GB/T 28799.3 - 2020 is the third part of the standard for heat-resistant polyethylene (PE) (PE - RT) piping systems for hot and cold water, which is specific to pipe fittings. It specifies the material requirements, structural dimensions, performance indicators of PE-RT pipe fittings, such as hydraulic resistance, Impact resistance and other test methods and qualification criteria. The standard provides the basis for the production, inspection and selection of pipe fittings, to ensure the fit and overall mass of pipe fittings and pipes in hot and cold water piping systems, and to ensure the safe and stable operation of the system under long-term hot and cold circulation environment.