Things to note when purchasing pipe flanges

When purchasing pipe flanges, it is necessary to comprehensively consider technical parameters, material standards, supplier qualifications and other factors to ensure the quality, applicability and economy of the flanges. The following are key considerations:

1. Clarify technical parameters

Pipeline system requirements:
The pressure level (such as PN10, PN16 or Class150, Class300) must match the system design pressure.
The flange diameter (DN) is consistent with the pipe size to avoid installation mismatch.
The sealing surface type (RF raised face, FF flat surface, RTJ ring connection, etc.) must be compatible with the connected equipment.

Temperature range: The material must adapt to the working temperature (stainless steel is selected for high temperature, and anti-brittle cracking materials are required for low temperature).

2. Material selection

Common materials:
Carbon steel (Q235, A105): general working conditions, low cost.
Stainless steel (304, 316): corrosion resistance, high temperature environment.
Alloy steel (16Mn, CrMo steel): high pressure and high temperature conditions (such as petrochemical).

Standard compliance:
American standard (ANSI/ASME B16.5), European standard (EN 1092-1), Chinese standard (GB/T 9119), etc., to ensure consistency with existing system standards. Select high-strength and corrosion-resistant materials that meet ASTM, EN and other standards, such as carbon steel (such as ASTM A105) and stainless steel (such as ASTM A182 F316) ‌

3. Flange type and connection method

Choose the appropriate flange type according to the usage scenario.

Type selection:
Plate flat welding flange (PL): Suitable for simple and quick connection occasions, such as low-pressure pipelines, and easy installation.
Butt welding flange (WN): Suitable for applications requiring high-strength connection, such as high pressure and high vibration occasions, with high flange strength.
Loose flange (LJ): Easy to align, suitable for frequent disassembly.
Threaded flange (TH): Suitable for frequent disassembly and reinstallation ‌

Bolt hole matching: Confirm that the number and diameter of flange bolt holes are consistent with the mating flange.

4. Supplier Qualification and Quality Control

Choose a qualified, technically competent and advanced manufacturing manufacturer to ensure that the quality of the flange meets the pressure requirements and avoid safety accidents.

Certification requirements:
The supplier must have ISO 9001 and special equipment manufacturing license (such as TS certification for pressure vessel flanges).
Material report (MTC) and third-party inspection certificate (such as SGS, BV) must be provided for the material.

Quality control:
Check the flange size tolerance and sealing surface finish (Ra≤3.2μm is common).
Require a non-destructive testing report (UT/RT) or hardness test (high pressure conditions).

5. Surface treatment and anti-corrosion

Anti-corrosion requirements:
Carbon steel flanges must be galvanized, painted or epoxy coated (for corrosive environments).
Stainless steel flanges must be pickled and passivated to avoid intergranular corrosion.

Clear marking: Permanent markings such as material, pressure rating, and standard number should be marked on the flange.

6. Price and delivery cycle

Price comparison strategy: compare multiple suppliers with the same quality to avoid low-priced and low-quality products.
Delivery time: confirm whether the production cycle meets the project schedule, and urgent orders need to be negotiated in advance.
MOQ (minimum order quantity): confirm whether the supplier accepts it when purchasing in small quantities.

7. Transportation and acceptance

Packaging protection: The sealing surface needs to be protected with plastic to avoid transportation damage.

Arrival acceptance:
Check the material report and size inspection (focus on the sealing surface and thickness).
Sampling pressure test (high-pressure flanges require water pressure test reports).

8. Special working conditions precautions

Extreme environment: For example, Charpy impact test is required for low temperature, and sulfur-resistant materials (such as 316L) are selected for acidic environment.
Non-standard flanges: Detailed design drawings are required, and the supplier's processing capabilities must be confirmed.

Purchasing precautions:

Avoid mixed standards: For example, the bolt hole spacing of American standard and Chinese standard flanges is different, and they cannot be mixed.
Weld neck flange groove inspection: Ensure that the welding groove angle meets the standard (such as 37.5°±2.5°).
Stock spare: It is recommended to reserve spare flanges that are vulnerable to damage to reduce the risk of downtime.

Through the systematic verification of the above steps, the procurement risk can be significantly reduced and the long-term reliable operation of the flange can be ensured. For critical working conditions, it is recommended to conduct a technical review with the technical department and the supplier.

Read more: Standard sizes of pipe flanges or Inspection standards for pipe flanges