OCTG Pipes Types

OCTG Pipes Types

What are OCTG pipes? Oil country tubular goods are pipes used for onshore and offshore oil & gas upstream operations (extract oil and gas from the wellbore). OCTG pipes may be classified into three main families: drill pipes (to perforate the soil and reach the reserve), casing pipes (to consolidate the well and prepare it for the actual extraction), and tubing pipes (to extract the product from the ground to the surface). API 5CT is the reference specification for OCTG pipes.

TYPES OF OCTG PIPE

First, OCTG is the acronym of “Oil Country Tubular Goods” – i.e. pipes for oil (and gas) extraction from the soil. The three main OCTG pipe types are:

  • Casing pipesare used to stabilize the wellbore. A casing pipe is subject to axial tensions and to internal pressures generated by the pumped oil or gas, by their heavyweight and the external pressures coming from the surrounding rocks
  • Tubing pipesare tubular goods through which the oil or gas is transported from the wellbore to the surface. Tubing segments are generally around 30′ long with a threaded connection on each end (standard or premium connections are available)
  • Drill pipesare heavyweight seamless tubular that rotate the drill bit and circulates the drilling fluid. Pipe segments of 30′ are coupled with tool joints. Drill pipe is subject to high torque by drilling, axial tension by their weight, and internal pressure due to the purging of the drilling fluid. Additionally, alternating bending loads due to non-vertical or deflected drilling may be superimposed on these basic loading patterns

The API 5CT specification covers seamless and welded casing and tubing pipes for upstream operations (pipes that belong to the OCTG family, as illustrated above).

Let’s review each type of OCTG pipe more in detail.

OCTG “CASING” PIPES

Function

OCTG casing pipes are a key structural component for an oil & gas well and have the following scope:

  • Keep the borehole stability in the well
  • Prevent the bore contamination from water sands
  • Prevent water from producing formations
  • Exercise a tight control of the wellbore pressures during the drilling, production, and repair operations

Casing pipes are used to install:

  • Blowout Preventers (BOP)
  • Other wellhead equipment necessary to extract hydrocarbons
  • Production tubing and packers

Casing pipes are also one major individual component of the overall cost of the well,  therefore the correct selection of the casing size, materials, connectors, and depth shall be at the top of design engineers (for cost and efficiency reasons).
The six basic types of casing strings are:

  • Conductor Casing
  • Surface Casing
  • Intermediate Casing
  • Production Casing
  • Liner
  • Liner tieback casing

Oilfield casing pipes are positioned into the wellbore and cemented in place to secure both subsurface formations and the wellbore from collapsing, also to enable drilling mud to circulate and extraction to take place.

The strict quality requirement for steel is due to the harsh working conditions of the casing.

The steel product should be produced and checked in accordance with special standards or specifications. ISO 11960 and API Spec 5CT have specified the steel product standards of the casing.

Dimensions and Materials

Casing pipes are available in a diameter range 4 1/2  to 20 inches, and in the following materials: H-40, J-55, K-55, N-80, L-80/C, 90/T, 95, P110, Q-125 – as discussed in more detail below.

End Connection Types

The main types of connections for casing pipes are STC (short threads), LTC (long threads), BTC (buttress threads) and premium gas-tight connections.

OCTG “TUBING” PIPES

Function

Tubing pipes are used to bring oil and gas from the underground reserves up to the field for further processing.

Tubing pipes need resistance to mechanical stress as they are subject to very high loads and deformations during the production operations.

In addition, tubing pipes sizes should be properly calculated to support the expected oil and gas flow from the ground to the surface (a too-small diameter would decrease the production rate and the return on investment on the wellbore licenses, whereas too large tubing would generate non-recoverable costs due to the greater amount of steel used for the bore construction vs. the actual requirement (steel for the casing and tubing pipes).

Sizes and Materials

Tubing pipes are manufactured in seamless and welded execution, in the size range of 1.050 to 5 1/2 inches (consult this article to see the AP5CT tubing pipes sizes) and in the following material grades: H-40, J-55, K-55, N-80, L-80, C-90, T-95, P-110, Q-125 (more details about API 5CT tubing materials are in this article).

End Connections

The main types of connections for tubing pipes are NUE (non-upset), EUE (external upset) and premium. Corrosion resistance under sour service conditions is a very important OCTG characteristic, especially for casing and tubing.

OCTG PIPE MANUFACTURING PROCESS

The manufacturing processes of casing and tubing pipes include:

  • Continuous mandrel-rolling process and the push bench process for sizes between 21 and 178 mm OD.
  • Plug mill rolling for sizes between 140 and 406 mm OD.
  • Cross-roll piercing and Pilger rolling for sizes between 250 and 660 mm OD.

These processes typically do not allow the thermo-mechanical processing customary for the strip and plate products used for welded pipes.

Therefore, the high-strength seamless pipe must be produced by increasing the alloying content in combination with a suitable heat treatment such as quench & tempering.

Meeting the fundamental requirement of a fully martensitic microstructure even at large pipe wall thickness requires good hardenability. Chrome (Cr) and Manganese (Mn) are the main alloying elements used to produce good hardenability in conventional heat-treatable steel.

However, the requirement for good sulfide stress cracking (SSC) resistance limits their use. Mn tends to segregate during continuous casting and can form large MnS inclusions that reduce hydrogen-induced cracking (HIC) resistance. Higher levels of Cr can lead to the formation of Cr7C3 precipitates with coarse plate-shaped morphology, which acts as hydrogen collectors and cracks initiators.

Alloying with Molybdenum can overcome the limitations of Mn and Cr alloying. Mo is a much stronger hardener than Mn and Cr, so it can easily recover the effect of a reduced amount of these elements.

Traditionally, OCTG grades were carbon-manganese steels (up to the 55-KSI strength level) or Mo-containing grades up to 0.4% Mo. In recent years, deep well-drilling and reservoirs containing contaminants that cause corrosive attacks have created a strong demand for higher-strength materials resistant to hydrogen embrittlement and SCC.

Highly tempered martensite is the structure most resistant to SSC at higher strength levels, and 0.75% is the Mo concentration that produces the optimum combination of yield strength and to SSC resistance.

OCTG PIPE DIMENSIONS

CASING PIPE

Note: P = plain end, S = short round thread, L = long round thread, B = buttress thread. Sizes per API 5CT specification
Source: API – American Petroleum Institute

OCTG Pipe Sizes
(Casing)
API5CT		 Weight
Lbs/ft		 Outside Diameter Wall Thickness Type End Finish
Grade
ln. mm ln. mm H-40 J-55 K-55 M-65 L-80C-95 N-80 C-90T-95 P-110 Q-125
7 5/8” 24.00 7.625 193.68 0.300 7.62 PS — — — — — — —
26.40 7.625 193.68 0.328 8.33 — PSLB PSLB PLB PLB PLB PLB —
29.70 7.625 193.68 0.375 9.53 — — PLB PLB PLB PLB PLB —
33.70 7.625 193.68 0.430 10.92 — — PLB PLB PLB PLB PLB —
39.00 7.625 193.68 0.500 12.70 — — — PLB PLB PLB PLB PLB
42.80 7.625 193.68 0.562 14.27 — — — PLB PLB PLB PLB PLB
45.30 7.625 193.68 0.595 15.11 — — — PLB PLB PLB PLB PLB
47.10 7.625 193.68 0.625 15.88 — — — PLB PLB PLB PLB PLB
51.20 7.625 193.68 0.687 17.45 — — — — — P — —
55.30 7.75 193.68 196.85 19.05 — — — — — P — —
7 3/4” 46.10 8.625 219.08 0.595 15.11 — — — P P P P P
8 5/8” 24.00 8.625 219.08 0.264 6.71 — PS PS — — — — —
28.00 8.625 219.08 0.304 7.72 PS — PS — — — — —
32.00 8.625 219.08 0.352 8.94 PS PSLB PSLB — — — — —
36.00 8.625 219.08 0.400 10.16 — PSLB PSLB PLB PLB PLB PSLB —
40.00 8.625 219.08 0.450 11.43 — — PLB PLB PLB PLB PLB —
44.00 8.625 219.08 0.500 12.70 — — PLB PLB PLB PLB PLB —
49.00 9.625 244.48 0.557 14.15 — — — PLB PLB PLB PLB PLB
9 5/8” 32.30 9.625 244.48 0.312 7.92 PS — — — — — — —
36.00 9.625 244.48 0.352 8.94 PS PSLB PSLB — — — — —
40.00 9.625 244.48 0.395 10.03 — PSLB PSLB PLB PLB PLB — —
43.50 9.625 244.48 0.435 11.05 — — PLB PLB PLB PLB PLB —
47.00 9.625 244.48 0.472 11.99 — — PLB PLB PLB PLB PLB PLB
53.50 9.625 244.48 0.545 13.84 — — — PLB PLB PLB PLB PLB
58.40 9.625 244.48 0.595 15.11 — — — PLB PLB PLB PLB PLB
59.40 9.625 244.48 0.609 15.47 — — — — — P — —
64.90 9.625 244.48 0.672 17.07 — — — — — P — —
70.30 9.625 244.48 0.734 18.64 — — — — — P — —
75.60 9.625 244.48 0.797 20.24 — — — — — P — —
OCTG Casing
Pipe Size
API5CT		 Weight Lb/ft Outside Diameter Wall Thickness Type End Finish
Grade
ln. mm ln. mm H-40 J-55
K-55		 M-65 L-80
C-95		 N-80 C-90T-95 P-110 Q-125
10 3/4” 32.75 10.75 273.05 0.279 7.09 PS — — — — — — —
40.50 10.75 273.05 0.350 8.89 PS PSB PSB — — — — —
45.50 10.75 273.05 0.400 10.16 — PSB PSB — — — — —
51.00 10.75 273.05 0.450 11.43 — PSB PSB PSB PSB PSB PSB —
55.50 10.75 273.05 0.495 12.57 — — PSB PSB PSB PSB PSB —
60.70 10.75 273.05 0.545 13.84 — — — — — PSB PSB PSB
65.70 10.75 273.05 0.595 15.11 — — — — — PSB PSB PSB
73.20 10.75 273.05 0.672 17.07 — — — — — P — —
79.20 10.75 273.05 0.734 18.64 — — — — — P — —
85.30 10.75 273.05 0.797 20.24 — — — — — P — —
11 3/4” 42.00 11.75 298.45 0.333 8.46 PS — — — — — — —
47.00 11.75 298.45 0.375 9.53 — PSB PSB — — — — —
54.00 11.75 298.45 0.435 11.05 — PSB PSB — — — — —
60.00 11.75 298.45 0.489 12.42 — PSB PSB PSB PSB PSB PSB PSB
65.00 11.75 298.45 0.534 13.56 — — — P P P P P
71.00 11.75 298.45 0.582 14.78 — — — P P P P P
13 3/8” 48.00 13.375 339.73 0.330 8.38 PS — — — — — — —
54.50 13.375 339.73 0.380 9.65 — PSB PSB — — — — —
61.00 13.375 339.73 0.430 10.92 — PSB PSB — — — — —
68.00 13.375 339.73 0.480 12.19 — PSB PSB PSB PSB PSB PSB —
72.00 13.375 339.73 0.514 13.06 — — — PSB PSB PSB PSB PSB
P-plain end；S-short round thread；L-long round thread；B-buttress thread

TUBING PIPE

Note: P = plain end, N = Non-upset thread and coupling, U = upset thread and coupling. Sizes per API 5CT specification
Source: API – American Petroleum Institute

OCTG
Pipe Sizes (Tubing)
API5CT		 Weight Lb/ft Outside Diameter Wall Thickness Nominal Weight Type End Finish
Grade
Nonupset Ex-upset mm mm Nonupset Ex-upset J-55 L-80 N-80 C-90 T-95 P-110
T & C T & C T & C T & C
2 3/8” 4 — 60.32 4.24 5.95 — PN PN PN PN PN —
4.6 4.7 60.32 4.83 6.85 6.99 PNU PNU PNU PNU PNU PNU
5.8 5.95 60.32 6.45 8.63 8.85 — PNU PNU PNU PNU PNU
6.6 — 60.32 7.49 9.82 — — P — P P —
7.35 7.45 60.32 8.53 10.94 11.09 — PU — PU PU —
2 7/8” 6.4 6.5 73.02 5.51 9.52 9.67 PUN PNU PNU PNU PNU PNU
7.8 7.9 73.02 7.01 11.61 11.76 — PNU PNU PNU PNU PNU
8.6 8.7 73.02 7.82 12.8 12.95 — PNU PNU PNU PNU PNU
9.35 9.45 73.02 8.64 13.91 14.06 — PU — PU PU —
10.5 — 73.02 9.96 15.63 — — P — P P —
11.5 — 73.02 11.18 17.11 — — P — P P —
3 1/2” 7.7 — 88.9 5.49 11.46 — PN PN PN PN PN —
9.2 9.3 88.9 6.45 13.69 13.84 PNU PNU PNU PNU PNU PNU
10.2 — 88.9 7.34 15.18 — PN PN PN PN PN —
12.7 12.95 88.9 9.52 18.9 19.27 — PNU PNU PNU PNU PNU
14.3 — 88.9 10.92 21.28 — — P — P P —
15.5 — 88.9 12.09 23.07 — — P — P P —
17 — 88.9 13.46 25.3 — — P — P P —
4” 9.5 — 101.6 5.74 14.14 — PN PN PN PN PN PN
10.7 11 101.6 6.65 — 16.37 PU PU PU PU PU PU
13.2 — 101.6 8.38 19.64 — — P — P P —
16.1 — 101.6 10.54 23.96 — — P — P P —
18.9 — 101.6 12.7 28.13 — — P — P P —
22.2 — 101.6 15.49 33.04 — — P — P P —
4 1/2” 12.6 12.75 114.3 6.88 18.75 18.97 PUN PNU PNU PNU PNU PNU
15.2 — 114.3 8.56 22.62 — — P — P P —
17 — 114.3 9.65 25.3 — — P — P P —
18.9 — 114.3 10.92 28.13 — — P — P P —
21.5 — 114.3 12.7 32 — — P — P P —
23.7 — 114.3 14.22 35.27 — — P — P P —
26.1 — 114.3 16 38.84 — — P — P P —

API 5CT TOLERANCES

Execution Outer Diameter Wall Thickness
Cold rolled Tube sizes(mm) Tolerances(mm)
＜114.3 ±0.79 －12.5％
≥114.3 －0.5％，＋1％

 OCTG PIPE MATERIALS

The most common materials for OCTG pipes are API H40, J55, K55, L80, N80, P110, and Q125 (casing and tubing pipes). These API grades feature increasing mechanical properties (tensile and yield strength).

OCTG casing and tubing pipes are available in the following material grades:

API H40

API H40 grade is for general purpose OCTG pipe material with the following mechanical properties:

Chemical Composition

  C Mn Mo Cr Ni Cu Ti P S Si V Al
Min – – – – – – – – – – – –
Max – – – – – – – 0.030 0.030 – – –

Mechanical Properties

Min Tensile Strength 414 MPa 60,000 psi min
Min Yield Strength 276 MPa 552 MPa max
40,000 psi 80,000 psi max
Total Elongation Under Load 0.500 % –

API J55

The J55 API-5CT casing pipe is a comparatively low steel grade in oil drilling. It is widely applied to shallow oil and gas extraction. Because of its low cost among other grades of steel, it enjoys wider applications,  can be generally used in shallow wells, geothermal wells, and water wells.

Chemical Composition

  C Mn Mo Cr Ni Cu Ti P S Si V Al
Min – – – – – – – – – – – –
Max – – – – – – – 0.030 0.030 – – –

Mechanical Properties

Min Tensile Strength 517 MPa 75,000 psi min
Min Yield Strength 379 MPa 552 MPa max
55,000 psi 80,000 psi max
Total Elongation Under Load 0.500 % –

API L80

L80 belongs to steel grades group of the corrosion-resistant casing. L80 API oilfield casing pipe includes L80-1, L80-9Cr, and L80-13Cr. L80-1 is used in the H2S environment, while L80-9Cr and L80-13Cr are used in the CO2 environment. In the corrosive environment in which carbon dioxide predominates, Super 13Cr has a higher corrosion resistance than L80-13Cr. With a relatively high price, the product applies to more complicated geological conditions and runs down deeper into the well. In the exploitation of oil and gas, the use of L80 is less frequent than J55, N80, and other materials.

Chemical Composition

  C Mn Mo Cr Ni Cu Ti P S Si V Al
Min – – – – – – – – – – – –
Max 0.430 1.900 – – 0.250 0.350 – 0.030 0.030 0.450 – –

Mechanical Properties

Min Tensile Strength 655 MPa 95,000 psi min
Min Yield Strength 552 MPa 655 MPa max
80,000 psi 95,000 psi max
Total Elongation Under Load 0.500 % –
Hardness 23 Max HRC 241 Max HBW

9Cr-L80 Chemical Composition

  C Mn Mo Cr Ni Cu Ti P S Si V Al
Min – 0.300 0.900 8.000 – – – – – – – –
Max 0.150 0.600 1.100 10.000 0.500 0.250 – 0.020 0.010 1.000 – –

9Cr-L80 Mechanical Properties

Min Tensile Strength 655 MPa 95,000 psi min
Min Yield Strength 552 MPa 655 MPa max
80,000 psi 95,000 psi max
Total Elongation Under Load 0.500 % –
Hardness 23 Max HRC 241 Max HBW

API N80

API-5CT N80 oilfield casing pipe contains N80-1 and N80-Q types. Those two materials are absolutely consistent regarding the chemical composition and mechanical attributes, they are just variations in the heat treatment.

During the heat treatment, N80-1 steel is treated by normalizing and tempering, while N80Q steel is treated by quenching and tempering. Therefore, the collapsing strength and internal pressure strength of N80Q are higher than that of N80-1. N80-1 or N80Q should be clearly shown by the designer when N80 casing is selected.

As its mechanical properties are higher than J55 and K55 types, it may very well be utilized to certain a little more challenging formations. With deeper downhole depth than J55 and K55 types, it can be applied for the exploitation of middle-level oil and gas.

Due to the high capability of the N80 material, those API-5CT casing pipes are broadly applied in natural gas as well as coal bed methane extraction, and geothermal wells.

Chemical Composition

  C Mn Mo Cr Ni Cu Ti P S Si V Al
Min – – – – – – – – – – – –
Max – – – – – – – 0.030 0.030 – – –

Mechanical Properties

Min Tensile Strength 689 MPa 100,000 psi min
Min Yield Strength 552 MPa 758 MPa max
80,000 psi 110,000 psi max
Total Elongation Under Load 0.500 % –
Hardness – –

API P110

The P110 API-5CT steel casing pipe is the high grade amongst other grades of steel. The white band is marked on the finished casing to point out the materials. During petroleum drilling and producing, this pipe is generally used in a variety of complicated territory due to its higher tensile strength and higher yield. It goes down the deepest into the well among other types.

However, the price is comparatively high, as well as the quantity of usage is comparatively few. P110 casing pipe is mainly used in a particular surrounding and when the drilling depth extends to a particular level.

API Q125

This API grade is generally used for deep wellbore service and not in sour condensate wells. The hardness testing (quadrant) is required without any specified limits other than the variation between readings.

The impact test is required for each heat and production lot. Non-destructive examination and inspection are required. The tables below list the materials used for OCTG casing and tubing pipes.

API5CT MATERIALS CHEMICAL COMPOSITION

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Group OCTG pipe materials Type C   Mn   Mo   Cr   Ni max. Cu max. P max. S max. Si max.
                               
min. max. min. max. min. max. min. max.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1 H40 – – – – – – – – – – – 0.03 0.03 –
J55 – – – – – – – – – – – 0.03 0.03 –
K55 – – – – – – – – – – – 0.03 0.03 –
N80 1 – – – – – – – – – – 0.03 0.03 –
N80 Q – – – – – – – – – – 0.03 0.03 –
R95 – – 0.45 c – 1.9 – – – – – – 0.03 0.03 0.45
2 M65 – – – – – – – – – – – 0.03 0.03 –
L80 1 – 0.43 a – 1.9 – – – – 0.25 0.35 0.03 0.03 0.45
L80 9Cr – 0.15 0.3 0.6 0.9 1.1 8 10 0.5 0.25 0.02 0.01 1
L80 13Cr 0.15 0.22 0.25 1 – – 12 14 0.5 0.25 0.02 0.01 1
C90 1 – 0.35 – 1.2 0.25 b 0.85 – 1.5 0.99 – 0.02 0.01 –
T95 1 – 0.35 – 1.2 0.25 d 0.85 0.4 1.5 0.99 – 0.02 0.01 –
C110 – – 0.35 – 1.2 0.25 1 0.4 1.5 0.99 – 0.02 0.005 –
3 P110 e – – – – – – – – – – 0.030 e 0.030 e –
4 Q125 1 – 0.35 1.35 – 0.85 – 1.5 0.99 – 0.02 0.01 –

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a The carbon content for L80 may be increased up to 0.50 % maximum if the product is oil-quenched.
b The molybdenum content for Grade C90 Type 1 has no minimum tolerance if the wall thickness is less than 17.78 mm.
c The carbon content for R95 may be increased up to 0.55 % maximum if the product is oil-quenched.
d The molybdenum content for T95 Type 1 may be decreased to 0.15 % minimum if the wall thickness is less than 17.78 mm.
e For EW Grade P110, the phosphorus content shall be 0.020 % maximum and the sulfur content 0.010 % maximum.
NL = no limit. Elements shown shall be reported in product analysis.

OCTG PIPE MATERIALS – MECHANICAL PROPERTIES

Group OCTG pipe materials Type Total elongation under load % Yield strength MPa Tensile strength min. MPa Hardness a max. Specified wall thickness mm Allowable hardness variation b HRC
min. max . HRC HBW
1 2 3 4 5 6 7 8 9 10 11
1 H40 – 0.5 276 552 414 – – – –
J55 – 0.5 379 552 517 – – – –
K55 – 0.5 379 552 655 – – – –
N80 1 0.5 552 758 689 – – – –
N80 Q 0.5 552 758 689 – – – –
R95 – 0.5 655 758 724 – – – –
2 M65 – 0.5 448 586 586 22 235 – –
L80 1 0.5 552 655 655 23 241 – –
L80 9Cr 0.5 552 655 655 23 241 – –
L80 13Cr 0.5 552 655 655 23 241 – –
C90 1 0.5 621 724 689 25.4 255 ≤ 12.70 12.71 to 19.04 19.05 to 25.39 ≥ 25.40 3.0 4.0 5.0 6.0
T95 1 0.5 655 758 724 25.4 255 ≤ 12.70 12.71 to 19.04 19.05 to 25.39 ≥ 25.40 3.0 4.0 5.0 6.0
C110 – 0.7 758 828 793 30 286 ≤ 12.70 12.71 to 19.04 19.05 to 25.39. ≥ 25.40 3.0 4.0 5.0 6.0
3 P110 – 0.6 758 965 862 – – – –
4 Q125 1 0.65 862 1034 931 b – ≤ 12.70 12.71 to 19.04 ≥ 19.05 3.0 4.0 5.0
a In case of dispute, laboratory Rockwell C hardness testing shall be used as the referee method.
b No hardness limits are specified, but the maximum variation is restricted as a manufacturing control in accordance with 7.8 and 7.9 of API Spec. 5CT.

The API5CT specification can be purchased here.