Low temperature test is an important means to verify the performance of low temperature valves. The valve low temperature test method specified in the current standard is different from the actual working conditions. Improper operation can easily cause distortion of test results and even damage to the tested valve. This paper mainly analyzes the problems that are easy to occur in the low temperature test of the valve, and proposes some countermeasures based on the actual operation experience.
1 The ball valve has the characteristics of rapid opening and closing, reliable sealing, simple structure, light weight and small flow resistance.
Safety precautions The low temperature test of the valve is a dangerous work, and safety precautions are very important. Its dangers are mainly reflected in: local hypoxia caused by a large amount of volatilization of liquid nitrogen, which will cause personnel suffocation; possible low-temperature "scalding" to personnel; refrigerant splash caused by a large amount of leakage of test medium; and low temperature of instruments and meters. damage. Therefore, the workplace of the low temperature test should maintain good ventilation, and if necessary, artificial forced ventilation should be carried out.
It is necessary to scientifically and reasonably formulate the operating procedures for the low temperature valve test of the enterprise on the basis of relevant standards. Operators must hold certificates and be equipped with necessary safety protection equipment. Special attention should be paid to the protection of exposed body parts such as face and hands. During low temperature operation, it is strictly forbidden for one person to work on site. The emergency stop function should be set on the test equipment, and its operating parts should be placed in the most conspicuous and easy-to-operate position.
For high-pressure, large-diameter and other high-parameter tests, remote operations should be carried out as far as possible. The valve under test shall have fixing and clamping measures in the low temperature test tank. The selection of instruments and meters should pay attention to their low temperature resistance characteristics and performance stability at low temperature, so as to prevent their non-low temperature resistant parts from contacting the low temperature environment. For exposed low-temperature equipment or low-temperature parts of the equipment, warning signs should be set up and isolated to avoid accidental injury to unrelated personnel.
There is a certain difference between the valve low temperature test method specified in the current standard and the actual operating condition of the low temperature valve. The cooling rate, cooling method and holding time should be reasonably controlled to make the test conditions as close to the actual working conditions as possible. For the low temperature test of the ball valve, attention should be paid to the low temperature characteristics of its component materials to prevent the damage to the tested valve such as low temperature locking and cold flow. The refrigerant and test medium in the low temperature test of the valve are expensive and consume a lot, so attention should be paid to the consumption control, or they should be recycled and reused. It is necessary to strengthen safety precautions to prevent the harm of low temperature to personnel and equipment.