5.7 Hydrostatic Test
5.7.1 After the erection of boiler heating surface system，hydrostatic test for utility boiler shall be carried out.The pressure of overpressure test shall be determined according to the manufacturer's provisions.If there is no specific provision，the test pressure shall meet the following requirements.
1 The test pressure for steam drum and the boiler primary system shall be 1.25times of steam drum design pressure.
2 The test pressure for the once-through boiler primary system shall be 1.25times of the design pressure for superheater outlet header and it shall be no less than 1.1times of the design pressure for the economizer inlet header.
3 Reheater test pressure shall be 1.5times of the design pressure for the inlet header.
5.7.2 Hydrostatic test for the main steam and reheat steam pipes in the supercritical and ultrasupercritical boilers should be carried out by using hydrostatic plugging valves or special temporary plugging devices provided by the manufacturer.The strength of the temporary pipes and plugs for hydrostatic test shall be calculated and verified with reference to Appendix K.
5.7.3 Prior to the boiler hydrostatic test，pressure decay test at 0.2MPa-0.3MPa shall be carried out once with compressed air.
5.7.4 The ambient temperature for the boiler hydrostatic test shall be above 5℃.Otherwise，the reliable freeze protection measures shall be taken.
5.7.5 The water quality and the inlet temperature for hydrostatic test shall meet the requirements of equipment technical documents.If there is no specific provision，they shall meet the related provisions in DL/T 889 Guide of Chemistry Supervision of Thermal Equipment for Power Station Capital Construction，DL 647 Inspection Code for Boiler and Pressure Vessel in Thermal Power Plant and DL 612 Supervision Code for Boiler and Pressure Vessel of the Power Industry.
5.7.6 During hydrostatic test，there shall be at least two spring tubular pressure gauges in the boiler，which have been calibrated as being qualified and whose precisions are no less than grade 1.0.The scale limit values should be 1.5times-2.0times the test pressure.The reading of the pressure gauge at steam drum or superheater outlet header shall be taken as the test pressure.The reading of the pressure gauge at reheater outlet header shall be taken as the test pressure of reheater.
5.7.7 The pressure change rate for hydrostatic test shall not exceed 0.3MPa/min.When the pressure reaches about 10% of the test pressure，the preliminary inspection shall be carried out.If there is no leakage，the test pressure shall be increased up to the work pressure，and inspection shall be carried out to verify whether there is any water leakage or abnormal phenomenon.Then the pressure shall be further inceased up to the test pressure，and the pressure change rate shall be less than 0.1MPa/min during the overpressure stage.After the pressure has been maintained for 20 minutes，the pressure shall be lowered to the work pressure，and the comprehensive inspection shall be carried out.The pressure shall be maintained to be constant during inspection.The qualified criterias of hydrostatic test are listed as follows:
1 The metal wall and welds of pressure components shall be leakfree and not wet.
2 There shall be no obvious residual deformation in any pressure component.
5.7.8 The boiler hydrostatic test under the test pressure shall be carried out as little few times as possible.
5.7.9 After the boiler have passed hydrostatic test，the certification shall be handled in time.The period from hydrostatic test to chemical cleaning shall be as short as possible.If the boiler need conservation，the corrosion measures shall be implemented according the requirements of DL/T 889 Guide of Chemistry Supervision of Thermal Equipment for Power Station Capital Construction.