The design of the pressure vessel is affected by the environment
Release time：2018-09-05 Browse：414
The working pressure, working temperature and internal medium of the container will not exceed the design range, but the external environment will be abrupt due to various reasons (such as the environment). Pressure vessels, water pressure and pH changes, etc.), pressure vessels that are still in a safe life cycle become unsafe, especially when serious new defects are discovered, and re-inspection and safety assessment must be carried out in time.
1. The re-inspection of the inspection content should be based on macroscopic inspection, wall thickness measurement and surface non-destructive testing. If necessary, ultrasonic testing, radiographic testing and hardness should be used. Measurement, metallographic examination and other means. The main contents of the macro inspection are: cracks, deformation and leakage of the body, interface parts, welded joints, etc.; corrosion and mechanical damage of the inner and outer surfaces; safety accessories inspection and container support, foundation integrity. Pressure vessels with insulation and lining should also be aware of any abnormalities such as breakage, shedding, and penetration. The determination of wall thickness as a primary means of testing is self-evident. According to the requirements of the TSG R7001-2004 Pressure Vessel Periodic Inspection Rules, the location of the measurement should be representative and have sufficient number of measurement points. The selection point should be selected according to the following aspects: the part where the liquid level fluctuates frequently; the part which is easy to corrode and eroded; the part where the wall thickness is thinned during molding and the part which is easy to be deformed and worn during use; Suspicious part; take-over part.
2. Test techniques and experience In the actual inspection process, special attention should also be paid to the following aspects: (1) It should be understood what the working environment is abrupt. The situation, such as one or several changes in temperature, humidity, pH or several changes exist simultaneously. (2) Because the change of environment directly leads to the change of corrosion rate, the corrosion margin has changed with respect to the original design parameters. Can the wall thickness meet the strength check requirements during the inspection cycle, and whether the container can be safely used? The beginning of an inspection, as an inspector responsible for the safety of the container, needs to be reconsidered. The selection of the corrosion margin in the strength check should be re-determined based on a large amount of measured data, ensuring relevant scientific and serious attitudes. The data is true and accurate. (3) There are some experiences in the thickness measurement technique for reference: before the test, the large-area rust area is removed by the circumferential grinder, and then the rust-proof area of the area is carefully derusted by a shovel or a trowel. Grinding out the flat metal body thickness measurement area to ensure accurate measurement; the container head center area, head bend area and section mutation area are the parts that are easy to produce the thinnest point, which should be used as the detection focus; The probe is easy to couple in many places with severe pits and large curvature, and the thickness measurement is convenient. For example, the commonly used Japanese AD-3253 type probe has a diameter of 6 mm, while the UTM-110 original probe has a diameter of 10 Mm, the former has obvious advantages when actually measuring thickness; if the thinnest point is found, the number of measuring points should be increased around it, and the thickness of the measuring point should be extended around the diameter of the probe to draw a partial enlarged view for detailed recording. For the inspection of corrosive media, especially in the case of the inability to open the tank to confirm the internal conditions, it is necessary to prevent the illusion due to the good external surface, resulting in missed inspection or According misreading; often noted in thickness measurement instrument should be calibrated, generally at least measured 10 every 1 checkpointing, to ensure the data authenticity. Non-destructive testing of surface can be carried out according to the characteristics of the container. Magnetic cleaning or penetration testing should be carried out. The polishing joint should be thoroughly derusted to ensure that the defect marks can be clearly displayed on the metal body of the container to avoid leakage inspection. The inspection of the butt joint and the fillet weld should not be numb. In the inspection, if it is impossible to open the can to confirm the internal situation, it is usually necessary to use the endoscope and other methods for inspection. For the problems found in the inspection, the inspector and the non-destructive testing personnel should cooperate with each other to ensure that the inspection work is comprehensive and meticulous.
3, a large outer steel plant test examples 1 set pickling plant specifications: 1 000 mm 2 130 mm, volume V = 1. 5 m 3, the design wall thickness = 8 mm, made of Q235 A, working pressure P w = 0. 8 MPa, the working temperature is room temperature. After the container was put into use for one year, the first inspection was in good condition, the safety status rating was rated 2, and the inspection validity period was 5 years. It should be emphasized that the factory made an iron work shed for the container to prevent the acid mist discharged from the exhaust pipe of the pickling workshop from directly corroding the container. In the first 2 years, the shed effectively blocked the corrosion of acid mist, but as time passed, the top of the shed gradually rusted. Due to the lack of follow-up precautions, a large amount of acid mist fell directly on the top and sides of the container, causing The paint peeled off and eventually formed a large area of severe corrosion. Safety valves and pressure gauges were also basically rust-resistant. We received more than two years from the original report when we received the re-inspection task. The re-inspection results show that the minimum wall thickness of the top head of the container has been reduced from the original 8 mm to 5.1 mm. According to the current corrosion rate, the inspection period for the safe use of the container to the original report is Impossible, and many cracks were found in the magnetic particle test. If the container continues to be used, the consequences are unimaginable. We negotiated with the factory to decide to replace the container as soon as possible, and learn lessons to build concrete houses to strengthen the protection of new containers.
