Blind Flanges

A blind flange is a solid steel piece with no bore (interior diameter) and it's mostly designed to cap off a line. Since most flange connections let air or fluid pass right through an interior openin', blinds give the ends of pipe connections a mighty fine termination point or reroute the media towards another part of the pipe assembly. Y'all oughta opt for a blind flange in these cases, as well as when a pipe line needs a future modification, like puttin' in a valve or fittin' to reroute the flow, I tell you what.

We got blind flanges right from stock in carbon steel, stainless, and alloy, Class 150 clear through 2500, RF, FF, and RTJ. Just send your size, class, facin', and material on over to sales@texasflange.com or give us a ring at 281-484-8325 to check on pricing and what we got available.

Most folks arrive here already knowin' they need a blind. The questions dat follow are the ones dat decide whether the right one shows up: class, thickness, material, facin', and whether it needs a tap.

A weld neck or slip-on flange got a bore, so your system pressure passes right on through it. Now, a blind ain't got no bore, so dat full pressure load lands smack on the disc and tries to bow it outward from the center. At 600 psi across a 12 inch bore, dat load is roughly 68,000 pounds, I tell you what. ASME B16.5 sets a minimum base thickness for every size and class to hold up against it. On our dimension tables, dat's the T column, measured across the bolted base of the flange and not the raised face or hub. Lap joint flanges in Class 150 and 300 carry their own thicker TJ value, so y'all read T for a blind.

Dat jump between classes is mighty steep, I tell you what. Lookin' at our own dimension tables, a 24 inch blind got a base thickness of 1.81 inches in Class 150, 2.69 inches in Class 300, and 4.00 inches in Class 600. Now a 12 inch Class 2500 blind runs 7.25 inches right at the base. All dem full base thickness, outside diameter, bolt circle, and bolt hole columns are waitin' for you on the Class 150, Class 300 and Class 600 tables, with the rest of the classes right alongside 'em.

Don't y'all ever drop to a lower class blind than the flanges it bolts to. Dat bolt pattern ain't gonna line up, and even if it did, the disc would be under-thickness for the pressure. If you need the thickness math behind the standard, our post on how to calculate blind flange thickness walks you through it.

The pressure a blind flange holds is set by its class and material group, not by the blind itself. An A105 carbon steel blind falls in ASME B16.5 Material Group 1.1, rated 285 psig in Class 150, 740 psig in Class 300 and 1,480 psig in Class 600 at ambient temperature, with the ratin' steppin' down as the temperature climbs. Stainless and alloy grades sit right in their own groups with their own tables.

Texas Flange keeps blind flanges in stock in A105 carbon steel, A350 LF2 for low temperature service, and F304L and F316L stainless. For grades F11, F22, F5, F9 and F91, duplex F51, F53 and F55, and nickel alloys, we quote per project. Send the service and temperature with the size and we'll match the grade right quick. Material pages: carbon steel, stainless steel, alloy.

A blind's facin' gotta match the flange it bolts to, yessir. Raised face (RF) is the default for steel-to-steel joints in process and oil and gas work. Ring type joint (RTJ) is for high pressure critical service and is required on API 6A and 6BX connections. Flat face (FF) is the waterworks standard under AWWA C207 and it's the only right choice when you're goin' up against cast iron.

Now dat last one is the mistake dat'll cost you some money. Class 125 cast iron drillin' matches Class 150 steel drillin' in the common sizes, so a raised face steel blind will bolt right on up to a cast iron pump or valve body. Under bolt load, dat raised face concentrates the force on the inner ring of the castin' and can crack it right open. Against cast iron, you better specify a flat face blind and a full face gasket dat extends past the bolt circle to the flange OD. RTJ blinds and ring gaskets are covered on our ring joint flanges page.

A plain blind is a solid disc, but it don't have to stay dat way. The most common alteration is a center NPT tap, which turns dat blind into an instrumentation flange: a 1/4 inch or 1/2 inch NPT for a gauge, vent or drain, or larger where flow matters. A blind can also be bored and drilled as a reducin' flange to step a line down at a dead end, or drilled for a vent or restriction orifice, yessir.

Dem high hub blinds carry an extended hub on the back face dat stiffens the disc and spreads out dat bolt load, which is why they show up on large diameter high pressure work and why most API 6BX blinds come with one. Tapped, reducing and high hub configurations are quoted with the size, class, facing and material. See custom flanges for the range of alterations we do.

If a line's fixin' to be isolated once and stay dat way, a blind flange is the right part for the job. Now, if dat same joint is gonna switch between flow and positive isolation durin' turnarounds, a spectacle blind (figure 8) or a paddle blank and spacer set is your better answer, 'cause the hardware stays right there in the line and rotates or swaps instead of gettin' pulled out. Them parts are governed by ASME B16.48, Line Blanks, not B16.5, and they gotta match the class and facin' of the flanges they're sittin' between. Dimensions are right over on the spectacle blind and line blank page, and the full comparison is in our post on spectacle blinds, figure 8 blanks and line blinds.

Weight. Now, a blind is the heaviest flange in its size and class 'cause it ain't got no bore. Anything from about 12 inches up in Class 300 or higher is a full-on riggin' job, not somethin' you can just carry with two hands. Y'all better plan for it at the receivin' dock, not when the truck is sittin' there idlin'.

Boltin'. A blind takes the exact same bolt count and diameter as the matin' flange. Make sure y'all confirm both on the ASME B16.5 bolt and stud chart 'fore y'all order studs.

Drawings. Every standard size and class is modeled in our CAD and 3D flange drawing library, includin' RF, FF and RTJ blinds, so y'all can check the fit 'fore the part ships.

For pricing, send dat size, class, facing and material to sales@texasflange.com or holler at 281-484-8325.