The main materials, equipment and products used in construction are short of technical quality appraisal documents or product qualification certificates that meet the current standards issued by the state or ministry.
The quality of the project is not up to standard, there are hidden dangers of accidents, and it can not be delivered on time, so it must be repaired and repaired, which causes delay in the construction period and increases the input of labor and materials.
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Resin sand casting, etc.
The main materials, equipment and products used in water supply, drainage and heating and sanitation projects shall be technical quality appraisal documents or product qualification certificates issued by the state or ministry in accordance with the current standards; the product name, model, specifications, national quality standard code, date of leaving the factory, name and location of the manufacturer, and inspection certificate of the product leaving the factory shall be marked. Ming or code.
Necessary quality inspection shall not be carried out before the valve is installed.
In the operation of the system, the valve switch is not flexible, the closure is not strict and the phenomenon of water leakage (steam) occurs, resulting in rework and repair, and even affecting the normal water supply (steam).
Before valve installation, compressive strength and tightness test should be done. The test shall be carried out in 10% of the quantity of each batch (same brand, same specification, same model), and not less than one batch. Strength and tightness tests should be done one by one for the closed-circuit valves installed on the main pipe to cut off. Valve strength and tightness test pressure should comply with the "Code for Acceptance and Acceptance of Construction Quality of Building Water Supply and Drainage and Heating Engineering" (GB 50242-2002).
Installation valve specifications, models do not meet the design requirements. For example, the nominal pressure of the valve is less than the test pressure of the system; when the diameter of the feedwater branch pipe is less than or equal to 50 mm, the gate valve is used; the dry and riser of hot water heating adopts the stop valve; and the suction pipe of the fire pump adopts the butterfly valve.
Affect the normal opening and closing of valves and adjust resistance, pressure and other functions. Even in the operation of the system, valve damage is compelled to be repaired.
Familiar with the application scope of various types of valves, according to the design requirements to select the specifications and models of valves. The nominal pressure of the valve should meet the requirement of system test pressure. According to the requirements of construction specifications: cut-off valves should be used when the diameter of feedwater branch pipe is less than or equal to 50 mm, and gate valves should be used when the diameter of pipe is greater than 50 mm. Gate valves shall be used for hot water heating, dry and vertical control valves, and butterfly valves shall not be used for fire pump suction pipes.
The valve installation method is wrong. For example, the water (steam) flow direction of globe valve or check valve is opposite to the mark, the stem is installed downward, the check valve installed horizontally is installed vertically, the open stem gate valve or butterfly valve handle has no open or closed space, and the stem of the concealed valve does not face the check door.
Valve failure, switch maintenance difficulties, valve stem down often cause leakage.
Installation is carried out strictly according to the valve installation instructions. Open stem gate valve retains sufficient elongation opening height, butterfly valve fully considers the rotating space of the handle, and all kinds of valve rods can not be lower than the horizontal position, let alone downward. Undercover valves should not only be equipped with check doors to meet the needs of valve opening and closing, but also the stem should be oriented towards the check door.
The butterfly valve flange uses the ordinary valve flange.
The size of butterfly valve flange is different from that of common valve flange. Some flanges have small inner diameter, while the disc of butterfly valve is large, which causes the valve to be damaged because it cannot be opened or opened rigidly.
Flange should be machined according to the actual size of butterfly valve flange.
No holes and embedded parts are reserved in the construction of building structures, or the size of the reserved holes is too small and the embedded parts are not marked.
In the construction of heating and sanitation projects, the safety performance of buildings is affected by chipping the building structure and even cutting the stressed steel bars.
Familiar with the construction drawings of heating and sanitation projects, according to the installation needs of pipelines and hangers, actively and conscientiously cooperate with the reserved holes and embedded parts in the construction of building structures, referring specifically to the design requirements and construction specifications.
When the pipeline is welded, the misalignment of the pipe behind the counterpart is not on a central line, the gap is not left in the counterpart, the groove of the thick-walled pipe is not shoveled, and the width and height of the weld seam do not meet the requirements of the construction specifications.
The absence of pipe misalignment in a central line directly affects the welding quality and sensory quality. When the width and height of the weld do not meet the requirements, the weld strength can not meet the requirements.
After welding the pipe, the pipe can not be crossed. In a central line, the counterpart should be cleared, and the thick-walled pipe should be shoveled. In addition, the width and height of the weld should be welded in accordance with the specifications.
Pipeline is directly buried in frozen soil and untreated loose soil. Pipeline pier spacing and location are inappropriate, even in the form of dry bricks.
Pipeline is damaged in the course of backfill compaction due to unstable support, resulting in rework repair.
Pipeline shall not be buried in frozen soil or untreated loose soil. Pile spacing shall conform to the requirements of construction specifications. Pipe cushions shall be firm, especially at pipe interfaces, and shall not bear shear stress. Brick piers should be built with water and sediment slurry to ensure integrity and firmness.
Expansion bolts for fixing pipe brackets are inferior in material. The bore diameter of the expansion bolts is too large or the expansion bolts are installed on brick walls or even light walls.
Pipeline bracket loosening, pipeline deformation, or even fall off.
Expansion bolt must select qualified products, if necessary, sampling test should be carried out. The hole diameter of installation expansion bolt should not be greater than 2 mm. Expansion bolt should be applied to concrete structure.
The strength of flange and liner of pipeline connection is not enough, and the connecting bolt is short or thin in diameter. Rubber pads are used in thermal pipes, asbestos pads are used in cold water pipes, double-layer pads or inclined pads are used, and flange pads are protruded from human pipes.
The flange connection is not tight, even damaged, and leakage occurs. Flange liner penetrating into the pipe will increase the flow resistance.
Flange and liner for pipeline must meet the requirements of pipeline design working pressure. Rubber asbestos pad is suitable for flange pad of heating and hot water supply pipeline, and rubber pad is suitable for flange pad of water supply and drainage pipeline. The liner of the flange shall not protrude into the pipe, and the outer circle of the liner shall reach the bolt hole of the flange. No oblique cushion or several gaskets should be placed in the middle of the flange. The bolt diameter of the connecting flange should be less than 2 mm than that of the flange, and the length of the bolt protruding nut should be 1/2 of the nut thickness.
In the hydraulic strength test and tightness test of pipeline system, only the change of pressure and water level is observed, and the leakage inspection is not enough.
Leakage occurs after pipeline system operation, which affects normal operation.
When the pipeline system is tested according to the design requirements and construction specifications, besides recording the pressure or water level changes within the specified time, it is particularly important to carefully check whether there is leakage.
Sewage, rainwater and condensate pipes are concealed without water closure test.
It may cause leakage and user loss.
Closed water test shall be checked and accepted strictly in accordance with the specifications. Underground burial, suspension roof, pipes and other hidden sewage, rainwater, condensate pipes, etc. to ensure that no leakage.
The flushing of pipeline system before completion is not serious, and the flow rate and speed can not meet the requirements of pipeline flushing. It even replaces flushing with hydraulic strength test.
Water quality can not meet the requirements of pipeline system operation, and often causes the reduction or blockage of pipeline cross-section.
Rinse with the maximum set juice flow rate or flow rate not less than 3m/s in the system. The discharge water color, transparency and the intake water color, transparency visual measurement should be qualified.
Hydraulic test is carried out under negative temperature during winter construction.
Because the pipe freezes quickly during the hydraulic test, the pipe is frozen out.
Water pressure test should be carried out as far as possible before winter operation, and after pressure test, the water should be blown clean, especially the water in the valve must be cleared, otherwise the valve will freeze and crack. The project must be carried out under positive indoor temperature during hydraulic test in winter, and the water should be blown clean after pressure test. Compressed air can be used when hydraulic test cannot be carried out.