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Petroleum casing pipes are steel pipes used to support the walls of oil and gas wells to ensure the normal operation of the entire oil well after drilling and completion. Each well uses several layers of casing according to different drilling depths and geological conditions. Cement is used to cement the casing after the casing is down. It is different from the tubing and drill pipe and cannot be reused. It is a one-time consumable material. Therefore, casing consumption accounts for more than 70% of all oil well pipes.
Petroleum casing is a steel pipe used to support the wall of oil and gas wells to ensure the normal operation of the entire oil well after the drilling process and completion. Each well uses several layers of casing according to different drilling depths and geological conditions. Cement is used to cement the well after casing is down. It is different from tubing and drill pipe and cannot be reused. Tubing is a disposable consumable material. Tubing has wellhead casing and downhole casing.
According to the purpose of cementing and the function of the casing, the casings run in the well can be divided into surface casings, technical casings and oil casings.
(1) Surface casing: It is the outermost casing in the oil and gas well casing program. After drilling the hole, drill into the bedrock below the surface soil layer, or drill to a certain depth, and run the surface casing.
The functions of the surface casing are as follows: ①Isolate the upper aquifer and prevent surface water and surface groundwater from penetrating into the wellbore; ②Protect the wellhead and reinforce the well wall of the well section of the surface soil layer; A blowout preventer is installed on the surface casing to prevent blowout. The gap between the surface casing and the well wall must be sealed with cement, that is, when cementing the well, the cement slurry must be returned to the wellhead to isolate the formation and protect the well wall.
The depth of the surface casing is at least 100 meters.
(2) Technical casing: also known as intermediate casing. It is a casing with one or two layers in the middle of the casing program cover. The depth of the well is large, and it can isolate the stratum and protect the wellbore for the easy collapse, easy leakage, high pressure, and salt-bearing formations in the middle section of the wellbore.
Running the technical casing can ensure the smooth drilling of the lower wellbore; it can also ensure the safety of drilling into the oil and gas reservoir; the technical casing is equipped with a casing head and a four-way blowout preventer to prevent blowouts.
The intermediate casing is run in because of the technical requirements of drilling, so it is also called technical casing. The height of cement plugging between the technical casing and the well wall should be at least 200 meters above the isolated stratum.
(3) Oil layer casing: also known as production casing. It is the last layer of casing in the casing program of an oil and gas well, running from the wellhead to below the oil and gas layer that it passes through. The depth of the casing in the oil layer is basically the depth of the drilling.
The role of oil layer casing is the passage of oil and gas to the ground, isolating oil and gas from all formations, and ensuring that oil and gas pressure does not leak. After the oil and gas wells are transferred to production, the quality of the oil layer casing must be guaranteed to maintain a certain period of production.
On the one hand, the cementing quality of oil layer casing is related to being an exploratory well and is the key to oil and gas testing; on the other hand, it is related to being a production well, which directly affects the life of the well. The cement plugging height of the gap between the oil layer casing and the well wall is at least 500 meters above the oil and gas layer, or up to 200 meters in the upper layer of casing. . Therefore, casing consumption accounts for more than 70% of all oil well pipes.
Oil casing is the lifeline to maintain the operation of oil wells. Due to the different geological conditions, the downhole stress state is complicated, and the combined action of tensile, compressive, bending and torsion stresses on the pipe body, which puts forward higher requirements on the quality of the casing itself. Once the casing itself is damaged for some reason, the entire well may be reduced or even scrapped.
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, etc. Different well conditions and depths have different steel grades. In a corrosive environment, the casing itself is also required to have corrosion resistance. In places with complex geological conditions, the casing is also required to have anti-collapse performance.
Processing form of casing end: short round thread, long round thread, partial trapezoid thread, special buckle, etc. Used in oil well drilling, it is mainly used to support the well wall during the drilling process and after completion, to ensure the progress of the drilling process and the normal operation of the entire oil well after completion.
It should be noted that among the commonly used thread types of API, the air tightness of the round thread casing is low, and the strength of the threaded connection part is only 60%~80% of the pipe body;Partial trapezoidal thread although the connection strength is higher, but the sealing is not ideal.Therefore, with the change of oilfield exploitation environment and the increasingly strict requirements for casing and connection strength and sealing, the application proportion of special buckle with higher strength is also increasing.
Pipe in Api5ct is mainly used for drilling of oil and gas wells and transportation of oil and gas. Oil casing is mainly used to support the borehole wall during and after the completion of the well to ensure the normal operation of the well and the completion of the well.
Grade :J55,K55,N80,L80,P110, etc
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Grade |
Type |
Total Elongation Under Load |
Yield Strength |
Tensile Strength |
Hardness a,c |
Specified Wall Thickness |
Allowable Hardness Variation b |
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min |
max |
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HRC |
HBW |
mm |
HRC |
|
H40 |
— |
0.5 |
276 |
552 |
414 |
— |
— |
— |
— |
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J55 |
— |
0.5 |
379 |
552 |
517 |
— |
— |
— |
— |
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K55 |
— |
0.5 |
379 |
552 |
655 |
— |
— |
— |
— |
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N80 |
1 |
0.5 |
552 |
758 |
689 |
— |
— |
— |
— |
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N80 |
Q |
0.5 |
552 |
758 |
689 |
— |
— |
— |
— |
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R95 |
— |
0.5 |
655 |
758 |
724 |
— |
— |
— |
— |
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L80 |
1 |
0.5 |
552 |
655 |
655 |
23.0 |
241.0 |
— |
— |
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L80 |
9Cr |
0.5 |
552 |
655 |
655 |
23.0 |
241.0 |
— |
— |
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L80 |
l3Cr |
0.5 |
552 |
655 |
655 |
23.0 |
241.0 |
— |
— |
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C90 |
1 |
0.5 |
621 |
724 |
689 |
25.4 |
255.0 |
≤12.70 |
3.0 |
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12.71 to 19.04 |
4.0 |
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19.05 to 25.39 |
5.0 |
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≥25.4 |
6.0 |
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T95 |
1 |
0.5 |
655 |
758 |
724 |
25.4 |
255 |
≤12.70 |
3.0 |
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12.71 to 19.04 |
4.0 |
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19.05 to 25.39 |
5.0 |
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≥25.4 |
6.0 |
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C110 |
— |
0.7 |
758 |
828 |
793 |
30.0 |
286.0 |
≤12.70 |
3.0 |
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12.71 to 19.04 |
4.0 |
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19.05 to 25.39 |
5.0 |
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≥25.4 |
6.0 |
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P110 |
— |
0.6 |
758 |
965 |
862 |
— |
— |
— |
— |
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Q125 |
1 |
0.65 |
862 |
1034 |
931 |
b |
— |
≤12.70 |
3.0 |
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12.71 to 19.04 |
4.0 |
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19.05 |
5.0 |
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| 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. | |||||||||
| c For through-wall hardness tests of Grades L80 (all types), C90, T95 and C110, the requirements stated in HRC scale are for maximum mean hardness number. | |||||||||
In addition to ensuring chemical composition and mechanical properties, hydrostatic tests are performed one by one, and flaring and flattening tests are performed. . In addition, there are certain requirements for the microstructure, grain size, and decarburization layer of the finished steel pipe.
Tensile Test:
1. For the steel material of the products, manufacturer should perform tensile test. For the elecrtrice welded pipe, depondeds on manufacturer's choice, tensile test can be performed on the steel plate that used to make pipe or perfomred on steel pipe directly. An test performed on a product can also be used as a product test.
2. The test tubes shall be randomly selected. When multiple tests are required, the sampling method shall ensure that the samples taken can represent the beginning and end of the heat treatment cycle (if applicable) and both ends of the tube. When multiple tests are required, the pattern shall be taken from different tubes except that the thickened tube sample may be taken from both ends of a tube.
3. The seamless pipe sample can be taken at any position on the circumference of the pipe; the welded pipe sample should be taken at about 90 ° to the weld seam, or at the option of the manufacturer. Samples are taken at about a quarter of the strip width.
4. No matter before and after the experiment, if the sample preparation is found to be defective or there is a lack of materials irrelevant to the purpose of the experiment, the sample may be scrapped and replaced with another sample made from the same tube.
5. If a tensile test representing a batch of products does not meet the requirements, the manufacturer may take another 3 tubes from the same batch of tubes for re-inspection.
If all the retests of the samples meet the requirements, the batch of tubes is qualified except the unqualified tube that was originally sampled.
If more than one sample is initially sampled or one or more samples for retesting do not meet the specified requirements, the manufacturer may inspect the batch of tubes one by one.
The rejected batch of products can be reheated and reprocessed as a new batch.
Flattening Test：
1. The test specimen shall be a test ring or end cut of not less than 63.5mm (2-1 / 2in).
2. Specimens may be cut before heat treatment, but subject to the same heat treatment as the pipe represented. If a batch test is used, measures shall be taken to identify the relationship between the sample and the sampling tube. Each furnace in each batch should be crushed.
3. The specimen shall be flattened between two parallel plates. In each set of flattening test specimens, one weld was flattened at 90 ° and the other flattened at 0 °. The specimen shall be flattened until the tube walls are in contact. Before the distance between the parallel plates is less than the specified value, no cracks or breaks should appear in any part of the pattern. During the entire flattening process, there should be no poor structure, welds not fused, delamination, metal overburning, or metal extrusion.
4. No matter before and after the experiment, if the sample preparation is found to be defective or there is a lack of materials irrelevant to the purpose of the experiment, the sample may be scrapped and replaced with another sample made from the same tube.
5. If any sample representing a tube does not meet the specified requirements, the manufacturer may take a sample from the same end of the tube for supplementary testing until the requirements are met. However, the length of the finished pipe after sampling must not be less than 80% of the original length. If any sample of a tube representing a batch of products does not meet the specified requirements, the manufacturer may take two additional tubes from the batch of products and cut the samples for re-testing. If the results of these retests all meet the requirements, the batch of tubes is qualified except for the tube originally selected as the sample. If any of the retest samples does not meet the specified requirements, the manufacturer may sample the remaining tubes of the batch one by one. At the option of the manufacturer, any batch of tubes can be re-heat treated and retested as a new batch of tubes.
Impact Test:
1. For tubes, a set of samples shall be taken from each lot (unless documented procedures have been shown to meet regulatory requirements). If the order is fixed at A10 (SR16), the experiment is mandatory.
2. For casing, 3 steel pipes should be taken from each batch for experiments. The test tubes shall be randomly selected, and the sampling method shall ensure that the samples provided can represent the beginning and end of the heat treatment cycle and the front and back ends of the sleeve during heat treatment.
3. Charpy V-notch impact test
4. No matter before and after the experiment, if the sample preparation is found to be defective or there is a lack of materials irrelevant to the purpose of the experiment, the sample may be scrapped and replaced with another sample made from the same tube. Specimens should not be simply judged defective simply because they do not meet the minimum absorbed energy requirements.
5. If the result of more than one sample is lower than the minimum absorbed energy requirement, or the result of one sample is lower than 2/3 of the specified minimum absorbed energy requirement, three additional samples shall be taken from the same piece and retested. The impact energy of each retested specimen shall be greater than or equal to the specified minimum absorbed energy requirement.
6. If the results of a certain experiment do not meet the requirements and the conditions for the new experiment are not met, then three additional samples are taken from each of the other three pieces of the batch. If all the additional conditions meet the requirements, the batch is qualified except the one that failed initially. If more than one additional inspection piece does not meet the requirements, the manufacturer may choose to inspect the remaining pieces of the batch one by one, or reheat the batch and inspect it in a new batch.
7. If more than one of the initial three items required to prove a batch of qualifications are rejected, re-inspection is not allowed to prove the batch of tubes is qualified. The manufacturer may choose to inspect the remaining batches piece by piece, or reheat the batch and inspect it in a new batch.
Hydrostatic Test：
1. Each pipe shall be subjected to hydrostatic pressure test of the whole pipe after thickening (if appropriate) and final heat treatment (if appropriate), and shall reach the specified hydrostatic pressure without leakage. The experimental pressure holding time was made up less than 5s. For welded pipes, the welds of the pipes shall be checked for leaks under test pressure. Unless the whole pipe test has been performed at least in advance at the pressure required for the final pipe end condition, the thread processing factory should perform a hydrostatic test (or arrange such a test) on the whole pipe.
2. Pipes to be heat treated shall be subjected to a hydrostatic test after the final heat treatment. The test pressure of all pipes with threaded ends shall be at least the test pressure of threads and couplings.
3 .After processing to the size of the finished flat-end pipe and any heat-treated short joints, the hydrostatic test shall be performed after the flat end or the thread.
Outter Diameter:
| Range | Tolerane |
| ＜4-1/2 | ±0.79mm（±0.031in） |
| ≥4-1/2 | +1%OD~-0.5%OD |
For thickened joint joint tubing with a size smaller than or equal to 5-1 / 2, the following tolerances apply to the outer diameter of the pipe body within a distance of approximately 127mm (5.0in) next to the thickened part; The following tolerances apply to the outer diameter of the tube within a distance of approximately equal to the diameter of the tube immediately adjacent to the thickened portion.
| Range | Tolerance |
| ≤3-1/2 | +2.38mm~-0.79mm（+3/32in~-1/32in） |
| ＞3-1/2~≤5 | +2.78mm~-0.75%OD（+7/64in~-0.75%OD） |
| ＞5~≤8 5/8 | +3.18mm~-0.75%OD（+1/8in~-0.75%OD） |
| ＞8 5/8 | +3.97mm~-0.75%OD（+5/32in~-0.75%OD） |
For external thickened tubing with a size of 2-3 / 8 and larger, the following tolerances apply to the outer diameter of the pipe that is thickened and the thickness gradually changes from the end of the pipe
| Rang | Tolerance |
| ≥2-3/8~≤3-1/2 | +2.38mm~-0.79mm（+3/32in~-1/32in） |
| ＞3-1/2~≤4 | +2.78mm~-0.79mm（+7/64in~-1/32in） |
| ＞4 | +2.78mm~-0.75%OD（+7/64in~-0.75%OD） |
Wall Thickness：
The specified wall thickness tolerance of the pipe is -12.5%
Weight：
The following table is the standard weight tolerance requirements. When the specified minimum wall thickness is greater than or equal to 90% of the specified wall thickness, the upper limit of the mass tolerance of a single root should be increased to + 10%
| Quantity | Tolerance |
| Single Piece | +6.5~-3.5 |
| Vehicle Load Weigh≥18144kg（40000lb） | -1.75% |
| Vehicle Load Weigh＜18144kg（40000lb） | -3.5% |
| Order Quantity≥18144kg（40000lb） | -1.75% |
| Order Quantity＜18144kg（40000lb） | -3.5% |