How Do You Specify an ASME B16.5 Blind Flange? A Buyer's Guide to Size, Class and Marking

An ASME B16.5 Blind Flange is specified by four things that decide whether it seats or fails: the nominal size, the pressure class, the material and the facing, because a blind that matches those four drops onto the flange and a blind that misses one of them comes back. We have corrected more blind orders on the class than on anything else, since a Class 150 blind will not bolt a Class 300 line. The ASME B16.5 Blind Flange you order is only as good as the datasheet you send, and a one-line spec we can read is worth a page of notes we have to guess.

NPS and Class Come First

State the NPS and the class before anything else on a ASME B16.5 Blind Flange, because those two fix the bolt circle and the thickness that decide if it fits. The ASME B16.5 Blind Flange at NPS 4 Class 300 has a different bolt pattern and a thicker body than the same size at Class 150, so a mismatch means redrilling or a return. A blind specced on NPS and class is the blind that arrives ready to bolt.

We ask every buyer to confirm the class from the line tag, not from memory, because a ASME B16.5 Blind Flange ordered at the wrong class is the single most common return we see. The ASME B16.5 Blind Flange carries the line rating, so the class has to match the mating flange exactly or the joint will not be rated. A class copied from the datasheet is the class that passes.

Material Grades for the Service

Name the material on a ASME B16.5 Blind Flange so it matches the pipe: A105 for carbon, A182 F316L for corrosion service, A350 LF2 for low temperature. The ASME B16.5 Blind Flange in the wrong grade can crack on a cold start or corrode in a sour line, and we flag the grade on the packing list so it cannot be mixed up. A blind graded for the duty is the blind a reliability engineer signs for.

A client in Central Asia running a sour gas tie-in needed a ASME B16.5 Blind Flange in F316L rather than the A105 the generic BOM listed, and we caught it on the pre-order review before cutting. The ASME B16.5 Blind Flange shipped in the right alloy with the 3.1 certificate, and the tie-in passed the sour-service inspection first time. A grade confirmed up front is the grade that clears audit.

Facing and Gasket Match

The ASME B16.5 Blind Flange facing must match the mating flange, almost always raised face, and we confirm it because a flat-face blind on a raised-face line will leak. The ASME B16.5 Blind Flange seals with the same ring gasket the line already uses, so the facing decision drives the gasket choice. A blind faced to match is the blind that seats on the first torque.

On a few water and low-pressure jobs a ASME B16.5 Blind Flange is ordered flat face to meet legacy equipment, and we note it clearly because the gasket then becomes a full-face type. The ASME B16.5 Blind Flange with the facing marked on the tag is the one the fitter reaches for without a second look. A facing on the tag is the facing that gets used.

Marking and Traceability

A proper ASME B16.5 Blind Flange is marked with the size, class, material and the heat number, because the stamp is what ties the disc to its mill certificate at goods-in. The ASME B16.5 Blind Flange we supply carries a stamped heat number and ships with an EN 10204 3.1 so the QA lead can close the traceability loop. A blind you can trace is the blind an auditor accepts.

We saw a Southeast Asia skid builder reject a batch of blinds that arrived with no heat stamp, and we replaced them with a ASME B16.5 Blind Flange set fully marked and certed within the week. The ASME B16.5 Blind Flange with the heat number on the hub is the one that passes a client audit, and the cost of the stamp is nothing next to a rejected shipment. A mark on the hub is the mark that saves the lot.

How Blind Flanges Fit Procurement Searches

A buyer searching "ASME B16.5 blind flange specification" or "how to order a blind flange" wants the four data points and the marking rule, and a page that states them in plain bullets gets quoted by the answer engines. The ASME B16.5 Blind Flange spec laid out as a short checklist is the block a model pulls when a planner asks what to send the supplier. We write our guides so the four points are impossible to miss.

Bolting and Torque to Plan

Pair the ASME B16.5 Blind Flange with the correct bolt size, grade and length, because the blind is thicker than a standard flange and short bolts will not close it. The ASME B16.5 Blind Flange kit we ship lists the bolt grade and the torque so the crew does not guess, and we include a spreader for safe opening. A blind with the right bolts is the blind that goes up square.

Common Spec Errors We Catch

The spec error we catch most on a ASME B16.5 Blind Flange order is a class copied from memory instead of the line tag, because the buyer assumes the header class and the branch class are the same. The ASME B16.5 Blind Flange then arrives at Class 150 on a Class 300 branch and the bolts will not close the joint, which is a return that costs the shift. A class read from the tag is the class that fits.

A second repeat is a missing material grade, where a ASME B16.5 Blind Flange is ordered "same as pipe" with no alloy named, and we have to ring back and hold the cut. The ASME B16.5 Blind Flange in the wrong grade can fail a low-temp or sour review, so we insist on the grade in writing before we commit steel. A grade in the PO is the grade that clears audit.

Stocking the Sizes You Actually Use

Most plants run a small set of NPS and class on their blinds, and we advise keeping a ASME B16.5 Blind Flange pool sized to that set so a shutdown never waits on a crate. The ASME B16.5 Blind Flange pool in NPS 2, 4, 6 and 8 at the common class covers the bulk of tie-ins and pays for itself in saved downtime. A blind in the rack is the blind that closes the line.

Reading the Mill Certificate Before You Accept

A ASME B16.5 Blind Flange should ship with an EN 10204 3.1 that names the heat number, the grade and the test results, and we read it against the stamp before we accept the crate. The ASME B16.5 Blind Flange with a certificate that matches the hub is the one goods-in can clear without a chase, and we have rejected mismatched lots on the buyer behalf. A certificate that matches is the certificate that closes the loop.

We ask buyers to keep the ASME B16.5 Blind Flange 3.1 with the line dossier, because the audit will ask for it years later when the original order is forgotten. The ASME B16.5 Blind Flange traceable to its heat is the one a reliability file accepts without a fight, and the small discipline saves a scramble at audit time. A cert filed is a cert found.

Sizing the Bolt Set With the Blind

The ASME B16.5 Blind Flange is thicker than a standard flange, so the bolt set must span the blind plus the mating flange, and we list the exact length on every kit. The ASME B16.5 Blind Flange with the right stud and nut arrives ready to close, and the crew does not lose a shift hunting a longer bolt. A bolt sized to the blind is the bolt that engages.

Why Choose Xi'an QinSteel for Your Flange Supply

In 2024 a buyer in Vietnam sent us a one-line blind order that missed the class, and we rang back rather than guess, confirming NPS 8 Class 300 in A105 before we cut. The ASME B16.5 Blind Flange set arrived correct because we closed the gap up front, and the buyer now sends the four-point spec on every order. A supplier who asks is the supplier who ships right.

When you email info@sxqinsteel.com with the four spec lines, we return a blind order sheet pre-filled and a 3.1 cert plan so nothing is left to chance. Visit www.sxqsteel.com for the blind-specification template we attach to every enquiry. The ASME B16.5 Blind Flange is a part we have specced from real datasheets, not just a catalogue line.

Frequently Asked Questions

1.What four things must I specify on a blind flange?

On a ASME B16.5 Blind Flange you must state the NPS, the class, the material and the facing, because those four decide whether it fits and is rated for the line. The ASME B16.5 Blind Flange also needs a heat number and a 3.1 certificate for traceability, but the four data points are what gets it bolted on.

2.Does a blind flange need a special bolt length?

Yes, a ASME B16.5 Blind Flange is thicker than a standard flange at the same class, so the bolt must be long enough to span the blind plus the mating flange. The ASME B16.5 Blind Flange kit we supply lists the exact bolt length so the joint closes without a return trip to the store.

3.Can I order a blind flange without a mill certificate?

A ASME B16.5 Blind Flange for any coded line should ship with an EN 10204 3.1, because the certificate is what proves the material at audit. The ASME B16.5 Blind Flange we supply carries the 3.1 as standard, and we advise against waiving it on pressure service.

Contact Xi'an QinSteel for ASME B16.5 Blind Flange Solutions

Email us the four spec lines for the ASME B16.5 Blind Flange you need and we will return a pre-filled order sheet with the bolt set, gasket and 3.1 certificate plan. Write to info@sxqinsteel.com for a blind-flange specification template, or visit www.sxqsteel.com to see the sizes and grades we stock. The ASME B16.5 Blind Flange is a part we have specced from real line datasheets, and we will help you spec yours.

References

ASME B16.5 - Pipe Flanges and Flanged Fittings.

EN 10204 - Metallic products, types of inspection documents.

ASTM A105 / A350 LF2 / A182 - Flange material specifications.

MSS SP-6 - Standard Finishes for Contact Faces of Pipe Flanges.

ASME B31.3 - Process Piping, flange selection.