Octagonal metal ring gasket (groove) processing and sealing research

Octagonal metal ring gasket is widely used in petrochemical, shipbuilding, nuclear power, heavy machinery and other industries; our company every year will manufactures more than one set of equipment using octagonal metal ring gasket, but how to ensure that the octagonal metal ring gasket once through the manufacturing process of the pressure test, especially after the equipment to the owner of the installation site disassembly and inspection, how to once through the installation of the site of the pressure test, but has always been troubled by the subject of ours. With the company’s winding tube heat exchanger applications continuing to expand and the development of large-scale, octagonal metal ring gasket size specifications increasing to ensure that the seal is more of a problem.

1. Introduction of octagonal metal ring gasket

Octagonal metal gasket sealing surface according to the technical requirements of machining, octagonal groove, gasket center distance of ± 0.18mm tolerance, sealing bevel angle of ± 0.5 ° tolerance. According to the provisions of SH3501 pipeline installation, flange ring groove sealing surface and metal ring gasket for contact line check. In order to meet the technical requirements of mechanical processing, the requirements of octagonal groove and octagonal metal ring gasket sealing surface on both sides of the rotation of 90 ° orientation, the sealing surface must be all continuous contact. In the octagonal metal ring gasket center distance negative deviation, octagonal groove center distance positive deviation, although to meet the machining inspection requirements, but cannot meet the requirements of the field pipeline installation, the machining of higher requirements.

2. Processing of ring groove sealing surface

Ring groove sealing surface, drawing octagonal groove, gasket center distance has a tolerance of 0.18mm, sealing bevel angle has a tolerance of 0.5 °. Still, the test pressure of 250KG or more and gasket width of 40 or more of the octagonal metal ring gaskets, to a certain extent, lost the role of the self-tightening. In the process of processing, often due to the slot center distance angle of the positive deviation and octagonal metal ring gasket center distance angle of the negative deviation of the sealing line near the bottom of the octagonal groove, resulting in the beginning of the test pressure sealing line in the inner, to be increased to the pressure of the gasket expansion, the sealing line from the inner to the outer side of the transfer process caused by the test pressure leakage. So, in the gold processing octagonal groove and gasket are used to control the center distance and angle tolerance band.

Flange octagonal groove machining control dimensions.

Octagonal metal ring gasket in the pressure process for the expansion of the sealing surface of the outward extrusion process. So, the center distance of the gasket is required to take the positive deviation. Octagonal metal ring gasket sealing surface for the line contact, so the gasket sealing surface inclination to take the positive deviation, in order to make the sealing of the line contact position near the top of the groove octagonal groove.

Octagonal metal ring gasket machining control dimensions.

3. Octagonal metal gasket sealing surface in the test pressure before the control requirements

(1) In the octagonal groove, machining is completed before the test pressure in order to ensure that the sealing surface of the fit performance must be on the octagonal groove grinding. Octagonal groove test pressure is completed, often due to the hardness; test pressure tire on the sealing surface caused by the second damage must be the octagonal groove for the second grinding before leaving the factory.

Grinding tire production: octagonal groove in machining after cast iron grinding (not allowed to use 16Mn carbon steel instead), grinding tire processing center distance and angle should be close to the 0 position in order to increase the grinding contact surface. The grinding tire ring width size than the octagonal metal ring gasket width of 5mm, grinding tire ring top width than the octagonal metal ring gasket top width of 2mm. So as to ensure that the grinding sealing surface of an effective role in the size and finish and to ensure that the tire is repeated use.

Grinding process control: in the octagonal groove grinding, three people need to work together: two people to do the circumferential movement of the tire and a person to control the longitudinal force of the grinding tire. In the grinding sand, check the tire contact surface to prevent foreign objects from extrusion and damaging the sealing surface.

(2) According to the petrochemical department requirements of the metal ring gasket material hardness value should be lower than the flange material hardness value of HB30-40; surfacing welding flange sealing surface hardness and octagonal metal ring gasket hardness is similar to the octagonal metal ring gasket caused by the test pressure did not occur in the octagonal metal ring gasket has not been self-tightening deformation of the flange octagonal groove sealing surface subsidence. Surfacing octagonal groove flange in the transition layer after surfacing without processing arrangements, resulting in an uneven thickness of the surface layer and the sealing surface hardness phenomenon.

Due to the principle of octagonal metal ring gasket test pressure, the test pressure before the octagonal metal ring gasket inspection, including hardness, dimensional data and octagonal metal ring gasket surface defects (knock marks, chip tumors).

4. Ring groove sealing surface inspection control requirements

Qualified octagonal metal ring gasket/ring joint surface (RJ) sealing surface according to SH3501 for the contact line check. To meet the unilateral sealing surface of all continuous contact, some users and supervisory requirements on both sides of the sealing surface must be all continuous contact, undoubtedly improving the octagonal metal ring gasket/ring joint surface (RJ) sealing surface inspection requirements. In order to meet user requirements, the need to take special measures in machining so that the octagonal metal ring gasket/ring connecting surface (RJ) sealing surface of the center distance deviation is close to “0”.

(1) General project inspection requirements

According to the octagonal metal ring gasket interview pressure principle, the octagonal metal ring gasket, including hardness, surface roughness, and octagonal metal ring gasket surface defects (knock marks, chip tumors) test.

Octagonal metal ring gasket test requirements:

• 1) Hardness requirements: requirements in line with the technical requirements of an octagonal metal ring gasket, and hardness should be uniform and should be avoided filler welding.
• 2) Surface roughness requirements: test octagonal metal ring gasket sealing surface roughness;
• 3) Defects inspection: octagonal metal ring gasket sealing surface visual and feel test to prevent the sealing surface on the knock, processing chip tumors scratching the sealing surface.

(2) Provide molds

On the basis of the provisions of SH3501, the implementation of more stringent requirements of the company, with standard octagonal ring gasket/ring mold acceptance of octagonal metal ring gasket/ring connecting surface (RJ) sealing surface. The ring joint surface (RJ) and the standard metal ring gasket are inspected for contact lines on both sides, and the octagonal metal ring gasket is inspected for contact lines with the standard ring joint surface (RJ).

Standard octagonal metal gasket sealing surface coated with coloring agent (red Dan, etc.), into the octagonal ring to be inspected to connect the surface (RJ), rotate 45 ° orientation, the ring connecting surface (RJ) should meet the contact line inspection of the two sides of the sealing surface of all the same time continuous contact requirements, as a qualification basis for the octagonal ring connecting surface (RJ).

To be tested octagonal metal gasket sealing surface coated with coloring agent (red Dan, etc.), into the standard octagonal ring joint surface (RJ), rotate 45 ° orientation, octagonal ring joint surface (RJ) should meet the contact line to check the sealing surface on both sides of all the same time continuous contact requirements, as a qualified basis for the octagonal metal gasket sealing surface.

(3) Does not provide molds

In the absence of processing mold conditions, in order to ensure the sealing performance of the octagonal metal ring gasket/ring joint (RJ) sealing surface, the company put forward higher requirements on the tolerance of the key dimensions. In the octagonal metal ring gasket/ring joint (RJ) sealing surface, the center distance of the drawings generally has a tolerance of ± 0.18mm and a sealing bevel angle of ± 0.5 ° tolerance.

In order to make the sealing surface contact on the outside, to avoid the installation of metal ring gasket damage flange ring connecting surface (RJ) sealing surface, to improve service life, the center distance between the two by the original ± 0.18mm, adjusted to the octagonal metal ring gasket +0.18mm, ring connecting surface (RJ) for the -0.18mm. the two angular tolerance by the original 23 ° ± 0.5 °, adjusted to the octagonal metal ring gasket 23 ° ± 0.5 °, adjusted to the octagonal metal ring gasket 23 ° +0.5 °, sealing bevel angle tolerance. +0.5°, ring joint surface (RJ) 23°-0.5°.

Author: Mao Yun