Class 150 Blind Flange Dimensions

Standard

ASME B16.5

Flange type

Blind Flange

Pressure class

Class 150

Size range

NPS 1/2 – NPS 24

Raised face height

0.06 in (1.5 mm)

Rating at 100 °F (A105)

285 psig (19.7 bar)

Where a Class 150 blind flange is used

Class 150 is the lightest class in ASME B16.5 and by a wide margin the most used. It covers cooling water, utility, fire water and low-pressure process service, and it is the class most pumps, vessels and valves in general service are nozzled to.

A blind flange closes the end of a line or a nozzle. At this class it is the usual closure for spare nozzles, manways and the ends of headers left for future extension.

The number 150 is a designation and not a pressure. A Class 150 flange in A105 carbon steel is rated 285 psig (19.7 bar) at 100 °F, 200 psig at 400 °F, 140 psig at 600 °F and 80 psig at 800 °F. In Type 304 stainless, Group 2.1, it starts at 275 psig and still holds 80 psig at 800 °F, so the material and the metal temperature have to be fixed before the class can be.

Dimensions in every size

Dimensions are given in inches, with the millimetre equivalent beneath in grey.

Flange thickness excludes the raised face. Bolt diameter is nominal; stud bolts are normally ASTM A193 B7 with A194 2H nuts.

Across the 20 sizes published in Class 150, the flange grows from 3.50 in (88.9 mm) across and 0.38 in (9.7 mm) thick at NPS 1/2 to 32.00 in (812.8 mm) across and 1.81 in (46.0 mm) thick at NPS 24. The bolt count goes 4 from NPS 1/2, 8 from NPS 3 1/2, 12 from NPS 10, 16 from NPS 16 and 20 from NPS 20, always in multiples of four so that the holes can straddle the centrelines. The largest bolt in the class is 1 1/4 in, first needed at NPS 24.

A blind flange has no bore and no hub, so the flange outside diameter, thickness, bolt circle and bolting are the whole of its dimensional definition. Thickness shown is the minimum required by B16.5 — many mills supply heavier.

Weight and end load

With a blind flange the two figures most often wanted are not in B16.5 at all: what the flange weighs, for lifting and for support loads, and how much force the contained pressure puts on it. Both are calculated here from the dimensions above. The end load is what the bolts must resist in addition to the load needed to seat the gasket.

Weight is a solid-disc estimate from the outside diameter and the minimum thickness at 0.2836 lb/in³, and ignores the raised face, so it runs slightly light against a real forging. End thrust is the 100 °F rating for A105 acting on the raised face area; it is not a bolt-load calculation, which must also cover gasket seating.

Bolt holes, spacing and torque

Bolt holes in ASME B16.5 flanges are drilled 1/8 in larger than the nominal bolt and are set to straddle the vertical and horizontal centrelines, never to sit on them. Spacing is the distance between neighbouring holes measured round the bolt circle, which shows how much room there is for a wrench or a tensioner. The torque column is a starting figure for a lubricated stud, not a joint-specific value.

Torque is T = K·F·d with nut factor K = 0.16 and a bolt stress of 50,000 psi on the tensile stress area. The bolt torque guide gives the method and other nut factors.

Guides and comparisons for this page

Same flange, other classes

Same class, other flange types

Every class in one size