IEEE 62582-3-2012 pdf free download – Nuclear power plants – Instrumentation and control important to safety – Electrical equipment condition monitoring methods – Part 3: Elongation at break.
3 General description
A test specimen is extended along its longitudinal axis at constant speed until the specimen fractures. During the test, the load sustained on the specimen and its elongation are measured. For this standard, elongation at break is the measured parameter. NOTE Elongation at break rather than tensile strength is used because for some polymers, particularly thermoplastics, the strength may remain consistently equal to the yield strength after ageing even when the elongation has decreased to ? 50 % absolute.
4 Applicability and reproducibility
The method is related to the long chain molecular structure of the polymer. As degradation proceeds, changes in the molecular structure occur as a result of cross-linking, chain scission, oxidation and other degradation mechanisms. These changes usually decrease the elongation at break. This method is primarily suited to samples taken from equipment that are based on thermoplastic or elastomeric polymers. The method is generally not suitable for fibre reinforced polymers or resins such as epoxides. The method cannot be used in the field in the nuclear power plant but uses samples taken from the plant, which are then measured in the laboratory. Each tensile elongation measurement in the laboratory can take between 5 min and 1 0 min to complete.
NOTE Round robin tests using a method close to the current standard have shown a typical laboratory variation in results of measurements of elongation at break on identical specimens of 8 % to 1 0 %. The mechanical properties of some polymeric materials may be affected by the moisture content. Most organic and polymeric materials currently used in-containment are not significantly hygroscopic. However, if hygroscopic materials are used, the influence of the moisture content of the material on elongation at break may need to be considered, particularly after artificial thermal ageing as a consequence of long term exposure to high temperature in an oven.
5 Measurement procedure
5.1 Stabilisation of the polymeric materials An appropriate time period shall be allowed for the polymeric materials in recently manufactured equipment to stabilise before any condition monitoring or accelerated ageing programmes are carried out. The time period over which the polymeric materials stabilise is normally dependent on the processing additives and polymer composition. If manufacturers’ stabilisation time data are not available, a period of 6 months should be allowed before commencing ageing to allow initial values from unaged samples to become stable.
5.2 Sampling
5.2.1 General Measurements of tensile elongation provide information on the status of the equipment only at the specific location which has been sampled. Knowledge of the environmental conditions in representative areas during plant operation is a prerequisite for selecting sample locations for condition monitoring. It is important that these locations represent as wide a range of ageing conditions as possible with special consideration given to locations where ageing conditions could be severe, e.g. hotspots. The location of the sampling and available information about the environmental time history at the sample location selected shall be documented. Sampling procedures shall comply with local instructions, taking into account safety of personnel and equipment. Handling of equipment during removal of samples from the plant should be minimised e.g. cables should not be bent more than is necessary to remove the sample.IEEE 62582-3 pdf download.