Exploring the Revolutionary A350 LF2 CL3 B16.5 Low-Temperature Carbon Steel Blind Flange

A blind flange is a solid disk with no bore that bolts to the end of a pipe to close it off, isolate a section, or cap a future tie-in. In low-temperature service an A350 LF2 blind to ASME B16.5 keeps that seal through cold starts and shutdowns. For the mating face, see our flange gaskets and flange products.

What an A350 LF2 Blind Flange Is

A350 LF2 is a forged low-temperature carbon steel with chemistry and impact toughness tested in the cold. Class 1 is tested at -29 deg C, Class 2 at -46 deg C — the grades used where the line can see winter or cryogenic upset. The blind is a full, un-drilled disk with the same bolting pattern and facing as the mating flange, so it seals a bore with a standard gasket.

What a Blind Flange Does

• Closes the end of a new or abandoned line during construction and outage.
• Isolates a vessel or section for safe inspection, cleaning, or hydrotest.
• Caps a spare nozzle or future tie-in point until it is needed.
• Acts as a solid, pressure-rated blank where a valve would be overkill.

Blind Versus Other Flanges

Why Low-Temperature Grade

A blind flange sees the same pressure and thermal shock as the rest of the joint, and a brittle disk at low temperature can crack rather than yield. A350 LF2's tested toughness means the blind stays ductile through cold trips, so the cap does not become the weak link in a line that operates or is tested in the cold.

Key Benefits

• Forged low-temperature steel with certified impact toughness.
• Simple, bore-free seal that is easy to fit and remove.
• Full ASME B16.5 rating, so it matches the line it closes.
• Reusable — unbolt, store, and re-fit at the next outage.

Where They Are Used

Low-temperature blind flanges sit at the ends of cold-service lines in refineries, gas plants, LNG and tank-farm piping, and any system that is hydrotested or idled in winter. They are the cap you reach for when a line must be shut without a valve.

In the Joint

The blind bolts to the open flange; the gasket between the faces makes the seal, while the flange body carries the same rating as the line. Size the blind to the flange class and bolting so the cap is never the limiting part.

Installation and Care

Fit the blind square to the mating flange, seat the gasket, and bolt up evenly in a star pattern to the rated torque. Because a blind takes the full end load, do not under-tighten — a loose blind can weep or, at pressure, blow out. Mark and store removed blinds by size and class, and inspect the facing for nicks before re-use.

Frequently Asked Questions

CL1 or CL2 for a blind?

Match the line's low-temperature class: CL2 (-46 deg C) where the service runs colder than CL1 (-29 deg C). The blind must meet the same low-temperature spec as the joint.

Why forge, not plate, for cold service?

Forging gives A350 LF2 the uniform grain and tested toughness cold service needs; a cut plate blank cannot guarantee that impact resistance.

Can a blind replace a valve?

For isolation during outage or test, yes. But a blind gives no quick shut-off, so it is not a substitute for a valve in normal operation.