1. Start with your service conditions

Write down your operating conditions before you compare flange options:

• Design pressure and temperature, which set the pressure class you need.
• Fluid and environment, such as hydrocarbons, chemicals, seawater, or cryogenic service like LNG.
• Pipe size and schedule of the line the flange will slide over.
• Mating flange face and gasket type already used in the system.
• Inspection and documentation required by your project specification.

The product page describes the slip-on flange as suited to low to medium pressure systems in the oil, gas and chemical sectors. Use that as your first fit check.

2. Pressure class: where a slip-on flange fits

The listed scope runs from ASME B16.5 Class 150 to Class 2500, and the page also lists ASME B16.47 Class 75 to 900. The same page calls slip-on flanges the economic choice for Class 600 and below. It says this is because they use less material and need simpler processing.

In practice:

• Class 150 to 600, low to medium pressure lines: this is where the supplier positions the slip-on design as the cost-effective option.
• Higher classes: the class range is listed, but the product material itself points to low and medium pressure service. For high-pressure, high-cycle or critical service, compare the design against a weld neck flange and check what your project code or engineer requires.

3. Nominal pipe size, including 3, 4 and 8 inch

The listed size range is 1/2" (15 mm) to 60" (1500 mm). Common sizes such as a 3 slip on flange, 4 slip on flange or 8 slip on flange fall inside this range. The listing covers both B16.5 and B16.47, so confirm which standard applies to your size and class before you order. This matters most for large diameters.

The page gives one thickness example for NPS 4": 12.7 mm for Class 150 and 19.1 mm for Class 300. Check flange thickness, outside diameter, bolt circle and bore against the dimension table in the edition of ASME B16.5 your project uses. Then ask the supplier to confirm the values on the drawing or quotation.

4. Material grade

Three material options are listed. Each one suits a different service condition:

The temperature figures above are material-level values from the product page. They are not pressure ratings. The allowable working pressure at a given temperature depends on both the material group and the pressure class. Confirm it against the pressure–temperature ratings in ASME B16.5.

5. Sealing face type

The listed face options are Flat Face (FF), Raised Face (RF), Male-Female (MFM) and Tongue-Groove (TG). Match the face to the mating flange and the gasket. A mismatched face can make a joint hard to seal even when everything else is correct. The supplier lists machining tolerances of flatness ≤0.05 mm/m and hole position ±0.3 mm, with CNC monitoring of sealing face flatness and bolt-hole position.

6. Testing, traceability and quality controls

• Testing: 100% MT (magnetic particle) for neck welds, UT (ultrasonic) for Class 1500, and hydrostatic testing. The stated hydrostatic test is 1.5x design pressure with a 30-minute leak-free hold.
• Raw material checks: spectral analysis to verify Cr/Ni content and material grade before production.
• Forging: open die forging for NPS ≤12".
• Heat treatment: normalization at 890–920℃ for carbon steel.
• Threads: ASME B1.1 Unified National Coarse (UNC).

These are process descriptions, not third-party certifications. If you need mill test certificates, third-party inspection or specific approvals, put that in your inquiry and ask for the documents to be confirmed in writing.

7. Slip-on vs. weld neck: when the recommendation does not apply

The supplier says the slip-on design allows faster alignment and simpler outer fillet welding than weld-neck types, and uses less material. That makes it a practical choice for many low and medium pressure lines.

An ASME B16.5 slip on flange may not be the right choice when:

• your project specification requires weld neck flanges for the service or class;
• the line runs at high pressure or high class beyond what the supplier positions as economical (above Class 600);
• the joint sees conditions your engineer judges to need a butt-welded connection;
• the material, size or face type you need is not among the listed options.

In these cases, check the alternatives with your piping engineer before you request a quote.

Quick selection checklist

1. Confirm design pressure and temperature, then choose the class.
2. Confirm NPS and the governing standard (B16.5 or B16.47).
3. Choose A105, F304/F316 or LF2 to suit the media and temperature.
4. Match the face type (FF, RF, MFM, TG) to the mating flange and gasket.
5. Check dimensions against the ASME B16.5 tables.
6. State testing and documentation requirements in your inquiry.
7. Ask for price, lead time and any certifications in writing. They are not covered here.

For the full published specification, see the ASME B16.5 Slip On Flange product page.