During winter construction, hydraulic pressure tests are conducted under negative temperatures.
Because the inside of the pipe freezes quickly during the hydraulic pressure test, the pipe freezes.
Try to conduct a hydraulic pressure test before construction in winter, and blow out the water after the pressure test. In particular, the water in the valve must be completely cleared, otherwise the valve will freeze and crack.
The project must be conducted at a positive indoor temperature (above 0°C) when conducting hydraulic pressure tests in winter, and the water must be blown away after the pressure test. When hydraulic testing is not possible, compressed air can be used for testing.
If the pipeline system is not flushed carefully before completion, the flow rate and speed cannot meet the pipeline flushing requirements. Even water pressure test draining is used instead of flushing.
If the water quality does not meet the operating requirements of the pipeline system, it will often cause the pipeline cross-section to be reduced or blocked.
Use the maximum design flow rate in the system or a water flow speed that should not be less than 3m/s for flushing. The discharge water color and transparency should be consistent with the color and transparency of the inlet water according to visual inspection.
Sewage, rainwater and condensate pipes shall be concealed without being tested for water closure.
Water leakage may occur and cause losses to the user.
The closed water test work should be inspected and accepted strictly in accordance with the specifications. Concealed sewage, rainwater, condensate water pipes, etc. buried underground, in suspended ceilings, between pipes, etc. must be ensured to ensure no leakage.
During the hydraulic strength test and tightness test of the pipeline system, only the pressure value and water level changes are observed, and leakage inspection is not enough.
Leakage occurs after the pipeline system is in operation, affecting normal use.
When the pipeline system is tested according to the design requirements and construction specifications, in addition to recording the pressure value or water level changes within the specified time, it is especially necessary to carefully check whether there are leakage problems.
Butterfly valve flange uses ordinary valve flange.
Butterfly valve flanges are of different sizes than ordinary valve flanges. Some flanges have small inner diameters, while butterfly valves have large discs, which can cause the valve to fail to open or be hard to open, causing damage to the valve.
The flange plate must be processed according to the actual size of the butterfly valve flange.
There are no reserved holes and embedded parts during the construction of the building structure, or the reserved holes are too small and the embedded parts are not marked.
During the construction of heating and sanitation projects, the building structure is chiseled and even the stress-bearing steel bars are cut, which affects the safety performance of the building.
Carefully familiarize yourself with the construction drawings of heating and sanitary engineering projects, and proactively and conscientiously cooperate with the construction of building structures to reserve holes and embedded parts according to the installation needs of pipelines and supports and hangers. Specifically refer to the design requirements and construction specifications.
When welding pipes, the staggered joints of the pipes after matching are not on the same center line, no gap is left for the matching, thick-walled pipes are not beveled, and the width and height of the weld do not meet the requirements of the construction specifications.
The misalignment of the pipe joints directly affects the welding quality and visual quality. If there is no gap between the joints, no beveling of thick-walled pipes, and the width and height of the weld do not meet the requirements, the welding will not meet the strength requirements.
After welding the joints of the pipes, the pipes must not be misaligned and must be on a center line. There should be a gap between the joints. Thick-walled pipes must be beveled. In addition, the width and height of the welding seam must be welded in accordance with the specifications.
The pipelines are directly buried in frozen soil and untreated loose soil, and the spacing and location of pipeline buttresses are improper, and even dry-coded bricks are used.
Due to unstable support, the pipeline was damaged during the tamping process of backfill soil, resulting in rework and repair.
Pipelines must not be buried in frozen soil or untreated loose soil. The spacing between buttresses must comply with the requirements of construction specifications. The support pads must be firm. Especially the pipe interfaces should not bear shearing force. Brick buttresses must be built with cement mortar to ensure integrity and firmness.
The expansion bolts used to fix the pipe supports are of inferior material, the holes for installing the expansion bolts are too large, or the expansion bolts are installed on brick walls or even lightweight walls.
The pipe supports are loose and the pipes are deformed or even falling off.
Qualified products must be selected for expansion bolts, and sampling should be conducted for test inspection when necessary. The hole diameter for installing expansion bolts should not be larger than 2 mm outside the outer diameter of the expansion bolts. Expansion bolts should be used on concrete structures.
The flange and gasket of the pipe connection are not strong enough, and the connecting bolts are short or thin in diameter. Use rubber gaskets for heating pipes, asbestos gaskets for cold water pipes, and double-layer or beveled gaskets with flange gaskets protruding into the pipes.
The flange connection is not tight or even damaged, causing leakage. The flange gasket protrudes into the pipe and increases flow resistance.
① Pipe flanges and gaskets must meet the design working pressure requirements of the pipeline.
② Rubber asbestos pads should be used for flange linings of heating and hot water supply pipes; rubber pads should be used for flange linings of water supply and drainage pipes.
③ The flange gasket must not protrude into the pipe, and its outer circle should reach the flange bolt hole. Bevel pads or several pads must not be placed in the middle of the flange. The diameter of the bolt connecting the flange should be less than 2 mm than the flange plate hole diameter. The length of the bolt rod protruding from the nut should be 1/2 of the nut thickness.
The valve is installed incorrectly.
For example, the water (steam) flow direction of the stop valve or check valve is opposite to the sign, and 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 and closing space. The valve stem of the concealed valve is installed. Not toward the inspection door.
The valve fails, the switch is difficult to repair, and the valve stem is downward, often causing water leakage.
Install strictly in accordance with the valve installation instructions. For rising-stem gate valves, allow sufficient valve stem extension and opening height. For butterfly valves, fully consider the handle rotation space. All valve stems cannot be lower than the horizontal position, let alone downward. Concealed valves must not only be equipped with an inspection door that meets the valve opening and closing requirements, but also the valve stem should be facing 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; gate valves are used when the pipe diameter of the water supply branch pipe is less than or equal to 50mm; stop valves are used for dry and standpipe pipes of hot water heating; butterfly valves are used for fire water pump suction pipes.
Affects the normal opening and closing of the valve and the adjustment of resistance, pressure and other functions. It may even cause the valve to be damaged and have to be repaired while the system is running.
① Be familiar with the application scope of various types of valves, and select valve specifications and models according to design requirements.
② The nominal pressure of the valve must meet the system test pressure requirements.
③ According to the requirements of construction specifications: when the diameter of the water supply branch pipe is less than or equal to 50mm, a stop valve should be used; when the pipe diameter is greater than 50mm, a gate valve should be used.
④ Gate valves should be used for hot water heating dry and vertical control valves, and butterfly valves should not be used for fire water pump suction pipes.
Failure to carry out necessary quality inspections as required before valve installation.
During the operation of the system, the valves are inflexible in opening and closing, are not closed tightly, and water (steam) leaks occur, causing rework and repairs, and even affecting the normal water supply (steam).
Before the valve is installed, pressure strength and tightness tests should be carried out. The test should randomly check 10% of each batch (same brand, same specification, same model), and no less than one.
For closed-circuit valves installed on main pipes with a cutting function, strength and tightness tests should be conducted one by one.
The main materials, equipment and products used in construction lack technical quality appraisal documents or product certificates that comply with current national or ministerial standards.
The quality of the project is unqualified and there are potential accidents. It cannot be delivered on time and must be reworked and repaired. This results in delays in the construction period and increased investment in labor and materials.
The main materials, equipment and products used in water supply, drainage and heating and sanitation projects should have technical quality appraisal documents or product certificates that comply with current standards issued by the state or the ministry; their product names, models, specifications, national quality standard codes, Date of manufacture, name and location of the manufacturer, inspection certificate or code number of the manufactured product.