ASTM A350

ASTM A350 (ASME SA350) is the standard specification for carbon steel and low alloy steel forged flanges and flanged fittings for low temperature services.

Common use grade is ASTM A350 LF2 Class 1, corresponding material for piping in ASTM A333 Grade 6 and pipe fittings in ASTM A420 WPL6. With yield strength minimum 240 Mpa, and tensile strength in 480 Mpa to 655 Mpa, impact test temperature at -45℃.

ASTM A350 covers several grades of carbon and low-alloy steel forged or ring-rolled flanges, forged fittings and valves intended primarily for low-temperature service and requiring notch toughness testing. They are made to specified dimensions, or to dimensional standards, such as the ASME and API Specifications referenced in Section 2. Although this specification covers some piping components machined from rolled bar and seamless tubular materials, it does not cover raw material produced in these product forms.

Product furnished in ASTM A350/ ASME SA350 shall conform to the requirements of Specification A961/A961M, including any supplementary requirements that are indicated in the purchase order. Failure to comply with A961/A961M will be considered nonconformance with A350. And in case of conflict between ASTM A350 and A961/A961M, this specification shall prevail.

ASTM A350 Chemical composition requirements

Element	Composition, w.t % Grades
	LF1	LF2	LF3	LF5	LF6	LF9	LF787
C	≤0.30	≤0.30	≤0.20	≤0.30	≤0.22	≤0.20	≤0.07
Mn	0.60-1.35	0.60-1.35	≤0.90	0.60-1.35	1.15–1.50	0.40–1.06	0.40–0.70
P	≤0.035	≤0.035	≤0.035	≤0.035	≤0.025	≤0.035	≤0.025
S	≤0.040	≤0.040	≤0.040	≤0.040	≤0.025	≤0.040	≤0.025
Si	0.15-0.30	0.15-0.30	0.20-0.35	0.20-0.35	0.15-0.30	...	≤0.40
Ni	≤0.40	≤0.40	3.30-3.70	1.00-2.00	≤0.40	1.60-2.24	0.70–1.00
Cr	≤0.30	≤0.30	≤0.30	≤0.30	≤0.30	≤0.30	0.60–0.90
Mo	≤0.12	≤0.12	≤0.12	≤0.12	≤0.12	≤0.12	0.15-0.25
Cu	≤0.40	≤0.40	≤0.40	≤0.40	≤0.40	0.75–1.25	1.00-1.30
Cb	≤0.02	≤0.02	≤0.02	≤0.02	≤0.02	≤0.02	≥0.02
V	≤0.08	≤0.08	≤0.03	≤0.03	0.04-0.11	≤0.03	≤0.03
N	...	...	...	...	0.01–0.030	...	...

*1. When vacuum carbon-deoxidation is required, the silicon content shall be 0.12% maximum.
*2. For grades LF1, LF2 & LF6, the sum of Cu, Ni, Cr, V and Mo shall not exceed 1.00 % on heat analysis.
*3. For all grades except grade LF787, the sum of Cr and Mo shall not exceed 0.32 % on heat analysis.
*4. For grades LF1 & LF2, the limit for Cb may be increased up to 0.05 % on heat analysis and 0.06 % on product analysis.
*5. The carbon equivalent C.E = [C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15] shall not exceed 0.45%.

ASTM A350 mechanical properties

Grade/Class	Tensile Strength		Yield Strength, min.		Elongation, min.	Hardness, max.
	ksi	MPa	ksi	MPa	%	HBW
LF1 CL1	60-85	415–585	30	205	25	197
LF5 CL1	60-85	415–585	30	205	25	197
LF2 CL1	70–95	485–655	36	250	22	197
LF2 CL2	70–95	485–655	36	250	22	197
LF3 CL1	70–95	485–655	37.5	260	22	197
LF3 CL2	70–95	485–655	37.5	260	22	197
LF5 CL2	70–95	485–655	37.5	260	22	197
LF6 CL1	66–91	455–630	52	360	22	197
LF6 CL2	75–100	515–690	60	415	20	197
LF6 CL3	75–100	515–690	60	415	20	197
LF9	63–88	435–605	46	315	25	197
LF787 CL2	65-85	450-585	55	380	20	197
LF787 CL3	75-95	515-655	65	450	20	197

*1. The elongation values are on the basis of standard round specimen, or small proportional specimen, min % in 4D gauge length.
*2. The yield strength shall be determined by either the 0.2 % offset method or the 0.5 % extension under load method.

Tension Tests Requirements—The material shall conform to requirements for tensile properties in below table.

Heat Analysis and Product Analysis

A chemical heat analysis and product analysis in accordance with Specification A961/A961M shall be made and conform to the requirements as to chemical composition prescribed in this table. Leaded steels shall not be permitted. Product analysis

As specified by ASTM A350, after hot working and before reheating for heat treatment, the forging shall be allowed to cool substantially below the transformation range. Forgings of grades other than Grade LF787 shall be furnished in the normalized, or normalized and tempered, or quenched and tempered condition. All quenched forgings shall be then tempered at 1100 °F [590 °C], minimum, holding at temperature a minimum of 30 min/in. [30 min/25 mm] of maximum thickness, but in no case less than 30 min. Grade LF787 forgings shall be furnished in either the normalized-and-precipitation heat treated condition or in the quenched-and-precipitation heat treated condition.

For Grade LF1 and LF2 forgings, the weld metal shall be deposited using carbon steel electrodes E 7015, E 7016, or E 7018, complying with AWS A 5.1. For Grade LF2 forgings, the weld metal shall be deposited using low-alloy steel electrodes E 7015-A1; E 7016-A1, or E 7018-A1 complying with AWS 5.5; for Grade LF3 forgings, the weld metal shall be deposited using low-alloy steel electrodes E 8016-C2 or E 8018-C2 complying with AWS A 5.5; for Grades LF5, LF9, and LF787 forgings, the weld metal shall be deposited using low-alloy steel electrodes E 8016-C1 or E 8018-C1 complying withAWS A 5.5. For Grade LF6, the electrodes shall be low-hydrogen, E-XX15, E-XX16, or E-XX18 complying with AWS A 5.1 or A 5.5, as applicable.

The dimensional standards for ASTM A350 forgings

ASME B16.5	Steel Pipe Flanges and Flanged Fittings
ASME B16.9	Factory-MadeWroughtSteelButt-WeldingFittings
ASME B16.11	Forged Steel Fittings, Socket-Welding and Threaded4
ASME B16.34	Valves-Flanged, Threaded, and Welding End
ASME B16.47	Large Diameter Steel Flanges
API 600	Steel Gate Valves with Flanged or Butt-Welding Ends
API 602	Compact Design Carbon Steel Gate Valves for Refinery Use
API 605	Large Diameter Carbon Steel Flanges

Referenced Documents

ASTM Standards:

• A788/A788M Specification for Steel Forgings, General Requirements
• A961/A961M Specification for Common Requirements for Steel Flanges, Forged Fittings, Valves, and Parts for Piping Applications

ASME Standards:

• B 16.5 Steel Pipe Flanges and Flanged Fittings
• B 16.9 Factory-Made Wrought Steel Butt-Welding Fittings
• B 16.10 Face-to-Face and End-to-End Dimensions of Ferrous Valves
• B 16.11 Forged Steel Fittings, Socket-Welding and Threaded
• B 16.30 Unfired Pressure Vessel Flange Dimensions
• B 16.34 Valves-Flanged, Threaded, and Welding End
• B 16.47 Large Diameter Steel Flanges
• ASME Boiler and Pressure Vessel Code

AWS Standards:

• A 5.1 Mild Steel Covered Arc-Welding Electrodes
• A 5.5 Low-Alloy Steel Covered Arc-Welding Electrodes

API Standards:

• 600 Steel Gate Valves with Flanged or Butt-Welding Ends
• 602 Compact Design Carbon Steel Gate Valves for Refinery Use
• 605 Large Diameter Carbon Steel Flanges

Manufacture – Melting and Forging

Melting Process – The steel shall be produced by any of the following primary processes: open-hearth, basic oxygen, electric-furnace, or vacuum-induction melting (VIM). The primary melting may incorporate separate degassing or refining, and may be followed by secondary melting using electroslag remelting (ESR), or vacuum-arc remelting (VAR).

Discard – A sufficient discard shall be made to secure freedom from injurious piping and undue segregation.

Forging Process

Material for forgings shall consist of ingots, or forged, rolled, or strand cast blooms, billets, slabs, or bars.

Heat Treatment

After hot working and before reheating for heat treatment, the forging shall be allowed to cool substantially below the transformation range.

Forgings grades except Grade LF787, should be heat treated in normalized, or normalized and tempered, or quenched and tempered. By manufacturer’s option, material that performed in quenched and tempered could be normalized prior to the austenitize/quenched operation.

No limitation on size is intended beyond the ability of the manufacturer to obtain the specified requirements. However, Class 3 of Grade LF787 is only available in the quenched-and-precipitation heat treated condition.

Hydro-static Test

Forgings manufactured under ASTM A350/ ASME SA350 shall be performed with a hydro-static test compatible with the rating of the finished item. Such tests shall be conducted by the manufacturer only when Supplementary Requirement S57 of Specification A961/A961M is specified.