The industrial flange grade determines whether a flange can handle the system’s pressure, how it performs at operating temperature, and how it aligns with specific industry dimensional standards. This guide covers the four most common carbon steel flange grades in industrial use:
What is a Carbon Steel Flange Grade?
Carbon steel is defined primarily by its carbon content, which ranges from 0.05% to 2.1% by weight. That percentage governs tensile strength, hardness, ductility, and weldability.
- Grades in the mild/low carbon range (up to 0.30%) weld easily and are highly ductile, but have lower strength limits.
- Grades in the medium carbon range (0.30–0.60%) offer higher strength and perform under sustained pressure and elevated temperature.
Carbon Steel Flange ASTM Grade Overview
| Carbon Steel Flange ASTM Grade | Product Form | Carbon % | Primary Service | Key Standard |
|---|---|---|---|---|
| A36 | Plate / structural | 0.29% max (varies by thickness) | Low-temp, non-pressure, structural | ASTM A36/A36M |
| A105 | Forging | 0.35% max | Ambient to high-temp pressure piping | ASTM A105/A105M |
| A694 | Forging | Varies by grade (F42–F70) | High-pressure oil and gas pipelines | ASTM A694/A694M |
| A516 | Plate | 0.31% max (varies by grade and thickness) | Pressure vessels, moderate temperature | ASTM A516/A516M |
ASTM A36 — Mild Carbon Steel Plate Flanges
In flange applications, A36 is used as a plate material, not a forging.
Plate flanges cut from A36 stock serve non-pressure and low-pressure systems (up to 300psi) where ASME piping code compliance is not required. The grade does not qualify under ANSI/ASME B16.5 for pressure-rated service, but it is widely used and practically suited for waterworks, HVAC, and large-diameter structural connections.
ASTM A36 Mild Carbon Steel Plate Flanges
A36 Flanges Are Used in Projects:
A36 plate flanges are the standard material for the following applications: municipal water mains, treatment plants, and irrigation infrastructure.
HVAC and Industrial Ventilation
Large duct connections and air handling equipment
Structural and Agricultural Connections
Irrigation mainlines, pipe supports, and non-pressure structural pipe frames
What Is A36 Not Suited For?
Because A36 is primarily a structural specification, it is not suited for high-pressure or high-temperature process piping. While piping codes like ASME B31.3 technically permit A36 under highly restricted, low-pressure conditions, it lacks the pressure-temperature ratings required to qualify under standard ASME B16.5 flange tables.
If your project is governed by a piping code, A105 forged flanges are the required specification. Substituting A36 in a pressure application is a specification error that will be identified during code review or third-party inspection.
ASTM A105 Medium Carbon Forged Flanges
ASTM A105 is the standard specification for carbon steel forgings used in pressure piping. It covers flanges, fittings, valves, and similar parts that are made for ambient and elevated temperature service. A105 is the material referenced in ANSI/ASME B16.5 and ANSI/ASME B16.47 standards, which govern the majority of pressure-rated carbon steel pipe flanges produced worldwide.
The forging process gives A105 a key structural advantage over plate-cut materials. When steel is forged, the steel aligns and compresses the material’s grain structure to follow the contour of the component. This continuous, directional grain flow produces a stronger, tougher, and more uniform material capable of handling severe pressure cycles far better than standard plate stock.
ASTM A105 Medium Carbon Forged Flanges
Where A105 Flanges Are Used
Weld neck flanges and slip-on flanges in A105 are standard across process piping, refineries, power generation, and chemical facilities.
Process Piping
Process piping systems governed by ASME B31.3
Power Generation
Power piping systems governed by ASME B31.1
Oil & Gas
Oil and gas surface facilities and refineries
Chemical Industry
Chemical processing plants and petrochemical facilities
Steam Service
Steam lines and elevated-temperature service up to 800°F
Municipal Water
Municipal water infrastructure requiring ASME-rated components
A105 Flange Pressure Classes and Dimensional Standards
| Standard | Size Range | Pressure Classes |
|---|---|---|
| ANSI/ASME B16.5 | NPS ½” through NPS 24″ | 150, 300, 400, 600, 900, 1500, 2500 |
| ANSI/ASME B16.47 Series A | NPS 26″ through NPS 60″ | 150, 300, 400, 600, 900 |
| ANSI/ASME B16.47 Series B | NPS 26″ through NPS 60″ | 75, 150, 300, 400, 600, 900 |
| AWWA C207 | NPS 4″ through NPS 144″ | Up to 300 psi working pressure |
ASTM A694 High-Pressure Pipeline Flanges
ASTM A694 covers carbon and alloy steel forgings for pipe flanges, fittings, valves, and parts used in high-pressure oil and gas transmission service. This specification covers flanges in high-pressure pipeline systems. A694 is a grade-based specification. Each grade designation corresponds to a minimum yield strength in ksi — F42 through F70. This allows engineers to match the flange material to the pipeline system’s specific design pressure.
Key Characteristics
- Impact testing. While standard ASTM A694 does not mandate baseline Charpy V-notch testing, it can be ordered with supplementary impact requirements (or per MSS SP-75) to ensure low-temperature notch toughness in cold-weather pipeline networks.
- Higher yield strength. Each A694 grade designation reflects its minimum yield in ksi. F60 and F65 are the most commonly specified grades in modern high-pressure gas pipeline systems.
- Dimensional compliance. A694 flanges are dimensioned per ASME B16.5 and B16.47. They are a material upgrade, not a dimensional change.
ASTM A516 Pressure Vessel Plate Flanges
ASTM A516 is a specification for carbon steel plate intended for pressure vessels that operate at moderate and low temperatures. Its primary applications are pressure vessel shells, heads, and nozzle reinforcement pads, but it is also used to fabricate custom plate flanges for large-diameter pressure vessel nozzles and non-standard connections.
A516 comes in four grades (55, 60, 65, and 70), where the number denotes the minimum tensile strength in ksi. Grade 70 is the most widely specified.
Key Characteristics
Low-temperature toughness
A516 is designed for improved notch toughness at low temperatures.
ASME compliance
A516 is a listed material under ASME BPVC Section VIII, Division 1.
Flange applications
A516 flanges are used at pressure vessel nozzle connections and heat exchanger flanges where the vessel shell and flange need matching material.
Flange Grade Comparison
The following comparison highlights the differences between A36, A105, A694, and A516 Grade 70 carbon steel flange materials.
| Criteria | A36 flange | A105 flange | A694 flange | A516 Gr. 70 flange |
|---|---|---|---|---|
| Product form | Plate | Forging | Forging | Plate |
| Carbon content | 0.29% max (varies by thickness) | 0.35% max | Varies by grade | 0.31% max (varies by thickness) |
| Min yield strength | 36 ksi | 36 ksi | 42–70 ksi | 38 ksi |
| Min tensile strength | 58 ksi | 70 ksi | 60–82 ksi | 70 ksi |
| Max service temp | Low-temp only | 800°F (425°C) | Per design | Moderate-temp |
| Pressure rated | AWWA Only (≤300 psi) | Yes | Yes | Yes (ASME VIII) |
| ASME B16.5 listed | No | Yes (Group 1.1) | Yes | No |
| Impact testing req. | No | Optional | Optional/Supplementary requirement | Optional/Supplementary requirement |
| Primary application | Water, HVAC, structural | Process piping | Oil & gas pipelines | Pressure vessels |
In Closing
Carbon steel flange grades are not interchangeable. A36, A105, A694, and A516 each occupy a specific position in the specification landscape, determined by product form, mechanical properties, and the standards they comply with.
Getting the grade right at the specification stage prevents material rejections, failed inspections, and costly rework downstream.
JS FITTINGS-Carbon Steel Flanges Supplier
JS FITTINGS supplies carbon steel flanges fully machined to meet ASTM A105 material requirements, with dimensions and tolerances per ANSI/ASME B16.5 and ANSI/ASME B16.47 .
Our sales team specializes in navigating complex flange requirements to ensure your system meets its design specifications. Explore our comprehensive range of flanges in our online product catalog, or contact us for custom options tailored to your unique project needs.
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