M.S. & S.S. Slip-On Flanges

A slip-on flange has a bore slightly larger than the pipe outside diameter, so the pipe slides into the flange before welding. It is then fillet welded twice — once inside the bore at the pipe end and once behind the flange — and those two welds carry the load and seal the joint. Because there is no machined neck and no bevel to prepare, a slip-on flange is quicker to fit and costs less than a weld neck of the same size and drilling, and it forgives small errors in pipe length. I.S. Engineering Co. machines slip-on flanges at Darukhana, Mumbai in mild steel and stainless steel from 15mm to 600mm NB.

We make five slip-on sub-types: slip-on raised face (SORF), slip-on flat face (SOFF), hub slip-on, flat plate flange and reducing slip-on. SORF is the default for process and utility lines that use a ring gasket. SOFF is used where the mating face is flat and a full-face gasket is required. The hub type adds an integral boss around the bore for extra weld metal. The plate type is a plain drilled disc with no hub. The reducing type carries the bore of a smaller pipe with the drilling of the larger line. Any of them can be cut to your own drawing.

A hub flange is a slip-on flange with an integral raised hub around the bore. The hub puts extra metal exactly where the pipe meets the flange, so the outer fillet weld sits on a thicker section and the joint is stiffer than a plain plate flange of the same face thickness. Trade practice in India is to call the plain drilled disc a plate or flat flange and the hubbed version a hub flange; both bolt to the same drilling. We machine hub flanges from thicker plate or from forgings, depending on the size and grade you need.

A plate flange is a flat drilled disc with no hub, so the full flange thickness does the work and the pipe is welded straight to it. A slip-on flange is bored to slide over the pipe and is welded on both sides of that bore. Plate flanges are the cheapest option and are common on tank nozzles, ducting, low-pressure water lines and as loose backing flanges. Slip-on flanges are the better choice once the line has to hold pressure or take some bending.

Specify slip-on where the line is low to moderate pressure, the service is steady rather than cyclic, and fitting speed and cost matter — utility and cooling water, fire mains, HVAC chilled water, drainage and general plant piping. Specify weld neck where the joint has to take high pressure, thermal cycling, vibration or fatigue, or where a radiographed full-penetration weld is called for. A slip-on relies on two fillet welds and concentrates stress at the bore, which is why it is not used on critical high-pressure duty.

Mild steel to IS:2062 is our standard for slip-on, hub and plate flanges. In stainless steel we supply SS 304 and SS 304L, and SS 316 and SS 316L where chloride or acid service demands it. Tell us the line material and the service and we will match the flange grade. Mill test certificates are supplied with the material when you ask for them at the time of order.

Slip-on, hub and plate 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 rest of your line. 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.

A flat face flange takes a full-face gasket, one that covers the whole face including the bolt holes, so the bolt load is spread across the full face instead of bending the flange inwards. A raised face flange takes a ring gasket that sits inside the bolt circle. Do not put a ring gasket on a flat face joint, and do not bolt a raised face flange against a cast iron flat face flange, because the raised face can crack the casting.

Yes. We despatch regularly to Chennai, Coimbatore, Madurai and Tiruchirappalli in Tamil Nadu, Bengaluru and Hosur in Karnataka, Hyderabad in Telangana, Visakhapatnam in Andhra Pradesh, and Kochi and Mangaluru on the west coast — alongside Mumbai, Navi Mumbai, Thane, Pune, Nashik and Nagpur in Maharashtra and the rest of PAN India by the road or rail transport of your choice.

Yes. We supply slip-on, hub and plate flanges for export to Dubai and the wider UAE, Oman, Qatar, Kuwait and Saudi Arabia, shipping through Nhava Sheva (JNPT) and Mumbai Port. Send the sizes, drilling table, facing, material grade and quantity and we will quote ex-works Mumbai or FOB Nhava Sheva, with sea-worthy packing and the documents your buyer needs.

Four things settle a slip-on flange rate: the nominal bore of each size, the drilling table or ANSI class, the facing — raised, flat, hub or plain plate — and the material grade. Quantity per size and the pipe outside diameter help us set the bore correctly. 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.