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The maintenance tasks for pressure vessels during periods of inactivity include the following. 01 Keep pressure vessels dry and clean to prevent atmospheric corrosion. Scientific practice has shown that dry air generally does not cause corrosion in iron alloys such as carbon steel; corrosion only begins to occur in humid conditions (with a relative humidity of over 60%), and when there is dust, dirt, or old corrosion products on the metal surface. Therefore, to reduce corrosion of the outer surface of unused pressure vessels by the atmosphere, it is necessary to keep the vessel surface clean by regularly wiping away dust, ash, and other contaminants that accumulate on it, as well as to maintain dryness in both the pressure vessel and its surrounding area. 02 Paint the outer wall of the pressure vessel to prevent atmospheric corrosion; attention should also be paid to corrosion protection under the insulation layer and at the support points of the pressure vessel. 03 The pressure gauge should be kept clean; the glass on its dial must be clear and bright, so that the pressure reading indicated by the pointer inside the gauge is easily visible. If a fault is detected in the pressure gauge (including the pressure tapping tube), it should be addressed promptly. If there are doubts about the reading indicated by the pressure gauge, it should be calibrated immediately using a standard gauge; if the reading is incorrect, the gauge should be replaced. Pressure gauges must be calibrated regularly, with an interval of no less than 6 months. After calibration, the gauges should be fitted with a certificate of conformity and sealed with lead. 04 A pressure gauge should be discontinued from use and replaced if it exhibits one of the following conditions: a pressure gauge with a limit pin, in which the pointer cannot return to that limit pin when there is no pressure ； An infinite-range pressure gauge (referring specifically to positive-pressure gauges): when there is no pressure, the value at which the pointer sits relative to zero exceeds the allowable error of the gauge ； The dial cover glass is cracked or the dial markings are blurred ； The seal is damaged or has exceeded its validity period, the Bourdon tube inside the gauge is leaking, or the gauge pointer is loose ； Broken gauge pointers, severe corrosion of the casing, and other defects that affect the gauge’s accurate indication. 05 Pressure vessels are usually equipped with necessary safety devices according to the requirements of their operational characteristics. There are many types of safety devices, which should be installed and arranged properly, such as safety valves and pressure gauges. To keep the safety devices in good condition at all times, ensuring their accuracy, reliability, sensitivity, and effectiveness, it is necessary to strengthen their maintenance and care during the operation of the pressure vessel. 06 The accessory parts of pressure vessels must remain complete and undamaged. Pressure vessels with defective connection fasteners are prohibited from being put into operation. Many serious explosion accidents involving the ejection of end caps from pressure vessels are caused by damaged flange bolts on those end caps. 07 In pressure vessels, the end caps are opened for maintenance and cleaning; there are many bolts. Operators often install only a partial number of these bolts, and when the number of bolts installed is insufficient and the sealing performance is poor, they tend to tighten the nuts excessively. This results in a high pre-tightening force on the bolts, which can cause the flange bolts to break under pressure, leading to an explosion as the end cap is ejected. Therefore, for accessory parts such as the fastening bolts of pressure vessels, after being removed each time, they should first be cleaned and then inspected visually; only those fastening bolts that pass the inspection can be reused.