Material Reference
Carbon Steel Flanges & Fittings
Carbon steel is still the default for the majority of process, pipeline, water, and utility piping in North America. We stock ASTM A105 forgings as the workhorse, A350 LF2 and LF3 for low-temperature service, SA-516-70 and A36 plate for cut-blank fabrication, and the full A694 high yield family for transmission pipeline flanges from Class 600 on up.
ASTM A105 - The Workhorse
A105 is the carbon steel forging grade that covers the overwhelming majority of ASME B16.5 flanges in ambient and moderately elevated service. Pressure ratings run from roughly 20 psi at the top of the temperature curve up to 6,170 psi at ambient on a Class 2500 flange, with allowable service temperatures from cryogenic territory (with supplementary impact testing) up to about 1,000F at the very top end of the rating tables.
We carry A105 across the full standard size range: 1/2 inch nominal pipe size through 24 inch in forged B16.5 geometry, and 26 inch through 96 inch as plate-cut blanks machined to flange tolerance. The same grade covers weld neck, slip-on, blind, lap joint, threaded, and socket weld configurations under ASME B16.5, and ring joint blinds and large-bore patterns under B16.47 Series A and B.
ASME pressure-temperature tables derate A105 steeply above 500F, which is why high-temperature service typically shifts to chrome-moly alloy. For minimum design metal temperature below about -20F, A105 needs supplementary impact testing or a switch to A350 LF2.
A350 LF2 And LF3 - Low Temperature Carbon
A350 LF2 - Charpy Tested To -50F
LF2 is the impact-tested forging that takes over below the A105 limit. Charpy testing is performed at -50F 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.
A350 LF3 - Charpy Tested To -150F
LF3 carries about 3.5 percent nickel, which gives it Charpy performance down around -150F. 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 where the MDMT undercuts what LF2 can support.
Plate Materials - SA-516-70 And A36
When a flange is cut from plate rather than forged, the choice of plate steel matters more than the geometry it ends up cut to. Two grades cover almost everything we ship in plate-cut form.
SA-516 Grade 70 - Pressure Vessel Plate
SA-516-70 is the standard carbon pressure vessel plate under ASME Section II. It is the typical base material for cut-plate ring flanges, blinds, and large-diameter ring and hub flanges where pressure containment is the governing requirement. Often used as a direct substitute for A105 on cut-plate fabrications where the geometry is non-standard or the size exceeds forged B16.5 limits. Available in normalized condition when the spec calls for it.
A36 Plate - Structural And AWWA
A36 is general-purpose structural carbon plate. In flange work it shows up on AWWA C207 ring and hub flanges for large-diameter waterworks, on backing rings, on non-pressure structural connections, and on low-pressure utility service where SA-516-70 is more grade than the application warrants. Significantly cheaper than pressure vessel plate when the duty allows the substitution.
High Yield Carbon - The A694 Family
For transmission pipeline service the standard A105 yield strength of 36 ksi is not enough. ASTM A694 covers heat-treated carbon and low alloy steel forgings designed to match the higher yield grades of API 5L 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 in matching grades X42 through X70. The higher yield threshold is achieved through controlled heat treatment, which means welding procedures need to account for the property work the forging has already received. A sloppy weld can undo the 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 the full F65 or F70 property work. Pairs to X42, X46, and X52 line pipe.
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.
Finishes - Painted, Galvanized, And Coated
Carbon steel ships from the mill in one of a few standard surface conditions. Mill finish (black oxide) is the default and is suitable for service environments where the flange will be insulated or quickly painted in the field. Black paint or a thin oil dip is common on stock material for corrosion protection during shipping and storage. Hot dip galvanized per ASTM A153 adds a zinc layer that is standard on waterworks, structural, and outdoor utility installations. Specialty coatings (epoxy, phenolic, fusion bonded) are project-specific and quoted to spec.
Pick the finish to match the service. Painted A105 in a buried pipeline rots out fast without supplemental cathodic protection. Galvanized A105 in a steam line burns the zinc off in days. The fundamentals do not change with the coating.
Where Steel Replaced Cast Iron
A generation ago, large-diameter water transmission, sewer force mains, and low-pressure industrial utility piping were dominated by cast iron flanges per the old ANSI B16.1 standard. Cast iron is brittle, fails poorly under impact, and corrodes unpredictably. Most modern projects replace it with steel - either ductile iron under AWWA C110 for direct cast-iron compatibility, or carbon steel cut from SA-516-70 or A36 plate to AWWA C207 dimensions for ring and hub flanges.
Cast iron pattern flanges are still produced for retrofit and like-for-like replacement work. We can quote them when the project calls for it, but the conversation usually starts with whether the upgrade to steel is worth doing once the line is open anyway.
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 as AWWA C207 ring or hub flanges cut from A36 or SA-516-70 plate.
For applications that step outside carbon's comfort zone (temperatures above 800F, aggressive chemistry, sour gas, or cryogenic service) see our alloy steel, stainless steel, and exotic alloy sections.
Carbon Steel On A Schedule?
Standard A105 and LF2 typically ship the same week. A694 in any grade, quoted fast with mill test reports. SA-516-70 and A36 plate-cut blanks to your drawing.