The Versatility and Reliability of A350 LF2 CL2 B16.5 Carbon Steel Slip - On Forged Flanges

The A350 LF2 slip-on flange is a low-temperature carbon steel flange to ASME B16.5 that slides over the pipe and is fillet-welded on both faces. It is the economical choice for low-pressure and non-critical joints that still need certified low-temperature toughness. For the sealing face, see our flange gaskets and flange products.

What an A350 LF2 Slip-On Flange Is

A350 LF2 is a forged low-temperature carbon steel with controlled chemistry and impact toughness tested at low temperature. Class 1 (CL1) is tested at -29 deg C, Class 2 (CL2) at -46 deg C. The slip-on (SO) shape has a hub the pipe passes through; two fillet welds — one at the outside face, one at the back — hold it in place. Forging gives uniform grain and the toughness the low-temperature service demands.

Material and Classes

• A350 LF2 CL1 — low-temperature service to about -29 deg C.
• A350 LF2 CL2 — lower test temperature, about -46 deg C, for colder duty.
• Forged carbon steel — uniform grain, reliable impact toughness.
• Meets ASME B16.5 dimensions and pressure-temperature ratings.

Slip-On Versus Weld Neck

Why Choose Slip-On

The slip-on is quicker to line up because the pipe seats inside the hub, and it needs less skill and fill than a butt weld. For low-pressure utility, water, and non-critical process lines it delivers a sound joint at lower cost. It is not for lines with heavy fatigue, big thermal movement, or high-pressure cycles — there, use a weld neck.

Key Benefits

• Low-temperature toughness from forged A350 LF2, CL1 or CL2.
• Easy alignment and faster fit-up than weld neck.
• Lower material and welding cost for the same bore.
• Full ASME B16.5 pressure-temperature coverage at low pressure.

Where They Are Used

A350 LF2 slip-on flanges suit low-pressure piping in refineries, tank farms, water and utility systems, and process skids that see cold ambient or occasional low-temperature duty. They are common where the joint is accessible and the load is not severe.

In the Joint

The flange rides on the pipe; the gasket between the faces seals the line, while the flange body connects to the next spool. Fit the bore to the pipe so the pipe seats fully in the hub before welding.

Installation and Care

Slide the flange to the set position, tack and weld both fillets with procedure and filler suited to the low-temperature grade, and inspect the welds. Keep the raised face clean, seat the gasket square, and bolt up evenly. Because the fillet weld is the weak point, keep slip-on flanges to the lower-pressure services they are rated for.

Frequently Asked Questions

CL1 or CL2 — which do I need?

It follows the lowest design temperature. CL2 (-46 deg C) is for colder duty than CL1 (-29 deg C); the line specification sets the class.

Can slip-on replace weld neck?

Only at low pressure and mild loading. Slip-on has fillet welds and weaker fatigue life, so it is not for cyclic or high-pressure lines where weld neck is required.

Why forged, not plate?

Forging gives A350 LF2 the uniform grain and tested impact toughness that low-temperature service needs; cut plate flanges cannot guarantee that toughness.