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Inspection contents of gaskets, flanges and bolts

DataTime:[2023-11-14]

I. Gasket selection and quality assurance inspection content

Design drawings and the manufacturer's overhaul manual should be reviewed before construction, and the overhaul program and implementation of overhaul should be formulated strictly according to the requirements of drawings and manuals.
Gasket selection should be based on the flange type, medium temperature, pressure, selected gasket material and type.
Do not use gaskets with sealing surface scratches, damage and other effects on the sealing effect.
Gasket receiving and installation must be in accordance with the pipeline product standards specified in the design documents as well as the construction quality acceptance standards for acceptance, and records need to witness the sampling retest must be retested.
The number of bolts reserved for dismantling flanges and heads before opening shall be at least 50%.
It is strictly prohibited to install gaskets in the case of unqualified quality pipelines and flange installation in the case of barbaric and powerful groups; it is strictly prohibited to screw the bolts to the design value of tightening torque at one time.
High temperature, high pressure, toxic, hazardous, combustible media pipeline system tightness test process, due to the treatment of leaks after the replacement of gaskets, must be re-tested and leakage test, in the re-testing and leakage test after switching to production within 24 hours to strengthen the frequency of inspection tours, leaks found in a timely manner.
If the pipeline is leaking, the pressure must be reduced to deal with the replacement or adjustment of the installation of gaskets, which is strictly prohibited from operating under pressure.
High temperature, high pressure, toxic, hazardous, combustible media piping system after the use of the gasket may appear inside the cracks and other defects shall not be reused. 
As different types of gaskets require different preloads, so gasket replacement must be recalculated flange preload.
Replacement of equipment materials or update part of the parts material must be rechecked gasket material, type and so on.
Gasket raw materials (metal and non-metallic) suppliers should be relatively fixed; gasket manufacturers should be each batch of raw materials in proportion to the sampling and with the product to provide raw material analysis reports and quality certification documents. Each batch of gaskets must provide a product quality certificate. The quality certificate shall include (but not be limited to) the following contents:
  • 1) Manufacturer's name and date of manufacture;
  • 2) The official seal of the technical (quality) inspection department of the manufacturer;
  • 3) Signature of the quality inspector and date of inspection;
  • 4) Product name, specifications, materials and implementation standards;
  • 5) Gasket performance test data and qualified conclusions;
  • 6) Other user requirements to do the inspection report.
For the use of new gaskets, gasket manufacturers must provide the form of the gasket inspection report (the report must indicate the test method, test equipment, test data identification, etc.) and should provide the type of gasket in the same type of petrochemical plant to prove the success of the use of performance.

II. Gasket installation and maintenance of the inspection content

1. Inspection of gaskets
  • Before installation, it should be reconfirmed that each gasket to be installed has its specification, type, pressure level, material and matches with the process piping pressure, temperature and medium. There must be an inspection record.
  • Confirmation of test pressure and other temporary use of gaskets must be effectively removed.
  • The gasket surface is not allowed to have mechanical damage, radial scoring, serious corrosion, inside and outside the edge of the broken and other defects.
  • The gasket should be compatible with the flange sealing surface type.
2. Inspection of bolts and nuts
  • Whether the material, type and size of bolts and nuts meet the requirements. There must be inspection records.
  • The nut on the bolt rotation should be flexible but should not shake.
  • Bolts and nuts are not allowed to have scars and burrs.
  • Threads are not allowed to be broken.
  • The bolt should not be bent.
Check whether the type of flange meets the requirements, whether the sealing surface is smooth and clean, whether there is any mechanical damage, planing, turning marks, corrosion, radial scoring, etc., and whether the unevenness of the flange is less than 0.15% of the flange outer diameter.
4. Pipe and flange installation quality inspection:
There shall be no deviation, wrong mouth, open mouth, wrong hole and so on.
5. Gasket installation
Gaskets should be installed in the work bag, with the use of pick up, not allowed to be placed anywhere, to prevent contamination with debris affecting the sealing performance.
The two flanges must be on the same centerline and parallel. It is not allowed to use bolts or pointed steel braziers inserted in the bolt holes to correct the flange so as to prevent the bolts to withstand greater stress.
The sealing surface of the flanges and the water line (sealing line) should be carefully cleaned before installation. Wrap-around gaskets are best used for flanges that do not have a dense grain-like sealing line but can also be used for flanges with a waterline (sealing line).
Only one gasket can be added between two flanges, and the method of adding more gaskets is not allowed to eliminate the defects of two flanges that see too large a gap.
The gasket must be installed correctly; the vertical installation flange gasket needs to be fixed with tape, not skew, to ensure uniform pressure but also to avoid the gasket into the pipe by the medium erosion and causing an eddy current.
According to the existing tools to tighten the nut, when the nut in the M22 below, sampling torque wrench tightening, the nut in the M27 above the wind wrench can be used. The amount of gasket tightening needs to be measured.
In order to ensure that the gasket is uniformly pressurized, the bolt should be symmetrically and evenly tightened 2-3 times, and the nut should be pre-tightened according to the cross-distribution of four points when tightening. 
In order to avoid bending the bolt when tightening the nut and jamming it when loosening, add a light pad under the nut if the back of the flange is rough.
Do not allow mixed use of bolts and leakage of gaskets.
Bolts and nuts are installed, equipment technicians are required to check the quality of the installation records, the nut installation is uniform, and the nut should have at least exposed threads.

III. Storage and use inspection of gaskets

The winding gasket uses carbon steel as a reinforcing ring winding gasket, with the surface of the color-plated or plastic spraying for rust treatment; all gaskets are used between each piece of paper as a spacer to prevent damage to the sealing surface of the gasket. Gasket box around the use of PE film protection, gaskets and gaskets with foam filling between the blocking full. Gaskets should be stored off the ground; gaskets should not be placed vertically or vertically (unless the gasket is outside the reinforcing material or reinforcing packaging); the product should not be hung in the warehouse or the site of the wall of the nails, which will cause deformation of the product's original shape, or even fall apart. Therefore, they should be stored in boxes indoors. The storage environment should be clean, ventilated and dry at room temperature, protected from sunlight and avoided close to the heat source. The winding gasket should be taken along the inner and outer diameters of the gasket and should be lightly held and put down (pay attention to the nails not touching the sealing surface). The gasket should not be picked up by "dragging" but by "carrying". After unpacking, the gasket should be used as soon as possible and placed in a clean, flat place without particles to prevent scratches on the sealing surface and the gasket quality.
When packing metal ring gaskets, they need to be coated with antirust oil and wrapped with film to ensure the loss of antirust oil during transportation and storage. Metal ring pads in the packaging should pay attention to the product's center of gravity balance and do the necessary shock-proof processing storage of products within the wooden box gap to be filled with plastic foam and other substances. Metal ring pads should be stored in a clean, dry warehouse, are strictly prohibited by moisture rain, and cannot be mixed with corrosive chemicals.
Metal ring pad storage to eliminate random stacking to avoid mutual collision and extrusion between products. Different sizes cannot be stacked together. Metal ring gaskets in use should be light to take and light to put; for larger sizes, more people should work together with the installation to avoid product collision and deformation.
Non-metallic flat gasket packaging is generally wrapped with PVC film for wrapping type packaging; all the films used for packaging shall not use materials containing chlorine ions. Store in a cool, ventilated warehouse. Keep away from fire and heat. Store separately from oxidizing agents. Please do not leave the product in the air; use polyethylene bags or wrapping paper to isolate the air, and try to store it at a temperature of 10℃-30℃ (not exceeding 37℃), avoid direct sunlight, and in a dark place.
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