Notices in Pipeline Construction of Forged Steel Valves
Forged steel valves are mainly used in pipelines of various systems in thermal power plants, and can be used to control the flow of various types of fluids such as air, water, steam, corrosive media, mud, oil, liquid metal and radioactive media. Compared with other valve products, forged steel valves are characterized by high temperature and pressure resistance, unique self-sealing design, the higher the pressure, the more reliable the sealing. Because of the special performance, technical characteristics and working conditions, the products also have the characteristics that other products can not replace.
Forged steel valves can be classified as forged steel check valves, forged steel gate valves, forged steel ball valves, forged steel globe valves, self-sealing gate valves, self-sealing globe valves, self-sealing check valves, forged steel needle valves, forged steel insulation valves, high-pressure forged steel gate valves, forged steel bellows valves, etc.
Matters needing attention:
Taboo 1: The main materials, equipment and products used in construction lack technical quality identification documents or product certificates that meet the current national or ministerial standards.
Consequences: The quality of the project is unqualified. There are latent dangers of accidents. It cannot be accomplished and put into use on time, and it must be reworked and repaired, resulting in delays in construction period and increased investment in labor and materials. Measures: The main materials, equipment and products used in water supply, drainage, heating and sanitation projects shall have technical quality appraisal documents or product certificates that meet the current standards issued by the state or the ministry; their product names, models, specifications and national quality standards code, date of manufacture, manufacturer’s name and location, factory product inspection certificate or code shall be indicated.
Taboo 2: The forged steel valve is not subjected to the necessary quality inspection before installation.
Consequences: The forged steel valve switch is inflexible in the system operation, the shutdown is not strict and the phenomenon of water (steam) leakage occurs, causing reworking and repairing, and even affecting the normal water (steam) supply.
Measures: Before the installation of forged steel valves, the compression strength and tightness test should be done. The test should be carried on by checking 10% of each batch quantity (same brand, same specification, and same model), and not less than one. For closed-circuit forged steel valves that function as a cut-off and are installed on the main pipe, the strength and tightness tests shall be made one by one.
Taboo 3: The specifications and models of the installed forged steel valves do not meet the design requirements. For example, the nominal pressure of the forged steel valve is less than the system testing pressure. the gate valve is used when the pipe diameter of the water supply pipe is less than or equal to 50 mm; the dry pipe and the stand pipe of the hot water heating adopt a globe valve; and the fire pump suction pipe adopts a butterfly valve.
Consequences: It will affect the normal opening and closing of forged steel valves and affect the valve’s other function like adjusting the resistance and pressure. It may even cause the forged steel valve to be damaged and forced to repair during the system running.
Measures: Be familiar with the application range of all kinds of forged steel valves, and select the specifications and models of forged steel valves according to the design requirements. The nominal pressure of the forged steel valve must meet the requirements of the system testing pressure. According to the requirements of construction specifications: if the water supply pipe diameter is less than or equal to 50 mm, a forged globe valve should be used; when the pipe diameter is bigger than 50 mm, a forged gate valve should be used. The hot water heating dry and vertical control valves shall adopt gate valves, and the fire pump suction pipes shall not adopt butterfly valves.
Taboo 4: The installation method of the forged steel valve is wrong. For example, the water (steam) flow direction in the shut-off valve or check valve is opposite to the sign, the valve stem is installed downward, the horizontally mounted check valve is installed vertically, the rising stem gate valve or the butterfly valve handle has no opening and closing space, and the valve stem of the concealed installed forged steel valve does not face the inspection door.
Consequences: Forged steel valves do not work, switch maintenance is difficult, and the valve stem facing down often causes water leakage.
Measures: Install the forged steel valve strictly according to the installation instructions. For the rising stem gate valve, leave enough space for the stem opening and extending. For the butterfly valve, fully consider the handle rotation space. For all kinds of forged steel valves, the stems cannot be lower than the horizontal position, and cannot be installed downward. The concealed forged steel valve should not only be set to meet the inspection door required for the opening and closing of the forged steel valve, but also the valve stem should face the inspection door.
Taboo 5: A common forged steel valve flange plate is used for a butterfly valve flange.
Consequences: Butterfly valve flange plates and ordinary forged steel valve flange plates vary in size. Some common forged steel valve flanges have a small inner diameter, while the butterfly valve has a large valve flap, which causes the forged steel valve to be damaged due to inability to open or hard open.
Measures: The flange plate must be machined according to the actual size of the butterfly valve flange.
Taboo 6: There are no reserved holes and embedded parts in the construction of the building structure, or the reserved holes are small in size and the embedded parts are not marked.
Consequences: During the construction of the heating and sanitation project, the building structure is excavated and even the load bearing steel bars are cut off, affecting the safety performance of the building.
Measures: Conscientiously familiar with the construction drawings of the heating and sanitation project. According to the needs of the installation of pipelines and hangers, actively and conscientiously cooperate with the reserved holes and embedded parts for the construction of the building structure, with specific reference to the design requirements and construction specifications.
Taboo 7: When the pipe is welded, the mouths of the pipe after the alignment is not on a center line, no gap is left between the mouths, and the beveled edges of the thick walled pipe are not shoveled. The width and height of the weld do not meet the construction specifications.
Consequences: The misalignment of the pipe directly affects the welding quality and the appearance quality. If there is no gap between the mouths, and the beveled edges of the thick-walled pipe are not shoveled or the width and height of the weld do not meet the requirements, the welding cannot meet the strength requirement.
Measures: After the pipeline alignment, the pipe cannot be staggered. It should be on a center line, the gap should be reserved for the mouth, and the beveled edges should be shoveled for thick walled pipe. The width and height of the weld should be welded according to the specifications.
Taboo 8: The pipe is directly buried in the frozen soil and the untreated loose soil. The spacing and position of the pipe buttress are improper, even in the form of dry brick.
Consequences: Due to the unstable support of the pipeline, the pipeline was damaged during the back fill tamping process, resulting in rework and repair.
Measures: Pipes should not be buried in frozen soil and untreated loose soil. The distance between the piers should meet the requirements of construction specifications, and the support pads should be firm, especially at the pipe joints, and should not be subjected to shearing forces. Brick piers should be built with cement mortar to ensure completeness and firmness.
Taboo 9: The expansion bolts of the pipe fixing supports are inferior in material. The hole diameter for the expansion bolts installation is too large or the expansion bolts are installed on brick walls or even light weight walls.
Consequences: The pipe support is loose and the pipe is deformed or even falls off.
Measures: The expansion bolts must be selected as qualified products. If necessary, sampling inspection should be made. The hole diameter for the installation of expansion bolts should not be larger than the outer diameter of the expansion bolts by 2 mm. The expansion bolts are applied to the concrete structure.
Taboo 10: The flanges and gaskets of the pipe connections are not strong enough, and the connecting bolts are short or have a small diameter. Heat distribution pipelines use rubber gaskets, cold water pipes use asbestos gaskets, and double-layer gaskets or beveled gaskets with flange gasket protruding into the pipe.
Consequences: The flange connection is not tight, even damaged, and leakage occurs. The flange gasket protrudes into the tube and increases the flow resistance.
Measures: Flanges and gaskets for pipes must meet the pressure requirements for piping design. Rubber asbestos gaskets should be used for the flange gaskets of heating and hot water supply pipes; rubber gaskets should be used for the flange gaskets of water supply and drainage pipes. The gasket of the flange shall not protrude into the pipe. The outer circle of flange gasket is preferably to the bolt hole. No inclined gasket or several gaskets shall be placed in the middle of the flange. The bolt diameter of the connecting flange should be less than 2 mm than the flange diameter. The length of the bolt stem protruding nut should be 1/2 of the thickness of the nut.
Taboo 11: When conducting the hydraulic pressure test and tightness test of the pipeline system, only observe pressure values and water level changes, while carry out insufficient inspection of leaks,
Consequences: Leakage occurs after the pipeline system is in operation, affecting 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 water level change within the specified time, it is especially necessary to carefully check whether there is leakage.
Taboo 12: Sewage, rainwater, and condensate pipes are concealed without a closed water test.
Consequences: May cause water leakage and cause user losses.
Measures: The closed water test should be checked and accepted in strict accordance with the specifications. Concealed sewage, rainwater, condensate pipes, etc., buried underground, inside suspended ceilings, between pipelines, etc., must be ensured that they do not leak.
Taboo13: No flushing thoroughly before the completion of the piping system, and the flow rate and speed are not up to the pipeline flushing requirements. More terrible, water release after the water pressure test replaces flushing.
Consequences: Water quality does not meet the requirements for pipeline system operation, and often results in reduced or blocked pipe sections.
Measures: Flush with the maximum flow rate in the system or at a water flow rate of not less than 3 m/s. The water color and transparency of the discharge port should be consistent with the water color and transparency of the inlet water by visual inspection.
Taboo 14: The hydrostatic test is carried out at a negative temperature during winter construction.
Consequences: The tube freezes off quickly due to the rapid freezing of the tube water during the hydrostatic test.
Measures: Try to carry out the hydrostatic test before the winter application, and blow the water off after the pressure test, especially the water in the forged steel valve must be removed to the net, otherwise the forged steel valve will freeze. If the hydrostatic test must be carried out in a winter project, be sure that the test is carried out at a normal indoor temperature and the water must be blown off after the test. When the hydrostatic test is not possible, it can be tested with compressed air.
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
If you want to have more information about the article or you want to share your opinion with us, contact us at firstname.lastname@example.org
Please notice that you might be interested in the other technical articles we’ve published:
- Sealing Tests for Valves
- What are valves
- Nine Anti-Corrosion Measures of Valves
- The Selection of Control Valve
- Operation and Maintenance Manuals for Gate Valves
- When the control valves are used in liquid service
- Choosing Valves Based on Industry Characteristics
- Designs and Uses of Ball Valves for Submarine Pipelines
- What is a ball valve
- How to choose valves
- What are ball valves