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What is a boiler hydrotest? The boiler hydrotest is a test of strength and sealing performance conducted using pressurized water after the boiler is assembled. When is the boiler hydrotest conducted? 1. After the boiler is installed, the pressure-bearing components must undergo a hydrostatic test. 2. After major or minor repairs to the boiler, or after maintenance of its partial heating surfaces, a routine hydrostatic test must be carried out, with the test pressure being equal to the boiler’s maximum allowable operating pressure. The hydrostatic test should be supervised by maintenance personnel, with the participation of both operating and maintenance staff. 3. The boiler hydrostatic test is generally carried out during major and minor repairs. Depending on the specific technical condition of the equipment, and with the approval of the group company’s boiler supervision department, the interval between such tests can be appropriately extended or shortened. The overpressure test should be conducted in conjunction with major and minor repairs. When should a boiler pressure test be carried out? 1. When a newly installed boiler is put into operation. 2. When boilers that have been out of service for over a year are restarted. 3. After boiler modifications, or when pressure-bearing components undergo major repairs or replacements – such as when more than 50% of the water wall tubes are replaced, when components like superheaters, reheaters, and economizers are replaced as a set, or when the steam drum is subjected to major repairs. 4. When the boiler experiences a severe overpressure of 1.25 times the operating pressure or more. 5. When the heating surfaces undergo significant deformation due to severe water shortage in the boiler. 6. When, based on operational conditions, there are doubts regarding the safety and reliability of the equipment’s operation. Selection of boiler hydrostatic test pressure (taking a certain power plant as an example): The pressures for the routine hydrostatic test and overpressure test of the boiler are as follows: The superheater, water wall, and economizer are considered as a whole; the routine hydrostatic test is conducted at a pressure of 19.79 MPa, which corresponds to the operating pressure of the steam drum, while the overpressure test is carried out at 1.5 times this pressure, namely 26.69 MPa ； The reheat system is pressure-tested separately at 1.5 times the inlet operating pressure of the reheater, which is 4.4 MPa (6.60 MPa). Scope of the boiler hydrostatic test: 1. Superheated steam system: from the make-up water control panel to the electric isolation valve before the main steam hydrostatic test. 2. Reheat steam system: from the electric isolation valve for the cold reheat inlet pressure test to the isolation valve for the hot reheat outlet pressure test. 3. Pipeline components of the boiler body. 4. The drum level gauge is only used in routine hydrostatic tests, not in overpressure tests. 5. If the high-pressure heater is in operational condition, it participates in the regular hydrostatic test but not in the overpressure test. 6. The initial hydrostatic test of the boiler body should be carried out before the boiler pump motor is installed; at this time, the pump casing involved in the hydrostatic test is sealed with specialized hydraulic plugs. Since the pump casing is open, the outlet valves (10) of each boiler water pump can be opened to fill the boiler evenly with water. 7. Before the hydrostatic test during normal operation, the boiler water pump should be filled with water thoroughly. 8. For the overpressure test, the rotating parts of the boiler feed pump should be installed only after the overpressure hydrostatic test is completed ； During the hydrostatic test, the pump casing is isolated by a hydraulic cover plate. Inspections and preparations before the hydrostatic test: 1. Inspect the steam and water systems related to the boiler’s hydrostatic test; ensure that any maintenance work on these systems has been completed, that the work permits have been retrieved, and that there is no ongoing work in the furnace or flues. 2. Local pressure gauges with an accuracy class of 0.5, which have passed inspection, have been installed at the boiler and reheater inlets; the pressure gauge readings at these locations in the control room are accurately calibrated, and good communication equipment is available between the local areas and the control room. 3. Check that the boiler steam and water system has been reliably isolated from the turbine (isolate in accordance with the specific operation instructions). 4. During the hydrostatic test, the ambient temperature should be above 5°C; otherwise, reliable anti-freezing measures must be in place. The water temperature for hydrostatic testing is generally between 40 and 60°C; the difference between the water inlet temperature and the wall temperature of the steam drum should not exceed 28°C, while the temperature of the metal surfaces exposed to heat must be at least 21°C. 5. Demineralized water or condensate shall be used for the hydrostatic test, with a pH value of around 10.0. The water used for the hydrostatic testing of the reheater system should have a chloride ion content of less than 0.2 mg/L, to prevent chloride ions from causing intergranular corrosion in the high-reheating section. 6. The spring hangers of the pipes within the scope of the hydrostatic test should be secured with pins or positioning pieces before the test, to serve as temporary rigid hangers; they should be removed after the hydrostatic test. 7. Remove the interlock from the electric valves for superheater and reheater desuperheating water. 8. Contact the maintenance team to install temporary clamping devices on all safety doors, disconnect the electromagnetic relief valves, and close the manual isolation doors to prevent them from operating during the pressure test. 9. Before water is introduced, maintenance personnel must confirm that all debris inside the boiler’s pressure-bearing components has been removed. 10. In accordance with the operating procedures for the pump, carry out inspections and preparatory work on the electric feed water pump. 11. Check that the status of all valves in the boiler is correct according to the hydrostatic test checklist. Methods for conducting hydrostatic testing: 1. The hydrostatic testing should be supervised by the person in charge of maintenance, with the operators responsible for carrying out the tests and the maintenance staff responsible for conducting inspections. 2. Sequence of hydrostatic testing: Test the reheat steam system first, then the main steam system of the boiler ； For the hydraulic testing of the various valves in the boiler, start with the secondary valves and then proceed to the primary valves. 3. During the hydrostatic test of the superheated steam system, contact the thermal control personnel to disable the drum water level protection. First, fill the system with water using the electric pump; once the water level in the steam drum is visible, then fill it from the reverse direction through the secondary desuperheating water pipeline of the superheater. The water feeding rate should be no less than 2 hours in summer and no less than 4 hours in winter; it can be increased appropriately when the water temperature is close to the wall temperature of the steam drum. 4. When water continuously overflows from the air valves of the boiler, close each vent valve in the direction of the water flow and then increase the pressure. 5. During the water filling process, closely monitor changes in water level, and check whether there are any leaks in various components as well as whether the expansion of the heated surfaces is normal. If any abnormalities are detected, the cause should be identified immediately and eliminated. 6. Pressurization test of the reheater system: Water is injected into the reheating system via the reheater accident spray to increase pressure. The pressure increase should be done slowly; when the pressure is below 1 MPa, the rate of increase shall be ≤0.1 MPa/min. Once 1 MPa is reached, the process should be stopped for inspection, and after maintaining that pressure for 15 minutes, the pressure can be increased again at a rate of ≤0.3 MPa/min. Once the operating pressure of 4.4 MPa is attained, the pressure increase should be halted and the pressure maintained stable. A thorough inspection of the reheater system should be carried out; only after no abnormalities are found should the pressure be increased to the hydrostatic test pressure of 6.6 MPa, at which level it should be maintained for 5 minutes. After the hydrostatic test is successful, the pressure should be reduced back to the operating pressure, with the pressure being lowered at a rate of 0.3 MPa/min. 7. Hydrostatic test of the boiler’s main steam system: Pressure is increased using the superheater desuperheating valve. The increase in pressure should be gradual; at pressures below 9.8 MPa, the rate of pressure increase must be ≤0.3 MPa/min. When the pressure reaches 2 MPa, the process is paused for inspection. If nothing abnormal is found, the pressure is held steady for 15 minutes before continuing to increase it. Once the pressure reaches 5.88 MPa, the increase is halted again to monitor any changes in pressure. If everything is normal, the pressure is continued to be increased to 9.8 MPa. After that, the pressure is raised at a rate of ≤0.2 MPa/min until it reaches 11.77 MPa, after which the process is paused once more to check for any abnormalities. After no abnormalities are detected, the pressure is increased further to the drum operating pressure of 19.79 MPa; after maintaining this pressure for 5 minutes, the feed water valve is closed. The pressure drop within 5 minutes after the feed water valve is closed is recorded, and maintenance personnel are notified to conduct a thorough inspection. 8. If a overpressure test is to be conducted, the drum level gauge should be removed; once it is confirmed that everything is functioning properly, the pressure should be increased at the same rate until it reaches the overpressure test pressure of 29.69 MPa. This pressure level should be maintained for 30 minutes. The pressure should then be reduced using a steam trap at a rate of 0.3 MPa/min, until the drum reaches its normal operating pressure. At that point, the steam trap should be closed, and the normal test pressure should be maintained for a thorough inspection. 9. After the hydrostatic test is completed, relieve pressure using a series of valves or a steam trap, at a rate of 0.3 MPa/min. 10. When the pressure drops to 0.2 MPa, open all air valves and drain valves to release water. If the boiler is ready for operation and the water quality is satisfactory, the water level can be lowered to the ignition level; otherwise, all the water must be drained and fresh water added. The superheaters, main steam pipes, and reheaters should have all water drained. Notify maintenance to release the safety door clamping device. 11. If the boiler is not to be put into operation in the short term, close the pressure relief valve and carry out maintenance in accordance with the regulations for shutdown maintenance. Acceptance criteria for hydrostatic testing: 1. Criteria for passing the hydrostatic test at operating pressure: When the pressure is increased to the specified level during the hydrostatic test, the inlet valve should be closed for 5 minutes; the degree of pressure drop should be recorded. In the case of superheated steam systems, the pressure drop should not exceed 0.5 MPa. Moreover, there should be no signs of water droplets or mist leakage on the outer surface of the pressure-bearing components as well as at their welds. The compressed element shows no significant residual deformation. 2. Acceptance criteria for the pressure test: There should be no traces of water droplets or mist leakage on the metal walls and welds of the pressure-bearing components. The compressed element shows no significant residual deformation. Precautions for hydrostatic testing: 1. During hydrostatic testing, the ambient temperature should be no lower than 5°C; if it is below 5°C, anti-freezing measures must be taken. 2. Before introducing water for the hydrostatic test, all air valves on the pressure-bearing components must be opened; once all air has been expelled and water begins to flow continuously, the air valves should be closed one by one. 3. During the hydrostatic test, the flow rate of water in or the pressure release should be adjusted slowly to prevent sudden changes in pressure. 4. The pressure increase process must be monitored and adjusted by a dedicated person; as the pressure approaches the test pressure, the rate of pressure increase should be reduced to prevent overpressure. 5. During the overpressure test, no inspections shall be carried out until the pressure drops to the operating pressure; inspections can only be performed once the pressure has reached the operating level. 6. The turbine barring gear must be put into continuous operation before the boiler hydrostatic test. 7. Before the hydrostatic test, the boiler testing system and the turbine must be reliably isolated, and safety measures must be in place to prevent the isolation valves from opening accidentally. During the test, the cylinder temperature must be closely monitored for any changes. 8. During the overpressure test, the drum level gauge should be disconnected from the system, and all safety valves must be fitted with plugs for isolation. After the hydrostatic test is completed, remove the plugs from the safety door and the pins of the spring hanger. 9. It is prohibited to use the boiler water pump drain valve to relieve pressure and discharge water from the boiler itself, in order to prevent boiler water from entering the motor chamber. 10. Water treated with solid chemicals should not be used for pressure testing, to prevent solids from settling in the superheater or reheater. 11. Before filling the boiler with water, it is necessary to ensure that all foreign substances in the boilers and headers have been removed completely. 12. The rotating parts of the boiler water circulation pump (impeller, motor, etc.) should be installed only after the hydrostatic test is completed; during the hydrostatic test, the pump casing is sealed off using specialized hydrostatic plugs. During water filling, the outlet valves of the circulation pump should be opened to accelerate the boiler’s water filling process. 13. Before conducting a hydrostatic test at pressures higher than normal operating pressure, all safety valves shall be fitted with plugs or compression devices. 14. If the boiler is filled with water through a economizer, the valve in the economizer recirculation circuit should be kept fully open; this facilitates water filling and helps to minimize the amount of air that gets trapped.