The first time I signed off on a batch of forged flanges, I approved them on the grade stamp alone. ASTM A105 material was written on the tag, the price was right, and I moved on. Two weeks later a project engineer asked me to prove the normalizing condition, and I couldn’t — the MTR didn’t say. That lesson stuck. A105 is the workhorse grade for forged carbon-steel piping components, but the grade name on a tag tells you far less than most buyers assume. Here’s what I check now, and why.
What ASTM A105 material actually covers
A105 (formally A105/A105M) is a specification for forged carbon-steel piping components — flanges, forged fittings, and valve bodies — used in pressure systems at ambient and elevated temperatures. The key word is forged. A105 is not a pipe grade, and it is not a plate grade. If someone offers you “A105 pipe,” they’ve confused it with A106 (seamless pipe). The parts that carry an A105 certificate are weld-neck, slip-on, blind and socket-weld flanges, socket-weld and threaded fittings, and valve bodies. The standard also caps individual forgings at 10,000 lb (4,540 kg), which almost never bites in normal flange work but occasionally matters on large valve castings.
Why forged and not cast or plate-cut? Forging keeps the grain flowing along the shape of the part, which is exactly what you want in something holding pressure at a bolted joint. I’ve seen plate-cut “flanges” pass a quick visual and fail on the details later. For pressure service, insist on the forged product.
Chemical composition and mechanical properties
This is table-stakes, so let me put the real numbers down. These are the ASTM A105 limits, not a rounded-off version:
| Element | Limit |
|---|---|
| Carbon (C) | ≤ 0.35% |
| Manganese (Mn) | 0.60–1.05% |
| Phosphorus (P) | ≤ 0.035% |
| Sulfur (S) | ≤ 0.040% |
| Silicon (Si) | 0.10–0.35% |
| Cu / Ni / Cr / Mo / V | ≤ 0.40 / 0.40 / 0.30 / 0.12 / 0.08% |
Two combined limits catch people out: Cu+Ni+Cr+Mo+V must stay ≤ 1.00%, and Cr+Mo ≤ 0.32%. And here’s the one that generates the most “is my material wrong?” emails I get: for every 0.01% of carbon below the 0.35% maximum, the mill is allowed an extra 0.06% of manganese above the 1.05% line, up to 1.65% Mn. So an MTR showing Mn at 1.30% isn’t a red flag — it’s the spec working as written. (I’ve also seen a supplier datasheet online print P as 0.35% and S as 0.40%. Those are decimal typos. The real caps are 0.035% and 0.040%.)
On the mechanical side, A105 gives you a minimum 70 ksi (485 MPa) tensile and 36 ksi (250 MPa) yield, with 30% minimum reduction of area. Hardness is capped at 187 HBW under the specification. If a report shows hardness creeping toward or past that ceiling, ask questions before you accept it.
A105 vs A105N: the normalizing question
A105N is not a different chemistry — it’s A105 supplied in the normalized condition. Normalizing refines the grain, which improves toughness and batch-to-batch uniformity. For many sizes, A105 is allowed as-forged; larger flanges and certain valve and fitting classes require heat treatment, and normalizing is the common route.
The practical mistake is assuming “A105” implies “A105N.” It doesn’t. If your code or class needs the normalized condition, write A105N on the purchase order explicitly. That one letter was the gap in my very first batch, and it’s the single most common omission I see on POs today.
A105 vs A350 LF2 vs A106
These three get mixed up constantly because they all sound like “carbon steel.” They aren’t interchangeable:
| ASTM A105 | ASTM A350 LF2 | ASTM A106 | |
|---|---|---|---|
| Product form | Forged components | Forged components | Seamless pipe |
| Service temp | Ambient / high (used to ~800 °F) | Low temp / impact-tested at −46 °C (−50 °F) | Pressure pipe |
| Carbon max | 0.35% | 0.30% | — |
| Heat treatment | As-forged or heat-treated | Mandatory normalize + temper | — |
| Impact test | Not required | Required (Charpy) | — |
The decision rule I use: ambient or hot service, and cost matters → A105. Cold or cryogenic service where brittle fracture is a real risk → A350 LF2. And because LF2’s chemistry sits inside A105’s envelope, a single part can be dual-certified A105 / A350 LF2 Class 1 when the impact results pass. On export projects into colder climates I now default to asking for dual cert — it removes a whole category of “wrong grade” risk for a small premium.
How I verify A105 before approving a PO
Grade on the tag is the start of due diligence, not the end. Before I release a forged-component order for fabrication, I walk through the same short checklist I’d hand any junior engineer — much of it lines up with a fuller reference I keep bookmarked on ASTM A105 Material. My working checks are:
- MTR / CMTR present and traceable. Chemistry, mechanicals, and heat-treatment condition, each tied to a heat number. No heat number, no release.
- Normalizing condition stated if the class or cold service calls for it — I want to see “normalized,” not infer it.
- The C/Mn balance on the actual report, so a high-manganese reading doesn’t get flagged downstream by someone who doesn’t know the tradeoff.
- Dimensional standard called out separately — a flange is “A105 and ASME B16.5” (or B16.47 for the big ones). Material and dimensions are two different approvals.
- Certification type — EN 10204 3.1 for mill-certified, 3.2 when the project wants third-party witnessing.
Missing heat traceability is the one that stalls jobs. I’ve had a lot rejected at fabrication release for exactly that, and no amount of “but the tag says A105” fixes it after the fact.
Real application scenarios
A refinery steam line I supported ran ordinary A105 weld-neck flanges — hot service, no toughness concern, straightforward. On a Middle East export EPC package, the same nominal parts had to be dual-certified A105 / A350 LF2 because a portion of the line saw cold ambient starts; ordering plain A105 there would have meant a full re-buy. And the rejected batch I mentioned earlier? Perfectly good steel, correct chemistry, but the MTR couldn’t tie the parts to a heat. The metal was probably fine. The paperwork sank it. Those three cases cover most of what actually goes wrong in the field: right grade, wrong condition, or right material with unprovable documentation.
FAQ
Is ASTM A105 the same as A105N? Same chemistry, different condition. A105N is A105 supplied normalized, which refines grain structure for better toughness and uniformity. If your class or code needs the normalized state, specify A105N explicitly on the PO — plain “A105” does not guarantee it.
When do I need A350 LF2 instead of A105? Choose A350 LF2 for low-temperature or cryogenic service where impact toughness matters; it’s Charpy-tested at −46 °C (−50 °F). A105 suits ambient and high-temperature service and costs less, but it isn’t impact-tested for cold duty.
Can a flange be dual-certified A105 and A350 LF2? Yes. When a part’s chemistry and impact results satisfy both specifications, mills routinely dual-certify it as A105 / A350 LF2 Class 1. It’s a common, convenient way to cover both ambient and low-temperature requirements from one item.
Is ASTM A105 the same as A106? No. A105 covers forged components — flanges, fittings, valve bodies. A106 is seamless carbon-steel pipe. They’re often used together in one system, but they are different product forms and different specifications.
What is the temperature limit for A105 material? A105 is intended for ambient and elevated temperatures and is commonly applied up to around 800 °F (425 °C). It is not suited to cold or cryogenic service without switching to (or dual-certifying with) A350 LF2.
Why does my MTR show manganese above 1.05%? Because the specification allows it. For each 0.01% carbon below the 0.35% maximum, an extra 0.06% manganese is permitted above 1.05%, up to 1.65%. A high-manganese reading within that tradeoff is compliant, not defective.
Bottom line
ASTM A105 material earns its reputation — it’s strong, weldable, and economical for forged pressure components. But the grade name is where verification begins, not ends. Put the exact condition (A105 or A105N), the service temperature, and the dimensional standard on the PO, and demand an MTR with a real heat number behind it. Get those three things right and you’ll almost never see a forged flange come back on you.
