pressure valves, etc., with the outlet of these pipes connected back to the storage tank.
(4) To simulate typical light water reactor power plant circulating water environments, the high-pressure vessel is required to maintain a stable seal and long-term operation in temperatures between 280-325°C and pressures ranging from 8-16.5 MPa of high-temperature, high-pressure water.
(5) To ensure key water chemical parameters during the test environment, real-time precise monitoring and control of dissolved oxygen content in the circulation water are necessary.
(6) To guarantee a successful measurement under high-temperature, high-pressure water conditions, an insulation check should be conducted after the loading is completed and pressure applied to ensure that the specimen is electrically insulated from the high-pressure vessel.
(7) To maintain the water chemical parameters of the high-temperature, high-pressure water in the high-pressure vessel, it is stipulated that the flow rate of the circulation water must allow for a complete exchange of water within the vessel every hour.
(8) To ensure smooth, safe, and effective high-temperature, high-pressure water electrochemical and stress corrosion testing, operators are required to strictly follow operating procedures during the test.
(9) To ensure safety, automatic alarms and system shutdown should occur when the outflow temperature is too high. A rupture valve should be installed at the entrance of the high-pressure vessel so that it can burst and depressurize in case the pressure inside rises due to a fault. Automatic alarms and system shutdowns should also occur if the high-pressure vessel, preheater, heat exchanger, etc., leak or if cooling water supply is interrupted.