Blind Flanges

A blind flange is a solid disc with bolt holes on the rim and no bore, bolted to a flanged pipe end, nozzle or valve to close it completely. Because it is bolted rather than welded it can be taken off again, which is why blind flanges are used to terminate a line that may be extended later, to close a spare tee branch or vessel nozzle, and to seal a section for hydrostatic testing. I.S. Engineering Co. machines blind flanges at Darukhana, Mumbai in mild steel and stainless steel from 15mm to 600mm NB.

We make five blind sub-types: blind raised face (BLRF), blind flat face (BLFF), ring type joint blind (RTJ or RJ), tapped or drilled blind, and spectacle blind and spade-and-spacer line blinds. BLRF is the default where the mating flange is raised face and a ring gasket is used. BLFF suits a flat face mating flange and a full-face gasket. The RTJ blind carries a machined ring groove for a metal ring gasket. A tapped blind carries a threaded boss for a vent, drain, gauge or thermowell. Spectacle blinds and spade-and-spacer sets are cut and drilled to the same pattern as the line flange.

A blind flange bolts onto an existing flanged pipe end and can be unbolted; an end cap is butt welded onto the pipe and is permanent. Specify a blind flange wherever the end has to be opened again for inspection, cleaning, pressure testing or a future extension. Specify an end cap where the end is genuinely final and you want no gasket, no bolts and nothing to maintain.

A spectacle blind is two discs of the same drilling joined by a short web, one solid and one bored, so the fitter loosens the joint, slides the plate across and either blanks the line or opens it. It suits a joint that has to be blanked and unblanked repeatedly, and it lets an operator see at a glance whether the line is open or shut. A plain blind flange is the cheaper choice when the end will rarely be opened.

A spade is a solid plate that goes between two flanges to block the line, and the spacer is a matching ring of the same thickness that replaces it when the line is back in service. Spade and spacer sets are used instead of a spectacle blind on large sizes, where a single joined plate would be too heavy to handle. Both are cut to the drilling of the flanges they sit between, so send us the table or class along with the size.

For Table E work, use the thickness column in the chart on this page: our blind flanges are made to the same thickness as the corresponding flange in that table. A blind flange takes bending across its whole face, so thickness rises with both size and pressure, and higher ANSI classes are machined thicker. If you are pressure testing above the working pressure of the line, tell us the test pressure and we will confirm the thickness before cutting.

Mild steel to IS:2062 is our standard for blind flanges. In stainless steel we supply SS 304 and SS 304L, and SS 316 and SS 316L for chloride, effluent or acid service. A blind has no bore to machine, so an odd grade or an odd thickness is usually easy for us to accommodate. Mill test certificates are supplied with the material when you ask for them at the time of order.

Blind flanges are made from 15mm NB to 600mm NB. Drilling can be Table D, E, F or H, or ANSI B16.5 class drilling, to match the flange it bolts against. The Table E drilling we hold as regular is published on this page — outside diameter, pitch circle, bolt count, hole size, bolt size and thickness for every size from 15mm to 600mm NB. Table D, F and H charts and ANSI class charts are sent on request.

Yes, blanking a section with blind flanges is the normal way to hydrotest a line. The point to watch is that the blind and its bolting have to hold the test pressure, not the working pressure, and test pressure is usually well above it. Give us the test pressure along with the size and drilling and we will confirm the thickness and the bolt size. Keep clear of a bolted blind while a line is being pressurised.

Yes. We despatch across India from Darukhana, Mumbai — Navi Mumbai, Thane, Pune, Nashik and Nagpur in Maharashtra, and regularly to Chennai, Coimbatore, Madurai, Tiruchirappalli, Bengaluru, Hosur, Hyderabad, Visakhapatnam, Kochi and Mangaluru in South India, as well as Ahmedabad, Delhi NCR, Kolkata and the rest of PAN India. Export orders for Dubai and the wider UAE, Oman, Qatar, Kuwait and Saudi Arabia ship through Nhava Sheva (JNPT) and Mumbai Port.

Four things settle a blind flange rate: the nominal bore of each size, the drilling table or ANSI class, the facing — raised, flat or RTJ — and the material grade. Add the quantity per size, and the test pressure if the blinds are for hydrotesting. Send it on WhatsApp to +91 99220 47887 or email sales.isengineeringco@gmail.com. A drawing or a sample flange is welcome if you have one.