What is a steel casing pipe

What is a steel casing pipe?

steel casing pipe or tube used in drilling well or any underground installation is called casing tube or pipe. Steel Casing Pipe, also known as encasement pipe, is most commonly used in underground construction to protect utility lines of various types from getting damaged.

API Spec 5CT – Specification 5CT/ISO 11960, Specification for Casing and Tubing, Eighth Edition, Petroleum and natural gas industries-Steel pipes for use as casing or tubing for wells.

Casing pipes are used for casing oil & gas wells. In casing a large diameter pipe is assembled and is inserted into a drilled section of a bore-hole.

Why is casing done?

  • It prevents contamination of fresh water
  • It provides stronger upper foundation for dipper drill
  • Enables smooth bore for installing equipment
  • Seals high pressure zone surface to ward from getting blown off

Benefits of steel casing pipe:
Casing pipes manufactured out of steel are smelted in the electric furnace, treated with synthetic slags and cast by continuous casters. This process ensures the achievement of chemically pure steel with reference to sulphur and phosphor contents providing high tensile, ductility and corrosion resistance properties of pipes to be operated at low temperatures in various corrosion media. Pipes are heat-treated in a computerized walking beam furnace.

Steel grades and heat treatment regimes applied allow high-strength pipe to be obtained. Steel casing pipes and tubing are applied to furnishing and installing cased tunnels, where they indicate to pass other utilities or obstructions without open excavation. Steel casing pipes and tube have smooth wall and a minimum yield strength of 35,000 psi. Corrosion-proofing water-based paint is applied on the outside pipe surface to protect against atmospheric corrosion during transportation and storage.

The pipes can be delivered with metal or composite caps at both ends for thread protection.


The production of casing pipes are from steel smelted in electric furnaces, treated with synthetic slag and cast by continuous casters. This steel-making process guarantees the attainment of chemically pure steel, given the phosphor and sulfur contents. This provides highly ductile, malleable and corrosion-resistant pipes, which can operate at low temperatures in a number of corrosive media. Steel grades and heat-treatment regime application allows production of high-strength pipe.


Steel casing pipes should have minimum yield strength of 35,000 psi. Casing pipes need to have smooth walls and be exceptionally straight and round. Casing pipe and joint construction should be of uniformly thick steel to avoid any matter leaking from the casing. The outside diameter, size and wall thickness should conform to ASTM Designation A252. Use pull-on or wrap-around rubber varieties of “casing end seals” to seal the ends of the steel casing pipe. Apply corrosion-proofing water-based paint to the exterior pipe surface to safeguard against atmospheric corrosion during shipping and storage.

Quality Control

In accordance with the requirements of ANSI/AWS D1.1, all welding should be performed by qualified welding operators. Complete one reduced section tension test specimen for each lot of 1,000 feet of each size and wall thickness. Verify that the tensile strength is not less than 95 percent of the minimum strength specified for the grade of steel used, except when waived by the customer. No hydrostatic testing is required. Examine all connections to make sure they are free of injurious defects at the time of shipment. Otherwise, prior to shipping, reject and repair that section.

Production Standard, Grade, Steel No:

  • API 5L PSL1 L175/A25, L210/A, L245/B, L290/X42, L320/X46, L360/X52, L485/X70
  • PSL2 L245R/BR, L290N/X42N, L320N/X46N, L360N/X52N, L415/X60N
  • API 5CT PSL1, PSL2, PSL3, H40, J55, K55, N80
  • GB/T 9711.1 L175, L210, L245, L290, L320, L360
  • GB/T 9711.2 L245NB, L290NB, L360NB
  • GB/T 9711.3 L245NC, L290NC, L360NC

Characteristic of casing pipe

Casing is important to oil drilling equipment, and its main equipment includes drill, core pipe and casing, drill collars and drilling small diameter steel pipe and so on.

The casing is used to support oil and gas wall of the pipe, to ensure that the drilling and completion of the process of the normal operation of the wells. Depending on the drilling each well depth and geological conditions, to use several layers of casing. Casing cementing go down after using it with tubing, drill pipe are different, can not be reused, a one-time consumable materials. Therefore, the total consumption of the casing is 70% of the oil well pipe. Casing can be divided according to usage: catheter, surface casing, casing and production casing. Casing is a large-diameter pipe, play a fixed oil and gas wells, or wellbore wall effect. The casing is inserted into the well hole, fixed with cement to prevent the formation and borehole spaced borehole collapse and to ensure circulation of the drilling mud to the drilling mined.

Casing is mainly used for drilling oil wells during drilling and after completion of the support wall to ensure that the conduct of the drilling process and completion of the wells after the regular oil casing normal operation. OCTG mainly used for oil and gas well drilling and oil and gas transportation. It includes oil drilling pipe, oil casing, pump tubing. Oil drill pipes are mainly used to connect the drill collar and drill and pass drilling power. Casing is mainly used for drilling and completion of the right wall of the support, to ensure that the conduct and completion of the drilling process after the normal operation of the wells. Pumping wells at the bottom of the tubing will mainly oil, gas transported to the ground.

Casing is to maintain the wells run lifeline. As different geological conditions, underground complex stress state, pulling, pressing, bending, torsional stress acting on the combined effect of the tube, which the casing itself, the quality of the higher requirements. Once the casing itself is damaged for some reason, could lead to the whole production wells, or even scrapped.

Types of Steel Casing Pipe
Steel casing pipe is a versatile product that can be used to protect a variety of types of utility and carrier pipes. They used as steel casing including straight seam steel pipe, spiral weld pipe, seamless steel pipe, and rolled and welded pipe.
Straight Seam Steel Casing Pipe: Straight seam steel casing pipe is so called because the pipe is rolled from strip and formed with one longitudinal weld . This straight seam steel casing pipe is generally manufactured by an Electric Weld or a DSAW type of manufacture. This steel casing pipe is available in a variety of thicknesses and grades depending on your application. This DSAW pipe is formed by first rolling steel plates into cylindrical shapes. The edges of the rolled plate are then shaped so that V-shaped grooves are formed on the interior and exterior surfaces at the location of the seam. The pipe seam is then formed with a single pass of an arc welder on the interior and exterior surfaces and the welding arc is submerged under flux. A main benefit of using this process when making steel casing is that the welds penetrate 100% of the pipe wall and produces a very strong bond. ERW pipe is similar but fused together instead of welded.
Spiral Welded Steel Casing Pipe: This steel casing pipe is a very durable and economical product that gives your project the long lasting reliability you require. The weld seam on spiral weld pipe is in a spiral around the pipe, said to be like a barberpole style This pipe can be manufactured to meet a specific outer diameter, wall thickness, grade, steel strength, and length.
Rolled and Welded Steel Casing: Rolled and Welded steel casing pipe is created by rolling and welding larger diameter pipe cylinders from steel plate, and then welding those cylinders into a longer lengths as needed. This rolled and welded steel pipe type of manufacture is generally used to make large diameter steel casing pipe, these are more “specialty” sizes and not made generally in large production capacity. The general size range starts at 30” diameter on up to very large diameter steel casing pipe.

API Spec 5CT Casing pipe

API Spec 5CT Casing pipe - What is a steel casing pipe

API Spec 5CT – Specification 5CT/ISO 11960, Specification for Casing and Tubing, Eighth Edition, Petroleum and natural gas industries-Steel pipes for use as casing or tubing for wells.

Standard: API SPEC 5CT

API 5CT pipe Size (mm):
  • Outer Dimensions: 6.0mm – 219.0mm
  • Wall Thickness: 1.0mm – 30 mm
  • Length: max 12000mm

Application: gas, water and oil transportation in both oil and natural gas .

The main steel grade of API 5CT:
  • API 5CT J55
  • API 5CT K55
  • API 5CT N80
  • API 5CT L80
  • API 5CT P110

Packing: Bare/bundles/crates/crate protection at the both sides of tubes or as per customers’ requirements .

This International Standard is applicable to the following connections in accordance with ISO 10422 or API Spec 5B:

  • short round thread casing (STC);
  • long round thread casing (LC);
  • buttress thread casing (BC);
  • extreme-line casing (XC);
  • non-upset tubing (NU);
  • external upset tubing (EU);
  • integral joint tubing (IJ).

For such connections, this International Standard specifies the technical delivery conditions for couplings and thread protection.

For pipes covered by this International Standard, the sizes, masses, wall thicknesses, grades and applicable end finishes are defined.

This International Standard may also be applied to tubulars with connections not covered by ISO/API standards.

Chemical Composition of API 5CT
Grade C≤ Si≤ Mn≤ P≤ S≤ Cr≤ Ni≤ Cu≤ Mo≤ V≤ Als≤
J55 0.34-0.39 0.20-0.35 1.25-1.50 0.020 0.015 0.15 0.20 0.20 / / 0.020
K55 0.34-0.39 0.20-0.35 1.25-1.50 0.020 0.015 0.15 0.20 0.20 / / 0.020
N80 0.34-0.38 0.20-0.35 1.45-1.70 0.020 0.015 0.15 / / / 0.11-0.16 0.020
L80 0.15-0.22 1.00 0.25-1.00 0.020 0.010 12.0-14.0 0.20 0.20 / / 0.020
J P110 0.26-035 0.17-0.37 0.40-0.70 0.020 0.010 0.80-1.10 0.20 0.20 0.15-0.25 0.08 0.020
Mechanical Properties of API 5CT
Steel Grade Yield Strength (Mpa) Tensile Strength (Mpa)
J55 379-552 ≥517
K55 ≥655 ≥517
N80 552-758 ≥689
L80 552-655 ≥655
P110 758-965 ≥862
API Spec 5CT standard replaced by:
  • API Spec 5CT – Specification 5CT/ISO 11960, Specification for Casing and Tubing, Eighth Edition, Petroleum and natural gas industries-Steel pipes for use as casing or tubing for wells
  • This product references:
  • API Spec 5B – Specification for Threading, Gauging, and Thread Inspection of Casing, Tubing, and Line Pipe Threads (US Customary Units) (Includes March 2004 Addendum)
  • ISO 10422:1993 – Petroleum and natural gas-industries; threading, gauging, and thread inspection of casing, tubing and line pipe threads; specification
  • This product replaces:
  • API 5CT – Specification for Casing and Tubing (U.S. Customary Units)
  • ISO 11960 was prepared by Technical Committee ISO/TC 67, Materials, equipment and offshore structures for petroleum, petrochemical and natural gas industries, Subcommittee SC 5, Casing, tubing and drill pipe.

J55 and K55 Oil Casing in API 5CT

J55 and K55 Oil Casing in API 5CT - What is a steel casing pipe

API Spec 5CT – Specification 5CT/ISO 11960, Specification for Casing and Tubing, Eighth Edition, Petroleum and natural gas industries-Steel pipes for use as casing or tubing for wells.

Heat treatment

PSL1 requirements: J55 and K55 same way (can be rolled-state delivery); 
PSL2 requirements: J55, K55 product should be normalized or normalized and tempered overall, if thick, should be normalized or normalized and tempered after thickened.

Tensile test

Data yield strength tensile minimum elongation
J55 379MPa ~ 552MPa ≥517MPa 19%
K55 379MPa ~ 552MPa ≥655MPa 15%

Impact test

J55 and K55 impact test must be done, the minimum size of the sample lateral impact energy 20J, the smallest full-size sample longitudinal impact energy 27J.

Wall thickness detection

PSL1: J55 and K55 for measuring the wall thickness of no coverage requirements; 
PSL2: J55 and K55 for wall thickness measurement and recording deal with the entire length of the best coverage of the surface area of automatic detection system should reach 25%. 


PSL1: J55 and K55 on the tube did not do destructive testing mandatory requirements; 
PSL2: J55 and K55 for all pipe shall be one or more of the criteria specified in 10.15.5 tested to find the inner surface of the outer surface of the pipe and can receive the level of L4 longitudinal imperfections.

N80 Casing Pipe
N80 steel pipe is generally casing pipe. N80 casing pipe is an important equipment for oil drilling, and its main equipment also includes drill pipe, core tube and casing, drill collar and small diameter drilling steel pipe.
Domestic casing to geological drilling steel by hot-rolled or cold drawn, steel with “geological” (DZ) said that the commonly used casing steel DZ40, DZ55, DZ753 species.
(1) Casing pipe mainly imported countries: Germany, Japan, Romania, Czech Republic, Italy, Britain, Austria, Switzerland, the United States, Argentina, Singapore also imports. Import standard reference to the American Petroleum Institute Standard API5A, 5AX, 5AC. Steel grade is H-40, J-55, N-80, P-110, C-75, C-95 and so on. Specifications for the main 139.77.72R2,177.89.19R-2,244.58.94R-2,244.510.03R-2,244.511.05R-2.
(2) API provides a length of three: R-1 is 4.88 ~ 7.62m, R-2 is 7.62 ~ 10.36m, R-3 is 10.36m to longer.
(3) Part of the imported goods marked LTC words, that is, long thread buckle casing.
(4) Such as Nippon Steel, Sumitomo, Kawasaki, etc., the steel number is NC-55E, NC-80E, NC-L80, and NC-80E, NC-80HE and so on.
(5) In the case of claims, there have been black buckle, thread damage, pipe folding, broken buckle and thread close distance tolerance, coupling J value of the appearance of defects such as defects and casing brittle fracture, low yield strength quality problem.

The difference between the J55 and N80

J55 and N80 are a common part of the oil casing material. However, these two materials are some differences.
The difference between the J55 and N80:
  • Yield strength of the N80 is higher than the J55 up to 173 ~ 206 MPa.
  • On the same area of the sample, the elongation of N80 is higher than J55.
  • Under the same size, the same sample orientation, the same minimum sample size, J55 grade couplings, coupling stock, coupling material, semi-finished and coupling attachment material can absorb lower than N80 steel grade.
  • The nondestructive testing methods of seamless pipe,coupling stock, welded tube with J55 and N80 is differeent.
  • J55 and N80 steel grade is not the same color: length greater than or equal 1.8m, J55 painted a bright green, N80 painted a red;
  • J55 chosen by the manufacturer, or organize according to the order specified length normalized (N), normalizing and tempering (N & T) or quenching and tempering (Q & T). N80 is a whole, full-length heat treatment is mandatory. By the manufacturer selected for normalizing (N) or normalizing and tempering (N & T) + quenching (Q).

Threaded Casing with Short/Long Round Thread or Buttress

Threaded Casing and Supply supplies new and used steel casing pipe, piling pipe, surplus pipe, and used steel pipe.

Standard: API Spec 5 CT:
O.D. (mm) Weight T&C W.T. Steel grade
Lb/ft Kg/m mm H40 J55 K55 N80 L80 C95 P110
4 1/2 114,3 9,5 14,2 5,21 S S S
    10,5 15,6 5,69 S;B S;B
    11,6 17,3 6,35 S;L;B S;L;B L;B L;B L;B L;B
  13,5 20,1 7,37 L;B L;B L;B L;B
    15,1 22,5 8,56
5 127 11,5 17,1 5,59 S S
  13 19,4 6,43 S;L;B S;L;B
    15 22,3 7,52 S;L;B S;L;B L;B L;B L;B L;B
    18 26,8 9,19 L;B L;B L;B L;B
    21,4 31,9 11,1 L;B L;B L;B L;B
    23,2 34,6 12,14 L;B L;B L;B L;B
    24,1 35,9 12,7 L;B L;B L;B L;B
5 1/2 139,7 14 20,9 6,2 S S S
    15,5 23,1 6,98 S;L;B S;L;B
    17 25,3 7,72 S;L;B S;L;B L;B L;B L;B L;B
    20 29,8 9,17 L;B L;B L;B L;B
    23 34,3 10,54 L;B L;B L;B L;B
6 5/8 168,3 20 29,8 7,32 S S;L S;L
    24 35,7 8,94 S;L S;L

Where: S = Short Round ThreadL = Long Round ThreadB = Buttress ThreadWeight per unit calculation formula:w = (O.D. – W.T.) x W.T. x 0.0246615 (kg/m)w = (O.D. – W.T.) x W.T. x 10.68 (lb/ft)

Steel Requirements:
Steel grade Chemical requirements Mechanical requirements
C Mn Ni Cu P S Si Tensile strength Yield strength Elongation A min.
max. max. max. max. max. max. max.
(%) (%) (%) (%) (%) (%) (%) N/mm2 N/mm2 (%)
H40 0,03 0,03 min. 414 276-552 calculation
J55 0,03 0,03 min. 517 379-552 according
K55 0,03 0,03 min. 655 379-553 to the wall
N80 0,03 0,03 min. 689 552-758 thickness
L80 0,43 1,9 0,25 0,35 0,03 0,03 0,45 min. 655 552-655  
C95 0,45 1,9 0,03 0,03 0,45 min. 724 655-758  
P110 0,03 0,03 min. 724 655-758  

LENGTHS: Range I : 4,88-7,62 metersRange II : 7,62-10,36 metersRange III : 10,36-12,00 meters
PROTECTIONUnprotected or external protectionEach pipe is provided with plastic protectors at both ends.
MARKINGDie stamped or/and paint stenciled according to standard or per customer request.
DELIVERYIn bundles of maximum 2500 kg, tied in minimum four places with steel strps.
MILL TEST REPORT Mill test reports are issued to customer requirements.Usually they comply with EN 10204 – 3.1.B (DIN 50049 – 3.1.B)

Application of Casing Pipe
Casing pipe is typically used to encase and protect something. A typical uses for casing pipe is in underground construction to protect utility lines from damage. This steel casing protects utility lines not only from the elements but from future construction activity such as digging or drilling. 
1. Directional Drilling. Directional drilling also described as slant drilling is a form of drilling horizontally rather than a vertical shaft. It is used in both the oilfield and utility industries to steer the drill bit to reach a desired point. This technique is used for installing horizontal pipelines under roads, underwater and through rock, often as a conduit for fiber optic lines, utility, and power lines. 
2. Rode Bore Casing/Horizontal Casing. Road Bore Casing also know as horizontal casing is used to encase and protect utility lines, cable and pipelines and to keep the shaft from collapsing while boring under roads and rivers. 
3. Open Cut Casing. This pipe is more or less the same as road bore casing, but it installed into an open trench and then covered. 
4. Vertical Casing Pipe. Casing pipe is used for both oil and gas wells and water well applications an privides a steel pipe casing for the drill pipe and bit. After the drilling is completed, the steel pipe casing remains in place to allow for the tubing to be installed so the oil, case or waster can be extracted. This is also known as conductor hole, rat hole, or mouse hole pipe. 

Notice of oil casing corrosion problems

As the number of cars now constantly increases, we will use the time to the exploitation of oil in the oil casing, as crude oil, which contain this more corrosive substances, so when we make oil casing when you need attention, when we use the oil casing to the exploitation of oil, when oil casing will be very prone to corrosion oil casing corrosion when in problems that need attention are as follows:

(1) When we use the oil casing transport water, it should ensure that during the making use of the time, the quality of the water to compliance, quality time during the use of water to compliance before they can, and to be discharged during the time implement remediation dispensing. During the time used to strengthen the work of the main water pipe cleaning, to ensure progress after the oil casing pipe using internal corrosion is not residual material. Ensure oil casing during use when you can live longer.

(2) for injection wells have been put into production, we make use of the time should be taken to protect the inside with some of the annulus fluid for maintenance work, and regularly fill such measures as adding protection solution to become a seed system, we want to regularly add oil casing inside, the only way to guarantee oil casing when you can use during the long-term use.

(3) the use of oil casing, there will be mechanical abrasion, these scratches will affect the oil casing corrosion, accelerated corrosion oil casing, it is recommended for use during the time in tubing coupling top with a rubber band, so that you can reduce the oil casing corrosion.

Source: China Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at [email protected]

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