Prohibitions for installing chemical industry valves – for construction technicians

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Prohibitions for the installation of chemical industry valves: Prohibition 1 – Conducting hydrostatic testing at negative temperatures during winter construction. Consequence: The pipes were damaged by freezing due to rapid ice formation inside them during the hydrostatic test. Measure: Try to conduct the hydrostatic test before winter construction, and after the testing, blow out all the water; in particular, the water inside the valves must be completely removed, otherwise the valves may rust in mild cases or crack due to freezing in severe cases. When conducting hydrostatic testing on the project during winter, it must be carried out at a positive indoor temperature, and the water must be completely drained after the testing is complete. Prohibition 2: Failure to carry out thorough flushing of the piping system before it is completed, resulting in flow rates and speeds that do not meet the requirements for piping flushing. Even using a water pressure strength test to drain water as a substitute for flushing. Consequences: The water quality fails to meet the requirements for the operation of the pipeline system, and this often leads to a reduction in the pipe’s cross-sectional area or even blockages. Measure: Flush using the maximum designed flow rate within the system, or a water flow velocity of not less than 3 m/s. It is considered qualified if the color and transparency of the water discharged are visually consistent with those of the water entering. Prohibition 3: Sewage, rainwater, and condensate pipes shall not be covered up without undergoing a water-tightness test first. Consequences: It may cause leaks and result in losses for the user. Measure: The water retention test should be strictly inspected and accepted in accordance with the specifications. Plumbed sewage, rainwater, condensate pipes, etc., that are installed concealed underground, within ceilings, or between pipes must be made leak-free. Prohibition 4: During the hydrostatic strength test and leak-tightness test of piping systems, only pressure values and water level changes are monitored, which is insufficient for detecting leaks. Consequence: Leaks occur in the pipeline system after it starts operating, affecting normal use. Measure: When testing the piping system in accordance with the design requirements and construction specifications, in addition to recording the pressure values or water level changes within the specified time frame, it is particularly important to carefully check for any signs of leakage. Prohibition 5: Do not use ordinary valve flanges for butterfly valve flanges. Consequence: The flanges of butterfly valves differ in size from those of ordinary valves; some flanges have a small inner diameter, while the valve disc of a butterfly valve is large, which prevents the valve from opening or forces it to open, resulting in damage to the valve. Measure: The flange should be manufactured according to the actual dimensions of the butterfly valve flange. Prohibition 6: In building structure construction, there are no pre-made holes or embedded components, or the size of the pre-made holes is too small and the embedded components are not marked. Consequences: During the construction of heating and ventilation systems, the building structure is damaged, and in some cases the load-bearing rebar is cut, which affects the safety of the building. Measures: Thoroughly study the construction drawings for heating and plumbing projects, and proactively and carefully cooperate with the construction of building structures by providing the necessary holes and embedded components as required for the installation of pipes and supports, in accordance with the design requirements and construction specifications. Prohibition 7: During pipe welding, if the pipes are not aligned such that their edges are on the same center line after alignment, if there is no gap between them, if thick-walled pipes are not prepared with appropriate bevels, or if the width and height of the weld do not meet the requirements specified in the construction standards. Consequence: When the ends of the pipes are not aligned on the same center line, it directly affects the welding quality as well as the overall appearance. There are no gaps at the joints; thick-walled pipes do not require beveling. If the width and height of the welds do not meet the specified requirements, the welds will not have the necessary strength. Measure: After aligning the pipes for welding, they must not be misaligned; they should all be on the same center line ； A gap should be left for alignment ； Thick-walled pipes require beveling. In addition, the width and height of the welds should be welded in accordance with the specification requirements. Prohibition 8: Pipes shall not be directly buried in permafrost or untreated loose soil; the spacing and placement of pipe supports are incorrect, and even dry brick stacking methods are used. Consequence: The pipeline was damaged during the compaction of the backfill due to unstable support, resulting in rework and repairs. Measures: Pipes must not be buried in frozen soil or untreated loose soil. The spacing between supports must comply with the requirements of construction standards, and the supports must be secure, especially at the pipe joints, which should not be subjected to shear forces. Brick piers should be built with cement mortar to ensure they are complete and sturdy. Prohibition 9: The expansion bolts used to fix pipe supports are of poor quality, the diameter of the holes in which these bolts are installed is too large, or the expansion bolts are installed in brick walls or even lightweight walls. Consequences: The pipe supports become loose, the pipes deform, and may even fall off. Measures: Qualified products must be selected for expansion bolts; sampling tests should be conducted when necessary. The diameter of the hole in which the expansion bolt is installed should not be more than 2 mm larger than the outer diameter of the bolt, and expansion bolts should be used in concrete structures. Prohibition 10: The flanges and gaskets used for pipeline connections are not strong enough, and the connection bolts are too short or have a too small diameter. Rubber gaskets are used for hot water pipes, while double-layer or beveled gaskets are employed for cold water pipes; the flange gasket extends into the pipe. Consequence: The flange connection is not tight, or may even be damaged, resulting in leaks. The flange gasket protruding into the pipe increases water flow resistance. Measure: The flanges and gaskets used for pipes must meet the requirements of the design working pressure of the pipes. Rubber-asbestos gaskets are recommended for the flange gaskets of heating and hot water supply pipes ； Rubber gaskets are recommended for the flange gaskets of water supply and drainage pipes. The gasket of the flange shall not protrude into the pipe; its outer edge should be at the level of the flange bolt holes. No inclined shims or multiple gaskets shall be placed in the middle of the flange. The diameter of the bolts used to connect the flanges should be at least 2 mm smaller than the diameter of the flange holes, and the length of the bolt shaft protruding from the nut should be half the thickness of the nut. Prohibition 11: Incorrect valve installation method. For example, in the case of globe valves or check valves, if the flow direction of water (steam) is opposite to that indicated by the markings, the valve stem should be installed downward; horizontally mounted check valves should be installed vertically. Gate valves or butterfly valves with exposed stems do not have any space for opening and closing, while the valve stems of concealed valves are not oriented toward the inspection door. Consequences: Valve failure, difficulty in maintaining the switch; a valve stem pointing downward often leads to leaks. Measures: Install the valves strictly in accordance with the installation instructions. For gate valves with visible stems, ensure sufficient clearance for the stem to extend in order to open the valve; for butterfly valves, take into account enough space for the handle to rotate. The stems of all types of valves must not be below the horizontal position, let alone tilted downward. For concealed valves, not only must inspection doors be provided to meet the requirements for opening and closing the valves, but the valve stem should also face toward those inspection doors. Prohibition 12: The specifications and models of the installed valves do not meet the design requirements. For example, the nominal pressure of the valve is lower than the system test pressure ； Gate valves are used for water supply branch pipes when the diameter is 50 mm or less ； Isolating valves are used for the supply and return pipes in hot water heating systems ； Butterfly valves are used for the suction pipes of fire pump systems. Consequences: It affects the normal opening and closing of the valve, as well as functions such as resistance and pressure regulation. It even caused the valves to get damaged during system operation, forcing repairs. Measure: Be familiar with the application ranges of various types of valves, and select the appropriate specifications and models of valves in accordance with the design requirements. The nominal pressure of the valve must meet the requirements of the system’s test pressure. According to construction specifications: globe valves shall be used for water supply branch pipes with a diameter of 50 mm or less ； Gate valves should be used when the pipe diameter is greater than 50 mm. Gate valves should be used for the dry and vertical control valves in hot water heating systems, and butterfly valves should not be used for the suction pipes of fire pumps. Prohibition 13: Failing to conduct the necessary quality inspections as required before installing the valve. Consequences: During system operation, the valves fail to operate smoothly, do not close properly, and leakage of water (steam) occurs, leading to rework and repairs, and even affecting normal water (steam) supply. Measure: Before installing the valve, pressure resistance and tightness tests should be conducted. The test should involve sampling 10% of the items in each batch (of the same grade, specifications, and model), with a minimum of one sample. For the closed-loop valves installed on the main pipes to serve as shut-off devices, strength and tightness tests shall be conducted on each one individually. The test pressures for the strength and tightness of valves shall comply with the provisions of the \"Code for Acceptance of Construction Quality of Building Water Supply, Drainage and Heating Engineering\" (GB 50242-2002). Prohibition 14: The main materials, equipment, and products used in construction lack technical quality certification documents or product certificates that meet ** or the current industry standards. Consequences: The project quality is substandard, there are potential accident hazards, it cannot be delivered for use on schedule, and it must be reworked and repaired ； This leads to delays in the project timeline and increased costs for labor and materials. Measure: The main materials, equipment, and products used in water supply, drainage, heating, and ventilation projects shall be accompanied by technical quality certification documents or product certificates that meet ** or the current standards issued by relevant departments ； It should indicate the product name, model, specifications, **quality standard code, date of manufacture, name and location of the manufacturer, as well as the certificate or code verifying the quality of the product. Prohibition 15: Consequences of installing valves in the wrong orientation – Valves such as stop valves, throttle valves, pressure relief valves, and check valves all have a directional requirement; if installed incorrectly, throttle valves will affect their performance and lifespan ； The pressure relief valve doesn’t work at all, and the check valve can even be dangerous. Measure: For ordinary valves, there are direction indicators on the valve body ； In the event that it is not present, it should be correctly identified based on the working principle of the valve. The valve chamber of the stop valve is asymmetrical on the left and right; the fluid must flow through the valve opening from bottom to top, which results in low fluid resistance (due to the shape of the valve). It is easier to open the valve as the medium pressure acts upward, and once closed, the medium does not exert pressure on the packing, facilitating maintenance. This is why stop valves cannot be installed in reverse. The gate valve must not be installed in an inverted position (with the handwheel facing downward), as this will cause the medium to remain in the space above the valve cover for an extended period, leading to corrosion of the valve stem. It is also prohibited by certain process requirements. It is also very inconvenient to replace the packing at the same time. Straight-through gate valves should not be installed underground, as moisture can cause corrosion of the exposed valve stem. For lift-type check valves, it is necessary to ensure that their valve discs are vertical during installation, so as to allow for smooth lifting and lowering. For swing check valves, it is necessary to ensure that their pin shafts are horizontal during installation, so as to allow for smooth swinging. The pressure relief valve must be installed vertically on a horizontal pipe, without any tilt in any direction. Prohibition 16: Do not operate manual valves with excessive force. Consequences of doing so: in mild cases, the valve may be damaged; in severe cases, it can lead to safety accidents. Measures: The handwheel or handle of a manual valve is designed to accommodate normal human strength, taking into account the strength of the sealing surface and the necessary force required for closing it. Therefore, it cannot be moved using a long lever or long wrench. Some people* are used to using wrenches, and they must be careful not to apply excessive force, as this can easily damage the sealing surfaces or break the wrench, the wheel, or the handle. When opening or closing the valve, apply force smoothly without any impact. The various components of certain high-pressure valves that are operated by impact have taken this impact force into account, as it is not the same as that in ordinary valves. For steam valves, they should be preheated and of the condensed water removed before being opened. The opening process should be carried out as slowly as possible to avoid water hammer. After the valve is fully open, turn the handwheel slightly in the opposite direction to ensure a tight fit between the threads, thereby preventing loosening and damage. For straight-stem valves, remember the position of the stem when the valve is fully open and fully closed, to avoid hitting the dead center when it is fully open. It also facilitates checking whether it is functioning properly when fully closed. If the valve seat comes loose, or large debris gets trapped between the valve core seals, the position of the valve stem when the valve is fully closed will change. When the pipeline is used for the first time, it contains a lot of dirt inside. The valve can be slightly opened to allow the high-speed flow of the medium to carry away this dirt, after which it should be closed gently (it must not be closed quickly or forcefully to prevent residual impurities from damaging the sealing surfaces). The valve should then be opened again, and this process repeated several times until all the dirt is removed, after which normal operation can resume. For normally open valves, dirt may adhere to the sealing surface; when closing them, it is necessary to clean them using the aforementioned method before closing them properly. If the handwheel or handle is damaged or lost, it must be replaced immediately; adjustable wrenches should not be used as a substitute, as this may damage the square shape of the valve stem, resulting in poor operation of the valve and potential accidents during production. In some media, cooling after the valve is closed causes the valve components to contract; therefore, the operator should close it again at an appropriate time to ensure that no gaps remain in the sealing surfaces. Otherwise, the medium will flow rapidly through these gaps, easily eroding the sealing surfaces. During operation, if it is found that the task is too difficult to carry out, the reasons should be analyzed. If the packing is too tight, it can be loosened slightly; if the valve stem is skewed, personnel should be notified for repair. In some valves, when they are closed, the closing element expands due to heat, making it difficult to open them. If it is necessary to open them at this time, the valve cover threads can be loosened by half a turn to one full turn to relieve stress on the valve stem, after which the handwheel can be turned. Prohibition 17: Consequences of improper valve installation in high-temperature environments – leakage accidents. Measures: For valves operating at temperatures above 200°C, since they are installed at normal temperatures and the temperature rises during normal use, causing the bolts to expand due to heat and the gaps to increase, it is necessary to tighten them again; this process is known as “thermal tightening”. Operators must pay attention to this step, as failure to do so can lead to leakage. Prohibition 18: Failing to take timely drainage measures in cold weather: When the weather is cold and the water valves remain closed for extended periods, the water accumulated behind the valves should be drained. After the steam valve stops supplying steam, the condensate must also be drained. There is a plug at the bottom of the valve, which can be opened to drain water. Prohibition 19: Non-metallic valves – excessive force required for opening and closing. Solution: Some non-metallic valves are hard and brittle, while others have low strength; therefore, the force used for operating them should not be too great, and forceful actions should especially be avoided. Be careful to prevent the items from being bumped. Prohibition 20: Over-tightening the packing of new valves. Solution: When using new valves, the packing should not be tightened too much; it should be adjusted so that there is no leakage. This prevents excessive stress on the valve stem, which could accelerate its wear and make it difficult to operate the valve. The quality of valve installation has a direct impact on its performance; therefore, great attention must be paid to the direction and position of the valves, the valve installation process, the protective measures for the valves, bypass systems and instruments, as well as the replacement of valve packing. Prohibition 21: No space for operation at the installation location – Measure: The valve must be installed in a location where it is easy to operate ； Even if installation is temporarily difficult, it is necessary to consider the operators’ long-term work. It is best for the valve handwheel to be at chest level (usually 1.2 meters above the operating floor), as this makes it easier to open and close the valve. The handwheel of the floor valve should face upward and not be tilted, to avoid awkward operation. For wall-mounted units, space must also be left near the device’s valves for the operator to stand. It is necessary to avoid working with the head raised, especially when dealing with acids, bases, toxic substances, etc., as it is very unsafe. Prohibition 22: Measures to avoid impact on valves made of brittle materials – Care must be taken during installation to prevent any impact on valves constructed from brittle materials. Before installation, the valve should be inspected to verify its specifications and model, and to check for any damage, especially to the valve stem. It needs to be turned a few more times to check if it is skewed, as the valve stem is most likely to become misaligned during transportation. The debris inside the valve also needs to be removed. When lifting the valve, do not tie the rope to the handwheel or valve stem, as this may damage those components; instead, it should be tied to the flange. The pipeline connected to the valve must be thoroughly cleaned. Compressed air can be used to blow away iron oxide filings, sediment, slag, and other debris. These debris not only easily scratch the sealing surfaces of the valves, but large particles of debris (such as weld slag) can also block small valves, rendering them ineffective. When installing threaded valves, the sealing filler (flax mixed with lead grease or PTFE tape) should be wrapped around the pipe threads, avoiding contact with the inside of the valve, so as to prevent accumulation there and disrupt the flow of the medium. When installing flanged valves, be careful to tighten the bolts symmetrically and evenly. The valve flange and the pipe flange must be parallel with an appropriate gap, to prevent excessive pressure from being generated on the valve, which could even lead to cracking. Special attention should be paid to brittle materials and valves with low strength. For valves that need to be welded to pipes, spot welding should be performed first, followed by fully opening the closing element, and then performing a full weld. Prohibition 23: Valves lack insulation and cooling measures. Solution: Some valves also require external protective facilities, namely insulation and cooling. Heating steam pipelines are sometimes also added inside the insulation layer. It depends on the production requirements to determine which types of valves should be insulated or insulated from heat. In principle, whenever the temperature of the medium inside the valve drops too much, it can affect production efficiency or cause the valve to be damaged by freezing; in such cases, insulation is necessary, and sometimes even heat tracing ； When valves are exposed, which is detrimental to production or can cause problems such as frosting, insulation is required. Insulation materials include asbestos, slag wool, glass wool, perlite, diatomaceous earth, vermiculite, etc.; thermal insulation materials include cork, perlite, foam, plastic, etc. Prohibition 24: Lack of bypass measures for hydrophobic valves: Some valves require not only necessary protective devices but also bypass systems and instruments. A bypass has been installed to facilitate the maintenance of the steam trap. Other valves also have bypasses for installation. Whether to install a bypass depends on the condition of the valve, its importance, and the requirements of production. Prohibition 25: Failure to replace the packing regularly – In inventory valves, some packing is no longer functional, and some is not suitable for the medium being used; therefore, it is necessary to replace the packing. Facing a wide variety of different media, ordinary packing is always used in the stuffing box of valves; however, when in use, it is necessary to ensure that the packing is suitable for the specific medium. When replacing the packing, press it in circle by circle. The seams between each loop should be at a 45-degree angle, with the seams between loops offset by 180 degrees. The packing height must take into account the amount of further compression that the gland can provide; at the same time, it is necessary to allow the lower part of the gland to compress the packing chamber to an appropriate depth, which is generally 10-20% of the total depth of the packing chamber. For high-demand valves, the seam angle is 30 degrees. The joints between the circles are offset by 120 degrees. In addition to the fillers mentioned above, shaped fillers such as rubber O-rings (natural rubber is resistant to weak alkalis at temperatures below 60 degrees Celsius, nitrile rubber is resistant to oils at temperatures below 80 degrees Celsius, and fluororubber is resistant to various corrosive agents at temperatures below 150 degrees Celsius), triple-layered polytetrafluoroethylene rings (resistant to highly corrosive agents at temperatures below 200 degrees Celsius), and nylon bowl-shaped rings (resistant to ammonia and alkalis at temperatures below 120 degrees Celsius) can also be used depending on the specific circumstances. Wrapping a layer of PTFE tape around the ordinary asbestos packing can improve the sealing effect and reduce the electrochemical corrosion of the valve stem. When compressing the packing, turn the valve stem at the same time to ensure even compression around the perimeter and prevent it from being too tight; apply even force when tightening the gland, without tilting it.