Standards, Specifications, Common Problems, Solutions, and Industry Application Characteristics of Flange Gaskets
Domestic standard GB/T 9126-2020 "Non metallic Flat Gaskets for Pipe Flanges"; GB/T 13403-2013 "Gaskets for Large Diameter Carbon Steel Pipe Flanges"; HG/T 20610-2009 (Ministry of Chemical Industry Standard), SH/T 3407-2018 (Petroleum Standard).
There is a certain difference in flange gasket size between the American standard (ASME B16.20) and the national standard (GB/T 9126) when comparing size standards at home and abroad. Taking DN100 flange gasket as an example, the outer diameter of the American standard gasket may be 152mm, while the national standard is 155mm. In international trade or foreign-related projects, it is necessary to strictly check the standards to avoid installation problems caused by size discrepancies. The European standard (EN 1514-3) has clear requirements for the compression and rebound testing methods of non-metallic gaskets, requiring a compression rate of 10% -30% and a rebound rate of ≥ 40%. The national standard has similar requirements for some indicators, but the testing details are slightly different.
When selecting gaskets, it is necessary to follow the corresponding standards for quality control based on the project location or customer requirements. In a multinational petrochemical project, the selection of pipeline flange gaskets must meet both ASME B16.20 (American standard) and HG/T 20610-2009 (Ministry of Chemical Industry standard). For high-temperature hydrogen pipelines, 316L stainless steel flexible graphite wrapped gaskets were ultimately selected, and their dimensions and performance parameters were strictly designed, manufactured, and inspected according to dual standards to ensure the smooth implementation of the project.
International standard ASME B16.20 (American standard metal gasket). EN 1514-3 (European standard non-metallic gaskets); JIS B2404 (Japanese standard gasket).
Common problems and solutions
Improper selection of gaskets for leakage reasons (such as choosing rubber gaskets that harden at low temperatures). Insufficient or uneven pre-tightening force of bolts. Flange deformation (large temperature difference or installation stress).
Gasket aging, corrosion, and wear.
Leakage detection method visual inspection: Regularly check whether there are any traces of medium leakage at the flange connection. If liquid leakage occurs, droplets or flow marks may form on the flange surface, and gas leakage may be accompanied by white mist (condensation of water vapor).
Ultrasonic testing: using an ultrasonic leak detector to detect high-frequency sound waves generated by leaks, the leak point can be quickly located without touching the flange, especially suitable for high-pressure and toxic gas pipelines.
Pressure drop detection: for closed systems, the presence of leaks is determined by monitoring changes in system pressure. If the pressure drops beyond the specified value within a certain period of time, there may be a leak.
Temporary plugging method for minor leakage: injection of glue under pressure (requires professional tools).
Emergency situation: temporary replacement of higher specification gaskets (such as using metal wrapped gaskets instead of rubber gaskets).
Principle of pressure sealing technology: inject sealing agent into the flange gap through a dedicated fixture to form a new sealing structure. Sealing agents are generally polymer materials with good plasticity and sealing properties.
Application scenario: it is suitable for temporary treatment of medium leaks with a pressure not exceeding 2.5MPa and a temperature not exceeding 200 ℃, such as when the pipeline has a slight leak but cannot be shut down for maintenance.
For metal gaskets with minor damage (such as surface scratches), repair and reuse can be achieved through grinding and polishing. If non-metallic gaskets are partially damaged, they can be cut and spliced without affecting the overall sealing performance, but the repaired gaskets must undergo strict sealing performance testing before use.
Visual inspection of gasket replacement timing: When the gasket shows obvious corrosion, cracks, deformation, or severe wear on the sealing surface, it needs to be replaced immediately.
Performance degradation: when the sealing performance of the gasket is found to have decreased through leakage detection and cannot be improved through methods such as thermal tightening, the gasket should be replaced. For example, after one to two years of use, rubber gaskets become hardened due to aging, significantly reducing their sealing performance and requiring timely replacement.
Improper gasket selection case:
A chemical plant used ordinary rubber gaskets for pipelines transporting benzene, which would dissolve the rubber and cause the gaskets to quickly fail and leak. The correct selection should be oil resistant nitrile rubber gaskets or polytetrafluoroethylene gaskets.
Preventive measures: establish a database of medium gasket materials, strictly screen gaskets based on the characteristics of the medium during selection, and conduct simulation tests if necessary.
Case study on bolt pre-tightening force: during the installation of a pipeline, the pre-tightening force of the bolts was uneven. Some bolts had excessive torque, causing the gasket to collapse locally, while others had insufficient torque to seal, ultimately resulting in leakage.
Solution: Use a torque wrench to precisely control the pre tightening force, strictly follow the symmetrical tightening sequence, and perform torque re inspection after installation.
The compression ratio of the gasket after installation is usually 10% to 30% of the reduction in gasket thickness compared to the original thickness. If it is too large, it is prone to failure, and if it is too small, the seal is not tight.
The ability of the rebound rate gasket to recover thickness after unloading, and a high rebound rate results in a long-lasting seal (metal wrap gasket rebound rate>70%).
Industry application characteristics
In the chemical industry, which is highly corrosive and subjected to high temperatures and pressures, PTFE coated pads and metal wrapped pads (316L tape+ graphite) are commonly used. In the ethylene cracking unit, the temperature of the quench oil pipeline is 200 to 300 ℃, the pressure is 1.0 ti 1.5MPa, and the medium is corrosive and prone to coking. Using 316L stainless steel flexible graphite wrapped gasket and spraying anti-coking coating on the surface of the gasket effectively prolongs the service life of the gasket and reduces the number of parking inspections caused by leakage.
Special requirements for the power industry: In the main steam pipeline of the conventional island of a nuclear power plant, the pressure is 6 to 7 MPa and the temperature is 300 to 350 ℃, with extremely high requirements for sealing and safety.
Metal toothed gaskets are used in conjunction with concave convex flanges, and an online leakage monitoring system is equipped to monitor the sealing status of the gaskets in real time, ensuring the safe and stable operation of the nuclear power plant.
Summary: oil and gas, high pressure, flammable and explosive, metal ring pads and toothed pads are preferred.
Food and medicine: hygiene grade requirements, using EPDM and silicone rubber pads, with a smooth and pore free surface.
Power industry: for high-temperature steam pipelines, graphite winding pads and metal waveform pads are selected.
Refrigeration system: for low-temperature conditions, choose nitrile rubber or fluororubber pads (resistant to refrigerant corrosion).
