Forged steel flange

01

Choose the pressure class at your design temperature

Wermac explains that ASME B16.5 flanges come in Classes 150, 300, 400, 600, 900, 1500 and 2500, and that the allowable pressure falls as temperature rises. Ratings are maximum allowable working gauge pressures at the metal temperature; linear interpolation between temperatures is permitted but not between classes, and the ratings assume bolting and gaskets within the standard's limits. [2]

Engineering ToolBox tabulates Group 1.1 (ASTM A105) ratings: Class 150 allows 19.6 bar from −29 to 38 °C, 13.8 bar at 200 °C and 6.5 bar at 400 °C; Class 300 allows 51.1, 43.8 and 34.7 bar at the same temperatures. [1]

Editorial calculation from those values: a Class 150 A105 flange at 200 °C allows about 30% less than at ambient, and at 400 °C about a third of its ambient rating. Check the edition of B16.5 your project specifies and the material group of your flange.

Give the supplier the design pressure and temperature, the fluid, the pipe size and schedule, the standard and edition, and the material. Class follows from the rating table, not from the operating pressure alone.

02

Choose the flange type for strength, fatigue and welding

Wermac describes the weld neck flange's long tapered hub as reinforcement for high pressure, sub-zero or elevated temperature and repeated bending, welded with a single full-penetration butt weld and easily radiographed. A slip-on flange's strength under internal pressure is about two-thirds and its fatigue life about one-third of a weld neck's. [3]

Socket weld flanges were developed for small high-pressure piping, with the pipe withdrawn about 1.6 mm from the socket shoulder before welding; the remaining crevice can cause corrosion in some services. Lap joint flanges with stub ends can swivel for bolt alignment, but Wermac puts their fatigue life at about one-tenth of a weld neck's. [3]

03

Choose the facing and finish for the gasket

Wermac explains that raised face (RF) flanges concentrate gasket stress on a smaller area; the raised face is about 1.6 mm high in Classes 150 and 300 and about 6.4 mm in Classes 400 to 2500. Wermac states: “The typical flange face finish for ASME B16.5 RF flanges is 125 to 250 µin Ra (3 to 6 µm Ra).” Flat-face flanges mate with cast flanges and must not be bolted to raised-face flanges. [4]

Ring-type joint (RTJ) flanges, with metal ring gaskets, are, per Wermac, “typically used in high pressure (Class 600 and higher rating) and/or high temperature services above 800°F (427°C)”, and need a finer finish, 63 µin for the ring groove per Wermac. Match the finish to the gasket: Wermac's finish page specifies 125–250 µin AARH for spiral wound gaskets. [4] [5]

04

Specify the material and its requirements

Wermac summarises ASTM A105 as covering forged carbon steel piping components for ambient and elevated temperature, up to 4,540 kg per forging, with minimum tensile strength 485 MPa, yield 250 MPa and maximum hardness 197 HBW. Heat treatment is not a mandatory requirement for A105 piping components, with listed exceptions that include B16.5 flanges of Classes 400, 900, 1500 and 2500. [6]

For low temperature, A350 LF2 is the corresponding carbon steel flange grade; for high temperature alloy service, A182 F11, F22 and similar grades. Ask for mill certificates that show heat number, chemistry, mechanical tests and heat treatment, and check the marking on each flange. [6]

05

A105 B16.5 flanges, EN and JIS flanges and heavy open-die forgings on supplier pages

Haihao lists A105 B16.5 forged flanges including blind, lap joint and orifice types; Epower lists flanges to ASME, EN 1092-1, DIN, JIS and other standards; Huixuan lists forged steel flanges among heavy open-die forgings; Longteng lists weld neck, slip-on and socket weld flanges alongside welding consumables. [7] [8]

06

Hub, gasket face, bolt circle, flange ring and marking

Only the hub changes with flange type: the weld neck's tapered hub is what gives it the strength and fatigue life Wermac credits it with, while the face, bolting and ring follow from class and material. [3]

07

Size, class, bolting, face finish and material grade for a flange order

Operating pressure and temperature are read together: an A105 Class 150 flange drops from 19.6 bar at ambient to 13.8 bar at 200 °C in the Group 1.1 table, so fill both rows before choosing the class. [1]

08

Send the line, design conditions and material together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Line: [NPS or DN; pipe schedule; fluid]
Design: [pressure; temperature; standard and edition (e.g. ASME B16.5); class]
Type: [weld neck, slip-on, socket weld, lap joint, threaded, blind]
Facing: [RF, FF or RTJ; finish for the gasket]
Material: [A105, A350 LF2, A182 grade or other; heat treatment]
Inspection: [mill certificate type; dimensional report; NDT if required; marking]
Quantity and delivery: [quantities by size; coating or protection]

See manufacturer records Send an enquiry through CNFX