4130 75K, 80K and L80: what each strength callout means
Buyers write 4130 75K, 4130 L80 or 4130 80K as if they were grades. They are strength levels, and each one means a specific set of minimums. Here is what they stand for and how to write a callout nobody can misread.
"75K", "80K" and "L80" are strength levels, not grades of steel. 75K is API 6A's designation for 75 ksi minimum yield and 95 ksi minimum tensile. L80 borrows API 5CT's controlled-yield limits: 80 to 95 ksi yield, 95 ksi minimum tensile and 23 HRC maximum. 80K and 85K are levels written into equipment makers' own specifications. On a 4130 order, name the steel, the heat treatment and every number the level stands for.
API 6A material designations
API Specification 6A, for wellhead and pressure control equipment, sets four material designations for bodies, bonnets and end and outlet connections. 4130 is quenched and tempered to meet the higher ones.
| Designation | Yield, min | Tensile, min | Elongation in 2 in, min | Reduction of area, min |
|---|---|---|---|---|
| 36K | 36 ksi (248 MPa) | 70 ksi (483 MPa) | 21% | No requirement |
| 45K | 45 ksi (310 MPa) | 70 ksi (483 MPa) | 19% | 32% |
| 60K | 60 ksi (414 MPa) | 85 ksi (586 MPa) | 18% | 35% |
| 75K | 75 ksi (517 MPa) | 95 ksi (655 MPa) | 17% | 35% |
The designations stop at 75K. Higher levels, such as 80K or 85K for 15,000 and 20,000 psi equipment, are set in the equipment maker's own material specification and written onto the purchase order.
L80: a casing grade borrowed for tube and fittings
L80 is an API 5CT casing and tubing grade whose "L" stands for its limited, or controlled, yield range. Its limits are 80 to 95 ksi (552 to 655 MPa) yield, 95 ksi (655 MPa) minimum tensile and 23 HRC maximum. Buyers of 4130 tube and fittings often write "4130 L80" to ask for those limits on a part that is not casing at all. Two cautions follow:
- A 4130 part heat treated to L80 limits is not an API 5CT product unless it is made and tested to API 5CT. Tubing and casing accessories made to API 5CT are on the API 5CT pup joints and couplings pages.
- For sour service, ISO 15156-2 caps carbon and low-alloy steels at 22 HRC, and only downhole tubulars and BOP rams of chromium-molybdenum steel have clauses allowing more. A sour-service 4130 fitting needs 22 HRC maximum, not the 23 HRC of L80.
The levels side by side
| Callout | Yield | Tensile | Hardness | Source of the numbers |
|---|---|---|---|---|
| 75K | 75 ksi min | 95 ksi min | To order | API 6A |
| L80 type | 80 to 95 ksi | 95 ksi min | 23 HRC max | API 5CT L80 limits |
| 80K, sour | 80 ksi min | To order | 22 HRC max | Equipment maker's specification |
| 85K for 15,000 psi | 85 ksi min | 110 ksi min | To order | Our standard 15,000 psi level |
Tempering raises toughness and lowers hardness and strength together. A part asked to meet a high minimum strength and 22 HRC maximum at once has little room between the two, so check that a callout is achievable before it goes on a drawing. We flag any line where we see that conflict in the quotation.
Writing the callout
A complete strength callout leaves nothing to interpretation. Each item below is one the supplier would otherwise have to guess:
| Item | Example |
|---|---|
| Steel | AISI 4130 (UNS G41300) |
| Product specification | ASTM A519 Grade 4130 for pipe; ASME B16.9 dimensions for fittings |
| Heat treatment | Quenched and tempered |
| Strength | 75 ksi min yield, 95 ksi min tensile |
| Ductility | 17% min elongation in 2 in, 35% min reduction of area |
| Hardness | 22 HRC max, or a range such as 197 to 237 HB |
| Impact | Charpy V-notch at -20 °F (-29 °C), with the minimum energy |
| Test location | Per your specification, for example a qualification test coupon to API 6A |
| Certificate | EN 10204 3.1 |
AISI 4130 (UNS G41300), quenched and tempered, 75 ksi min yield, 95 ksi min tensile, 17% min elongation, 35% min reduction of area, 22 HRC max, Charpy V-notch at -20 °F, EN 10204 3.1
Match the line
Pipe, fittings and long sweeps welded into one line should share a strength level and hardness limit, so the line has no weak link and the welding procedure qualifies against one material condition. Ordering them together does that; see 4130 pipe and 4130 fittings.
Frequently asked questions
Is "4130 75K" a standard grade?
It is shorthand. "75K" is API 6A's material designation for 75,000 psi minimum yield, with 95,000 psi minimum tensile, 17% elongation and 35% reduction of area. "4130 75K" means 4130 heat treated to meet those minimums. The order should still spell out the numbers and the heat treatment.
Is A519 4130 L80 the same as API 5CT L80 tubing?
No. "4130 L80" usually means 4130 tube heat treated to the L80 strength and hardness limits: 80 to 95 ksi yield, 95 ksi minimum tensile and 23 HRC maximum. It is an API 5CT product only if it is made and tested to API 5CT. For sour-service fittings and lines outside downhole tubulars, ISO 15156-2 still caps hardness at 22 HRC.
Which level should a 15,000 psi line use?
That comes from the line's design calculation, which ties wall thickness to the strength level. Our standard 15,000 psi long sweeps and fittings are quenched and tempered to 85 ksi minimum yield and 110 ksi minimum tensile; tell us if your design uses another level.
Sources
- API Specification 6A, material designations (as listed in Stream-Flo's API 6A purchasing guide, May 2020)
- API Specification 5CT, grade L80 limits
- NACE MR0175 / ISO 15156-2:2020, A.2.1.2, A.2.2.3 and A.2.3.2