Material Reference
Carbon Steel Flanges & Fittings
Carbon steel is still the default for the majority of process, pipeline, and utility piping in North America. The reference below covers the standard ASTM A105 and A350 grades for general and low temperature service, A516-70 plate for waterworks, and the full A694 high yield range for transmission pipeline service from Class 600 on up.
Standard Carbon Grades
ASTM A105 - Forged Flanges
A105 is the carbon steel forging grade that covers most ASME B16.5 flanges in ambient and moderately elevated service. It is suitable up to roughly 800°F, but ASME pressure-temperature tables derate the material steeply above 500°F, which is why high-temperature service typically shifts to chrome-moly alloy. For minimum design metal temperature below about -20°F, A105 needs supplementary impact testing or a switch to A350 LF2.
ASTM A350 LF2 - Low Temperature To -50°F
LF2 is the impact-tested forging that takes over below the A105 limit. Charpy testing is performed at -50°F as standard, making LF2 the workhorse for cold-climate gas processing, LNG export trains, ethylene and propylene service, and anywhere a low MDMT lands on the line list. Mechanically similar to A105, so substitution is usually transparent to downstream calculations.
ASTM A350 LF3 - Low Temperature To -150°F
LF3 carries about 3.5 percent nickel, which gives it Charpy performance down around -150°F. This is the spec for deep cryogenic carbon service before you have to step up into austenitic stainless or 9 percent nickel plate. Common on LNG and ethylene flange packages.
ASTM A516-70 - Pressure Vessel Plate
When a flange is cut from plate rather than forged, A516 Grade 70 is the standard carbon pressure vessel plate. It is the typical base material for cut-plate ring flanges, blinds, and the large-diameter AWWA ring and hub flanges used in waterworks. A516-70 is also routinely used as a substitute for A105 on cut-plate fabrications.
High Yield Carbon - The A694 Family
For transmission pipeline service, standard A105 yield strength is not enough. ASTM A694 covers heat-treated carbon and low alloy steel forgings designed to match the higher yield grades of line pipe. The grades are designated by minimum yield strength in ksi: F42, F46, F52, F56, F60, F65, and F70.
A694 forgings are governed by MSS SP-44, the standard for steel pipeline flanges, rather than ASME B16.5. They are typically specified in Class 600 and above and mate cleanly to API 5L pipe grades X42 through X70. Welding procedures need to account for the heat treatment - a sloppy weld can undo the property gains the forging spec delivers.
F42 through F52
The lower yield grades of the A694 family. Common on gathering systems and lower-pressure transmission lines where the operator wants A694 documentation without paying for full F65 or F70 property work.
F56 and F60
The middle of the range. F60 in particular shows up frequently on natural gas transmission where the pipe is X60 and the operator wants a matching flange yield without going to full F65.
F65
Probably the most-stocked A694 grade in the United States. Pairs to X65 line pipe, handles Class 900 and 1500 service, and is the typical specification on long haul gas transmission.
F70
The top of the standard A694 range. F70 is used on the highest-pressure transmission systems and on offshore risers where every pound of wall thickness saved at the flange matters.
Where Carbon Steel Fits
Carbon steel covers the bulk of the work in oil and gas production, midstream gathering and transmission, refineries, petrochemical plants, power generation balance-of-plant, and general industrial utilities. It is also the standard for municipal waterworks and large diameter water transmission, usually in the form of AWWA C207 ring or hub flanges cut from A36 or A516-70 plate.
For applications that step outside carbon's comfort zone - temperatures above 800°F, aggressive chemistry, sour gas, or cryogenic service - browse our alloy steel, stainless, and exotic alloy sections.
Known Limitations
Carbon steel corrodes. In wet or chloride-bearing service it corrodes faster, and in sour service it is subject to sulfide stress cracking unless hardness is controlled to NACE MR0175. Above roughly 800°F it loses strength rapidly, and above 900°F graphitization and creep become design concerns that push the spec into chrome-moly territory.
Carbon also has poor low-temperature toughness without supplementary testing, which is exactly why the A350 LF grades exist. Get the MDMT right at design time and the material picks itself.
Need Carbon Steel for a Project?
A105, LF2, LF3, A516-70, and the full A694 high-yield range. Send the line list to Texas Flange for pricing, availability, and mill test report scope.