API 5CT and API 5B couplings connecting casing and tubing lengths in the well string. Manufactured in matching or superior grade to the connected pipe — H40 through Q125 including 13Cr variants. Available with phosphating, zinc plating, chrome plating, or epoxy coating surface treatment. Pup joints supplied in the same grade range.
Applications
→Casing strings — connecting casing pipe lengths for surface, intermediate, and production strings
→Tubing strings — connecting production tubing from reservoir to wellhead
→Pup joints — length adjustment segments within casing or tubing strings
→Sour service completions — L80-1, C90, T95, C110 couplings matched to sour-service pipe grades
→Premium connection systems — ZC-series premium thread couplings for gas-tight applications
Standards & Certifications
API 5CT—Specification for Casing and Tubing — material grade requirements for coupling bodies
API 5B—Threading, gauging, and thread inspection — STC, LTC, BTC, and premium threads
EN 10204 3.1 / 3.2—Mill test certificate documentation
Thread Type Availability — Casing Couplings
Size
STC
LTC
BTC
4½″
●
●
●
5″
●
●
●
5½″
●
●
●
6⅝″
●
●
●
7″
●
●
●
7⅝″
●
●
●
8⅝″
●
●
●
9⅝″
●
●
●
10¾″
●
—
●
11¾″
●
—
●
13⅜″
●
—
●
16″
●
—
●
18⅝″
●
—
●
20″
●
●
●
Grades: H40, J55, K55, N80-1, N80Q, R95, L80-1, L80 13Cr, C90, T95, P110, C110, Q125. PSL-1, PSL-2, PSL-3. ZC-series premium connections available on request. Contact ZC to verify LTC availability for sizes 10¾″ and larger.
Thread Type Availability — Tubing Couplings
Size
NU
EU
SCC
S13
2⅜″
●
●
●
●
2⅞″
●
●
●
●
3½″
●
●
●
●
4″
●
●
—
●
4½″
●
●
—
●
SCC and S13 are ZC proprietary premium thread designations. NU = Non-upset (NUE); EU = External upset (EUE).
API 5CT grades manufactured and supplied by ZC Steel Pipe. Grade selection is driven by well depth, H₂S environment, and pressure containment requirements.
Grade
Yield MPa / ksi
Tensile MPa / ksi
Max Hardness
H₂S Service
Typical Application
H40
276 / 40
414 / 60
—
✗ No
Shallow, low-pressure wells
J55
379 / 55
517 / 75
—
✗ No
Shallow oil and gas wells
K55
379 / 55
655 / 95
—
✗ No
Surface casing, conductor
N80-1
552 / 80
689 / 100
—
✗ No
Medium-depth sweet wells
N80Q
552 / 80
689 / 100
—
✗ No
Medium-depth sweet wells (Q+T)
L80-1
552 / 80
655 / 95
23 HRC
✓ Yes
Mild sour service
L80 13Cr
552 / 80
655 / 95
23 HRC
✗ No
High CO₂ / gas condensate tubing
R95
655 / 95
724 / 105
—
✗ No
Medium-strength non-sour wells
C90
621 / 90
689 / 100
25.4 HRC
✓ Yes
Moderate sour service
T95
655 / 95
724 / 105
25.4 HRC
✓ Yes
Moderate sour / deep wells
P110
758 / 110
862 / 125
None
✗ No
Deep HPHT sweet wells
C110
758 / 110
793 / 115
29.0 HRC
✓ Yes
Severe sour / HPHT sour
Q125
862 / 125
931 / 135
None
✗ No
Ultra-deep HPHT wells
API 5CT casing and tubing dimensions and weight chart. Common sizes from 4½″ to 20″ casing and 1.050″ to 4½″ tubing — OD, wall thickness, weight range, and applicable grades per API 5CT. Contact us to confirm availability for specific size/grade combinations.
Casing — Common Sizes
OD (in)
OD (mm)
Weight Range (lb/ft)
Wall Range (mm)
Common Grades
Typical String
4½
114.3
9.50–15.10
5.21–8.56
N80, L80, L80-3Cr, R95, C90, T95, P110
Production casing / tubing
5
127.0
11.50–18.00
6.43–9.19
N80, L80, L80-3Cr, R95, C90, T95, P110, C110
Production casing
5½
139.7
14.00–23.00
6.98–10.54
N80, L80, L80-3Cr, R95, C90, T95, P110, C110
Production casing — most common
7
177.8
17.00–38.00
6.91–14.27
N80, L80, R95, C90, T95, P110
Intermediate / production casing
7⅝
193.7
24.00–45.30
8.33–15.11
N80, L80, R95, T95, P110, C110
Intermediate casing
9⅝
244.5
32.30–58.40
8.94–15.11
N80, L80, R95, T95, P110, C110
Intermediate casing
10¾
273.1
32.75–65.70
7.09–13.84
J55, K55, N80
Surface casing
13⅜
339.7
48.00–72.00
8.38–12.19
J55, K55, N80
Surface casing
16
406.4
65.00–109.00
9.53–15.88
J55, K55
Conductor / surface
20
508.0
94.00–133.00
11.13–15.88
H40, J55
Conductor pipe
Tubing — Common Sizes
OD (in)
OD (mm)
Weight Range (lb/ft)
Wall Range (mm)
Common Grades
1.050
26.7
1.14–1.80
2.41–3.91
J55, N80
1.315
33.4
1.70–2.90
2.90–4.55
J55, N80
1.660
42.2
2.30–3.40
2.90–4.85
J55, N80
1.900
48.3
2.75–4.70
3.18–5.08
J55, N80, L80
2⅜
60.3
4.00–6.40
3.18–5.54
J55, N80, L80, L80-3Cr, T95, P110
2⅞
73.0
6.40–10.40
5.51–7.82
J55, N80, L80, L80-3Cr, C90, T95, P110, C110
3½
88.9
7.70–12.95
5.49–8.31
J55, N80, L80, L80-3Cr, T95, P110
4
101.6
9.50–14.00
5.74–8.38
N80, L80, L80-3Cr, C90, T95, P110, C110
4½
114.3
12.60–26.10
6.88–16.00
N80, L80, L80-3Cr, C90, T95, P110, C110
Procurement Note — Size Confirmation
The tables above show common API 5CT sizes. Not every size/grade combination is held in stock — ZC Steel Pipe is order-to-make. Send us your full specification (OD, weight, grade, connection, PSL, quantity) and we will confirm availability and lead time within one business day.
ZC Steel Pipe manufactures casing and tubing exclusively by the seamless process. All grades from N80Q through Q125 are produced by quench and temper heat treatment for controlled yield and hardness.
1
Billet Inspection
Continuous cast or rolled billets inspected for surface defects and internal quality before entry to the pipe mill.
2
Hot Rolling / Piercing
Billets heated to rolling temperature and pierced on a mandrel mill or push bench to form the seamless mother tube.
3
Sizing & Straightening
Hot-rolled tube sized to target OD and wall, then hot straightened for dimensional conformance.
4
Heat Treatment
Q+T grades (N80Q, L80, T95, P110, C110, Q125) quenched and tempered in continuous furnace lines to achieve the API 5CT yield band and hardness ceiling.
5
Cold Straightening
Post-heat-treatment straightening to API 5CT straightness limits.
6
End Finishing
Pipe ends machined to customer connection specification — STC, LTC, BTC, or premium thread profile. Thread protectors fitted before dispatch.
7
Inspection & Testing
Full mechanical testing, NDE, dimensional inspection and MTC documentation. Third-party inspector witness available throughout.
All ZC Steel Pipe casing and tubing is tested and documented per API 5CT. PSL-2 orders include mandatory NDE and impact testing. Third-party inspection to EN 10204 3.2 available on request.
1Dimensional inspection — OD, ID, length, and thread gauging per API 5B
2Thread profile gauging — STC, LTC, BTC, and premium thread form per API 5B
3Hydrostatic pressure test — per API 5CT mill test pressure
4Visual and surface inspection — thread surface, coupling body, and coating finish
5Hardness verification — for L80-1, C90, T95, C110 sour-service grades
6Chemical composition analysis — heat analysis per API 5CT
7MTC documentation — EN 10204 3.1; 3.2 on request
PSL-1 vs PSL-2 Testing Requirements
Requirement
PSL-1
PSL-2
NDE — pipe body
Not mandatory
Full-length UT or EMI
NDE — pipe ends
Not mandatory
Mandatory UT
Charpy impact test
Not mandatory
Mandatory per Table C.36
Dimensional tolerance
Standard API
Tighter OD, wall, straightness
Traceability
Heat number
Heat + pipe number per joint
Hardness survey (SR15)
Optional
Required for NACE qualification
MTC format
EN 10204 3.1 typical
EN 10204 3.1 or 3.2
Recommended for
Sweet wells, shallow depth
All sour service; HPHT; IOC projects
Click any image to view full size.
API 5CT couplings — stacked production batch
Couplings — yard storage
Packaged couplings on pallet
Couplings — ready for dispatch
API 5CT casing pipe weight calculator and burst pressure calculator. Calculate pipe weight per metre (kg/m) or per foot (lb/ft) from OD and wall thickness. All formulas per API 5CT / TR 5C3.
Pipe Weight per Metre
Formula: W = 0.02466 × t × (OD − t) kg/m | API 5C3
Hydrostatic Test Pressure (API 5CT §10.12.3)
Formula: p = (2 × f × YS_min × t) / D | Rounded to 0.5 MPa. Max 69.0 MPa.
f = 0.6 for H40/J55/K55 with OD > 244.5 mm (9⅝"); f = 0.8 for all other grades and sizes.
Quick Unit Converter
Results update as you type.
These calculators are provided as engineering reference tools. Always verify critical design values against API 5CT tables before use in casing design.
