Key words: petrochemical plant; cryogenic valves; requirements Introduction Low temperature valves are mostly used in the medium temperature of -40 ℃ ~ -196 ℃ process, mainly used in air separation plant, LNG plant and liquefied petroleum gas plant, and plant production Has played a key role. With the continuous optimization of process, product quality continues to upgrade, the use of low-temperature valve performance and reliability put forward higher requirements. As a special valve, the low temperature valve in the design, manufacture, procurement and testing, and other aspects of the obvious difference with ordinary valves, so we not only clear the procurement specifications, models, but also the valve material, structure, performance, Technical conditions, etc. to be clearly defined, and through coordination with various manufacturers, the preparation of detailed technical documents to ensure the normal procurement work.
First, the preparation of low temperature valve procurement technical documents Before the valve procurement, we need to various workshops, equipment, materials, demand planning summary, this time the valve material table will be clearly marked valve specifications, model material, we can roughly its points For two categories, one is the ordinary valve, the other is a special valve. Normal metal valves have check valves , traps , gate valves , ball valves and globe valves , non-metallic lining valves check valves, globe valves and butterfly valves ; special valves by the wear-resistant valves, cryogenic valves and high temperature valves. As each manufacturer's valve performance parameters are not the same, so in the development of technical tender should be put forward their different requirements, respectively, in general, cryogenic valve should be used as a separate procurement package, and the need to prepare detailed procurement technical specifications.
A cryogenic valve operating technical requirements In order to ensure the selection of cryogenic valve to meet the requirements, we must advance the low temperature valve operating conditions require adequate understanding of the main operating conditions are operating temperature, operating pressure, which is the decision Cryogenic valve is the key parameters of the normal use. When the cryogenic valve belongs to an actuator, the manufacturer needs to determine the actuator specifications according to parameters such as the medium pressure difference. The size of the actuator determines the final product cost. Therefore, we must clarify these related parameters. In addition, due to the particularity of the chemical plant, the temperature of the medium can not always be the same, so we need to check whether the valve has sufficient strength in the event of medium temperature changes.
2 cryogenic valve special technical requirements Because the supplier is not determined, so that technical documents and ask the price of the final contract can not be used as a technical annex, and due to the tender of the manufacturers are not the same situation, inconvenient to put forward specific technical requirements. Therefore, we can put some problems that affect the quality of products to manufacturers for answering and resolving them. For example: Manufacturers of body material smelting methods, process evaluation, origin, structural characteristics, delivery status, delivery, quality assurance, after-sales service and the performance of similar products. Due to the particularity of the low-temperature valve, we should be made according to the different requirements of the use of cold-weather long bonnet structure, in order to ensure the packing box at the bottom of the temperature, the valve neck can be used with the same material as the steel pipe Surfacing to stuffing box and bonnet, heat treatment after welding is completed to eliminate residual stress. In the design as much as possible to the long neck and stem part of the convection heat loss to a minimum, in accordance with the relevant requirements to ensure strength, reduce the use of materials. In addition, the low-temperature valve should take appropriate measures to avoid the abnormal pressure chamber body cavity, mainly through the gate in the high-pressure side of the valve opening relief hole way, and the ball valve is designed through the relief hole or pressure relief structure to avoid Valve cavity abnormal pressure. For such special technical requirements of the valve, we need to strengthen the design aspects of the emphasis, in particular, to ensure that the performance of materials used to meet the environmental and temperature changes, the specific requirements are as follows: In normal working conditions, the valve body The material does not produce low temperature brittle damage; under normal working conditions, the valve structure of the material used is stable, will not produce deformation, especially part of the working temperature below -100 ℃ valve, the valve cover, body, seat, Valve stem and valve and other components in the processing, should be cryogenic treatment, and repeated multiple cycles to ensure the use of materials performance; valve welding operations, should take into account the particularity of the valve material, as well as the low temperature state The reliability of the weld; in low temperature conditions require frequent switching of valves need to strictly comply with "low-temperature valve technical conditions" GB / T24925-2010 in the relevant requirements to ensure that the material inside the piece to prevent scratches, occlusion, jamming, etc. The situation happened.
Second, the technical review aspects of the Notes Technical Review Links As an important part of the procurement process, we need at this stage for each manufacturer's technical tender for rigorous review and understanding, in order to truly complete master the comprehensive strength of the manufacturers, products Quality, ranking of excellent manufacturers through the way of comprehensive grading, under the premise of being able to effectively meet the requirements of use, to select the suppliers of quality and cheap products.
A survey of the manufacturer's performance and background of the calendar period At this stage, the valve market is highly competitive, a large number of enterprises have joined the market competition, so we need to conduct a proper investigation of the background of the valve manufacturers, the survey mainly includes registered capital, time of establishment, Research ability and development, etc. In addition, the sales volume and quality of its leading products should be investigated, and whether the required products are its leading products or not. In addition, we also need to conduct long-term market research on major domestic and foreign valve enterprises. For example, Baoyi Valve, China Nuclear Su Valve, Lanzhou High Pressure, Suzhou Neway, Radial Valve and Volkswagen Valves, etc., are at the forefront of ultra-low temperature series valves Paul is a valve, which through a joint approach with Zhejiang University, focused on the research strength in the ultra-low temperature special valve at the forefront at home and abroad.
Through the investigation of the manufacturer's background and performance, we can provide strong support for our selection of suppliers. For example, in the purchase of low-temperature valves, especially those complicated conditions, high performance valves we can choose over the years such valves sales of high quality, excellent quality manufacturers. In particular, manufacturers should get more attention when obtaining orders from similar devices and when the quality of their products meets their requirements effectively. In the process of selecting a supplier, we should pay attention to the following two points: the same type of equipment, operating conditions and operating conditions in the equipment are not the same, so we must ensure that the same type of device, under similar conditions Of the same type of valve performance, only such performance can be representative; followed by different manufacturers have different production capacity, so we need to ensure that the material, specifications, level of cryogenic valve is consistent with the requirements. Therefore, only by fully understanding the background of the manufacturer and the performance over the years, can we provide a strong basis for the selection of excellent valve manufacturers.
2 low temperature valve manufacturing inspection certification valve is one of the important components in the pressure pipeline, its manufacturing quality directly affects the safe operation of the device. At this stage, most of the pressure pipe valve manufacturers still belong to the undocumented production, which is beyond the scope of the special equipment manufacturing permit. In addition, it often happens that fake certificates and certificates are provided. In order to control this from the source, We need to have a detailed understanding of the valve product inspection and certification system. "Special equipment manufacturing license", such certificates issued by the State General Administration of Quality Supervision, Inspection and Quarantine, which is one of the valve manufacturers must have the certificate, the lack of such certificates, manufacturers can not be manufactured, which for a number of manufacturing qualified single As well as the lack of strength of the small manufacturers have been limited, we must increase product development efforts, and also need to obtain early manufacturing license. By querying the way of the permit, the valve manufacturer can be quickly and conveniently screened, excluding the unqualified manufacturers.
Third, the conclusion In summary, the petrochemical plant in the low-temperature valve has played a key role, not only effectively ensure the production, but also improve the convenience of the production process. Therefore, in the selection of cryogenic valves, we have to fully consider the various manufacturers background, qualifications and sales over the years to conduct an investigation to ensure that the valve can be purchased to effectively meet the needs of production safety. Finally, we also need to do a good job related technical reviews, to provide adequate theoretical basis for the purchase of cryogenic valves.
references:
[1] Li Shenghe. On the right petrochemical plant how to buy low-temperature valve [J]. Petrochemical Equipment, 2015 (11): 87-89.
[2] Zhang Hongguo. Current low-temperature valve of the relevant standards of the difference analysis [J]. Shandong Chemical Industry, 2013 (11): 57-59.
[3] Li Yongqing, Hao Chunsheng. Liquefied natural gas valve and low temperature performance test device [J]. Petrochemical Equipment, 2014 (06): 88-91.
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