If you order the grade of forged flange you may discover the mistake only when the plant starts running in winter. A cracked flange at -35°C costs more than the price difference between two grades. That is why engineers and buyers need to understand A105 carbon steel before they raise a purchase order.
A105 is the common carbon steel forging grade used in piping. It shows up in flanges, forged fittings and valve bodies in oil and gas power, chemical and water systems. This guide explains the ASTM A105 specification, its chemistry and mechanical limits, how it differs from A105N and A350 LF2 and what to check before you pick a supplier.
What Is A105 Carbon Steel?
A105 carbon steel is a forged carbon steel covered by ASTM A105/A105M (ASME SA105 for boiler and pressure vessel work). The specification covers carbon steel forgings that are used in piping components for higher‑temperature pressure service. Typical products include flanges, forged fittings and valve parts. A105 is usually rated for service from about -29°C to 425°C (-20°F to 800°F).
In short A105 is the default choice for forged carbon steel piping parts when the temperature is not extreme and the fluid is not highly corrosive.
ASTM A105 Specification: Scope and Key Requirements
The ASTM A105 specification sets the rules for chemistry, mechanical properties, heat treatment, testing and marking. It works together with ASTM A961/A961M, which covers the requirements for steel flanges, forged fittings and valves.
What the Standard Covers
Forgings made from killed carbon steel
Piping components such as flanges, fittings, valve bodies and similar parts
Forgings up to a maximum weight of 10,000 lb (4,540 kg). Heavier forgings are ordered under ASTM A266.
Both inch-pound and SI units
What It Does Not Cover
The standard does not cover bar or tubular material as a product form. It also does not cover pressure vessel shell components. For those buyers look at specifications such as ASTM A266.
Dimensions and Pressure Ratings
A105 itself defines material, not dimensions. Dimensions come from standards such as ASME B16.5 (flanges up to NPS 24) and ASME B16.47 ( flanges). Under ASME B16.5 A105 sits in Material Group 1.1 which sets its pressure‑temperature ratings for Class 150 up to Class 2500.
A105 Chemical Composition
The chemistry of A105 is tightly limited to protect weldability and strength. The table below shows the limits.
Element Requirement (wt %)
Carbon (C) 0.35 max
Manganese (Mn) 0.60 – 1.05
Phosphorus (P) 0.035 max
Sulfur (S) 0.040 max
Silicon (Si) 0.10 – 0.35
Copper (Cu) 0.40 max
Nickel (Ni) 0.40 max
Chromium (Cr) 0.30 max
Molybdenum (Mo) 0.12 max
The standard also limits vanadium and niobium. It caps the combined total of copper, nickel, chromium, molybdenum and vanadium. A carbon equivalent (CE) limit of 0.47–0.48% depending on section thickness applies to control weldability.
Manganese trade‑off: For each 0.01% of carbon below 0.35% the standard allows 0.06% manganese, up to 1.35%. This helps mills recover strength when carbon is lower. Always check the mill test certificate for the values not only the limits.
A105 Mechanical Properties
Every A105 forging must meet tensile and yield strength, plus elongation, reduction of area and hardness limits.
Property Requirement
Tensile strength 485 MPa (70 ksi) min
Yield strength 250 MPa (36 ksi) min
Elongation (50 mm / 2 in.) 22% min
Reduction of area 30% min
Hardness 187 HBW max
The maximum hardness is as important as the minimum strength. A cap of 187 HBW keeps the steel machinable and weldable. It supports hardness limits that some sour‑service rules require.
Heat Treatment: A105 vs A105N
Heat treatment is a source of confusion. The “N”, in A105N stands for normalized.
A105 has the chemistry as A105N.
Most forgings must go through heat treatment as the standard says except for some small forgings and lower‑class flanges.
Always look at the edition to see the exact rules.
A105N forgings are normalized.
The forging is heated above the range and then air‑cooled.
This makes the grain structure finer. Gives the steel a more uniform strength and better toughness.
The base metal is the same. I see that A105N is often chosen by EPC contractors and end users because normalizing makes the microstructure more consistent.
For flanges that run on lines A105N is often the minimum condition that will be accepted.
Always read your project piping class before you order.
A105 vs A350 LF2: Which One Do You Need?
I think the real difference between A105 and A350 LF2 is low‑temperature toughness, not how pressure they can hold.
| Feature | ASTM A105 | ASTM A350 LF2 |
Typical service range | –29 °C to 425 °C | –46 °C to about 345 °C |
| Charpy impact test | Not required unless specified | Mandatory at –46 °C |
| Carbon (max) | 0.35 % | 0.30 % |
Manganese (max) | 1.05 % | 1.35 % |
| Tensile strength (min) | 485 MPa | 485 MPa |
| Yield strength (min) | 250 MPa | 250 MPa |
| Best for | General process and utility piping Cold climates, LNG, depressurization risk |
Rule of thumb:
If your design temperature goes below –29 °C or if a fast drop in pressure could make the pipe cold (auto‑refrigeration) then choose A350 LF2, not A105.
Some suppliers give you material that is certified for both A105N and A350 LF2 when the steel satisfies both standards.
If you ordered LF2, double‑check that the mill certificate shows compliance with A350 LF2 and that it contains the impact test results.
Where Is A105 Carbon Steel Used?
I like A105 because it balances cost, strength and how easy it is to weld.
Common places for A105 are:
– Oil and gas: Wellhead piping, pipelines, gathering systems and refinery process lines
– Petrochemical and chemical plants: Hydrocarbon and non‑corrosive process fluids
– Power generation: Steam, feedwater and condensate lines within the temperature range
– Water and utilities: Fire water, cooling water and compressed air systems
– Valve manufacturing: Bodies and bonnets for gate, globe and check valves, such as small‑bore forged‑steel valves
Common A105 Products
– Weld neck, slip‑on, socket weld, threaded, blind and lap joint flanges
– Orifice flanges and spectacle blinds
– Forged fittings such as elbows, tees, couplings, unions and plugs (socket weld and threaded)
– Valve bodies and other pressure‑containing forgings
When A105 Is Not the Right Choice
engineering means knowing the limits.
Avoid A105. Add extra checks in these cases:
– Below –29 °C: Use A350 LF2 or LF3 with impact testing.
– Corrosive fluids: Carbon steel corrodes. Consider steel (such as A182 F304/F316) or lined systems.
– Sour service (H₂S): Check NACE MR0175 / ISO 15156 requirements, including hardness and chemistry limits.
– Long exposure above about 425 °C: Carbon steel can suffer graphitization. Low‑alloy grades such as A182 F11 or F22 are better.
– Large forgings: Forgings above 4,540 kg fall outside A105. Use A266.
How to Choose an A105 Supplier
I say that the grade is half the story.
A forging made to the standard but poorly controlled can still fail in service.
Use this checklist when you evaluate an A105 supplier.
1. **Ask for Full Material Traceability**
Each forging should carry a heat number stamped or marked on the part.
The heat number must match the mill test certificate (MTC).
2. **Insist on an EN 10204 3.1 Certificate**
An MTC 3.1 lists the chemistry, mechanical test results and heat treatment condition.
For projects ask for 3.2 certification with third‑party inspection by agencies such as TÜV, Bureau Veritas, SGS or Lloyds.
3. **Verify Heat Treatment**
Check that the certificate states the condition (as‑forged normalized, normalized and tempered or quenched and tempered).
If your order says A105N the certificate must show normalizing.
4. **Check the Test Reports Against the Limits**
Compare the values with the tables above.
Look at carbon hardness and yield strength.
A certificate that only repeats the standards limits, without values is a red flag.
5. Confirm Dimensional Standards and Inspection
Ask which dimensional standard applies, such as ASME B16.5, B16.47, B16.11, MSS SP-97, API 602 and so forth. Confirm that the supplier can perform PMI ( material identification) visual checks, dimensional checks and NDT when required.
6. Review Quality Systems
Look for ISO 9001 certification as a baseline. For pressure equipment ask whether the supplier can provide material for projects that require PED/CE or API documentation when needed.
7. Ask About Stock, Lead Time and Packing
Stock availability for sizes and classes shortens lead time. Good packing, such as varnished surfaces, plywood cases or pallets and protected flange faces prevents transit damage and rust.
8. Request a Sample Order or Past Project References
A supplier will share references and typical export documents without delay.
Common Mistakes When Buying A105 Carbon Steel
Mixing up A105 and A105N: Always state the heat treatment condition in the purchase order. Using A105 for low-temperature lines: Check the minimum design metal temperature (MDMT) first. Accepting certificates without checking them: Match heat numbers, dates and values to the product. Buying on price alone: A low quote may mean off-spec chemistry, missing heat treatment or no real testing. Ignoring the piping class: Match material, rating, facing (RF, FF, RTJ) and schedule to the project spec.
How to Write a Clear A105 Purchase Specification
A complete order prevents most disputes. Include:
Product type (for example weld neck flange)
Size (NPS). Schedule or bore
Pressure class (150 300 600 900 1500 2500)
Facing type (RF, FF, RTJ). Finish
Material: ASTM A105 or A105N
Dimensional standard: ASME B16.5 or B16.47
Certificate type: EN 10204 3.1 or 3.2
Special requirements: NACE impact test, NDT, third‑party inspection marking
Frequently Asked Questions
What is A105 carbon steel used for?
A105 carbon steel is used for forged piping components, mainly flanges, forged fittings and valve bodies. It suits ambient and elevated-temperature pressure service in oil and gas petrochemical, power and water systems between –29 °C and 425 °C.
What is the difference between A105 and A105N?
A105 and A105N share the chemistry. The difference is heat treatment. A105N is normalized, which refines the grain structure and gives uniform mechanical properties. Many project specifications require the condition for flanges and fittings.
Is A105 the same as A350 LF2?
No. Both are forged carbon steels. A350 LF2 has mandatory Charpy impact testing at –46 °C and tighter chemistry. A105 does not require impact testing unless you add it. Use A350 LF2 when the design temperature falls below –29 °C.
What is the yield strength of A105 carbon steel?
The minimum yield strength of A105 is 250 MPa (36 ksi). Minimum tensile strength is 485 MPa (70 ksi) with least 22 % elongation and a maximum hardness of 187 HBW.
Is A105 stainless steel?
No. A105 is carbon steel. Does not contain enough chromium to resist corrosion the way stainless steel does. For service consider stainless grades such as ASTM A182 F304/F304L or F316/F316L.
What is the difference between A105 and A234?
ASTM A105 covers forgings commonly used for flanges and socket weld or threaded fittings. ASTM A234 covers carbon and alloy steel fittings made from pipe or plate commonly used for butt‑weld elbows, tees and reducers.
Is A105 suitable for welding?
Yes. The carbon limit of 0.35 % and the carbon equivalent limit make A105 weldable using procedures. Thicker sections and higher‑strength heats may need preheat so follow the project welding procedure specification (WPS).
A105 carbon steel is the workhorse of forged piping. It offers strength, good weldability and a cost advantage over alloy and stainless grades as long as the service temperature and fluid fit its limits. Choose A105N when the project requires a condition move to A350 LF2, for cold service and always verify the mill test certificate before accepting delivery.
A dependable A105 supplier makes the difference between a project and costly rework. If you share your size, class and certification needs with the team, at Nakoda Steel Industry A105 supplier will help you match the grade to your application. Contact us for a quote. Browse our carbon steel flanges and fittings at Nakoda Steel Industry.