January 26, 2026
A slip on flange is a universal connecting fitting for industrial pipelines. Its sealing performance directly determines the safety of pipeline medium transportation, and the acceptance standards are the core basis for ensuring the proper installation and long-term stable operation of the flange. The following clarifies the application specifications of slip-on flange from two aspects: core sealing requirements and full-process acceptance standards, which are suitable for pipeline construction and acceptance scenarios in municipal engineering, the chemical industry, water supply and drainage, and other industries.
1. Qualified sealing surface accuracy: The sealing surface of the slip on flange shall be flat without defects such as scratches, air holes, and cracks, with the concave-convex error not exceeding the specified value. It shall make uniform contact with the sealing gasket to prevent medium leakage caused by irregular surface shape.
2. Proper gasket matching: Select suitable gaskets such as rubber, asbestos, and metal wound gaskets according to the pipeline working pressure, conveyed medium, and operating temperature. The gasket size shall be precisely matched with the flange sealing surface without eccentric or overlapping installation to ensure a good sealing fit.
3. Uniform connection stress: Maintain coaxial alignment when butting flanges, and tighten the bolts evenly diagonally, ensuring the tightening torque meets the requirements of the corresponding flange specifications. Avoid gasket damage due to over-tightening and sealing gaps due to under-tightening, and prevent flange deformation caused by uneven stress, which may affect the sealing effect.
4. Auxiliary welding sealing: Ensure full welding at the slip-on welding position without slag inclusion, incomplete welding, and weld bumps. The weld bead shall be smoothly connected with the flange and pipe material. Reliable welding reduces the leakage risk at the joint of the pipeline and flange, and helps to improve the overall sealing performance.
(I) Appearance and Dimension Acceptance
1. The body of the slip on flange shall be free from quality problems such as deformation, corrosion, and cracks. Dimensional parameters, including flange inner diameter, outer diameter, sealing surface diameter, and bolt hole spacing, shall comply with the national industrial pipeline flange standards with deviations within the allowable range.
2. After welding, the weld bead shall be flat in appearance without defects such as missing weld and air holes. The perpendicularity deviation of welding between the flange and pipe material shall be ≤1.5‰ to avoid adverse effects on subsequent sealing and pipeline operation caused by installation deviation.
(II) Sealing Performance Acceptance
1. Hydrostatic/pneumatic test: Conduct a tightness pressure test in accordance with the pipeline's design pressure. A flange is considered to be properly sealed if there is no leakage or pressure drop at the sealing surface and welding position during the pressure-holding period.
2. Static sealing inspection: Conduct a normal-state sealing inspection after the pressure test is qualified. There shall be no trace of medium leakage at the contact between the flange sealing surface and the gasket, no bolt loosening, and no deformation or damage of the gasket.
(III) Installation, Adaptation, and Acceptance
1. The butting gap of flanges shall be uniform, and the parallelism deviation of the sealing surfaces of adjacent slip on flanges shall comply with the specifications without obvious dislocation. All bolts shall be completely installed with specifications matching the flanges, without thread slipping or loosening.
2. Recheck the flange sealing position in the initial operation stage of the pipeline (72 hours). Confirm no medium leakage at the sealing position, no flange deformation, and no torque attenuation of bolts, meeting the sealing requirements for long-term operation.
(IV) Document Acceptance
Provide product qualification certificates, material inspection reports, welding process records, pressure test reports, and other documents of slip on flange during acceptance to ensure the traceability of product quality and construction process. Acceptance shall not be passed if the documents are incomplete or unqualified.
