API 5CT J55 Casing: Material, Specifications, Dimensions & Grade Comparison
What Is J55 Casing?
J55 is the most widely used and readily available grade in API 5CT, offering a minimum yield strength of 55,000 psi through a normalizing heat treatment process. Its balanced strength-to-cost ratio makes it the go-to choice for shallow to medium-depth wells in non-corrosive environments.
- Applicable Product:Casing & Tubing 4½″–20″.
- Thread Types: BC, STC / LTC.
- Available Lengths: R1 / R2 / R3.
| Element | Symbol | Typical Max (%) |
| Carbon | C | ≤ 0.34 |
| Manganese | Mn | ≤ 1.20 |
| Silicon | Si | ≤ 0.45 |
| Phosphorus | P | ≤ 0.030 |
| Sulfur | S | ≤ 0.030 |
| Chromium | Cr | ≤ 0.30 |
| Nickel | Ni | ≤ 0.25 |
| Molybdenum | Mo | ≤ 0.10 |
API 5CT does not mandate a fixed chemical composition for J55. The table below reflects typical mill chemistry adopted by major producers to consistently meet the grade’s mechanical requirements.
| Property | Metric | Imperial | Note |
| Yield Strength — Min | 379 MPa | 55,000 psi | API Requirement |
| Yield Strength — Max | 552 MPa | 80,000 psi | API Requirement |
| Tensile Strength — Min | 655 MPa | 95,000 psi | API Requirement |
| Elongation — Min | ≥ 0.5 × (A / 645)^0.2 formula per API 5CT | Wall-thickness dependent | |
| Hardness — Max | 22 HRC | 237 HBW | Full cross-section |
| Heat Treatment | Normalizing (N) | No Q&T required | |
| Impact Test | Required (Charpy V-notch) | Unlike H40, J55 is not exempt | |
| Sour Service (H₂S) | Not recommended | Use C90 / T95 for sour environments | |
Per API 5CT (latest edition). J55 is heat-treated by normalizing—no quench & temper required—making it the most cost-effective treated grade in the standard.
Product Knowledge
J55 Casing Pipe — Manufacturing Process
Complete step-by-step production flows for Seamless (SMLS) and Welded (ERW / SAWL) routes, manufactured to API 5CT / ISO 11960.
Seamless (SMLS)
Step 01
Raw Material Intake
Seamless billets / Continuous-cast blooms
Incoming round billets are inspected for surface defects, chemical composition, and dimensional tolerances before being admitted to the production line.
Step 02
Furnace Heating
1,150–1,280 °C uniform soaking
Billets are charged into a rotary-hearth or walking-beam furnace and soaked to achieve a uniform temperature gradient throughout the cross-section, ensuring plastic deformability during piercing.
Step 03
Rotary Piercing
Mannesmann process — hollow shell formation
The hot billet is fed between two barrel-shaped rolls set at opposing skew angles. Secondary tensile stresses open a cavity at the centre, and a piercing plug widens it into a thick-walled hollow shell (mother tube).
Reject &
Rework
Rework
Step 04
Continuous Rolling / Stretch Reducing
Controls OD and wall thickness
The hollow shell passes through a multi-stand continuous mill (or plug mill / push-bench) that elongates the tube and reduces wall thickness to near-final dimensions. A stretch-reducing mill then adjusts the OD across multiple stands.
Step 05
Sizing / Cooling Bed
Dimensional setting & controlled cooling
A sizing mill applies final OD correction to within API 5CT tolerances. Pipes then move onto a cooling bed where they air-cool under controlled conditions to minimise distortion and residual stress.
Q & T
Quench & Temper
Enhances mechanical properties
Pipe is austenitised, water-quenched to martensite, then tempered at 550–700 °C to achieve the J55 yield/tensile window with adequate toughness.
Normalise
Normalising / No Heat Treatment
Lower grades or specific grades
For J55 and similar grades, a single normalising cycle at ~900 °C refines grain structure. Some grades may be shipped as-rolled when mechanical targets are already met.
Step 07
Straightening
Bow ≤ 3 mm/m per API 5CT
Multi-roll rotary or press straighteners remove bend and ovality introduced during rolling and heat treatment, bringing the pipe within API 5CT straightness limits.
Step 08
Non-Destructive Testing (NDT)
Ultrasonic / Eddy current / Magnetic particle
Full-body automated UT detects laminations and wall flaws; eddy-current identifies surface seams; magnetic-particle (MPI) reveals near-surface cracks. Rejects are returned for re-rolling or scrapped.
Step 09
Pipe-End Machining & Thread Cutting
API or premium connection profiles
Both ends are faced and chamfered on CNC lathes. Threads (STC, LTC, BC, or premium) are cut per API 5B and gauged with calibrated Go / No-Go ring and plug gauges before accepting.
Step 10
Final Inspection & Hydrostatic Test
Dimensional / Mechanical / Seal integrity
Each pipe is hydrostatically pressure-tested per API 5CT, followed by dimensional checks (OD, WT, length) and visual examination of the body and thread surfaces. Hardness and tensile test coupons are sampled per heat lot.
Step 11
Marking, Coating & Warehousing
Finished product dispatch
Pipes receive API 5CT colour bands and stencil markings (grade, size, weight, heat number). External surfaces are coated or varnished; thread protectors are fitted. Mill Test Reports (MTR) are issued before dispatch.
Welded — ERW & SAWL
Step 01
Hot-Rolled Coil / Heavy Plate Intake
API 5CT-specified steel coils or plates
Hot-rolled skelp coils (for ERW) or discrete heavy plates (for SAWL) are received and subjected to incoming inspection: chemistry, mechanical coupons, and ultrasonic lamination check before release to production.
Step 02
Slitting / Levelling & Edge Milling
Controls strip width and flatness
Coils are slit to precise width; plates are cut and levelled. Both are edge-milled to remove oxidised skin and establish a flat, parallel edge profile essential for a sound weld seam.
ERW Route
Step 03a
ERW Roll Forming
Continuous cold bending into round tube
Strip passes through a series of breakdown, fin-pass, and side-roll stands that progressively bend it into an open-seam cylinder ready for welding.
Step 04a
High-Frequency Resistance Welding
HF-ERW — 350–450 kHz
High-frequency current flows along the open edges, heating them to forging temperature. Squeeze rolls press the edges together to forge-weld the seam with no filler metal.
Step 05a
ID / OD Bead Removal
Scarfing tool / grinding wheel
Internal and external weld flash (upset bead) is shaved flush with the pipe wall by a scarfing blade on the OD and a mandrel-mounted tool on the ID.
Step 06a
Weld-Seam Induction Normalising
Eliminates microstructural non-uniformity
An induction coil heats the weld zone to the austenite range and allows it to air-cool, eliminating the hard heat-affected zone (HAZ) and restoring homogeneous grain structure along the seam.
SAWL Route
Step 03b
Spiral (Helical) Forming
Continuous helical coiling into tube
Strip is fed at a controlled angle into forming rolls, spiralling continuously into a cylinder. The helical seam angle allows a single strip width to produce various pipe diameters.
Step 04b
Submerged Arc Welding (SAW)
Inside + outside passes — twin-wire / multi-wire
The helical seam is first welded from the inside, then from the outside under a flux blanket using twin or multi-wire SAW, achieving deep penetration and excellent bead geometry with low heat input.
Step 05b
In-Line Weld Seam UT
Real-time weld quality monitoring
Automated ultrasonic probes scan the spiral weld seam immediately after welding, detecting lack of fusion, porosity, and undercut in real time so defective sections can be flagged and repaired.
Step 06b
Cut-to-Length & Pipe-End Dressing
Plasma torch or cold saw
The continuous spiral tube is cut to specified lengths by a plasma torch or cold saw synchronised to the forming speed. Pipe ends are then bevelled and ground to API 5CT squareness tolerances.
Step 07
Full-Body Heat Treatment (Higher Grades)
Quench & Temper — P110 / Q125 etc.
For higher-strength grades, the entire pipe is austenitised and quenched, then tempered to develop the required yield strength, toughness, and hardness uniformity across the full pipe body and weld seam.
Step 08
Straightening
Bow ≤ 3 mm/m
Heat treatment invariably introduces some bow. Rotary or gag straighteners correct longitudinal curvature and cross-sectional ovality to meet API 5CT straightness requirements.
Step 09
Full-Body NDT
Ultrasonic + Eddy current + X-ray
Automated UT probes scan the full pipe wall including the weld seam; eddy-current detects surface and near-surface flaws; X-ray or digital radiography provides a permanent record of weld integrity for traceability.
Step 10
Thread Cutting
API or premium gas-tight connections
Pipe ends are threaded per API 5B (LTC, STC, BC) or customer-specified premium connection profiles. Each threaded end is gauged with certified ring / plug gauges and visually inspected for thread quality.
Step 11
Final Inspection & Hydrostatic Test
Dimensional / Mechanical / Seal integrity
Pipe undergoes API 5CT hydrostatic proof testing. Dimensional audit covers OD, WT, length, and straightness. Mechanical test coupons are pulled per heat lot to confirm yield strength, UTS, and elongation compliance.
Step 12
Marking, Coating & Warehousing
Finished product dispatch
Stencil marking (grade, size, weight, heat/lot number) and API colour banding are applied per API 5CT Annex B. External coating and thread protectors are fitted; Mill Test Reports issued for each heat before shipment.
J55 Casing & Tubing Dimensions and Specifications
API 5CT — Product Specification
J55 Casing & Tubing Size Reference
Full dimensional data per API 5CT / ISO 11960. Search, filter by size, and switch between metric and imperial units.
J55 Casing Thread Types and Connection Options
Three API-standard thread profiles are available for J55 casing. Selection depends on well depth, axial load, and torque requirements.
STC
Short Round Thread Casing
短圆螺纹
Round thread profile, 8 or 10 TPI — moderate thread engagement for standard well conditions.
Connection strength ~60–80% of pipe body tensile strength.
Suitable for shallow strings with low axial and bending load requirements.
Thread Form
Round
Engagement
Short
Typical Use
Shallow / low-load
LTC
Long Round Thread Casing
长圆螺纹
Same round thread form as STC but with longer engagement depth for improved makeup reliability.
Connection strength governed by the lesser of pin-fracture or jump-out strength per API 5CT.
Preferred over STC when slightly higher tensile rating or better sealability is needed.
Thread Form
Round
Engagement
Long (+2 threads)
Typical Use
Standard / intermediate
BTC
Buttress Thread Casing
偏梯形螺纹
Higher tensile rating than round threads — preferred for deep wells and high-load strings.
J55/K55 BTC coupling can be upgraded to L80 Type 1 coupling when specified on order.
Three variants: Regular, Special Bevel (better seal), Special Clearance (reduced OD).
Thread Form
Buttress (asymmetric)
Variants
Regular / SB / SC
Typical Use
Deep / high-load
Quick Comparison — STC · LTC · BTC
| Thread Type | Profile | Tensile Rating | Seal Mechanism | Primary Application | Coupling Upgrade |
|---|---|---|---|---|---|
| STC | Round (8 / 10 TPI) | 60–80% pipe body | Thread interference | Shallow, low-load strings | Standard only |
| LTC | Round (8 / 10 TPI, long) | Min (pin fracture, jump-out) | Thread interference | Intermediate depth | Standard only |
| BTC | Buttress (asymmetric) | Highest of the three | Metal-to-metal shoulder | Deep / high axial load | L80 Type 1 available |
Note: For sour-service (H₂S) environments, J55 with any of these thread types is not recommended. Specify C90 or T95 grades with appropriate premium connections for NACE MR0175 compliance.
J55 vs K55 vs L80 vs N80 vs P110:
API 5CT Grade Comparison
J55 vs K55 — Key Difference: Both grades share identical chemical composition and the same yield range of 379–552 MPa. The sole distinguishing factor is minimum tensile strength — K55 requires ≥ 655 MPa versus J55’s ≥ 517 MPa. In practice, K55 is produced from the same steel as J55 but with tighter heat treatment control to guarantee the higher tensile floor, making it better suited for thermal and heavy-oil wells.
J55
1 stripe
Yield Strength379–552 MPa
Min. Tensile≥ 517 MPa
Elongation≥ 24%
Heat TreatmentN / N+T / Q&T
HardnessNot specified
K55
2 stripes
Yield Strength379–552 MPa
Min. Tensile
≥ 655 MPa ↑
Elongation≥ 24%
Heat TreatmentN / N+T / Q&T
HardnessNot specified
Mechanical Properties — API 5CT
| Grade | Yield Strength (MPa) | Min. Tensile (MPa) | Max. Hardness (HRC) | Min. Elongation | Sour Service |
|---|---|---|---|---|---|
| J55 | 379–552 | ≥ 517 | — | ≥ 24% | Not rated |
| K55 | 379–552 | ≥ 655 | — | ≥ 24% | Not rated |
| L80-1 | 552–655 | ≥ 655 | ≤ 23 | ≥ 19% | NACE rated |
| N80 Type 1 | 552–758 | ≥ 689 | — | ≥ 19% | Not rated |
| N80Q Q&T | 552–758 | ≥ 689 | — | ≥ 19% | Not rated |
| P110 | 758–965 | ≥ 862 | — | ≥ 15% | Not rated |
Chemical Composition — Mass %
| Grade | C | Si | Mn | P ≤ | S ≤ | Cr | Other Elements |
|---|---|---|---|---|---|---|---|
| J55 | 0.34–0.39 | 0.20–0.35 | 1.25–1.50 | 0.020 | 0.015 | ≤ 0.15 | Ni ≤ 0.20, Cu ≤ 0.20 |
| K55 | 0.34–0.39 | 0.20–0.35 | 1.25–1.50 | 0.020 | 0.015 | ≤ 0.15 | Same as J55 — heat treatment differs |
| L80-1 | ≤ 0.43 | ≤ 1.00 | ≤ 1.90 | 0.020 | 0.010 | — | Controlled yield; H₂S service |
| N80 | 0.34–0.38 | 0.20–0.35 | 1.45–1.70 | 0.020 | 0.015 | ≤ 0.15 | V: 0.11–0.16 |
| P110 | 0.26–0.35 | 0.17–0.37 | 0.40–0.70 | 0.020 | 0.010 | 0.80–1.10 | Mo 0.15–0.25, V ≤ 0.08 |
The highlighted cell marks the sole chemical/mechanical difference between J55 and K55. All other parameters are identical. For sour-service (H₂S) environments, specify L80 Type 1 or higher with NACE MR0175 compliance — J55 and K55 are not qualified for sour service regardless of thread type.
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9-5/8″
OD 244.48 mm | 11 weight specs in stock
Weight Range32.30–75.60 lb/ft
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Thread TypesSTC · LTC · BTC
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13-3/8″
OD 339.72 mm | 5 weight specs in stock
Weight Range48.00–72.00 lb/ft
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OD 508.00 mm | 3 weight specs in stock
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J55 casing does not use EUE (EUE is the tubing thread type). Of the three API threads for casing, LTC is the most common choice for J55, offering a balanced performance in terms of tensile strength and sealing; BTC is used for applications with higher load requirements; STC is only used under extremely low loads. For even higher sealing performance, Premium thread type can be selected in conjunction with J55.
The economic advantages of J55 are most prominent in shallow wells. For a horizontal or vertical well within 1500 m, using J55 for the surface layer and casing can significantly reduce material costs. Beyond this depth, strength verification is usually required before deciding whether to upgrade the grade.
J55 is better than Grade 36 steel (ASTM A36), with a yield strength approximately 1.5 times that of Grade 36. However, J55 is used in the oil and gas industry, while A36 is primarily used in building structures.