Taboo 1
Winter construction carries out hydrostatic testing at negative temperatures.
Consequence: The pipe freezes and breaks due to ice formation inside the pipe during hydro testing.
Measures: Hydrostatic testing should be carried out as much as possible before winter construction, and the water should be blown clean after testing, especially the inside the valves must be completely removed. Otherwise, the valves will rust or even crack. When hydrostatic testing must be carried out in winter, it should be at positive temperatures indoors, and the water should be blown clean after testing.
Taboo 2
The flushing before the completion of the pipeline system is not thorough, and the flow rate and velocity do not meet the pipeline flushing requirements. In cases, water pressure strength tests are used instead of flushing.
Consequences: The water quality does not meet the operational requirements of the pipeline system, which can lead reduced cross-sectional area or blockages in the pipeline.
Measures: Flushing should be carried out with the maximum design flow rate of the system or a water velocity of no less than 3m/s. The flushing is considered合格when the color and transparency of the water at the outlet visually match those at the inlet.
Taboo 3
The sewage pipe, rainwater pipe, and condensate pipe are concealed without undergoing a water-sealing test.
Consequence: It may cause water leakage and result in losses for the user.
Measures: The water-sealing test work should be strictly inspected and accepted according to standards. For underground, ceiling, and inter-pipe concealed installations of sewage, rainwater, and condensate pipes, it must be ensured that they are non-leaking and non-infiltrating.
Taboo 4
During the pipeline system's hydrostatic strength test and tightness test, only the pressure value and water level changes were observed, and the inspection leaks was insufficient.
Consequence: After the pipeline system is put into operation, leakage occurs, affecting normal use.
Measures: When conducting tests on the pipeline system to design requirements and construction specifications, in addition to recording the pressure value or water level changes within the specified time, special attention should be paid to carefully checking for leakage issues.
Taboo 5
The butterfly valve flange is made of ordinary valve flanges.
Consequence: The butterfly valve flange and the ordinary valve flange are different size. Some flanges have smaller inner diameters, while the butterfly valve's valve flap is larger, causing it to be unable to open or forcing it open resulting in valve damage.
Measures: The flange should be processed according to the actual size of the butterfly valve flange.
Taboo 6
During the construction of the building structure, no reserved holes and embedded parts were provided, or the sizes of the reserved holes were too small and the embedded parts were not marked.
Consequences: During the construction of the heating and plumbing works, the building structure had to be chiseled, and even the stressed reinforcing bars were cut, which affected the safety performance of the building.
Measures: Thoroughly familiarize yourself with the construction drawings of the heating and plumbing works. According to the needs of the installation of pipelines and supports and hangers, actively and conscientiously cooperate with the construction of the building structure to reserve holes and embed parts. Specifically, refer to the design requirements and the provisions of the construction specifications.
Taboo 7
During the welding of pipelines, after the pipe ends are aligned, the misalignment of the pipes is not on the same center line, no gap is left at the pipe ends, the groove is not cut for thick-walled pipes, and the width and height of the weld seams do not meet the requirements of the construction specifications.
Consequences: The misalignment of the pipes not being on the same center line directly affects the welding quality and the appearance quality. When no gap is left at the pipe ends, the groove is not cut for thick-walled pipes, and the width and height of the weld seams do not meet the requirements, the welding will not meet the strength requirements.
Measures: After the pipe ends of the welded pipeline are aligned, the pipes should not be misaligned and should be on the same center line; a gap should be left at the pipe ends; the groove should be cut for thick-walled pipes. In addition, the width and height of the weld seams should be welded in accordance with the requirements of the specifications.
Taboo 8
Pipelines are directly buried in frozen soil or untreated loose soil, the spacing and position of pipeline piers are improper, and even the form of dry-laid bricks is adopted.
Consequence: Due to the unstable support, the pipeline is damaged during the backfilling compaction process, resulting in rework and repair.
Measure: Pipelines shall not be buried in frozen soil or untreated loose soil. The spacing of piers shall meet the requirements of the construction specification. The supports shall be firm, especially at the pipeline joints, which should not bear shear force. Brick piers shall be built with cement mortar to ensure integrity and firmness.
Taboo 9
The expansion bolts for fixing pipeline supports are of inferior quality, the hole diameter for installing expansion bolts is too large, or the expansion bolts are installed on brick walls or even lightweight walls.
Consequence: The pipeline supports become loose, the pipeline deforms, and even falls off.
Measure: Qualified expansion bolts must be selected, and sampling inspection shall be carried out if necessary. The hole diameter for installing expansion bolts should not be larger than 2mm of the outer diameter of the expansion bolt. Expansion bolts should be used on concrete structures.
Taboo 10
The flange plates and gaskets for pipeline connection have insufficient strength, and the connecting bolts are short or thin in diameter. Rubber gaskets are used for thermal pipelines, double-layer gaskets or beveled gaskets are used for cold water pipelines, and the flange gasket protrudes into the pipe.
Consequence: The connection of the flange plates is not tight, and even damaged, resulting in leakage. The protrusion of the flange gasket into the pipe will increase the water flow resistance.
Measure: The flange plates and gaskets used for pipelines must meet the requirements of the pipeline design working pressure. Rubber asbestos gaskets are suitable for the flange gaskets of heating and hot water supply pipelines; rubber gaskets are suitable for the flange gaskets of water supply and drainage pipelines. The flange gasket shall not protrude into the pipe, and its outer circle should be appropriate to the flange bolt holes. Beveled gaskets or several gaskets shall not be placed in the middle of the flange. The diameter of the bolts connecting the flange should be 2mm smaller than the flange hole diameter, and the length of the bolt rod protruding from the nut should be 1/2 of the nut thickness.
Taboo 11
Incorrect valve installation method. For example, the water (steam) flow direction of the stop valve or check valve is opposite to the mark, the valve stem is installed downward, the horizontal check valve is installed vertically, the handle of the gate valve or butterfly valve has no opening and closing space, and the valve stem of the concealed valve does not face the inspection door.
Consequence: The valve fails, and it is difficult to open, close and repair. The downward installation of the valve stem often causes water leakage.
Measure: Install strictly in accordance with the valve installation instructions. Leave sufficient valve stem extension opening height for the gate valve with exposed stem. Fully consider the handle rotation space for the butterfly valve. The valve stems of various valves cannot be lower than the horizontal position, let alone downward. For the concealed valve, not only an inspection door that meets the valve opening and closing needs should be set, but also the valve stem should face the inspection door.
Taboo 12
The specifications and models of the installed valves do not meet the design requirements. For example, the nominal pressure of the valve is less than the system test pressure; a gate valve is used when the diameter of the water supply branch pipe is less than or equal to 50mm; a stop valve is used for the main and riser pipes of hot water heating; a butterfly valve is used for the suction pipe of the fire pump.
Consequence: It affects the normal opening, closing, resistance regulation, pressure regulation and other functions of the valve. Even during the system operation, the valve is damaged and has to be repaired.
Measure: Be familiar with the application range of various valves and select the specifications and models of valves according to the design requirements. The nominal pressure of the valve should meet the requirements of the system test pressure. According to the construction specification requirements: a stop valve should be used when the diameter of the water supply branch pipe is less than or equal to 50mm; a gate valve should be used when the diameter is greater than 50mm. The control valves of the main and riser pipes of hot water heating should be gate valves, and the suction pipe of the fire pump should not be a butterfly valve.
Taboo 13
Necessary quality inspection is not carried out before valve installation according to regulations.
Consequence: During the system operation, the valve is not flexible in opening and closing, not tightly closed, and has water (steam) leakage, resulting in rework and repair, and even affecting the normal water supply (steam).
Measure: Before valve installation, a pressure resistance strength and tightness test should be carried out. The test should be carried out by sampling 10% of each batch (same brand, same specification, same model), and at least one. For the closed-circuit valves installed on the main pipe and playing a cutting-off role, a strength and tightness test should be carried out one by one. The test pressure of valve strength and tightness should meet the requirements of "Code for Acceptance of Construction Quality of Building Water Supply, Drainage and Heating Engineering" (GB 50242 - 2002).
Taboo 14
The main materials, equipment and products used in the construction lack the technical quality appraisal documents or product certificates that meet the current national or ministerial standards.
Consequence: The project quality is unqualified, there are potential accident risks, it cannot be delivered for use on schedule, and rework and repair are required; resulting in project delay, and increased labor and material inputs.
Measure: The main materials, equipment and products used in the water supply, drainage and heating and plumbing engineering should have technical quality appraisal documents or product certificates that meet the current national or ministerial standards; their product names, models, specifications, national quality standard codes, production dates, names and locations of manufacturers, and factory product inspection certificates or codes should be indicated.
Taboo 15
Valve installed upside down
Consequence: Valves such as stop valves, throttle valves, pressure reducing valves, and check valves have directionality. If installed upside down or reversed, the throttle valve will affect the service effect and service life; the pressure reducing valve will not work at all, and the check valve may even cause danger.
Measure: For general valves, there is a direction mark on the valve body; if not, the direction should be correctly identified according to the working principle of the valve. The valve cavity of the stop valve is asymmetrical left and right. The fluid should pass through the valve port from bottom to top, so that the fluid resistance is small (determined by the shape), the opening is labor-saving (due to the upward pressure of the medium), and after closing, the medium does not press the packing, which is convenient for maintenance. This is the reason why the stop valve cannot be installed reversely. The gate valve should not be installed upside down (that is, the handwheel is downward), otherwise the medium will remain in the valve cover space for a long time, which is easy to corrode the valve stem, and is also prohibited by some process requirements. At the same time, it is extremely inconvenient to replace the packing. The gate valve with exposed stem should not be installed underground, otherwise the exposed valve stem will be corroded due to humidity. When installing the lift check valve, ensure that its valve disc is vertical for flexible lifting. When installing the swing check valve, ensure that its pin shaft is horizontal for flexible swinging. The pressure reducing valve should be installed upright on the horizontal pipeline and should not be inclined in any direction.
Taboo 16
Excessive force is used to open and close manual valves.
Consequence: At best, the valve is damaged; at worst, a safety accident is caused.
Measure: The handwheel or handle of a manual valve is designed according to ordinary human power, considering the strength of the sealing surface and the necessary closing force. Therefore, long levers or long wrenches cannot be used to operate. Some people are used to using wrenches and should pay strict attention not to use excessive and violent force, otherwise the sealing surface is easily damaged, or the handwheel and handle are broken. When opening and closing the valve, the force should be stable and not impact. The various components of some high-pressure valves that are opened and closed by impact have considered this impact force and are different from ordinary valves. For steam valves, they should be preheated and the condensed water should be drained before opening. When opening, it should be as slow as possible to avoid water hammer phenomenon. When the valve is fully opened, the handwheel should be reversed a little to make the threads tight to avoid loosening and damage. For the gate valve with exposed stem, remember the valve stem position when fully open and fully closed to avoid hitting the top dead center when fully open and to facilitate checking whether it is normal when fully closed. If the valve disc falls off or large debris is embedded between the valve core seals, the valve stem position when fully closed will change. When the pipeline is first used, there are more internal dirt. The valve can be slightly opened to use the high-speed flow of the medium to wash it away, and then gently closed (not quickly or violently closed to prevent the residual impurities from scratching the sealing surface), opened again, and repeated several times to wash away the dirt and then put it into normal work. For the normally open valve, there may be dirt sticking on the sealing surface. When closing, it should also be washed clean with the above method and then officially closed tightly. If the handwheel or handle is damaged or lost, it should be replaced immediately. Do not use a monkey wrench instead to avoid damaging the square of the valve stem, resulting in poor opening and closing and even accidents in production. For some media, after the valve is closed, it cools down, causing the valve parts to shrink. The operator should close it again at an appropriate time to leave no fine gap on the sealing surface. Otherwise, the medium flows at high speed through the fine gap, which is easy to erode the sealing surface. When operating, if it is found that the operation is too laborious, the cause should be analyzed. If the packing is too tight, it can be appropriately loosened. If the valve stem is skewed, the maintenance personnel should be notified to repair it. For some valves, when in the closed state, the closing part expands due to heat, resulting in difficulty in opening; if it must be opened at this time, the valve cover thread can be loosened by half a turn to one turn to eliminate the valve stem stress, and then the handwheel can be turned.
Taboo 17
Improper installation of valves in a high-temperature environment.
Consequence: A leakage accident is caused.
Measure: For high-temperature valves above 200°C, since they are at normal temperature during installation and the temperature rises after normal use, the bolts expand due to heat and the clearance increases, so they must be tightened again, which is called "hot tightening". The operator should pay attention to this work, otherwise leakage is likely to occur.
Taboo 18
Failure to drain in time in cold weather.
Measure: When the weather is cold and the water valve is closed for a long time, the accumulated water behind the valve should be drained. After the steam valve stops steaming, the condensed water should also be drained. If there is a plug at the bottom of the valve, it can be opened to drain water.
Taboo 19
The opening and closing force of non-metallic valves is too large.
Measure: Some non-metallic valves are hard and brittle, and some have low strength. When operating, the opening and closing force cannot be too large, especially not using brute force. Also pay attention to avoiding collisions.
Taboo 20
The packing of new valves is too tight.
Measure: When using a new valve, the packing should not be pressed too tightly, just to the extent that there is no leakage, to avoid excessive pressure on the valve stem, accelerated wear, and difficult opening and closing. The installation quality of the valve directly affects its use, so attention must be paid to the direction and position of the valve, valve installation work, valve protection facilities, bypass and instrumentation, and valve packing replacement.
Taboo 21
There is no operating space at the installation position.
Measure: The installation position of the valve must be convenient for operation; even if the installation is temporarily difficult, it should also be considered for the long-term work of the operator. Preferably, the valve handwheel is at the same height as the chest (generally 1.2 meters from the operating floor). In this way, it is more labor-saving to open and close the valve. The handwheel of the floor-standing valve should face upward and not be inclined to avoid awkward operation. For the valve against the wall or equipment, also leave room for the operator to stand. Avoid operating with the face upward, especially for acid, alkali, toxic media, etc., otherwise it is very unsafe.
Taboo 22
Hitting valves made of brittle materials.
Measure: Installation construction must be careful and avoid hitting valves made of brittle materials. Before installation, the valve should be inspected, the specifications and models should be checked, and whether there is damage should be identified, especially for the valve stem. Also turn it a few times to see if it is skewed, because the valve stem is most likely to be skewed during transportation. Also remove the debris in the valve. When hoisting the valve, the rope should not be tied to the handwheel or valve stem to avoid damaging these parts, but should be tied to the flange. The pipeline connected to the valve must be cleaned thoroughly. Compressed air can be used to blow away iron oxide chips, sediment, welding slag and other debris. These debris not only easily scratch the sealing surface of the valve, but also large particle debris (such as welding slag) can block small valves and make them ineffective. When installing a screwed valve, the sealing packing (linen thread with lead paint or polytetrafluoroethylene raw material tape) should be wrapped around the pipe thread and not put into the valve to avoid accumulation in the valve and affect the medium flow. When installing a flange valve, pay attention to tightening the bolts symmetrically and evenly. The valve flange and the pipe flange must be parallel and the clearance is reasonable to avoid excessive pressure on the valve and even cracking. Pay special attention to valves made of brittle materials and valves with low strength. For valves that need to be welded to the pipe, spot welding should be carried out first, then the closing part should be fully opened, and then welded firmly.
Taboo 23
No heat preservation and cold insulation measures are taken for valves.
Measure: Some valves also need external protection facilities, which are heat preservation and cold insulation. Sometimes a heating steam pipeline is added in the heat insulation layer. Which valves should be heat-insulated or cold-insulated depends on the production requirements. Generally speaking, if the temperature of the medium in the valve decreases too much, which will affect production efficiency or freeze the valve, heat preservation is required, and even heat tracing; if the valve is exposed, which is unfavorable for production or causes adverse phenomena such as frosting, cold insulation is required. Heat insulation materials include asbestos, slag wool, glass wool, perlite, diatomaceous earth, vermiculite, etc.; cold insulation materials include cork, perlite, foam, plastic, etc.
Taboo 24
The bypass of the steam trap is not installed.
Measure: Some valves, in addition to necessary protection facilities, also need a bypass and instrumentation. Installing a bypass facilitates the maintenance of the steam trap. Other valves also have bypasses installed. Whether to install a bypass depends on the condition, importance and production requirements of the valve.
cTaboo 25
The packing is not replaced regularly.
Measure: For the valves in stock, some packings are no longer effective, and some do not match the medium used, so the packing needs to be replaced. The valve faces thousands of different media. The packing box is always filled with ordinary packing, but when in use, the packing must match the medium. When replacing the packing, it should be pressed in one circle at a time. The joint of each circle is preferably 45 degrees, and the joints of the circles are staggered by 180 degrees. The height of the packing should consider the room for further tightening of the gland, and at the same time, the lower part of the gland should press the packing chamber to an appropriate depth, which is generally 10 - 20% of the total depth of the packing chamber. For valves with high requirements, the joint angle is 30 degrees. The joints between the circles are staggered by 120 degrees. In addition to the above packings, shaped packings such as rubber O-rings (natural rubber is resistant to weak alkalis below 60°C, nitrile rubber is resistant to oils below 80°C, fluorine rubber is resistant to various corrosive media below 150°C), three-piece stacked polytetrafluoroethylene rings (resistant to strong corrosive media below 200°C), and nylon bowl-shaped rings (resistant to ammonia and alkali below 120°C) can also be used according to specific circumstances. Wrapping a layer of polytetrafluoroethylene raw material tape outside the ordinary asbestos packing can improve the sealing effect and reduce the electrochemical corrosion of the valve stem. When tightening the packing, turn the valve stem at the same time to keep it uniform around and prevent it from being too tight. Tighten the gland evenly and not obliquely.