Quick Answer
Quick Answer
API 5L covers seamless and welded steel line pipe for oil and gas transmission. It defines two product specification levels: PSL1 (basic) and PSL2 (enhanced chemistry, mechanical, and toughness requirements). Grades range from A and B up to X80, with the X-prefix grade number representing the minimum yield strength in ksi. PSL2 adds mandatory CVN impact testing, tighter carbon equivalents, and additional chemistry controls not required in PSL1.
API 5L is published by the American Petroleum Institute and governs line pipe used in pipeline transportation systems for the petroleum and natural gas industries. It covers pipe in the size range NPS ½ through NPS 80 (nominal) in both seamless (SMLS) and welded forms (ERW, SAW, COWL). The standard is recognized globally and is technically harmonized with ISO 3183, which uses the L-prefix grade designation system (e.g., L360 = X52).
Scope and Applicability
API 5L applies to:
- Seamless (SMLS) and welded steel pipe (ERW, HFW, SAW, COWL)
- Transmission pipelines for oil, natural gas, and water
- Offshore and onshore pipelines
- Sour service (with additional requirements per Annex H)
- Offshore service (with additional requirements per Annex J)
The standard does not apply to casing, tubing, or drill pipe (those are covered by API 5CT and API 5DP respectively).
Grade Coverage
| API 5L Grade | ISO 3183 Grade | SMYS MPa (ksi) | SMTS MPa (ksi) | PSL Availability |
|---|---|---|---|---|
| A | L175 | 175 (25) | 310 (45) | PSL1 only |
| B | L245 | 245 (35) | 415 (60) | PSL1, PSL2 |
| X42 | L290 | 290 (42) | 415 (60) | PSL1, PSL2 |
| X46 | L320 | 320 (46) | 435 (63) | PSL1, PSL2 |
| X52 | L360 | 360 (52) | 460 (67) | PSL1, PSL2 |
| X56 | L390 | 390 (56) | 490 (71) | PSL1, PSL2 |
| X60 | L415 | 415 (60) | 520 (75) | PSL1, PSL2 |
| X65 | L450 | 450 (65) | 535 (77) | PSL1, PSL2 |
| X70 | L485 | 485 (70) | 570 (82) | PSL2 only |
| X80 | L555 | 555 (80) | 625 (90) | PSL2 only |
SMYS = Specified Minimum Yield Strength; SMTS = Specified Minimum Tensile Strength. X70 and X80 are PSL2 grades only.
PSL1 vs PSL2: Key Differences
| Requirement | PSL1 | PSL2 |
|---|---|---|
| Chemistry limits | Basic C, Mn, P, S | Tighter C, Mn, P, S + CE limits + Nb+V+Ti cap |
| Carbon equivalent (CE) | Not required | Mandatory (IIW or Pcm formula) |
| Charpy V-notch impact | Not required | Mandatory for most grades and sizes |
| Tensile test frequency | Per standard lot | Higher frequency for SAW pipe |
| Hydrostatic test | Required | Required |
| Fracture toughness (DWT/CTOD) | Not required | Required for X65 and above in offshore/sour |
| Dimensional tolerances | Standard | Tighter for OD and wall thickness |
| Heat treatment traceability | Not required | Recommended / required by category |
Chemical Composition Requirements
PSL1 — Chemical Composition (wt%, ladle analysis)
| Grade | C max | Mn max | P max | S max | Si max | V max | Nb max | Ti max |
|---|---|---|---|---|---|---|---|---|
| A | 0.22 | 0.90 | 0.030 | 0.030 | 0.40 | 0.05 | 0.04 | 0.04 |
| B | 0.28 | 1.20 | 0.030 | 0.030 | 0.40 | 0.05 | 0.04 | 0.04 |
| X42 | 0.28 | 1.30 | 0.030 | 0.030 | 0.40 | 0.05 | 0.04 | 0.04 |
| X46 | 0.28 | 1.40 | 0.030 | 0.030 | 0.40 | 0.05 | 0.04 | 0.04 |
| X52 | 0.28 | 1.40 | 0.030 | 0.030 | 0.40 | 0.05 | 0.04 | 0.04 |
| X56 | 0.28 | 1.40 | 0.030 | 0.030 | 0.40 | 0.07 | 0.05 | 0.04 |
| X60 | 0.28 | 1.40 | 0.030 | 0.030 | 0.40 | 0.08 | 0.05 | 0.04 |
| X65 | 0.28 | 1.45 | 0.030 | 0.030 | 0.40 | 0.09 | 0.05 | 0.06 |
| X70 | — | — | — | — | — | — | — | — |
X70 and X80 are PSL2 grades only. For PSL1 SMLS pipe, the limits above apply. For PSL1 welded pipe (ERW/SAW), C max may be 0.02% lower in some grades.
PSL2 — Chemical Composition (wt%, ladle analysis)
| Grade | C max | Mn max | P max | S max | Si max | Nb+V+Ti max | CE (IIW) max | CE (Pcm) max |
|---|---|---|---|---|---|---|---|---|
| B | 0.24 | 1.20 | 0.025 | 0.015 | 0.45 | 0.15 | 0.43 | 0.25 |
| X42 | 0.24 | 1.30 | 0.025 | 0.015 | 0.45 | 0.15 | 0.43 | 0.25 |
| X46 | 0.24 | 1.40 | 0.025 | 0.015 | 0.45 | 0.15 | 0.43 | 0.25 |
| X52 | 0.24 | 1.40 | 0.025 | 0.015 | 0.45 | 0.15 | 0.43 | 0.25 |
| X56 | 0.24 | 1.40 | 0.025 | 0.015 | 0.45 | 0.15 | 0.43 | 0.25 |
| X60 | 0.24 | 1.40 | 0.025 | 0.015 | 0.45 | 0.15 | 0.43 | 0.25 |
| X65 | 0.24 | 1.45 | 0.025 | 0.015 | 0.45 | 0.15 | 0.43 | 0.25 |
| X70 | 0.24 | 1.65 | 0.025 | 0.015 | 0.45 | 0.15 | 0.43 | 0.25 |
| X80 | 0.24 | 1.85 | 0.025 | 0.015 | 0.45 | 0.15 | 0.46 | 0.25 |
Carbon Equivalent Formulas:
- IIW: CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15
- Pcm: Pcm = C + Si/30 + (Mn+Cu+Cr)/20 + Ni/60 + Mo/15 + V/10 + 5B
The applicable CE formula is selected based on carbon content: IIW is used when C > 0.12%; Pcm when C ≤ 0.12%.
Mechanical Properties
SMLS and Welded Pipe — Tensile Properties (body of pipe)
| Grade | SMYS MPa (ksi) | SMYS max MPa | SMTS MPa (ksi) | SMTS max MPa | YS/UTS Ratio max |
|---|---|---|---|---|---|
| A | 175 (25) | — | 310 (45) | — | — |
| B | 245 (35) | 450 | 415 (60) | — | — |
| X42 | 290 (42) | 495 | 415 (60) | — | — |
| X46 | 320 (46) | 525 | 435 (63) | — | — |
| X52 | 360 (52) | 530 | 460 (67) | — | — |
| X56 | 390 (56) | 545 | 490 (71) | — | — |
| X60 | 415 (60) | 565 | 520 (75) | — | — |
| X65 | 450 (65) | 600 | 535 (77) | — | — |
| X70 (PSL2) | 485 (70) | 635 | 570 (82) | — | 0.93 |
| X80 (PSL2) | 555 (80) | 705 | 625 (90) | — | 0.93 |
PSL2 yield strength upper limits are mandatory to ensure ductile failure modes. The SMYS max values listed are for PSL2; PSL1 does not specify maximum yield strength.
Elongation: Minimum elongation for all grades = Af min (%), where Af = 1944 × (Axc^0.2) / UTS^0.9, per API 5L formula. For most grades at standard wall, this results in approximately 15–22% in 50 mm gauge length.
CVN Impact Testing — PSL2 Requirements
Charpy V-Notch Requirements by Grade (PSL2)
| Grade | Test Temperature °C | Min CVN Energy (transverse) |
|---|---|---|
| B, X42, X46, X52 | 0 | 27 J (20 ft-lbf) average, 20 J min single |
| X56, X60 | 0 | 27 J average, 20 J min single |
| X65 | −5 | 40 J average, 27 J min single |
| X70 | −5 | 40 J average, 27 J min single |
| X80 | −10 | 40 J average, 27 J min single |
CVN test frequency: 1 test set (3 specimens) per lot. For sour service (Annex H) or offshore service (Annex J), lower test temperatures and higher energy values apply.
CVN for weld seam (SAW/ERW): The weld seam and HAZ must also be Charpy tested for PSL2 pipe in grades X56 and above. Test location and orientation are specified in Annex D.
HIC and SSC Testing for Sour Service
For pipeline service in H₂S-containing environments, API 5L Annex H specifies additional requirements:
Sour Service (Annex H) Requirements
| Test | Standard | Acceptance Criteria |
|---|---|---|
| HIC (Hydrogen-Induced Cracking) | NACE TM0284 | Crack Length Ratio (CLR) ≤ 15%, Crack Thickness Ratio (CTR) ≤ 5%, Crack Sensitivity Ratio (CSR) ≤ 2% |
| SSC (Sulfide Stress Cracking) | NACE TM0177 / ISO 15156 | No cracking in 720-hour constant load or 4-point bend test |
| Chemistry controls | Annex H | S max 0.003%, Ca/S ratio ≥ 1.5 (when Ca treatment applied), CE max reduced |
Additional sour service chemistry limits:
- S max: 0.003% (versus 0.015% for standard PSL2)
- Phosphorus max: 0.020%
- Carbon equivalent (Pcm): typically ≤ 0.21% for X52 sour service
Cross-Standard Equivalents
| API 5L Grade | ISO 3183 | DIN/EN | JIS G3458/G3456 | Notes |
|---|---|---|---|---|
| A | L175 | — | — | Rarely specified |
| B | L245 | StE240.7TM | STPY400 | Basic grade |
| X42 | L290 | StE290.7TM | — | Lower-strength transmission |
| X46 | L320 | StE320.7TM | — | — |
| X52 | L360 | StE360.7TM | STPT370 (approx) | Very common offshore |
| X56 | L390 | StE390.7TM | — | — |
| X60 | L415 | StE415.7TM | — | Gas distribution common |
| X65 | L450 | StE450.7TM | — | Offshore, deepwater |
| X70 | L485 | StE485.7TM | — | High-pressure transmission |
| X80 | L555 | StE555.7TM | — | Ultra-high-pressure (rare) |
ISO 3183 is the international equivalent and shares the same technical content as API 5L 46th edition (2018). The ISO grade uses the L-prefix followed by SMYS in MPa.
MTC Verification Checklist
When verifying a mill test certificate for API 5L pipe, confirm:
- Grade designation, PSL level (PSL1 or PSL2), and pipe type (SMLS/ERW/SAW) match the purchase order
- Heat number and pipe lot number are traceable to pipe markings
- Carbon, Mn, P, S, and Si comply with the applicable grade limits for the specified PSL
- For PSL2: carbon equivalent (IIW or Pcm) is reported and within limits
- For PSL2: Nb+V+Ti combined content ≤ 0.15%
- Yield strength is at or above SMYS and at or below PSL2 SMYS max (if PSL2)
- Tensile strength meets SMTS minimum
- CVN impact test results reported (PSL2): temperature, specimen orientation, individual and average values
- Hydrostatic test: mill test pressure and duration recorded
- If sour service (Annex H): HIC and SSC test reports included with CLR/CTR/CSR values
- Dimensional measurements (OD, WT, length) within tolerances
- API monogram (if licensed) or third-party inspection certification
Frequently Asked Questions
What is the difference between API 5L PSL1 and PSL2?
PSL1 is a basic specification covering chemistry, tensile properties, and hydrostatic testing. PSL2 adds mandatory carbon equivalent limits, tighter P and S limits, Charpy V-notch impact testing requirements, maximum yield strength limits (to ensure ductility), and additional dimensional tolerances. X70 and X80 grades are only available in PSL2.
What does the X number mean in API 5L grades?
The X-prefix number represents the specified minimum yield strength (SMYS) in ksi. X65 has an SMYS of 65 ksi (450 MPa), X70 has 70 ksi (485 MPa), and so on. The ISO 3183 equivalent uses the L prefix followed by SMYS in MPa — so X65 = L450 and X70 = L485.
Is API 5L X65 PSL2 suitable for sour service?
Standard X65 PSL2 is not automatically qualified for sour service. Sour service requires invoking Annex H, which adds HIC testing per NACE TM0284, tighter S limits (≤ 0.003%), and SSC testing per NACE TM0177 or ISO 15156. The purchase order must specifically request Annex H compliance.
What is the ISO 3183 equivalent of API 5L X52?
ISO 3183 L360 is the equivalent. Both specify an SMYS of 360 MPa (52 ksi). API 5L 46th edition (2018) and ISO 3183 3rd edition are technically harmonized, meaning a pipe certified to API 5L PSL2 X52 meets ISO 3183 L360 and vice versa.
What CVN impact test temperature is required for API 5L X65 PSL2?
API 5L requires Charpy V-notch testing at −5 °C for X65 PSL2, with a minimum average energy of 40 J (30 ft-lbf) transverse and a single-specimen minimum of 27 J. For offshore or arctic applications, lower temperatures are specified in Annex J or by the pipeline design code (e.g., DNV-ST-F101).
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