Tightening Methods and Requirements for Flange Bolts and Nuts
Tightening Methods and Requirements for Flange Bolts and Nuts
What are flange bolts and nuts? The flange bolts and nuts are one type of fastener mainly composed of a hexagonal head, a flange plate (the gasket below the hexagon is fixed together with the hexagon), and bolts and nuts (one cylindrical body with external threads). It needs to be matched with a nut and used to tighten and connect two parts with through holes. This type of connection is called bolt connection. If the nut is unscrewed from the bolt, it can separate these two parts. Therefore, the bolt connection is a detachable connection. Flange bolts are a common type of fastener. They are widely used in highway and railway bridges, including industrial and civil construction, cranes, excavators and other heavy machinery, with a wide range of applications.
Classification of flange bolts and nuts
1. Hexagonal flange types:
There are two types of hexagonal heads. One is flat headed and the other is concave headed.
2. Surface color category:
According to different needs, the surface is coated with dacromet that is white, military green, colored yellow, and will never rust.
3. Category of flanges:
Depending on the location of use of flange bolts and nuts, the size requirements for the disc vary. There are also flat bottomed and toothed types, with toothed ones serving as anti-slip agents.
4. According to the force distribution of the connection, there are ordinary and hinged holes. The flange bolts and nuts used for hinged holes should match the size of the holes. They are used when subjected to lateral forces. In addition, to meet the need for locking after installation, there are holes in the rod, which can prevent the bolt from loosening when subjected to vibration. Some flange bolts without threads need to be made thin, called thin rod flange bolts. This type of flange bolt is conducive to connection under variable forces. There are specialized high-strength bolts on the steel structure. The head will be made larger, and the size will also change.
Common materials for flange bolts and nuts
1. High carbon steel C%>0.45%. The material of hexagonal flange bolts and nuts is currently not widely used in the market.
2. Medium carbon steel 0.25% hex head bolts and nuts are commonly referred to as 35 # and 45 # steel in China, and commonly referred to as 1035, CH38F, 1039, 40ACR, etc. in foreign countries. It is mainly used for grade 8 nuts, grade 8.8 bolts, and grade 8.8 hexagonal products.
3. Low carbon steel with C% ≤ 0.25% is commonly referred to as A3 steel in China. It is commonly referred to as 10081015181022 in foreign countries. It's mainly used for grade 4.8 bolts, grade 4 nuts, small bolts and nuts and other products without hardness requirements. (Note: The drilling tail nail is mainly made of 1022 material.)
4. Alloy steel: Adding alloying elements to ordinary carbon steel increases some special properties of the steel, such as 35, 40 chromium molybdenum, SCM435 and 10B38. Hexagonal flange bolts are mainly made of SCM435 chromium molybdenum alloy steel, with main components including C, Si, Mn, P, S, Cr, and Mo.
Tightening methods and requirements for flange bolts and nuts
1. No torque ring wrench or hammer wrench.
It is suitable for fastening general equipment and pipeline flanges, selected according to the size of bolts and nuts and flange pressure rating. The tightening requirements are as follows.
1) The maintenance unit shall develop a fastening plan, symmetrically tighten the flanges, and number them in the tightening sequence.
2) Use four bolts and nuts to position the gasket at positions 1, 2, 3, and 4, ensuring that the center of the wound gasket is within the edge of the flange.
3) Tighten the positioning bolts and nuts by hand, then insert other stud bolts and nuts and tighten them to balance the load, ensuring that at least 2 threads are exposed at each end of the nut.
4) According to the on-site equipment and flanges, the calculation should be based on tightening one circle at a time. The number of tightening times (at least 3 times) and the impact load (force) for each tightening should be reasonably determined. The impact load (force) should be tightened in order from small to large (such as 50%, 80%, 100% increase), and the load should not be loaded too quickly or too large to prevent gasket sealing failure.
5) The sequence of each tightening of a torque free ring wrench or hammer wrench.
a. Tighten the two radially opposite bolts and nuts to the predetermined hammering load (force) of the bolts and nuts.
b. Tighten another pair of bolts and nuts approximately 90 degrees apart from the previous two bolts and nuts along the circumference.
c. Continue tightening until all other bolts and nuts are tightened to the predetermined hammer load.
Finally, tighten all bolts and nuts in a clockwise or counterclockwise direction at 100% hammer load (force).
1. Torque wrench
It is suitable for important equipment and pipeline flanges such as high temperature and pressure, flammable and explosive materials. The tightening requirements are as follows.
1) The maintenance unit needs to develop a fastening plan, develop appropriate torque, and design a review based on parameters such as the strength of bolts and nuts, initial sealing pressure of the gasket, working sealing pressure, medium pressure, etc. We want to prevent breakage of bolts and nuts and gasket loss of elasticity due to excessive tightening force, resulting in sealing failure.
2) Tighten the flanges symmetrically and number them in the tightening sequence.
3) Use four bolts and nuts to position the gasket at positions 1, 2, 3, and 4, ensuring that the center of the wound gasket is within the edge of the flange.
4) Tighten the positioning bolts and nuts by hand, then insert other stud bolts and nuts and tighten them to balance the load, ensuring that at least 2 threads are exposed at each end of the nut.
5) Based on the on-site equipment and flanges, the calculation should be based on tightening one circle at a time, and the number of tightening times (at least 3 times) and each tightening torque should be reasonably determined. The tightening torque should be tightened in order from small to large (such as 50%, 80%, 100% increase), and the load should not be loaded too quickly or too large to prevent gasket sealing failure.
6) The sequence of torque wrench tightening each time
a. Tighten the two radially opposite bolts and nuts to the predetermined torque of the bolts and nuts.
b. Tighten another pair of bolts and nuts approximately 90 degrees apart from the previous two bolts and nuts along the circumference.
c. Continue tightening until all other bolts and nuts are tightened to the specified torque.
7) Finally, tighten all bolts and nuts in a clockwise or counterclockwise direction at 100% torque value.
8) Record the torque value as a reference for future maintenance.
1. The stretcher of bolts and nuts
It is suitable for important equipment and pipeline flanges such as high temperature and pressure, flammable and explosive materials. The tightening requirements are as follows.
1) The maintenance unit formulates a fastening plan, formulates appropriate tensile strength, and conducts design reviews based on parameters such as the strength of bolts and nuts, initial sealing pressure of the gasket, working sealing pressure, and medium pressure to prevent the breakage of bolts and nuts and gasket loss of elasticity due to excessive clamping force, resulting in sealing failure.
2) When tightening bolts and nuts individually (in steps) with a stretcher of bolts and nuts, follow the principle of the tightening uniformity of bolts and nuts and refer to the tightening sequence of a torque wrench for tightening.
3) The stretching and tightening process of the stretcher of bolts and nuts involves a reasonable number of stretching and tightening cycles. The pressure is applied sequentially from small to large (such as 50%, 80%, 100%), evenly, and after each increase in pressure, it should be stabilized before increasing to avoid excessive impact tension that may affect the pre-tightening effect of the bolts and nuts.
4) Record the pressurization value as a reference for future maintenance.
What are flange bolts and nuts? The flange bolts and nuts are one type of fastener mainly composed of a hexagonal head, a flange plate (the gasket below the hexagon is fixed together with the hexagon), and bolts and nuts (one cylindrical body with external threads). It needs to be matched with a nut and used to tighten and connect two parts with through holes. This type of connection is called bolt connection. If the nut is unscrewed from the bolt, it can separate these two parts. Therefore, the bolt connection is a detachable connection. Flange bolts are a common type of fastener. They are widely used in highway and railway bridges, including industrial and civil construction, cranes, excavators and other heavy machinery, with a wide range of applications.
Classification of flange bolts and nuts
1. Hexagonal flange types:
There are two types of hexagonal heads. One is flat headed and the other is concave headed.
2. Surface color category:
According to different needs, the surface is coated with dacromet that is white, military green, colored yellow, and will never rust.
3. Category of flanges:
Depending on the location of use of flange bolts and nuts, the size requirements for the disc vary. There are also flat bottomed and toothed types, with toothed ones serving as anti-slip agents.
4. According to the force distribution of the connection, there are ordinary and hinged holes. The flange bolts and nuts used for hinged holes should match the size of the holes. They are used when subjected to lateral forces. In addition, to meet the need for locking after installation, there are holes in the rod, which can prevent the bolt from loosening when subjected to vibration. Some flange bolts without threads need to be made thin, called thin rod flange bolts. This type of flange bolt is conducive to connection under variable forces. There are specialized high-strength bolts on the steel structure. The head will be made larger, and the size will also change.
Common materials for flange bolts and nuts
1. High carbon steel C%>0.45%. The material of hexagonal flange bolts and nuts is currently not widely used in the market.
2. Medium carbon steel 0.25% hex head bolts and nuts are commonly referred to as 35 # and 45 # steel in China, and commonly referred to as 1035, CH38F, 1039, 40ACR, etc. in foreign countries. It is mainly used for grade 8 nuts, grade 8.8 bolts, and grade 8.8 hexagonal products.
3. Low carbon steel with C% ≤ 0.25% is commonly referred to as A3 steel in China. It is commonly referred to as 10081015181022 in foreign countries. It's mainly used for grade 4.8 bolts, grade 4 nuts, small bolts and nuts and other products without hardness requirements. (Note: The drilling tail nail is mainly made of 1022 material.)
4. Alloy steel: Adding alloying elements to ordinary carbon steel increases some special properties of the steel, such as 35, 40 chromium molybdenum, SCM435 and 10B38. Hexagonal flange bolts are mainly made of SCM435 chromium molybdenum alloy steel, with main components including C, Si, Mn, P, S, Cr, and Mo.
Tightening methods and requirements for flange bolts and nuts
1. No torque ring wrench or hammer wrench.
It is suitable for fastening general equipment and pipeline flanges, selected according to the size of bolts and nuts and flange pressure rating. The tightening requirements are as follows.
1) The maintenance unit shall develop a fastening plan, symmetrically tighten the flanges, and number them in the tightening sequence.
2) Use four bolts and nuts to position the gasket at positions 1, 2, 3, and 4, ensuring that the center of the wound gasket is within the edge of the flange.
3) Tighten the positioning bolts and nuts by hand, then insert other stud bolts and nuts and tighten them to balance the load, ensuring that at least 2 threads are exposed at each end of the nut.
4) According to the on-site equipment and flanges, the calculation should be based on tightening one circle at a time. The number of tightening times (at least 3 times) and the impact load (force) for each tightening should be reasonably determined. The impact load (force) should be tightened in order from small to large (such as 50%, 80%, 100% increase), and the load should not be loaded too quickly or too large to prevent gasket sealing failure.
5) The sequence of each tightening of a torque free ring wrench or hammer wrench.
a. Tighten the two radially opposite bolts and nuts to the predetermined hammering load (force) of the bolts and nuts.
b. Tighten another pair of bolts and nuts approximately 90 degrees apart from the previous two bolts and nuts along the circumference.
c. Continue tightening until all other bolts and nuts are tightened to the predetermined hammer load.
Finally, tighten all bolts and nuts in a clockwise or counterclockwise direction at 100% hammer load (force).
1. Torque wrench
It is suitable for important equipment and pipeline flanges such as high temperature and pressure, flammable and explosive materials. The tightening requirements are as follows.
1) The maintenance unit needs to develop a fastening plan, develop appropriate torque, and design a review based on parameters such as the strength of bolts and nuts, initial sealing pressure of the gasket, working sealing pressure, medium pressure, etc. We want to prevent breakage of bolts and nuts and gasket loss of elasticity due to excessive tightening force, resulting in sealing failure.
2) Tighten the flanges symmetrically and number them in the tightening sequence.
3) Use four bolts and nuts to position the gasket at positions 1, 2, 3, and 4, ensuring that the center of the wound gasket is within the edge of the flange.
4) Tighten the positioning bolts and nuts by hand, then insert other stud bolts and nuts and tighten them to balance the load, ensuring that at least 2 threads are exposed at each end of the nut.
5) Based on the on-site equipment and flanges, the calculation should be based on tightening one circle at a time, and the number of tightening times (at least 3 times) and each tightening torque should be reasonably determined. The tightening torque should be tightened in order from small to large (such as 50%, 80%, 100% increase), and the load should not be loaded too quickly or too large to prevent gasket sealing failure.
6) The sequence of torque wrench tightening each time
a. Tighten the two radially opposite bolts and nuts to the predetermined torque of the bolts and nuts.
b. Tighten another pair of bolts and nuts approximately 90 degrees apart from the previous two bolts and nuts along the circumference.
c. Continue tightening until all other bolts and nuts are tightened to the specified torque.
7) Finally, tighten all bolts and nuts in a clockwise or counterclockwise direction at 100% torque value.
8) Record the torque value as a reference for future maintenance.
1. The stretcher of bolts and nuts
It is suitable for important equipment and pipeline flanges such as high temperature and pressure, flammable and explosive materials. The tightening requirements are as follows.
1) The maintenance unit formulates a fastening plan, formulates appropriate tensile strength, and conducts design reviews based on parameters such as the strength of bolts and nuts, initial sealing pressure of the gasket, working sealing pressure, and medium pressure to prevent the breakage of bolts and nuts and gasket loss of elasticity due to excessive clamping force, resulting in sealing failure.
2) When tightening bolts and nuts individually (in steps) with a stretcher of bolts and nuts, follow the principle of the tightening uniformity of bolts and nuts and refer to the tightening sequence of a torque wrench for tightening.
3) The stretching and tightening process of the stretcher of bolts and nuts involves a reasonable number of stretching and tightening cycles. The pressure is applied sequentially from small to large (such as 50%, 80%, 100%), evenly, and after each increase in pressure, it should be stabilized before increasing to avoid excessive impact tension that may affect the pre-tightening effect of the bolts and nuts.
4) Record the pressurization value as a reference for future maintenance.