T/CNS 3-2018 in English

Scope

In the course of writing this standard, references were made to national standards including GB/T 10123-2001 General Terms and Definitions for Corrosion of Metals and Alloys, GB/T 24196-2009 Guide for Electrochemical Polarization Measurement Methods for Corrosion Testing of Metals and Alloys, as well as ASTM standards such as ASTM G3-14 Standard Practice for Conventions Applicable to Electrochemical Measurements in Corrosion Testing, ASTM G5-14 Reference Test Method for Making Potentiodynamic Anodic Polarization Measurements, ASTM G31-72 Standard Practice for Lab Immersion Corrosion Testing of Metals, and ASTM G61-86 Standard Test Method for Conducting Cyclic Potentiodynamic Polarization Measurements for Localized Corrosion Susceptibility of Iron-, Nickel-, or Cobalt-Based Alloys. In addition, the technical document for a rapid evaluation method on electrochemical tests and stress corrosion cracking sensitivity of nuclear water reactor materials in high-temperature, high-pressure water was also referenced, developed by the Metal Research Institute of the Chinese Academy of Sciences (CAS). This standard was formulated based on the implementation experiences from the CAS's metal research institute as well as relevant international research institutions regarding high-temperature/high-pressure electrochemical tests and rapid evaluations for stress corrosion cracking sensitivity. The following is a detailed explanation of specific technical content.

(1) Due to the special nature of high-temperature electrochemical testing and evaluation of stress corrosion cracking sensitivity, work electrode samples are not encapsulated in any form; their bare metal surfaces directly participate in the test. Precise control over sample dimensions and surface roughness must be ensured.
(2) To ensure the validity of electrochemical test data, each test point generally needs to be repeated three times.
(3) To facilitate the extraction of electrical signals from high-temperature/high-pressure water environments, it is recommended that a metal wire with the same or similar material as the sample be used as a conductor. The surface should be insulated using a hot shrink tube made of polytetrafluoroethylene (PTFE). A spot welding method should connect this to the test sample; it is recommended that the spot weld position be on the side of the sample.
(4) To enable real-time monitoring and control of high-temperature/high-pressure water solution chemical parameters, a recirculating cooling system must be configured in the rapid evaluation device for stress corrosion cracking sensitivity under high-temperature/high-pressure water conditions. This includes components such as a storage tank, circulating pump, high-pressure pump, heat exchanger, preheater, condenser, backpressure valve, and ion exchange resin. The outlet of the storage tank is connected to the circulation pump via piping. The outlet of the circulation pump is split into two: one for the water chemistry monitoring loop and another for the high-temperature/high-pressure water loop. On the water chemistry monitoring loop are conductivity probes, dissolved oxygen probes, pH probes, ion exchange resins, etc., which return to the storage tank. The high-temperature/high-pressure water loop includes components such as a high-pressure pump, heat exchanger, test fixture, high-pressure vessel, condenser, backpressure valve, and so on. These are connected via piping to the outlet of the storage tank.
(5) To simulate typical light-water reactor nuclear power plant service cycle water environments, it is stipulated that the high-pressure vessel should be able to maintain stable sealing and long-term operation under conditions of 280-325°C and 8-16.5 MPa high-temperature/high-pressure water.
(6) To ensure key water chemistry parameters in the experimental environment are monitored accurately and controlled precisely, real-time monitoring and control over dissolved oxygen content in the circulation water is required.
(7) To maintain the operational stability of external reference electrodes, it is recommended that their electrolyte solution be replaced regularly and their potential corrected. It is suggested a replacement cycle of two weeks.
(8) To ensure the success rate of electrochemical tests under high-temperature/high-pressure water conditions, an insulation test should be conducted after sample loading and pressure application to ensure that the samples are insulated from the high-pressure vessel body.
(9) To maintain the water chemistry parameters within the high-pressure vessel, it is stipulated that circulation flow rates must allow for a complete replacement of the water in the high-pressure vessel every hour.
(10) To ensure smooth, safe, and effective operation of rapid evaluations on electrochemical testing and stress corrosion cracking sensitivity under high-temperature/high-pressure water conditions, operators should strictly follow operating procedures during the experiment.
(11) To ensure safety, it is stipulated that an automatic alarm system will be activated when the outflow temperature is too high, shutting down the system. A burst valve is installed at the entrance of the high-pressure vessel to vent pressure if the internal pressure due to a fault increases; an alarm and shutdown mechanism will also activate when the high-temperature vessel or its components such as preheaters or heat exchangers leak, as well as in cases where cooling water flow is interrupted.
(12) To ensure stability and reliability of the testing apparatus, regular accuracy checks should be conducted on electrochemical workstations, temperature sensors within the high-pressure vessel, temperature sensors for the preheater, dissolved oxygen probes, hydrogen probes, pressure sensors, etc., in accordance with relevant regulations.