Valves are the most common equipment in chemical enterprises. It seems easy to install valves, but if they are not executed in accordance with relevant technologies, safety accidents will occur...
Hydrostatic test was carried out under negative temperature in winter.
Consequence: the tube freezes quickly during the hydrostatic test, causing the tube to freeze.
Measures: water pressure test should be carried out as far as possible before winter application, and the water should be blown clean after pressure test, especially the water in the valve must be cleared in the clean, otherwise the valve will be light rust, heavy freeze crack.
During the hydrostatic test in winter, the project must be carried out at a positive indoor temperature and the water must be blown clean after the pressure test.
The pipeline system is not flushed carefully before completion, and the flow rate and speed cannot meet the requirements of pipeline flushing.
Water pressure strength test was even used instead of flushing.
Consequences: The water quality does not meet the operation requirements of the pipeline system, which often leads to the reduction or blockage of the pipeline cross section.
Measure: Flush with the maximum flow rate or flow rate not less than 3m/s.The water color and transparency of the discharge outlet should be consistent with the visual measurement of the water color and transparency of the inlet.
Sewage, rainwater and condensate pipes shall be concealed without water closing test.
Consequences: may cause water leakage, and cause user losses.
Measures: The closed water test should be checked and accepted strictly according to the standard.Underground installation, ceiling, pipe and other hidden sewage, rainwater, condensate pipe to ensure that no leakage.
In the water pressure strength test and tightness test of pipeline system, only observe the change of pressure value and water level, and the inspection of leakage is not enough.
Consequences: Leakage occurs after the operation of the pipeline system, which affects the normal use.
Measures: When the piping system is tested in accordance with the design requirements and construction specifications, the pressure value or water level changes shall be recorded within the specified time, and in particular, the leakage shall be carefully checked.
Butterfly valve flanges use ordinary valve flanges.
Consequence: butterfly valve flange and the general valve flange size is not the same, some flange diameter is small, and butterfly valve disc is large, resulting in not open or hard to open the valve damage.
Measures: according to the actual size of the butterfly valve flange flange processing flange.
In the construction of the building structure, there are no reserved holes and embedded parts, or the reserved holes are too small in size and the embedded parts are not marked.
Consequence: in the construction of warm sanitation project, picking out the building structure, or even cutting off the reinforced bar, affecting the safety performance of the building.
Measures: Be familiar with the construction drawings of heating and sanitation project, and actively and seriously cooperate with the construction of reserved holes and embedded parts according to the installation requirements of pipes, supports and hangers, and refer to the design requirements and construction specifications for details.
During pipeline welding, the wrong opening of the pipe after the opposite port is not in a center line, no clearance is left for the opposite port, no groove is removed for the thick-wall pipe, and the width and height of the welding seam do not meet the requirements of the construction code.
Consequence: the wrong orifice of the pipe is not in a center line, which directly affects the welding quality and perception quality.No clearance is left for the counterpart, no slotting is done for the thick-walled pipe, and the welding strength cannot be reached if the width and height of the welding seam do not meet the requirements.
Measures: After welding the pipe to the other side, the pipe should be on the center line instead of the other side.A gap should be left at the opposite mouth;Thick - walled pipes should be slotted.In addition, the width and height of the weld shall be welded in accordance with the requirements of the code.
Pipelines are directly buried in frozen soil and untreated loose soil, and the piers are not properly spaced and located, or even in the form of dry code bricks.
Consequence: The pipe was damaged in the process of compaction of backfill earth due to unstable support, which caused rework and repair.
Measures: The pipe shall not be buried in frozen soil and loose soil without treatment. The distance between piers shall meet the requirements of construction code, and the supporting pad shall be firm. In particular, the pipe connection shall not bear shear force.Brick piers to use cement mortar masonry, ensure integrity, firm.
The material of the expansion bolts for fixing the pipe bracket is inferior, the aperture of the installation expansion bolts is too large or the expansion bolts are installed on the brick wall or even the light wall.
Consequences: Loose pipe support, pipe deformation, and even fall off.
Measures: qualified products must be selected for expansion bolts. If necessary, samples should be taken for test inspection. The diameter of expansion bolts installed should not be 2mm larger than the outside diameter of expansion bolts.
Flanges and gaskets for pipe connections are not strong enough, and the connecting bolts are short or thin in diameter.Rubber pads are used for heat pipes, double or bevel pads for cold water pipes, and flange gaskets protruding into the pipes.
Consequence: flange connection is not tight, even damaged, leakage phenomenon.The penetration of the flange gasket into the tube will increase the flow resistance.
Measures: flanges and gaskets used in pipelines must meet the requirements of working pressure in pipeline design.
Rubber asbestos gaskets should be used for flange gaskets of heating and hot water supply pipes;Rubber gasket should be used for flange gasket of water supply and drainage pipeline.
The gasket of the flange shall not protrude into the tube, and the outer circle to the flange bolt hole shall be appropriate.Bevel pads or several gaskets shall not be placed in the middle of the flange. The diameter of the bolt connecting the flange should be less than 2mm than the diameter of the flange flange. The length of the bolt protruding nut should be 1/2 of the thickness of the nut.
Incorrect valve installation method.
For example, the water (steam) flow of globe valves or check valves is opposite to the sign, the stem is installed downward, horizontal check valves are installed vertically, the handle of rising stem gate valve or butterfly valve has no open and closed space, the stem of hidden valve is not oriented toward the inspection door.Consequences: valve failure, switch maintenance difficulties, valve stem down often cause water leakage.
Measures: Install in strict accordance with the valve installation instructions, keep the stem of the rising gate valve open height, fully consider the rotation space of the butterfly valve handle, all kinds of valve stem should not be lower than the horizontal position, let alone down.The hidden valve should not only set the inspection door to meet the needs of opening and closing the valve, but also the stem should face the inspection door.
The installation valve specifications and models do not meet the design requirements.
For example, the nominal valve pressure is less than the system test pressure;When the diameter of water supply branch pipe is less than or equal to 50mm, use gate valve;Cut-off valves are used in the dry and riser pipes for hot water heating.Butterfly valve is used for water suction pipe of fire pump.
Consequences: Affect the valve normal open and close and adjust resistance, pressure and other functions.Even caused damage to the valve during the operation of the system and forced repair.
Measures: Familiar with the application range of all kinds of valves, according to the design requirements to choose the valve specifications and models.Nominal valve pressure to meet the requirements of system test pressure.According to the requirements of the construction code: cut-off valve shall be used for the water supply branch pipe diameter less than or equal to 50mm;Gate valves should be used when pipe diameter is greater than 50mm.Hot water heating dry, vertical control valve should be used gate valve, fire water pump suction pipe should not be used butterfly valve.
The valve does not perform necessary quality inspection before installation.
Consequences: In the operation of the system, the valve switch is not flexible, the shutdown is not strict and the phenomenon of leakage (steam) occurs, causing rework and repair, and even affecting the normal water supply (steam).
Measure: Before installation, the valve should be tested for compressive strength and tightness.The quantity of each batch (same brand, same specification, same model) shall be randomly checked by 10% and not less than one.The strength and tightness test should be done one by one for the closed - circuit valve installed on the main pipe.The strength and tightness test pressure of the valve should comply with the "Construction Quality Acceptance Code for Building Water Supply, Drainage and Heating Engineering" (GB 50242-2002).
The main materials, equipment and products used in the construction are in lack of technical and quality appraisal documents or product certificates conforming to the current national or ministry standards.
Consequences: the project quality is not qualified, there are potential accidents, can not be delivered to use on schedule, must be reworked and repaired;Delay of construction, increase of manpower and material input.
Measures: The main materials, equipment and products used in water supply and drainage and heating and sanitation engineering shall meet the technical and quality identification documents or product qualification certificates issued by the state or the Ministry;The product name, model, specification, national quality standard code, date of manufacture, name and place of manufacturer, inspection certificate or code of the ex-factory product shall be indicated.
The valve inversion
Consequences: Check valve, throttle valve, pressure reducing valve, check valve and other valves have directionality, if installed in reverse, throttle valve will affect the service effect and life;Pressure relief valves do not work and check valves can be dangerous.
Measures: General valves, direction marks on the body;In case of no, the valve should be correctly identified according to the working principle.The valve chamber of the globe valve is asymmetrical, the fluid should be let from the bottom to the top through the valve mouth, so that the fluid resistance is small (determined by the shape), open to save effort (due to the medium pressure up), closed after the medium does not pressure packing, easy to repair.This is why the globe valve cannot be reversed.
Gate valves should not be inverted (i.e., handwheel down), as this can cause media to remain in the cover space for a long time, corrode the stem, and is No- No to certain process requirements.It is inconvenient to change packing at the same time.
Open stem gate valves should not be installed underground or the exposed stem may corrode due to moisture.
Lifting type check valve, when the installation to ensure that its disc vertical, in order to lift flexible.
Swing check valve, install to ensure its pin shaft level, so that the swing flexible.
Pressure relief valves should be installed upright in a horizontal pipe line, do not tilt in all directions.
Manual valve opening and closing, too much force
Consequences: light valve damage, serious safety accidents
Measure: The manual valve, its handwheel or handle, is designed according to ordinary manpower, taking into account the strength of the sealing surface and the necessary closing force.So you can't use a long lever or a long plank to move the plank.Some people are used to using the board hand, should be strict attention, do not exert too much force, otherwise easy to damage the sealing surface, or plate broken handwheel, handle.Open and close the valve, the force should be smooth, not impact.Some impact open and close high pressure valve components have been considered the impact and the general valve can not wait.For the steam valve, before opening, should be pre-heated, and exclude condensate, open, should be as slow as possible, so as not to occur water hammer phenomenon.When the valve is fully open, the handwheel should be reversed a little, so as to tighten between threads, so as not to loosen and damage.For open stem valves, remember stem positions when fully open and fully closed to avoid hitting the upper dead center when fully open.It is convenient to check whether it is normal when closed.If the valve does fall off, or between the valve core seal embedded larger debris, when the valve stem position is about to change.When the pipeline is first used, there are a lot of internal dirt, the valve can be slightly opened, using the high-speed flow of the medium, wash it away, and then gently closed (can not close quickly, violently closed, in case of residual impurities caught in the sealing cover), open again, so repeated many times, clean the dirt, then put into the normal work.Often open the valve, sealing surface may be sticky with dirt, when closed, also want to use the above method to flush clean, and then formally close.If the handwheel or handle is damaged or lost, it should be fitted immediately, and can not be replaced by the movable plate hand, so as to avoid damage to the valve stem square, not open and close properly, so as to cause accidents in production.Some media, cooled after the valve closed, so that the valve parts shrink, the operator should be closed at the appropriate time again, so that the sealing surface without fine seam, otherwise, the medium from the fine seam high-speed flow, it is easy to erosion sealing surface.During the operation, if the operation is found to be too strenuous, the reason should be analyzed.If packing is too tight, loosen appropriately. If stem is askew, advise repair.Some valves, in the closed state, the closure of the thermal expansion, causing difficulty in opening;If it must be opened at this time, unscrew the bonnet half to one turn to eliminate stem stress and then turn the plate.
Improper installation of valve in high temperature environment
Consequences: Causing a spill
Measures: The high-temperature valve above 200℃ is at room temperature when installed, but after normal use, the temperature rises, the bolt expands in heat, the gap increases, so it must be tightened again, called "hot tight", the operator should pay attention to this work, otherwise it is easy to leak.
Cold weather does not drain in time
Measures: when the weather is cold, the water valve should be closed for a long time, the water should be removed after the valve.After the steam valve stops steam, condensate should also be removed.The bottom of the valve is like a silk plug, it can be opened to drain.
Nonmetal valve with too much opening and closing force
Measure: nonmetal valve, some hard and brittle, some low strength, operation, open and close force can not be too big, especially can not make strong.Also be careful not to bump objects.
The new valve packing is too tight
Measures: when the new valve is used, the packing should not be pressed too tight, with no leakage as a degree, so as not to pressure the valve stem is too big, speed up the wear and tear, and open and close laboriously.The quality of valve installation directly affects use, so careful attention must be paid to valve direction and position, valve construction, valve protection, bypasses and instrumentation, and valve packing replacement.
The installation position has no operating space
Measures: the valve installation position must be convenient for operation;Even if the installation is temporarily difficult, the operator's long-term work should be considered.Best valve handwheel and chest even (generally 1.2 meters away from the operation floor), so, open and close the valve more energy saving.Landing valve hand wheel should be up, do not tilt, so as not to operate awkwardly.The wall machine depends on the valve of the equipment, also want to leave room for the operator to stand.To avoid relying on the sky operation, especially acid and alkali, toxic medium, otherwise very unsafe.
Hit a valve made of brittle material
Measures: installation and construction must be careful, do not hit the valve made of brittle materials.Before installation, check the valve to see if there is any damage, especially to the stem.Also turn a few times to see if the valve is skewed, because during transportation, the most prone to skew valve stem.Also remove debris from the valve.When the valve is hoisted, the rope should not be tied to the handwheel or stem to avoid damaging these parts. It should be tied to the flange.Be sure to clean the line to which the valve is attached.Iron oxide chips, sand, welding slag and other sundries can be blown by compressed air.These sundries, not only easy to scratch the sealing surface of the valve, including large particles sundries (such as welding slag), but also can block the small valve, make its failure.When installing the screw valve, the sealing filler (wire and lead oil or polytetrafluoroethylene raw material belt) should be wrapped on the pipe thread, do not get into the valve, in order to avoid the memory of the valve, affect the medium flow.When installing flanged valves, pay attention to tighten bolts symmetrically and evenly.Valve flange and pipe flange must be parallel, reasonable clearance, to avoid valve too much pressure, or even cracking.Particular attention should be paid to brittle materials and low strength valves.The valve to be welded with the pipe should be spot-welded first, then fully open the closed parts, and then welded dead.
The valve is not insulated and cooled
Action: Some valves also require external protection, which is insulation and cooling.Steam lines are sometimes added to heat insulation.
What kind of valves should be insulated or cooled depends on production requirements.In principle, where the valve medium to reduce the temperature is too much, will affect the production efficiency or freeze damaged valve, the need for insulation, or even heat;Where the valve bare, adverse to production or cause frost and other adverse phenomena, the need to keep cold.Insulation materials include asbestos, slag wool, glass wool, perlite, diatomite, vermiculite, etc.Keep cold material to have cork, perlite, foam, plastic.
Bypass not installed on trap
Measures: Some valves, in addition to the necessary protection facilities, also have bypasses and instrumentation.Bypass is installed to facilitate maintenance of the trap.Other valves may also be bypassed.Bypass installation depends on valve condition, importance, and production requirements.
Packing not replaced regularly
Measures: inventory valve, some packing is not good, and some with the use of media, it is necessary to replace the packing.
The valve faces thousands of different media, packing box is always filled with ordinary packing, but when used, must let the packing and the medium to adapt.
When changing packing, press in round by round.The seams of each ring shall be 45 degrees, and the joints of the rings and rings shall be staggered 180 degrees.The height of the packing shall allow for further compaction of the gland and, at the present time, the proper depth of the packing chamber at the lower gland, normally 10-20% of the total depth of the packing chamber.
For high demand valves, seam Angle is 30 degrees.The seam between the loops is staggered by 120 degrees.
In addition to the packing, can also according to the specific situation, USES the rubber o-ring (natural rubber resistant to 60 degrees Celsius under weak base, butyl eyes below 80 degrees Celsius oil resistant rubber, fluorine rubber resistance to a variety of corrosive medium under 150 degrees Celsius) three fold type teflon ring (below 200 degrees Celsius) strong corrosive medium resistance of nylon bowl ring (below 120 degrees Celsius, ammonia alkali resistant) forming filler.A layer of polytetrafluoroethylene raw material belt outside the common asbestos packing can improve the sealing effect and reduce the electrochemical corrosion of the valve stem.
When pressing the packing, turn the stem simultaneously to keep all sides even and prevent too much dead, tighten the gland evenly without tilting.