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.
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:
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 are a key structural component for an oil & gas well and have the following scope:
Casing pipes are used to install:
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:
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.
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.
The main types of connections for casing pipes are STC (short threads), LTC (long threads), BTC (buttress threads) and premium gas-tight connections.
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).
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).
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.
The manufacturing processes of casing and tubing pipes include:
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.
The top OTCG pipes suppliers are:
Tenaris is based in Argentina and manufactures a wide range of mechanical, structural, process and OCTG pipes. In the OCTG area, Tenaris supplies drilling, casing and tubing pipes with standard and premium connections, and other tubular equipment for upstream operations (as sucker rods and coil tubes). Tenaris produces OCTG pipes in most major API grades (as listed below), including carbon, alloy, and higher grades. Besides being a mill, Tenaris is also involved in contracting and consulting in upstream, midstream and downstream oil & gas.
US Steel is a multinational steel company covering a wide range of industries, from food to oil and gas. The company has a key role in the OCTG industry, as it produces drill, casing, and tubing pipes API 5CT in most sizes and API material grades with different types of commercial and proprietary connections.
Nippon Steel is an accredited supplier of OCTG pipes, used throughout the world and recognized for their exceptional quality. The company has been very active in developing stronger materials and innovative connections. Further, the company has a well-established distribution business, able to support exploration and upstream activities in real-time.
Arcelor Mittal, a giant Indian/French steel conglomerate, is involved in the production and distribution of OCTG pipes for exploration and extraction operations. The Arcelor Mittal pipe and tubes division represents a small fraction of the whole company turnover (definitely less than 5%) but can be still be considered one of the major players in the oil exploration and upstream industries.
TMK is one of the top five pipe manufacturers in the world. Besides process pipes, TMK manufactures and distributes also seamless and welded OCTG pipes in various material grades through a consolidated network of regional offices.
Despite its troubled situation in the last few years, Vall0urec is a major player in the OCTG industry. The company manufactures and distributes drill, casing and tubing pipes with premium connections.
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 P8 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 PLB9 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 P13 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 PSBP-plain end；S-short round thread；L-long round thread；B-buttress thread
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 —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 grade is for general purpose OCTG pipe material with the following mechanical properties:
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.
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.
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 HBWAPI-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.
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.
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.
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.
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.