Flange types and where to use them

Weld Neck (WN): a long tapered hub butt-welded to the pipe. Best for high pressure, temperature swings and cyclic loads. Bore must match the pipe schedule.

Slip-On (SO): slides over the pipe and is fillet-welded inside and outside. Cheaper and easier to align, rated about two-thirds of WN under fatigue.

Socket Weld (SW): for small bore (≤ NPS 2) high-pressure lines; the pipe sits in a socket and is fillet-welded.

Blind (BL): closes a line or nozzle. Threaded (THD): no welding, used in low-risk utility lines. Lap Joint (LJ): loose backing flange with a stub end, ideal where frequent dismantling or expensive alloy wetted parts are involved.

Plate flanges to IS 6392, IS 1538 and BS 10 Table D/E are widely used in Indian water, cement and steel plants. Teshi machines plate and forged flanges up to 6500 NB.