What causes loose connections in seamless stainless steel elbows?
The looseness of seamless stainless steel elbow connections is generally related to inherent defects in the connection structure, mechanical environmental effects, and process control errors.
Inherent defects in the connection structure:
1. Failure of flange sealing surface
The aging of sealing gaskets or corrosion caused by corrosive media can lead to seal failure, resulting in a decrease in bolt preload force. The flange misalignment exceeds the limit (>0.5mm), causing local stress concentration and accelerating damage to the sealing surface.
2. Insufficient thread engagement
The actual metal contact surface between threads only accounts for 15%, and the remaining 85% is air gap, which is prone to micro slip and loosening under vibration environment. Burrs or contaminants in thread processing hinder complete engagement and reduce anti loosening ability.
Mechanical environmental effects:
1. Vibration and impact loads
Lateral vibration: The fluid turning at the elbow generates periodic shear forces, which are more likely to cause rotational loosening than axial loads (experimental results have shown that the loosening force of lateral vibration is three times that of axial).
Low frequency high amplitude vibration: such as pump valve start stop impact, causing bolts to gradually relax in a micro slip of 0.1-0.5mm amplitude.
2. Influence of temperature stress
The difference in thermal expansion coefficient between stainless steel and carbon steel pipelines (304 stainless steel: 17.3 × 10 ⁻⁶/℃), when the temperature fluctuates by 100 ℃, a 2.1mm expansion displacement can be generated at the DN100 elbow, continuously weakening the preload force.
Under high temperature, material creep causes plastic deformation of bolts, and the pre tightening force loss rate can reach 30% of the initial value.
Process control error:
1. Improper installation operation
Insufficient or excessive pre tightening force: When the torque is less than 20% of the design value, the risk of loosening doubles, and when it exceeds 30%, the thread tooth shear failure occurs.
Failure to use washers leads to stress concentration, and the nut is embedded in the base material (irreversible if the indentation depth is greater than 0.05mm).
2. Maintain deficiencies
Failure to regularly check bolt torque (recommended to tighten every 3 months); Corrosion resistant gaskets have not been replaced in corrosive environments (such as PTFE replacing rubber).
What causes loose connections in seamless stainless steel elbows?
The looseness of seamless stainless steel elbow connections is generally related to inherent defects in the connection structure, mechanical environmental effects, and process control errors.
Inherent defects in the connection structure:
1. Failure of flange sealing surface
The aging of sealing gaskets or corrosion caused by corrosive media can lead to seal failure, resulting in a decrease in bolt preload force. The flange misalignment exceeds the limit (>0.5mm), causing local stress concentration and accelerating damage to the sealing surface.
2. Insufficient thread engagement
The actual metal contact surface between threads only accounts for 15%, and the remaining 85% is air gap, which is prone to micro slip and loosening under vibration environment. Burrs or contaminants in thread processing hinder complete engagement and reduce anti loosening ability.
Mechanical environmental effects:
1. Vibration and impact loads
Lateral vibration: The fluid turning at the elbow generates periodic shear forces, which are more likely to cause rotational loosening than axial loads (experimental results have shown that the loosening force of lateral vibration is three times that of axial).
Low frequency high amplitude vibration: such as pump valve start stop impact, causing bolts to gradually relax in a micro slip of 0.1-0.5mm amplitude.
2. Influence of temperature stress
The difference in thermal expansion coefficient between stainless steel and carbon steel pipelines (304 stainless steel: 17.3 × 10 ⁻⁶/℃), when the temperature fluctuates by 100 ℃, a 2.1mm expansion displacement can be generated at the DN100 elbow, continuously weakening the preload force.
Under high temperature, material creep causes plastic deformation of bolts, and the pre tightening force loss rate can reach 30% of the initial value.
Process control error:
1. Improper installation operation
Insufficient or excessive pre tightening force: When the torque is less than 20% of the design value, the risk of loosening doubles, and when it exceeds 30%, the thread tooth shear failure occurs.
Failure to use washers leads to stress concentration, and the nut is embedded in the base material (irreversible if the indentation depth is greater than 0.05mm).
2. Maintain deficiencies
Failure to regularly check bolt torque (recommended to tighten every 3 months); Corrosion resistant gaskets have not been replaced in corrosive environments (such as PTFE replacing rubber).