Carbon Steel Flanges Material Properties

Carbon steel flanges are one of the widely used flanges in multiple industries due to their durability, strength and resistance to corrosion. They are form by heating and shaping carbon steel blocks into various shapes and sizes per the client’s requirements. Common standards include ASTM A694,ASTM A105N,ASTM A350. Accompanying pressure ratings are from class 150 to 2500.

Carbon steel flanges play an indispensable role in modern piping systems. These valuable elements are used in connect pipes, valves, pumps, and other pieces of equipment to develop assemblies without leakage.

What is Forging Carbon Steel

Forged carbon steel refers to a type of carbon steel that has undergone a forging process. Carbon steel is an alloy mainly compose of iron and carbon, with a carbon content typically ranging from about 0.02% to 2.11%.

During forging, the internal structure of the steel is refined. The grains of the metal are deformed and reoriented, resulting in a more uniform and compact microstructure. This leads to enhanced strength, toughness, and fatigue resistance of the forged carbon steel compared to non-forged counterparts.

Carbon steel pipe flanges usually adopt mild steel or low carbon steel, as it includes small percentage of carbon, strong and tough but not readily tempered. Which with lower cost and material could be used for many applications.

Low carbon steel: C content at 0.005% to 0.3%.

Medium carbon steel: 0.3 to 0.8% of Carbon.

High carbon steel: 0.8-2.0% of carbon.

Ultra high carbon steel: 1.25% to 2.0% of C.

Carbon Steel Flange Specification

Shape Type	WN,SO,SW,TH,LAPJ,BL
Sealing Face	RF, FF, FTJ
Size Range	1/2″ – 60″/ DN15 – DN1500
Pressure Rating	Class 150, 300, 600, 900, 1500, 2500lb
Standard	ASME B16.5, ASME B16.47 Series A/B
Carbon Steel	ASTM A105 / A105N
Low Temp Carbon Steel	ASTM A350 LF2/LF3
Pipeline Steel	ASTM A694 F42 / 46 / 56 / 60 / 65

Referred Standards

ASME B16.5 Dimensional standard for steel pipe flanges and flanges fittings

ASME B16.34 Valves connect by flanges, threaded and welding end

ASME B16.47 A/B Large diameter steel flanges

MSS SP44 Standard for steel pipe line flanges

API 605 large diameter carbon steel flanges

ASME B16.5 Standard

This standard covers pressure temperature ratings, materials, dimensions, tolerances, marking, testing and methods of designating openings for pipe flanges and flanged fittings. Such as weld neck flanges, slip-on flanges, socket weld flanges, threaded flanges, blind flanges, lap joint flanges and flangolets.

Dimension of ASME B16.5 Class 300 Blind Flange

Nominal Pipe Size		A	C	G	H	I	J	Weight
inch	mm	mm	mm	mm	Holes	mm	mm	kg / Piece
1/2	21.3	95.2	14.2	35.1	4	15.7	66.55	0.64
3/4	26.7	117.3	15.7	42.9	4	19	82.5	1.11
1	33.4	123.9	17.5	50.8	4	19	88.9	1.39
11/4	42.2	133.3	19	63.5	4	19	98.5	1.79
11/2	48.3	155.4	20.6	73.15	4	22.3	114.3	2.66
2	60.3	165. 1	22.3	91.9	8	19. 10	127	3.18
21/2	73.0	190.5	25.4	104.6	8	22.3	1.493	4.85
3	88.9	209.5	28.4	127	8	22.3	168.1	6.81
31/2	101.6	228.6	30.2	139.7	8	22.3	184.1	8.71
4	114.3	254	31.7	157.2	8	22.3	200.1	11.5
5	141.3	279.4	35	185.7	8	22.3	234.9	15.6
6	168.3	317.5	36.5	215.9	12	22.3	269.7	20.9
8	219. 1	381	1.620 41.10	269.7	12	25.4	330.2	34.3
10	273.0	444.5	47.7	323.9	16	28.4	387.3	53.3
12	323.8	520.7	50.8	381	16	31.7	450.8	78.8
14	355.6	584.2	53.8	412.8	20	31.7	514.3	105
16	406.4	647.7	57.15	469.9	20	35	571.5	137
18	457.2	711.2	60.45	533.4	24	35	628.6	175
20	508.0	774.7	63.5	584.2	24	35	685.8	221
24	609.6	914.4	69.85	692.2	24	41. 10	812.8	339

ASTM A105 Material Properties

ASTM A105 is a low-carbon alloy steel. It is a widely recognized standard specification for carbon steel flange used in various industrial applications, particularly in piping systems. It’s typical chemical composition includes elements such as carbon (C), manganese (Mn), phosphorus (P), sulfur (S), silicon (Si), and small amounts of other alloying elements.

Chemical Composition of ASTM A105 Carbon Steel Flanges

CHEMICAL	LIMITS	C	Mn	P	S	Si	Cu	Ni	Cr	Mo	V
ASTM A105	MIN		0.60			0.10
	MAX	0.35	1.05	0.035	0.040	0.35	0.40	0.40	0.30	0.12	0.08

Mechanical Properties

MATERIAL	T.S (MPA)	Y.S (MPA)	EL %	R/A %	HARDNESS
ASTM A105	485 min	250 min	22 min	30 min	197 max

ASTM A105 forgings are typically produced through forging processes. The raw steel is heated to a suitable temperature and then shaped using forging equipment, such as hammers or presses. This forging process refines the grain structure of the steel, improving its mechanical properties. After forging, the components may undergo heat treatment processes such as annealing or normalizing to further enhance their properties. For example, annealing can relieve internal stresses and improve the machinability of the material.

Advantages

Cost-Effective

Good Machinability

Compatibility

ASTM A350 LF2 Material Properties

ASTM A350 LF2 is a low-alloy, ferritic steel that is widely used in various industrial applications, especially in low-temperature service environments. 

ASTM A350 LF2 has a carefully controlled chemical composition. It contains elements such as carbon (C), manganese (Mn), phosphorus (P), sulfur (S), silicon (Si), and small amounts of other alloying elements. The low carbon content, typically around 0.30% maximum, contributes to good weldability and toughness. Manganese is added to enhance the strength and hardenability of the steel. Additionally, the controlled levels of other elements help to optimize the material’s performance in low-temperature conditions.

Chemical Composition of Low Temp Carbon Steel flanges

CHEMICAL	LIMITS	C	Mn	P	S	Si	Cu	Ni	Cr	Mo	V	Nb
ASTM A350 LF2	MIN		0.60			0.15
	MAX	0.30	1.35	0.035	0.040	0.35	0.40	0.40	0.30	0.12	0.08	0.02

Mechanical Properties

MATERIAL	T.S (MPA)	Y.S (MPA)	EL %	R/A %	HARDNESS
ASTM A350 LF2	485-655	250 min	22 min	30 min	197 max

Advantages of Carbon Steel Flanges

Reliability in Low Temperatures

Good Weld ability

Compatibility

ASTM A694 Material Properties

ASTM A694 is a specification that covers carbon and alloy steel forgings for flanges, fittings, valves, and other components used in high-pressure and high-temperature applications. 

ASTM A694 flanges are made from carbon and alloy steels with specific chemical compositions. The chemical composition can vary depending on the grade of the material. For example, common alloying elements may include chromium (Cr), molybdenum (Mo), and vanadium (V).

Chemical Composition Pipeline Steel Carbon Steel Flanges

CHEMICAL	LIMITS	C	Mn	P	S	Si
ASTM A694 F42	MIN					0.15
	MAX	0.30	1.60	0.025	0.025	0.35

Mechanical Properties

MATERIAL	T.S (MPA)	Y.S (MPA)	EL %
ASTM A694 F42	415 min	290 min	20 min

Differences between Carbon Steel Flanges and Stainless Steel Flanges

Material Composition

Carbon Steel Flanges

The main components of carbon steel flanges are carbon and iron, with the carbon content typically ranging from 0.0218% to 2.11%.

In addition to carbon, it may also contain small amounts of elements such as silicon, manganese, sulfur, and phosphorus. Silicon and manganese mainly play a role in deoxidation and strengthening in carbon steel. Sulfur and phosphorus are generally harmful impurities that can reduce the toughness and corrosion resistance of the steel.

Stainless Steel Flanges

Stainless steel flanges are alloy steels with chromium, nickel, and other alloying elements as the main additives. Common stainless steels include austenitic stainless steel (such as 304, 316, etc.).

Taking 304 stainless steel as an example, its main chemical composition includes approximately 18% – 20% chromium (Cr) and 8% – 10.5% nickel (Ni).

Corrosion Resistance

Carbon Steel Flanges

Carbon steel flanges have relatively poor corrosion resistance. In normal atmospheric environments, they are prone to rusting due to the reaction of iron with oxygen and moisture in the air.

Stainless Steel Flanges

Stainless steel flanges have excellent corrosion resistance due to the presence of chromium and other alloying elements. The chromium oxide film formed on the surface can prevent the steel from further reacting with the corrosive medium, thereby protecting the flange from corrosion.

Mechanical Properties

Carbon Steel Flanges

Carbon steel flanges generally have high strength and hardness, especially high-carbon steel flanges. However, their toughness and ductility may be relatively lower compared to stainless steel flanges. This means that carbon steel flanges are more likely to fracture under impact or sudden loads.

Stainless Steel Flanges

Stainless steel flanges, especially austenitic stainless steel flanges, have good toughness and ductility. They can withstand a certain degree of deformation without breaking, making them suitable for applications where flexibility and shock resistance are required.

Cost

Carbon Steel Flanges

Carbon steel is a relatively common and inexpensive material, so carbon steel flanges are generally more cost-effective. They are widely use in applications where corrosion resistance is not a critical requirement, such as some general industrial piping systems.

Stainless Steel Flanges

Due to the addition of alloying elements and the more complex manufacturing process, stainless steel flanges are more expensive than carbon steel flanges.

Application of Carbon Steel Forged Flanges

Oil and Gas Industry

Petrochemical Industry

Chemical Industry

Water Treatment Industry

Power Generation Industry

January 3, 2025