A Complete Guide to Steel Flanges

Explore our complete guide of steel flanges, which will make you deeply understand what exactly steel flange is and according to that you can choose it as per your requirement of applications.

It is usually attached to other pipe fitting by using welding attachments and sealed to other flanges by using bolts and gaskets. Flange, connects various things that we use regularly in industrial process, such as for using in water pipelines to oil filtration machinery, food processing manufacturing and pressure vessels, etc.

All these industrial elements were manufactured in various specifications over years and each offer crucial role and their roles expands over several industries.

It is essential to keep the pipes connected safely in order to avoid leakages in the piping system. Flanges keeps the pipe connected accurately and help it work safely for a longer duration.

Steel Flanges Specification

Manufacturing standard of pipe flanges is ASME B16.5

It includes NPS ½ to NPS 24 metric inches, which covers of pressure-temperature ratings, dimensions, tolerance, materials, sizes, tolerances, marking, testing, and opening method of flanges.

The flange class rating includes of 150, 300, 400, 600, 900 and 1500 are available in sizes from NPS ½ to NPS 24 metric inches, and flange class rating of 2500 are available in sizes NPS ½ to NPS 12 are in metric and U.S common units with diameter of bolts and flange bolt holes stated in inch units.

ASME B16.5 flange is made from forged or cast materials. Blind flanges and specific reducing flanges are fabricated from forged, cast or plate materials. In this standard also includes requirements and suggestions with regards to flange bolting, flange gasket and even flange joints.

Different Types of Flanges

Weld Neck Flanges		This kind of flange is welded to the pipe ends at the neck Typically butt welded to a pipe Applied in high pressure situations Greater longevity than slip-on flanges when subjected to stress
Slip On Flanges		This pipe flange slip over the pipe Lower Price than weld neck flange Manufactured with an ID that is slightly bigger than the pipe’s OD
Socket Weld Flanges		It has a female socket in which pipe is fitted Fillet welding is done from OD on the pipe Similar to slip-on flange, but with a bore and a counter bore dimension Counter bore is than the O.D. of the matching pipe Suitable for pipes with a nominal dia of 150 or less
Lap Joint Flanges		Used on piping fitted with lapped pipe (lap joint stub ends) Having two components: stub end and a loose backing flange Stub end Similar to a slip-on flange, but with a radius where the flange face and bore meet
Threaded Flange		Also known as screwed flange Possessing a thread within the flange bore that aligns with the pipe’s male thread Used in utility services such as air and water Like to the Slip-On flange, but the bore is threaded
Blind Flange		A blind flange is a round plate with no centre hole and all the necessary boltholes Used to close off the ends of a piping systems
Orifice Flange		Used with orifice meters Measuring the liquid or gas flow rate in the appropriate pipeline
Long Welding Neck Flange		Has a very long neck Has a tapered neck and a bevel end Has a straight short pipe as the neck of a long weld neck flange
Weldoflange and Nipoflange		A Welding Neck flange combined with a purported Weldolet or Nipolet
Expander and Reducing Flange		Used to increase or decrease the bore size of a pipeline A strong substitute for butt weld reducers

Steel Pipe Flange Material Grades

Reducing weld neck flange have pressure rating of class 150 to class 2500

ASME creates the flange class, taking into account there are several pressure and temperature ratings. There are seven classes i.e. 150, 300, 400, 600, 900, 1500 and 2500. And the reducing weld neck flange can be worked at this pressure rating of class. The pressure rating specifies the highest tolerable pressure at a stated temperature. For instance, a class 2500 flange can resists more pressure and it is heavier compared to 1500 flange. Here, the class 2500 flange signifies that the flange is workable at this rated temperature without getting crack or damaged.

Galvanized Pipe Flange Working Pressure

Standard size range of socket weld and slip on flanges is 1/2″ to 24″

The range of standard size socket weld and slip on flanges are important for several industries as it gives fastening to the piping system. Socket weld and slip on flange are usually manufactured in the standard from ½” to 24”.

The categorization and distinction between the flanges from countries to countries are important to understand for flawless combination and consistency in global projects.

Flange standardization gives safety and similarity in the broad range of global industries. It enables global trade by offering a common base for fabricators, suppliers and consumers. 

Steel Flange Dimension Chart

WNRF Flange Weight Chart

Steel pipe flanges are available in different faces like RF, FF and RTJ

These are the three most important and most commonly used types of flange faces.

A raised face flange has a circular shape sealing face which extends from the flange bolting circle plane. It is available in all pressure class, therefore it is utilize for a broad range of temperature and pressure ratings. Its prime purpose is to compress more pressure on a smaller gasket part, whereby it increases the pressure capability of the joint. It is most commonly used for oil, gas and chemical engineering industries.

As its name signifies flat face flange doesn’t have any lump or raised surfaces. It utilize a “full face” gasket and have a large exposure sealing area. It is easy to align while installation and are usually more cost-effective as compared to other type of flanges. This type of flange face is the easiest method to protect against from damages and rust. It is used by applying adherent or magnetic flange guard.

Ring-Type Joint flange are usually used for more critical applications, mainly for high pressure or temperature applications. It is fabricated to offer a leak proof seal in critical conditions where standard gasket can fail. The surface of this kind of flange are machined groove.

Steel Flange Face Types

Plain Face/ Flat Face Flange

• non-metallic gaskets
• serrated sealing surface
• low pressure applications
• pressure classes 125 and 250

Raised Face Flange

• classes 150 and 300
• Height: 1/16 inch (1.6mm)
• class 300: 1/4 inch (6.4mm) raised face

Ring-Type Joint (RTJ)

• high pressure systems((>750⁰C / 1,382⁰F))
• typically used for class 900 and above
• Groups: R, RX and BX

Flange Face Type
Characteristics	Gasket Type	Sealing Face	Sealing Area	Pressure Class	Pressure Range	Temperature Range
Flat Face	Soft. Non-metallic.	Inner diameter to outer diameter.	Large	125#, 250#	Narrow. Low pressures only.	Narrow. Low temperatures only.
Ring-Type Joint	Hard.Â	Groove in flange face.	Small	All. Generally ≥ 900#.	Broad. Generally used for higher pressures.	Broad
Raised Face	Non-metallic, semi-metallic.	Inner diameter to raised face outer diameter.	Medium	All.	Broad	Broad

Check thickness and torque specs of plate flanges6

The thickness of the plate flange has a prime effect on the hardness and toughness of the connection. Which means as that, if the thickness of the flange is higher its toughness will greater and vice-a-versa.

The torque of plate flange, is the force which it can bear, a rotational force or the ratio of strength demanded to rotate an item. It is considered as the turning force utilize to move items which includes of bolts.

The torque of plate flange is essential to know the prolong life of flange. It gives a non-failing connection, such as for leak free liquid transmission, accurate gasket installation, and bolts must be screwed on the flange with accurate tension and balance over the complete face of the flange. It helps to secure two elements so that it can prevent pulling or slipping apart.

Reducing Weld Neck Flange Thickness Chart

SCH 20 Flange
NPS	½	1	¾	1 ¼	1 ½	2	3	4	5	6	8	10	12	14	16	18	20	22	24
SCH 20	–	–	–	–	–	–	–	–	–	–	0.25	0.25	0.25	0.31	0.35	0.36	0.4	–	0.45

Sch 80 Flange
NPS	¾	½	1 ½	1	1 ¼	2	4	3	6	5	8	12	10	14	18	16	20	24	22
SCH 80	0.15	0.14	0.2	0.17	0.19	0.21	0.33	0.3	0.43	0.37	0.5	0.68	0.59	0.75	0.93	0.84	1.03	1.21	–

SCH 120
NPS	¾	½	1	1 ½	1 ¼	2	4	3	5	8	6	10	14	12	16	20	18	22	24
SCH 120	–	–	–	–	–	–	0.43	–	0.5	0.71	0.56	0.84	1.09	1	1.21	1.5	1.37	–	1.81

Steel Pipe Flange Pipe Flange Torque Chart

Size (MM)	15	20	35	40	50	80	100	150	200	250	300	350	400	450	500	600
Size (Inch)	01/2	03/4	1	1 ½	2	3	4	6	8	10	12	14	16	18	20	24
No of Bolt	4	4	4	4	4	4	8	8	8	12	12	12	16	16	20	20
Bolt Dia	½”	½”	½”	½”	5/8”	5/8”	5/8”	¾”	¾”	7/8”	7/8”	1”	1”	1 1/8”	1 1/8”	1 ¼”
Thread Type	UNC	UNC	UNC	UNC	UNC	UNC	UNC	UNC	UNC	UNC	UNC	UN8	UN8	UN8	UN8	UN8
Bolt Stress(lb/in2)	25,000	30,000	33,000	50,000	50,000	50,000	40,000	45,000	45,000	40,000	40,000	41,000	40,000	40,000	40,000	40,000
Torque(lbf.ft.)	22	26	29	44	86	86	69	137	137	194	194	296	289	421	421	588
Torque(Nm)	30	36	39	60	117	117	93	185	185	263	263	401	392	571	571	797

Weld Neck Pipe Flange Bolt Chart

NPS		01/4	01/2	03/4	1	01 1/4	01 1/2	2	02 1/2	3	03 1/2	4
Pressure Class 300	Flange Dia	15.74	15.74	19.05	19.05	19.05	22.35	19.05	22.35	22.35	22.35	22.35
	Bolt Holes Dia (MM)	02 1/4	02 5/8	03 1/4	03 1/2	03 7/8	04 1/2	5	05 7/8	06 5/8	07 1/4	07 7/8
	Bolt Circle	3 3/8	3 3/4	4 5/8	4 7/8	5 1/4	6 1/8	6 1/2	7 1/2	8 1/4	9	10
	Bolts Number	4	4	4	4	4	4	8	8	8	8	8
	Bolts Dia(MM)	12.7	12.7	15.87	15.87	15.87	19.05	15.87	19.05	19.05	19.05	19.05
NPS		5	6	8	10	12	14	16	18	20	24
Pressure Class 300	Flange Dia	22.35	22.35	25.4	28.44	31.75	31.75	35.05	35.05	35.05	41.14
	Bolt Holes Dia (MM)	09 1/4	10 5/8	13	15 1/4	17 3/4	20 1/4	22 1/2	24 3/4	27	32
	Bolt Circle	11	12 1/2	15	17 1/2	20 1/2	23	25 1/2	28	30 1/2	36
	Bolts Number	8	12	12	16	16	20	20	24	24	24
	Bolts Dia(MM)	19.05	19.05	22.22	25.4	25.4	25.5	25.4	25.4	25.4	25.4

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