Discussion on Supervision and Inspection Issues in the Manufacture of Boiler Pressure Vessels

With economic development, special equipment such as boiler pressure vessels has been widely used in various fields of social activities. Safety inspections for special equipment like boiler pressure vessels are a means to ensure safety during the production process, not the end goal. The ultimate goal is to protect people's personal safety and national property. Therefore, it is necessary to conduct meticulous and comprehensive safety inspections on special equipment such as boiler pressure vessels using scientific methods, to ensure they meet all characteristic requirements.

1. Common Equipment Defects and Types of Accidents that are Prone to Occur

1.1 Equipment Defects

1. Structural defects of the equipment itself, including insufficient strength and rigidity, and poor stability;

2. Sealing defects between equipment, such as leaks of steam, chemicals, hot water through pipes and valves;

3. Lack of protective facilities, such as failure to erect scaffolding and other protective measures, including improper scaffolding support and insufficient protection distance.

1.2 Types of Accidents

1. Hazards of flammable and explosive substances, toxic chemicals, and corrosive substances;

2. Hazards caused by coal dust, soot, slag, smoke dust, soot, and other operational risks;

3. Environmental hazards such as narrow internal space, poor ventilation, and incorrect ventilation methods in the boiler tail flue or furnace fuel oil and gas.

2. Supervision and Inspection Content and Methods

2.1 Internal and External Inspection of Pressure Vessels

External inspection of pressure vessels must be carried out after a comprehensive cleaning of the interior of the vessel. The main contents of the inspection mainly include:

1. Inspecting the corrosion and wear of the inner and outer surfaces of the boiler pressure vessel;

2. Checking for cracks in all welds, head transition zones, and other critical areas. If it cannot be observed with the naked eye or a magnifying glass, ultrasonic or radiographic inspection can be used;

3. Measuring the inner wall thickness of the container. If the thickness is less than the minimum wall thickness of the container, it should be rechecked. If there is indeed a problem, it should be used with reduced pressure or corresponding repair measures should be taken;

4. Corresponding metal inspections should be carried out on boiler pressure vessels that may cause changes in the structure of metal materials. In addition, corresponding crack inspections should also be carried out on the boiler pressure vessels. Through comprehensive and meticulous internal and external inspections, the inspected container problems are analyzed, and corresponding repair suggestions are given. After repairs are made, re-inspection should be remembered.

2.2 Comprehensive Inspection of Pressure Vessels

In addition to internal and external inspections, the comprehensive inspection of boiler pressure vessels also requires pressure resistance testing. The main purpose of pressure resistance testing is to inspect the welds. However, for very low-pressure, non-flammable, non-toxic, and non-corrosive containers, if no defects are found, and some experience is gained, non-destructive inspection may not be required. The comprehensive inspection cycle of the container is generally at least once every six years. For qualified containers filled with air and inert gases, after gaining experience and confirming no corrosion after one or two internal and external inspections, the comprehensive inspection cycle can be appropriately extended.

3. Safety Valve Calibration for Boiler Pressure Vessels

The current "Safety Technical Supervision Regulations for Steam Boilers", "Safety Technical Supervision Regulations for Hot Water Boilers", and "Safety Technical Supervision Regulations for Pressure Vessels" all provide for safety valve calibration: the safety valves of boilers in use should be calibrated at least once a year. The inspection items are setting pressure, seating pressure, and tightness. The calibration of safety valves is generally carried out in the operating state of the boiler. If on-site calibration is difficult or after repairing the safety valve, it can be performed on the safety valve calibration bench. At this time, only the set pressure adjustment and tightness test are performed on the safety valve. However, the calibration medium on the calibration bench is generally air or nitrogen, and the temperature is room temperature, which is very different from the medium, medium temperature, and medium flow rate actually used in the safety valve. Therefore, there is a deviation between the set pressure and the actual opening pressure and seating pressure. However, if on-site calibration is selected, because used safety valves need to be repaired, on-site maintenance is difficult. Even for new valve calibration, because the safety valve and pressure gauge are not in the same location, the boiler pressure rise and fall take some time, and it is unrealistic for inspectors to calibrate one by one. Therefore, the current safety valves should adopt a manufacturing license system like boilers, pressure vessels, and pressurized equipment pipelines, and conduct factory supervision and