Discussion on the Installation, Maintenance and Management of Flange Valves
2023-06-29 09:51:54
Introduction
With the continuous improvement of industrialization, petrochemical plants are distributed on land and at sea. The storage and transportation of materials within or between the plants are mostly completed through equipment, valves, and pipeline systems. Among them, valves are important pipeline components used to control the movement of media within the pipeline system. They are also important control components that can manually or automatically adjust and change the pressure, flow rate, etc. of the media (liquids, gases, powders) flowing in the pipeline and other media flowing in the equipment pipeline, and control the flow direction of the pipeline media or the static direction of the fluid. According to the changes in the requirements of the media flow within the pipeline system, the opening, closing, and direction of the valves are controlled to make the conveyed media meet the requirements of movement, stop, or change the flow rate of the media, adjust the pressure of the conveyed media, etc. Valves are commonly used in the middle and end positions of pipelines. According to the requirements of process production technology, in order to facilitate manufacturing, transportation, installation, and maintenance, the vast majority of petrochemical equipment adopts detachable connection structures. It is composed of valve bodies, valve covers, valve seats, opening and closing accessories, drive control mechanisms, sealing packing, and connection fastener components. The driving mode of the valve can be selected arbitrarily, and the transmission methods include manual, pneumatic, hydraulic, electric, combined electric and pneumatic, combined electro-hydraulic drive, and combined electric and pneumatic drive methods, etc. It can operate according to pre-set conditions under the combined influence of various external physical forms such as air pressure changes, temperature changes, and signal transmission. The advantages of valves in connection, sealing, disassembly, etc. make valves the main connecting parts of production plants such as petrochemical plants, and the management of valves has become an important task in the construction of plants.
1. Valve Storage and Transportation
1.1 Classification and Storage of Valves
There are a wide variety of valves, and new valves with strong applicability, simple structure, novel materials, and wide applications are constantly being developed. According to the composition material, connection form, driving mode, nominal pressure, and the function of the valve, there are multiple classification methods. For example, there are metal valves and non-metal valves. Before long-term storage of metal valves, lubricating grease should be applied, and the storage space should be dry to prevent rust. Non-ferrous metal valves such as stainless steel valves can be wrapped with buffer materials and packed in wooden boxes. It should be noted that buffer materials must be padded on the sealing surface to prevent bumps. If it is a carbon steel valve, rust prevention protection is required. Wrap it with vapor-phase rust prevention materials, and at the same time use buffer materials, and then pack it in a wooden box. Each valve should be stored separately because the contact storage of metal materials of different materials and batch numbers will accelerate corrosion and rust due to the electrochemical effect. Non-metal valves are generally used in anti-corrosion occasions. They will not rust by themselves, but mechanical damage and deformation should be prevented.
1.2 Valve Transportation
(1) When transporting valves, first of all, the flange surfaces of the valves need to be protected. Apply lubricating grease on the sealing surface to prevent rust and affect the sealing effect, and then use plastic gaskets or wooden boards to block it.
(2) When transporting valves, use strip-shaped square timbers or soft-packed plastic foam and other materials to tie them firmly, and the outer packaging should be intact. Each valve should be packaged separately. Especially for non-metal valves, prevent bumps, extrusion, mechanical damage, deformation, etc., to avoid affecting the sealing effect of the valves.
(3) When transporting valves, non-ferrous metal valves, metal valves, and non-metal valves should be packaged and transported separately to avoid mutual contact between materials, cause chemical reactions, and cause contamination between valves.
2. Valve Installation
2.1 General Provisions and Precautions for Valve Installation
(1) For valves with direction requirements, there are direction marks on the outer shell, and during installation, it should be consistent with the medium direction in the drawing.
(2) When installing valves in the horizontal direction, the valve stem and handwheel are not allowed to be installed downward to avoid upward-facing operation.
(3) When the valve is installed vertically, when the valve center is higher than 1.8 m, an operation platform should be set up and arranged centrally.
(4) When multiple valves are installed vertically side by side, the centerlines of the valves should be as close as possible to be at the same height from the ground, and the minimum net distance between the valve handwheels should not be less than 100 mm.
(5) When valves are buried, the valve installation site should be treated as a well room. In the ground, rising-stem valves cannot be directly installed, and the valve stem should be protected to prevent rust.
(6) When hoisting large valves, the rigging should be tied to the lifting points of the valve body, and not tied to the valve stem or handwheel. Smaller valves should be handled with care during transportation and installation to prevent damage.
2.2 Strength Test and Leakage Test of Valves before Installation and Use
(1) When testing valves, they should be randomly selected from each batch of the same type of valves, and the number should not be less than 10%. When the number is small, at least one valve should be selected for the test. For closed-circuit valves installed on the main pipeline to play a cutting-off role, leakage and strength tests should be carried out one by one.
(2) The leakage test of the valve aims to test the internal structure of the valve, the sealing surface, the external valve cover and the sealing gasket, as well as the sealing degree of the packing. The leakage test pressure is 1.1 times the nominal pressure.
(3) The strength test of the valve aims to test the pressure-bearing capacity of the valve body material. The magnitude of the valve strength test pressure is 1.5 times the nominal pressure.
2.3 Construction According to the Drawing
(1) Before installing the valve, the valve tag number, pound grade, specification size, connection form, etc. should be carefully checked to ensure that the valve meets the design and use requirements and is consistent with the drawing. For valves with direction requirements, such as globe valves, check valves, and control valves, the medium flow direction of the pipeline system should be checked according to the requirements of the design drawing. There should be a certain distance for the gland bolts to ensure the adjustment size.
(2) Before installing the valve, carefully check the integrity of the water ripple lines on the flange surface. There should be no damage or bumps, and it should be in the closed state before installation. When installing the valve, the installation direction of the valve head handle or handwheel should take into account the requirements of convenient operation, convenient maintenance, and the safe passage of personnel.
2.4 Management of Tools and Equipment
(1) The installation equipment, tools, and machines for valves should meet the quality requirements of the project.
(2) Hydraulic torque equipment and tools should be calibrated within the specified cycle. The longest calibration cycle is 1 year. The calibration cycle for manual torque wrenches is usually one month, and for hydraulic torque wrenches, it is generally three months.
2.5 Personnel Qualifications and Training
(1) All personnel should learn and master the characteristics, functions, applicable scope, protection measures, installation and disassembly procedures, etc. of various valves, as well as the use procedures and methods of tools and equipment, and the acceptance methods after valve installation.
(2) All personnel must pass the training and assessment before they can take up their posts.
2.6 Valve Connection
(1) Before valve assembly, ensure that the water ripple lines on the flange surface are intact, without damage, bumps, etc.
(2) When connecting the valve, the valve flange and the pipeline flange should be arranged in parallel in the radial direction and coaxial and concentric in the axial direction without external force. If external force is used to disassemble the valve, relevant workers should calculate the stress before connection and then carry out the installation connection after meeting the process technical requirements.
(3) Select bolts and gaskets that meet the requirements of the design documents. During the installation process, the nut should be able to freely pass through the flange hole and rotate on the screw. After tightening the nut, 2 to 3 threads should be exposed.
(4) Apply lubricating grease on the bolts according to the relevant regulations to prevent rust.
(5) Select the corresponding bolt tightening torque value according to the requirements of the design documents.
(6) Mark the tightening sequence of the valve bolts in a clockwise diagonal direction with Arabic numerals, and tighten them in three steps. Adjust the torque of the first step to 1/3 of the maximum bolt torque for tightening, adjust the torque of the second step to 2/3 of the maximum bolt torque for tightening, and adjust the torque of the third step to 100% of the maximum bolt torque for tightening. Check the gap of the valve flange in a timely manner during tightening. If the gap between the flange surfaces is uneven, adjust it in a timely manner.
(7) After the bolts are tightened, manage and hang tags, and have a full-time inspector confirm and sign for quality acceptance according to the requirements of the acceptance specification.
2.7 Valve Bolt Tensioning
For valves with large diameters, after the bolts are pre-connected, they need to be tensioned through a professional bolt tensioner to ensure the reliability and tightness of the connection. Currently, a relatively advanced pre-tensioning technology is to use a hydraulic tensioner to pre-tighten the bolts.
2.7.1 Characteristics of the Bolt Tensioner
(1) The bolt tensioner uses the hydraulic principle to generate tension to directly stretch the bolts. There is no torsional shear force and lateral stress, and there is no frictional damage to the contact surface between the flange and the nut. It is an effective method to accurately control the pre-tightening force of the bolts during use.
(2) Compared with the hydraulic torque wrench, the bolt tensioner has the advantages of being sensitive and accurate in response, not generating torsional shear force, not causing frictional damage to the flange and the nut, and being able to pre-tighten multiple bolts synchronously.
(3) The bolt tensioner is widely used in many working occasions, especially in occasions with strict requirements for pre-tightening force.
(4) The disadvantages are that it has high requirements for the axial space of the bolts, and it will be limited in narrow places and cannot be fully operated; there is a certain range of requirements for the length of the bolts, and sufficient elongation allowance is required.
2.7.2 Pre-tightening Requirements of the Bolt Tensioner
(1) Before use, calculate the pre-tightening tension of the bolts according to the construction requirements, and adjust the corresponding oil pressure to avoid the working pressure exceeding the range and causing damage to the bolts.
(2) During the process of bolt tensioning, monitor the maximum designed operating stroke of the tensioner and do not exceed it.
(3) When pre-tightening different bolts step by step in sequence, there will be an interaction between the bolts pre-tightened in different steps. To avoid and reduce this interaction, the pre-tightening sequence of the bolts and the tension of the bolts should be planned. Generally, the number of tensioned bolts should be 50% according to the ratio of the tensioner to the bolts, and the tensioners should be evenly and symmetrically distributed. In certain situations, a matching ratio of 25% is also acceptable.
2.8 Valve Assembly Management Records
(1) Establish a valve data archive database. All valves should correspond to a unique number. The node information of each valve should be clearly recorded on the card, and at the same time, it should be recorded in the electronic file, including the installation and tightening date of the valve, the working pressure, working temperature, and connection form of the valve, the gasket material and bolt specification size, the bolt tightening torque value, the operator information, the tool and equipment information, the completion confirmation and acceptance information, etc.
(2) Conduct real-time tracking and full-process recording of valves in high-risk areas.
2.9 Valve Interface Protection
The sealing surface of the valve should be protected with emphasis. Corresponding protective measures should be taken during transportation, storage, and hoisting to prevent damage to the sealing surface.
(1) When the valve has corresponding flange protection, a rubber or plastic cover plate with a low density should be clamped between the two flanges for sealing. The thickness of the cover plate is preferably more than 3 mm.
(2) When using metal or non-metal blind plates to install at the valve ports, the fastening bolts should be evenly distributed and not less than 4.
(3) Use a metal or non-metal plastic circular protection device to fix it at the end of the valve connection pipe.
3. Valve Maintenance and Upkeep
3.1 Valve Maintenance
(1) The media conveyed in the valve pipeline system will, to a certain extent, cause wear and deformation, internal corrosion and leakage under the action of various external forces and the working environment, which will have a certain impact on the overall performance of the valve pipeline. During the normal operation of the valve pipeline system, carefully observe the valve pipeline system, check the media flow rate and the external noise generated, master the rules, and thus make a judgment on the valve pipeline system, make predictive information, make a detailed construction plan for the valves that may have problems, and carry out maintenance after approval by the relevant departments.
(2) Valve maintenance is a maintenance technology with rich experience, high technicality, and strong comprehensiveness, including on-site observation, that is, going to the operation site to check the appearance changes of the valve, such as liquid leakage, corrosion, rust, etc., obtaining important information and dealing with it in a timely manner. This method requires high experience of valve maintenance personnel, and they use their own eyes to observe the valve as a whole and master phenomena such as dripping, leakage, and running. Second, after the medium passes through the valve, vibration and noise will occur. Judge the magnitude of the vibration and noise, and plan to repair the valves that have a greater impact. Third, use a flowmeter to measure the flow rate and flow volume of the medium passing through the valve pipeline to determine whether the operation status of the valve pipeline system is good. Fourth, conduct a test on the shut-off state of the valve to prevent the phenomenon of internal leakage.
3.2 Valve Upkeep
(1) Under the influence of the external environment, the exposed outer surface of the valve will rust. In the case of continuous production, online maintenance should be carried out on the designated valves, mainly by applying rust-proof oil and winding anti-corrosion tapes.
(2) For valves that are frequently opened and closed, lubricate the rotating parts of the valve at least once a month.
(3) For valves that are normally open or normally closed, regularly rotate the handwheel or handle, and add lubricant to the valve screw rod to prevent jamming.
(4) Regularly check the integrity of each part of the valve. For example, if the handwheel or handle falls off, or the bolts and nuts are lost, do not make do with it. Otherwise, it will damage the square part at the upper part of the valve head, reduce the reliability of mutual cooperation, and even prevent the valve from being opened and closed.
(5) When the outdoor temperature is below 0 degrees Celsius, if the water valve is closed for a long time, the accumulated water behind the valve should be drained to prevent freezing and damage to the valve. After the steam valve stops steam supply, the condensed water generated should also be drained. Loosen the drain plug at the bottom of the valve to drain the condensed water from the valve body.
(6) If the valve is a driven valve in structure, regularly add lubricating oil to the drive mechanism and ensure the cleanliness of the valve.
4. Conclusion
Valve management is a systematic task. As a part of the equipment or pipeline, from the initial stage of plant construction to the operation after commissioning, it is an important quality control point and a key part of the patrol inspection. Preventing the phenomenon of media leakage such as dripping, running, and overflowing due to valve failure, and even larger accidents, can ensure the safe operation of petrochemical plants.
Cited from Chemical Industry Management (Journal), June 2023. Authors: Liang Chao, Yu Jianhua, Chen Lin, Luo Bingyang, Zhao Shouwei
