API 5CT N80Q Oil Casing Pipe: Complete Technical Guide for Global OCTG Buyers

API 5CT N80Q oil casing pipe is a medium-strength OCTG grade defined in API Specification 5CT and ISO 11960 standards. It is widely used for onshore and shallow offshore oil & gas wells requiring balanced strength and cost efficiency.

The "N80" designation indicates a minimum yield strength of 552 MPa (80 ksi), while "Q" represents quenched and tempered heat treatment, which provides improved toughness and mechanical stability compared with N80-1.

N80Q is commonly used in medium-depth sweet service wells (non-H₂S environments) and is typically selected for intermediate casing and production casing applications depending on well design conditions.

Item	N80-1 (Normalized)	N80Q (Quenched & Tempered)
Heat Treatment	Normalized / normalized + tempered	Full quenching + tempering
Microstructure	Ferrite + pearlite	Tempered martensite
Mechanical Stability	Moderate variation	High uniformity
Toughness	General	Improved low-temperature toughness
Collapse Resistance	Moderate	Higher and more stable
Recommended Well Type	Shallow-medium wells	Medium-deep wells
Typical Depth Range	≤ 2,500 m (design-dependent)	2,500–4,000 m (design-dependent)
Cost Level	Lower	Higher

Key engineering rule: N80Q is preferred for higher collapse load, low-temperature or complex well conditions.

API 5CT does NOT define fixed chemical composition for N80Q.
Chemistry is controlled by manufacturers to achieve required mechanical properties.

Element	Control Requirement
C, Mn, Si	Controlled for strength & hardenability
Cr, Ni, Mo, V	Optional alloying elements
P	≤ 0.025%
S	≤ 0.020%

Property	Requirement
Yield Strength	552 – 758 MPa (80–110 ksi)
Tensile Strength	≥ 689 MPa (100 ksi)
Elongation	API 5CT formula-based
Hardness	Not strictly limited by API base standard
Impact Test (CVN)	Required for PSL-2 / project-specific cases

Category	OD Sizes
Standard casing OD	4 1/2" – 20"

OD Range	Application
4 1/2" – 13 3/8"	Production & intermediate casing
16" – 20"	Surface & conductor casing

Item	Range
Wall thickness	0.205" – 0.875"
Weight	14 – 106.59 lb/ft

API Range	Length
R1	4.88 – 7.62 m
R2	7.62 – 10.36 m
R3	10.36 – 14.63 m

Type	Application
STC	Low-pressure surface casing
LTC	Medium-load wells
BTC	Medium-deep wells (most common for N80Q)

Feature	Description
Gas tightness	High sealing performance
Torque capacity	Higher makeup torque
Application	HPHT, directional, gas wells

N80Q casing is typically manufactured via seamless process:

Step	Description
1	Steel billet heating
2	Piercing & hollow tube forming
3	Hot rolling / sizing
4	Quenching + tempering (core step)
5	Straightening & cutting (R1/R2/R3)
6	End finishing & threading
7	Hydrostatic + NDT inspection
8	Marking & MTC issuance

N80Q requires uniform Q+T heat treatment, Seamless production is the industry practice for N80Q due to heat treatment uniformity requirements.

Item	PSL1	PSL2 / PSL3
Hydrostatic test	Optional	100% required
NDT (UT/EMI)	Limited	Full-length inspection
Impact test	Not required	Required
Traceability	Basic	Full heat traceability

PSL level must be clearly specified in procurement contracts.

Ask for SGS / BV / TÜV Third-Party Inspection Support

Medium-depth onshore oil & gas wells
Intermediate casing strings
Production casing in sweet service wells
Shallow offshore development wells
CBM & geothermal wells

N80Q is not suitable for H₂S sour service environments due to lack of NACE MR0175 qualification and SSC resistance requirements.

Condition	Recommended Grade
Mild CO₂	L80 9Cr
Sour + chloride	L80 13Cr
Severe corrosion	13Cr / CRA materials

Pain Point	Solution
Confusing N80 vs N80Q selection	Provide well depth + load-based engineering selection
Inconsistent heat treatment quality	Require MTC + Q+T traceability records
Lack of API certification confidence	Provide API monogram + ISO documentation
Thread mismatch risk	Confirm BTC/LTC/STC + torque specs
Export inspection uncertainty	Support SGS / BV / TÜV third-party inspection