Valves are relatively common equipment in chemical companies. Installing valves may seem easy, but if they are not implemented in accordance with relevant technologies, safety accidents will occur. Today, Xiaobian will share with you some experience and knowledge about valve installation.
The water pressure test is carried out under negative temperature during winter construction.
Consequences: The tube freezes due to the rapid freezing of the tube during the hydrostatic test.
Measures: try to carry out the water pressure test before the winter application, and blow the water after the pressure test, especially the water in the valve must be cleaned, otherwise the valve will be rusted in light, and cracked in heavy.
When the water pressure test is carried out in winter, the project must be carried out at a positive indoor temperature, and the water must be blown out after the pressure test.
Before the completion of the pipeline system, the flushing is not serious, and the flow and speed cannot meet the requirements of pipeline flushing. Even flushing is replaced by water pressure test drainage.
Consequences: the water quality does not meet the operating requirements of the pipeline system, which often results in the reduction or blockage of the pipeline section. Measures: Flush with a larger design flow in the system or a water flow speed that should not be less than 3m/s. The water color and transparency of the outlet should be visually consistent with the water color and transparency of the inlet water.
Sewage, rainwater and condensate pipes are concealed without a closed water test.
Consequences: It may cause water leakage and cause user losses.
Measures: The closed water test work should be checked and accepted in strict accordance with the specifications. Buried underground, in the ceiling, between pipes, etc., concealed installation of sewage, rainwater, condensate pipes, etc., must ensure that they are not leaking.
In the hydraulic strength test and tightness test of the pipeline system, only the pressure value and the water level change are observed, and the leakage inspection is not enough. Consequences: leakage occurs after the operation of the pipeline system, which affects the normal use. Measures: When the pipeline system is tested according to the design requirements and construction specifications, in addition to recording the pressure value or the water level change within the specified time, it is especially necessary to carefully check whether there is any leakage problem.
Common valve flanges are used for butterfly valve flanges. Consequences: Butterfly valve flanges are different in size from ordinary valve flanges. Some flanges have a small inner diameter, while the disc of the butterfly valve is large, resulting in failure to open or hard opening and damage to the valve.
Measures: Process the flange according to the actual size of the butterfly valve flange.
There are no reserved holes and embedded parts in the construction of the building structure, or the size of the reserved holes is too small and the embedded parts are not marked. Consequences: During the construction of heating and sanitary engineering, the building structure is chiseled, and even the stressed steel bars are cut off, which affects the safety performance of the building. Measures: Familiarize yourself with the construction drawings of the heating and sanitary engineering, and actively cooperate with the construction of the building structure to reserve holes and embedded parts according to the needs of the installation of pipes and supports and hangers, and refer to the design requirements and construction specifications for details.
When the pipes are welded, the staggered ends of the pipes are not on the same center line after the counterparts, no gaps are left for the counterparts, and the thick-walled pipes are not shoveled, and the width and height of the welds do not meet the requirements of the construction specification.
Consequences: the misalignment of the pipe directly affects the welding quality and visual quality. No gap is left between the counterparts, thick-walled pipes are not shoveled, and the welding seam width and height do not meet the requirements.
Measures: After welding the opposite ends of the pipes, the pipes should not be staggered, and should be on the same center line; the opposite should be left with a gap; thick-walled pipes should be beveled. In addition, the width and height of the weld shall be welded according to the specification requirements.
The pipeline is directly buried on the frozen soil and untreated loose soil, and the spacing and position of the pipeline piers are improper, even in the form of dry yard bricks. Consequences: Due to the unstable support, the pipeline was damaged during the backfill compaction process, resulting in rework and repair.
Measures: The pipeline shall not be buried on the frozen soil and untreated loose soil, the spacing of the piers shall meet the requirements of the construction specification, and the support pads shall be firm, especially the joints of the pipelines, which should not be subjected to shearing force. Brick buttresses shall be built with cement mortar to ensure integrity and firmness.
The material of the expansion bolts for fixing the pipeline supports is poor, the hole diameter of the expansion bolts is too large, or the expansion bolts are installed on brick walls or even lightweight walls.
Consequences: the pipe support is loose, the pipe is deformed, or even falls off.
Measures: Qualified products must be selected for expansion bolts. If necessary, samples should be taken for test inspection. The diameter of the installation expansion bolts should not be greater than the outer diameter of the expansion bolts by 2mm. The expansion bolts should be used on concrete structures.
The flanges and gaskets of the pipeline connection are not strong enough, and the connecting bolts are short or small in diameter. Rubber pads are used for heat pipes, double-layer pads or inclined pads are used for cold water pipes, and flange gaskets protrude into the pipes.
Consequences: The flange connection is not tight, or even damaged, and leakage occurs. Flange gaskets protrude into the pipe, increasing the resistance to water flow. Measures: The flanges and gaskets used for the pipeline must meet the requirements of the design working pressure of the pipeline. Rubber asbestos gaskets should be used for flange gaskets of heating and hot water supply pipes; rubber gaskets should be used for flange gaskets of water supply and drainage pipes.
The gasket of the flange shall not protrude into the pipe, and its outer circle should reach the bolt hole of the flange. No inclined surface pads or several pads shall be placed in the middle of the flange. The diameter of the bolt of the connecting flange should be less than 2mm than the diameter of the flange plate, and the length of the nut protruding from the bolt rod should be 1/2 of the thickness of the nut.
Valve installation method is wrong.
For example, the water (steam) flow direction of the globe valve or check valve is opposite to the sign, the valve stem is installed downward, the horizontally installed check valve is installed vertically, the handle of the rising stem gate valve or butterfly valve has no opening or closing space, and the valve stem of the concealed valve is installed. Not towards the inspection door. Consequences: the valve fails, the switch is difficult to repair, and the valve stem is facing down, which often causes water leakage.
Measures: Strictly follow the valve installation instructions for installation, leave enough valve stem to extend the opening height of the open stem gate valve, fully consider the handle rotation space for the butterfly valve, and the various valve stems cannot be lower than the horizontal position, let alone downward. For concealed valves, not only should an inspection door meet the needs of valve opening and closing, but also the valve stem should face the inspection door.
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; the gate valve is used for the water supply branch pipe when the pipe diameter is less than or equal to 50mm; the stop valve is used for the dry and riser pipes of hot water heating; the butterfly valve is used for the suction pipe of the fire pump. Consequences: Affect the normal opening and closing of the valve and adjust the resistance, pressure and other functions. Even caused the valve to be damaged and forced to be repaired during the operation of the system. Measures: Be familiar with the application range of various valves, and select the specifications and models of the valves according to the design requirements. The nominal pressure of the valve should meet the requirements of the system test pressure. According to the requirements of the construction specification: the water supply branch pipe diameter is less than or equal to 50mm, the stop valve should be used; when the pipe diameter is greater than 50mm, the gate valve should be used. Hot water heating dry and vertical control valves should use gate valves, and fire pump suction pipes should not use butterfly valves.
The necessary quality inspections are not carried out as required before the valve is installed.
Consequences: During the operation of the system, the valve switch is not flexible, the closing is not strict and water (steam) leakage occurs, resulting in rework and repair, and even affecting the normal water supply (steam). Measures: Before the valve is installed, the compressive strength and tightness test should be done. For the test, 10% of the quantity of each batch (same brand, same specification, same model) shall be randomly checked, and not less than one.
For the closed-circuit valve installed on the main pipe to cut off, the strength and tightness test shall be carried out one by one. The strength and tightness test pressure of the valve shall comply with the “Code for Acceptance of Construction Quality of Building Water Supply and Drainage and Heating Engineering” (GB 50242-2002).
The main materials, equipment and products used in the construction lack technical quality appraisal documents or product qualification certificates that meet the current standards issued by the state or the ministry.
Consequences: The quality of the project is unqualified, there are hidden dangers of accidents, and it cannot be delivered for use on schedule, so it must be reworked and repaired; resulting in delays in the construction period and increased investment in labor and materials.
Measures: The main materials, equipment and products used in water supply and drainage and heating and sanitary projects should have technical quality appraisal documents or product qualification certificates that meet the current standards issued by the state or the ministry; their product names, models, specifications, and national quality standards should be marked. Code, date of manufacture, name and location of the manufacturer, inspection certificate or code of the manufactured product.
Valve upside down
Consequences: Valves such as check valves, throttle valves, pressure reducing valves, and check valves are all directional. If they are installed upside down, the throttle valve will affect the use effect and life; the pressure reducing valve does not work at all, and the check valve even dangerous. Measures: For general valves, there is a direction mark on the valve body; if not, it should be correctly identified according to the working principle of the valve. The valve cavity of the globe valve is asymmetrical, and 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 (because the pressure of the medium is upward), and the medium does not press the packing after closing, which is convenient for maintenance. . This is the reason why the globe valve cannot be reversed. The gate valve should not be installed upside down (that is, the handwheel is downward), otherwise the medium will remain in the bonnet space for a long time, which will easily corrode the valve stem, and is prohibited by certain process requirements. It is extremely inconvenient to replace the packing at the same time. The rising stem gate valve should not be installed underground, otherwise the exposed valve stem will be corroded due to moisture. When installing the lift check valve, ensure that its disc is vertical so that it can be lifted flexibly. When installing the swing check valve, ensure that its pin shaft is level so that it can swing flexibly.
The pressure reducing valve should be installed upright on the horizontal pipeline, and should not be inclined in all directions.
Manual valve opening and closing, excessive force
Consequences: light valve damage, serious safety accidents
Measures: The manual valve, its handwheel or handle, is designed according to ordinary manpower, considering the strength of the sealing surface and the necessary closing force. Therefore, it is not possible to use a long lever or a long wrench to move the board. Some people are accustomed to using a wrench, and they should pay strict attention not to use too much force, otherwise the sealing surface will be easily damaged, or the handwheel and handle will be broken. To open and close the valve, the force should be stable and not impacted. Some components of high-pressure valves that are opened and closed by impact have taken into account the impact force that cannot be equal to that of general valves. For the steam valve, it should be pre-heated before opening, and the condensed water should be removed. When opening, it should be as slow as possible to avoid water hammer. When the valve is fully opened, the handwheel should be reversed a little to make the threads tight to avoid loosening and damage. For rising stem valves, remember the stem position when fully open and fully closed to avoid hitting the top dead center when fully open. And it is convenient to check whether it is normal when fully closed. If the valve does fall off, or if there is a large debris embedded between the valve core seals, the position of the valve stem will change when it is fully closed. When the pipeline is first used, there is a lot of internal dirt. The valve can be slightly opened, and the high-speed flow of the medium can be used to flush it away, and then gently close (can not be closed quickly or violently to prevent residual impurities from pinching the sealing surface), Turn it on again, repeat this many times, flush the dirt, and then put it into normal work. Normally open valve, there may be dirt on the sealing surface, when it is closed, it should be washed clean by the above method, and then officially closed. If the handwheel and handle are damaged or lost, they should be assembled immediately, and cannot be replaced with a flexible wrench, so as to avoid damage to the valve stem, ineffective opening and closing, and accidents in production. Some media cool down after the valve is closed to shrink the valve parts. The operator should close it again at an appropriate time, so that the sealing surface does not leave slits. Otherwise, the medium flows through the slits at a high speed and it is easy to erode the sealing surface. . During operation, if it is found that the operation is too laborious, the reason should be analyzed. If the packing is too tight, it can be loosened appropriately. If the valve stem is skewed, the personnel should be notified for repair. For some valves, when the valve is closed, the closing member is heated and expanded, which makes it difficult to open; if it must be opened at this time, the bonnet thread can be loosened by half a turn to one turn to eliminate the stress of the valve stem, and then the hand wheel is turned.
Improper installation of valve in high temperature environment
Consequences: Leakage accident measures: high temperature valves above 200°C are installed at room temperature, but after normal use, the temperature rises, the bolts are thermally expanded, and the gap increases, so they must be tightened again, called “hot tightening”, the operator Pay attention to this work, otherwise leakage is easy to occur.
Not draining water in time in cold weather
Measures: When the weather is cold, the water valve is closed for a long time, and the water behind the valve should be removed. After the steam valve is stopped, the condensed water should also be removed. The bottom of the valve is like a plug, which can be opened to drain.
Non-metallic valve, the opening and closing force is too large
Measures: Some non-metallic valves are hard and brittle, and some have low strength. When operating, the opening and closing force should not be too large, especially not violent. Also be careful not to bump objects.
New valve packing is too tight
Measures: When the new valve is used, the packing should not be pressed too tightly, so as not to leak, so as to avoid too much pressure on the valve stem, speed up the wear and tear, and it is difficult to open and close. The quality of valve installation directly affects the use, so careful attention must be paid to the direction and position of the valve, valve construction, valve protection facilities, bypass and instrumentation, and valve packing replacement.
The installation location has no operating space
Measures: The installation position of the valve must be convenient for operation; even if the installation is temporarily difficult, the long-term work of the operator must be considered. It is better to align the valve handwheel with the chest (usually 1.2 meters away from the operating floor), so that it is easier to open and close the valve. The handwheel of the landing valve should be upward, not inclined, so as to avoid awkward operation. The valve of the machine against the wall should also leave room for the operator to stand. It is necessary to avoid operation in the sky, especially acid and alkali, toxic media, etc., otherwise it is very unsafe.
Impact valves made of brittle materials
Measures: The installation and construction must be careful, and avoid hitting the valve made of brittle materials. Before installation, the valve should be inspected to check the specifications and models to identify whether there is damage, especially for the valve stem. Turn it a few times to see if it is skewed, because it is easier to hit the valve stem during transportation. Also remove debris from the valve. When the valve is lifted, the rope should not be tied to the handwheel or valve stem to avoid damage to these parts, and should be tied to the flange. For the pipeline connected to the valve, be sure to clean it. Compressed air can be used to blow off iron oxide filings, mud sand, welding slag and other debris. These debris not only easily scratch the sealing surface of the valve, but also block the small valve and make it invalid. When installing a screw valve, the sealing packing (line hemp plus lead oil or PTFE raw material tape) should be wrapped on the pipe thread, and do not get into the valve, so as not to accumulate in the valve and affect the flow of the medium. When installing flanged valves, pay attention to tightening the bolts symmetrically and evenly. The valve flange and the pipe flange must be parallel with a reasonable gap to avoid excessive pressure or even cracking of the valve. Special attention should be paid to brittle materials and valves with low strength. Valves that must be welded to the pipe should be spot welded first, then the closing parts should be fully opened, and then welded to death.
The valve has not taken heat preservation and cold preservation measures
Measures: Some valves must also have external protection facilities, which are heat preservation and cold preservation. Heat tracing steam lines are sometimes added in the insulation layer. What kind of valve should be kept warm or cold depends on the production requirements. In principle, if the medium in the valve lowers the temperature too much, which will affect the production efficiency or freeze the valve, it needs to be kept warm, or even heat traced; when the valve is exposed, it is unfavorable to production or causes adverse phenomena such as frost, it needs to be kept cold. Insulation materials include asbestos, slag wool, glass wool, perlite, diatomite, vermiculite, etc.; cold insulation materials include cork, perlite, foam, plastic, etc.
Trap not bypassed
Measures: For some valves, in addition to the necessary protection facilities, there are also bypasses and instruments. A bypass is installed for easy steam trap service. Other valves also have bypasses installed. Whether to install a bypass depends on the valve condition, importance and production requirements.
The packing measures are not regularly replaced: some of the packings of the stock valves are not good, and some are not in line with the medium used, which requires replacing the packing. The valve faces thousands of different media, and the stuffing box is always filled with ordinary packing, but when using it, the packing must be adapted to the medium. When replacing the packing, press it in circle by circle. The seam of each circle is preferably 45 degrees, and the circle and the circle seam are staggered by 180 degrees. The packing height should consider the room for the gland to continue to be pressed, and now let the lower part of the gland press the packing chamber to an appropriate depth, which can generally be 10-20% of the total depth of the packing chamber. For demanding valves, the seam angle is 30 degrees. The seams between the circles are staggered by 120 degrees. In addition to the above fillers, three pieces of rubber O-rings (natural rubber resistant to weak alkalis below 60 degrees Celsius, nitrile rubber resistant to oils below 80 degrees Celsius, and fluororubber resistant to various corrosive media below 150 degrees Celsius) can also be used according to specific conditions. Stacked PTFE ring (resistant to strong corrosive medium below 200 degrees Celsius) nylon bowl ring (resistant to ammonia and alkali below 120 degrees Celsius) and other forming fillers. Outside the ordinary asbestos packing, wrap a layer of PTFE raw material tape, which 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 keep the circumference even and prevent it from being too dead. Tighten the gland with even force and do not tilt.