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Oil Casing

Shaanxi World Iron & Steel Co.,Ltd | Updated: Dec 05, 2018


The oil special pipe is mainly used for drilling oil and gas wells and conveying oil and gas. It includes oil drill pipes, oil casings, and oil pipes. Oil drill pipes are mainly used to connect drill collars and drill bits and transmit drilling power. The oil casing is mainly used for supporting the well wall during and after the completion of the drilling process to ensure the drilling process and the normal operation of the entire well after completion. The oil pipe mainly transports the oil and gas at the bottom of the oil well to the ground.

Oil casing is the lifeline for maintaining oil well operations. Due to different geological conditions, the downhole stress state is complex, and the combined action of tension, compression, bending and torsion stress acts on the pipe body, which puts high requirements on the quality of the casing itself. Once the casing itself is damaged for some reason, it may result in a reduction in production and even scrapping of the entire well.

According to the strength of the steel itself, the casing can be divided into different steel grades, namely J55, K55, N80, L80, C90, T95, P110, Q125, V150 and so on. The well conditions and well depth are different, and the steel grades used are also different. The casing itself is also required to have corrosion resistance in a corrosive environment. It is also required that the casing has anti-crushing properties in places with complicated geological conditions.

Preparation editing

27MnCrV is a new type of steel for the production of TP110T steel grade oil pipe sleeves. The conventional production of TP110T steel grade oil pipe sets is 29CrMo44 and 26CrMo4. Compared with the latter two, 27MnCrV contains less Mo element, which can greatly reduce the production cost. However, after the production of 27MnCrV by normal austenitizing quenching process, there is obvious high temperature temper brittleness, resulting in low impact toughness and instability.

Solving such problems is usually handled in two ways: First, the method of rapid cooling after tempering avoids high temperature brittleness and obtains toughness. Second, the sub-temperature quenching method improves the toughness by effectively improving the harmful elements and impurities through incomplete austenitization of the steel. In the first method, the heat treatment equipment is relatively strict and requires additional costs.

27MnCrV steel AC1 = 736 ° C, AC3 = 810 ° C, heating temperature during sub-temperature quenching is selected between 740-810 ° C. The sub-temperature quenching selects the heating temperature of 780 ° C, the quenching heating holding time is 15 min; the quenching and tempering selects the temperature of 630 ° C, and the tempering heating and holding time is 50 min. Since the sub-temperature quenching is heated in the α+γ two-phase region, quenching is performed while retaining a portion of the undissolved ferrite, and the toughness is improved while maintaining high strength.

At the same time, the low temperature quenching is lower than the conventional temperature, which reduces the quenching stress, thereby reducing the quenching deformation, thus ensuring the smooth operation of the heat treatment production, and providing a good raw material for the subsequent wire processing.

The process has been applied in the pipe processing plant of Tianjin Pipe Group. The quality assurance data shows that the yield strength of the steel pipe after heat treatment is 820-860MPa, the tensile strength Rm is 910-940MPa, and the impact toughness Akv is between 65-85J. The anti-destructive performance is 100% qualified. The data shows that the 27MnCrV steel pipe is a relatively high-quality high-grade oil casing, and on the other hand, it shows that the sub-temperature quenching process is an excellent method to avoid high-temperature brittleness in the production of steel products.

Use editing

The oil casing is a large-diameter pipe that acts as a fixed oil and gas well wall or wellbore. The casing is inserted into the wellbore and fixed with cement to prevent the wellbore from separating the formation and the wellbore from collapsing, and to ensure that the drilling mud circulates for drilling.

Steel grades for oil casings: H40, J55, K55, N80, L80, C90, T95, P110, Q125, V150, etc. Casing end machining form: short round thread, long round thread, trapezoidal thread, special buckle, etc. It is mainly used for oil well drilling mainly for supporting the well wall during and after drilling to ensure the drilling process and the normal operation of the entire well after completion.

The important position of oil pipeline

The oil industry is an industry that uses a large number of oil pipes. Oil pipes play an important role in the oil industry:

1. The oil pipe has a large amount of consumption and spends a lot of money, and has great potential for saving expenses and reducing costs. The consumption of oil well pipes can be calculated based on the annual drilling scale. According to the specific conditions of China, 62kg of oil well pipe is required for every 1m drilled, including 48kg casing and 10kg oil pipe. Drill pipe 3kg, drill collar 0.5kg;

2. The mechanics and environmental behavior of petroleum pipelines have an important impact on the adoption of advanced technologies and increased production and efficiency in the petroleum industry;

3. The loss of oil pipe failure is huge, and its safety, reliability and service life are of great importance to the petroleum industry.

Structure editing

Weight calculation

[(outer diameter - wall thickness) * wall thickness] * 0.02466 = kg / m (weight per meter)

chemical composition

(1) According to SY/T6194-96. The casing and its couplings are of the same steel grade. Sulfur content <0.045%, phosphorus content <0.045%;

(2) Take chemical analysis samples according to the provisions of GB/T222-84. Conduct chemical analysis according to the relevant provisions of GB223;

(3) American Petroleum Institute API SPEC 5CT 1988 first edition. Chemical analysis was prepared according to the latest version of ASTM E59 and chemical analysis was performed according to the latest version of ASTM E350.

Physical properties

(1) According to SY/T6194-96. For the flattening test (GB246-97) tensile test (GB228-87) and hydraulic test;

(2) According to the American Petroleum Institute APISPEC5CT 1988 first edition for hydrostatic pressure test, flattening test, sulfide stress corrosion cracking test, hardness test (ASTME18 or E10 latest version of the provisions), tensile test, lateral impact test ( ASTMA370, ASTME23 and the latest edition of the relevant standards are specified), grain size determination (the latest version of ASTM E112 or other methods).

Category editing

Different types of casing used in oil extraction: Surface oil casing protects the well from contamination by shallow water and shallow gas, supports wellhead equipment and maintains the weight of the other layers of the casing. The technical oil casing separates the pressure at different levels so that the drilling fluid is properly circulated and the production casing is protected. In order to install the anti-burst device, the leak-proof device and the tail pipe in the well. Oil-in-oil casings export oil and gas from the subsurface storage. Used to protect the well and stratify the drilling mud. When producing oil casings, the outer diameter is usually 114.3 mm to 508 mm.

Protect the well from contamination by shallow water and shallow gas, support wellhead equipment and maintain the weight of the other layers of the casing.

The technical oil casing separates the pressure at different levels so that the drilling fluid is properly circulated and the production casing is protected. In order to install the anti-burst device, the leak-proof device and the tail pipe in the well.

Oil layer oil casing - Exports oil and natural gas from the subsurface storage layer. Used to protect the well and stratify the drilling mud. When producing oil casings, the outer diameter is usually 114.3 mm to 508 mm.

The types and packaging of oil casings are divided into two types: short sleeves and their couplings and long threaded sleeves and their couplings according to SY/T6194-96 "Petroleum Casing".

Historical development editor

After nearly 20 years of hard work, China's oil casing production has gone from scratch, from low price to high price, from low steel grade to API series products to non-API products with special needs, from quantity to quality are close. The level of foreign oil casing products. The domestic market share of China's oil well pipes has exceeded 80%, and has been a net export product for many years.

In 2011, China's crude oil output reached 204 million tons, an increase of 0.32% compared with the same period in 2010; natural gas production reached 102.531 billion cubic meters, a year-on-year increase of 6.9%, a record high. China is still in the stage of rapid development of urbanization and industrialization. It is expected that oil demand will grow at an average annual rate of about 4% in the next few years. The continuous increase in oil demand has promoted the increasing demand for oil drilling equipment in China.

From the perspective of China's domestic distribution, the demand for oil casings is no longer concentrated in the eastern region. From the trend of domestic oil and gas field development, from the initial development of Daqing, Liaohe, Shengli and other eastern oil fields, it will turn to the development of western oil fields such as Sichuan and Xinjiang, paying attention to the trend of offshore oil fields, and will also develop from land to tidal flats and from shallow seas to deep seas. Drilling depth is getting deeper and deeper, drilling work conditions are becoming more and more complex, and the requirements for oil casings are bound to become higher and higher.

Note editing

Anti-corrosion measures for oil casing

1. Firstly, we must do a good job in water quality compliance and strict water quality testing and management. Implement decontamination and re-injection, strengthen the cleaning of the main water pipeline, achieve the standard water quality in the station and the bottom of the well, and reduce the introduction of corrosion sources into the annular space;

2. For the water injection wells that have been newly put into operation, adopt an annulus protection liquid based on dosing and sterilization, and form a system to regularly add;

3. In view of the acceleration of the corrosion of the oil casing by mechanical abrasion, it is recommended to add a rubber ring to the oil pipe coupling or add a centralizer to the serious part of the well inclination to avoid the oil pipe scratching the casing during the operation and water injection. One side contact sleeve;

4. In case of serious bacterial corrosion under scale and slow growth and killing of SRB at high temperature, periodically inject 100 degrees Celsius of high temperature water or water vapor into the annulus to kill SRB under scale;

5. It is not recommended to promote cathodic protection and coated casing before the corrosion in the casing of the injection well is effectively controlled.

Packaging storage editor

According to the American Petroleum Institute standard APISPEC5CT 1988 first edition, casing steel grades H-40, J-55, K-55, N-80, C-75, L-80, C-90, C-95, P- 110, Q-125 a total of 10 kinds. The bushings shall be supplied with threads and couplings, or in the form of any of the following pipe ends: flat end, round thread without coupling or with coupling, trapezoidal threaded coupling with or without coupling, direct connection Type thread, special end machining, seal ring structure.

Place of origin

(1) The main importing countries of oil casings are: Germany, Japan, Romania, Czech Republic, Italy, Britain, Austria, Switzerland, the United States, and Argentina and Singapore. The import standards refer to the American Petroleum Institute standards API5A, 5AX, 5AC. The steel grades are H-40, J-55, N-80, P-110, C-75, C-95 and the like. The specifications are mainly 139.77.72R-2, 177.89.19R-2, 244.58.94R-2, 244.510.03R-2, 244.511.05R-2 and the like.

(2) The API has three lengths: R-1 is 4.88 to 7.62 m, R-2 is 7.62 to 10.36 m, and R-3 is 10.36 m to longer.

(3) Some imported goods are marked with the word LTC, namely the filament buckle casing.

(4) In addition to the API standard, the import of casing from Japan has a small number of Japanese factory standards (such as Nippon Steel, Sumitomo, Kawasaki, etc.), and the steel numbers are NC-55E, NC-80E, NC-L80. NC-80HE and so on.

(5) In the case of claim, there have been black buckles, thread damage, tube folding, broken buckles and thread tight distance tolerance, coupling J value is poor and other appearance defects and casing brittle fracture, low yield strength, etc. quality problem.


According to SY/T6194-96, domestic casings should be bundled with steel wire or steel belt. The exposed portion of each bushing and coupling thread should be screwed with a guard ring to protect the threads.

1) The domestic casing is stipulated in SY/T6194-96, and the length of the casing is not fixed.

Oil Casing

Oil Casing

Its range is 8-13m. However, casings not shorter than 6 m can be supplied, and the number must not exceed 20%.

(2) The inner and outer surfaces of the casing shall be free from folding, hairline, separation, cracking, rolling and crusting. These defects should be completely removed and the depth of removal should not exceed 12.5% of the nominal wall thickness.

(3) The outer surface of the coupling shall not have defects such as folding, hairline, separation, crack, rolling, crusting and so on.

(4) The surface of the casing and coupling threads shall be smooth and shall not be allowed to be burred, torn, and other defects sufficient to cause the thread to interrupt the strength and tight connection.

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