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In recent years, some coal resource producing areas have established coal chemical projects. With the increase in the size of coal chemical plants, the diameter of the equipment is also increasing, the pressure is getting higher and the wall thickness is getting thicker and thicker. The increase in wall thickness of coal chemical equipment has raised new requirements for materials, design, manufacture, inspection, and installation. Most of the current use of composite steel plate, the need for simultaneous heat treatment and intergranular corrosion inspection, which increases the difficulty of equipment manufacturing, testing.
Such as separators and heat exchangers, in the annual production of 200,000 tons of methanol production facilities, the wall thickness is less than 30 mm, due to the need to do the whole equipment to eliminate the stress heat treatment, equipment, welding easier to pass the intergranular corrosion sensitivity test. After the large-scale installation, the wall thickness of the equipment exceeds 30 mm, and the welding test is greatly improved by the intergranular corrosion test.
According to the reporter's understanding, due to the lack of uniform standards, when manufacturing equipment is used for welding qualification tests, the cumulative heat treatment time of manufacturing companies is 10 hours, some 12 hours, and some 16 hours. Gao Gong Song Wenxuan of Shanghai Coking Co., Ltd. introduced that this time was proposed by design institutes and manufacturing factories, and the time requirements were different. Zhou Xiaoqin, chief engineer of the Chemical Industry Equipment Quality Supervision and Inspection Center, stated that some manufacturers have specified in the technology contract that the cumulative heat treatment time of simulated post-weld heat treatment is 12 hours, but only after 10 hours will they barely meet the specified value. On the issue of time, there will be disputes between the design institutes and the owners. The heat treatment time in the manufacturing process will be short, affecting the quality of the equipment and there will be potential safety hazards after the equipment is operated.
It is understood that last year the coal gasifier of a coal chemical company was put into operation for less than half a year, and cracks occurred in the welded parts of the transforming equipment pipelines. Gas leakage accidents occurred because the welds were not tested for intergranular corrosion as required during equipment manufacturing. Caused. Another domestic large-scale coal chemical company's conversion furnace used to have an intermediate burst during normal operation, mainly due to the fact that the welds were not heat treated as required during equipment manufacturing.
According to industry insiders, because intergranular corrosion has a certain degree of concealment, it is not easy to inspect and discover, and it will suddenly leak without any sign of danger, which is very harmful. It is understood that many domestic pressure vessel manufacturers do welding evaluation tests, there are problems to reduce the cumulative heat treatment time. At the same time, for water-slurry gasifier water-cooled chilling chambers and washing towers, many design institutes did not raise requirements for intergranular corrosion inspections, and some company installations were in operation and cracks in the welding site caused gas leakage accidents. Prove that the acid gas in the raw material gas will cause the intergranular corrosion of stainless steel.
Wang Yongsheng, deputy general manager of Henan Yongmei Group Zhongxin Chemical Co., Ltd., said that the corrosion between the equipment and the pipeline is very complicated. At present, the concealed corrosion of the inter-crystal corrosion by the owner is difficult to find, and after the problem arises, the design institute puts the problem again. Push to the owner.
Song Wenxuan stated that for the longest accumulated time of heat treatment, the domestic engineering company's design institute, pressure vessel manufacturing plant, and material supplier are not clear in the technical requirements. She suggested that relevant domestic agencies should pay attention to the unified requirements of this standard. They should unify the standard requirement. The simulated post-weld heat treatment time for steel plate and forging suppliers must be longer than the time required by the buyer, and the equipment manufacturer must simulate the post-weld heat treatment time on the test plate. Must be greater than the maximum length of post-weld heat treatment of the manufacturing process of the factory, so as to truly guarantee the final performance of the equipment.
Engineer Yan Junnian, the chief engineer of Henan Longzi Coal Chemical Industry Co., Ltd., believes that in the production process of coal chemical plants, it is necessary to perform regular wall thickness inspections on the diversion and reduction of all kinds of pipe fittings and pipelines, and to each pipe and important pipe fittings. Establish a detailed corrosion technology file so that the corrosion of pipelines and pipe fittings can be accurately and timely controlled to prevent the occurrence of pipeline leakage accidents.
In fact, potential hidden dangers in the manufacturing of coal chemical equipment not only pose a threat to safe production, but also affect the long-term stable operation of the equipment. For example, pressure vessels in methanol synthesis plants are mostly made of carbon steel materials, and carbon steel materials and synthetic gas are in contact with each other to generate carbonyl iron, which leads to synthetic catalyst poisoning and affects production stability. According to industry insiders, research on the mechanism of carbonyl iron production and how it is selected has not yet attracted the attention of companies.
On December 28 last year, at the third plenary session of the inter-ministerial joint meeting on the supervision of hazardous chemicals safety production, Luo Lin, director of the State Administration of Work Safety, pointed out that the current problem of safe production in coal chemical industry has become a prominent issue and has become the fourth largest area of ​​hazardous chemicals safety. One of the outstanding issues. The reporter learned from the interview that, with the rapid development of China's coal chemical industry and the increasing size of installations, the performance requirements of the materials used have become higher and higher, and the difficulty of production has also increased. At the same time, the standards used in equipment manufacturing are inconsistent. The safety problems behind the manufacture of coal chemical equipment, especially some hidden safety issues that are not easily detected in inspections, are threatening the stable and safe operation of coal chemical installations.
January 16, 2019