API 5CT

In the API standard, steel pipe products are usually divided into several categories, including API 5L (steel pipes for pipelines), API 5CT (casing and tubing for oil fields), API 5B (threaded joint standard), etc.

API SPEC 5CT is a technical specification standard for oil casing issued by the American Petroleum Institute (API), mainly used in the field of oil and gas extraction. The standard specifies the steel grade system, chemical composition, mechanical properties, dimensional tolerance and other technical indicators of casing and tubing. The standard covers more than ten steel grades such as H40, J55, N80, P110, etc., and has strict restrictions on the content of elements such as carbon, manganese, and phosphorus, and puts forward specific requirements for mechanical properties such as tensile strength (≥517-965MPa) and yield strength (379-965MPa). The following will be detailed through technical parameters, dimensional specifications, specification levels, etc.:

Technical parameter system

The standard has established a complete parameter system, including the following core elements:

1. Chemical composition

The carbon content is 0.34-0.43%, the manganese content is ≤1.90%, the phosphorus content is ≤0.030%, the sulfur content is ≤0.030%, and other element indicators are specified. Among them, the L80 steel grade contains 12.0-14.0% chromium, and the P110 steel grade contains 0.15-0.25% molybdenum.

2. Mechanical properties

The minimum yield strength of the J55 steel grade is 379MPa, and the P110 steel grade is up to 965MPa.

The elongation requirement is set in the range of 18-32% according to different steel grades.

Hardness indicators such as the Brinell hardness of the L80 steel grade is ≤241HB.

Dimensional specifications

The standard makes clear provisions for the size:

1. Outer diameter tolerance

When ≤101.60mm, a deviation of ±0.79mm is allowed.

≥114.30mm implements +1.0%/-0.5% tolerance zone.

2. Wall thickness deviation is controlled within the range of 0 to -12.5%.

3. Length classification

Casing pipe is divided into three categories: 4.88-7.62m, 7.62-10.36m, and 10.36-14.63m.

The standard length of oil pipe is 6.10-9.75m.

Specification level (PSL)

According to the quality requirements of the product, the API 5CT standard divides it into three product specification levels (PSL-1, PSL-2, PSL-3). Among them:

PSL-1

is the basic level, suitable for steel pipe products in ordinary environments, and is often used in application scenarios without stringent requirements.

PSL-2

is a medium level, requiring steel pipes to have good corrosion resistance, tensile strength, impact resistance, etc., and is suitable for oil and gas projects that require certain environmental adaptability.

PSL-3

is the highest level, requiring steel pipes to have excellent performance under high pressure, low temperature and extreme environments, and is often used in high-demand projects such as deep-sea mining and high-pressure natural gas transportation.

Material and performance requirements

The API 5CT standard has very strict material requirements for steel pipes. Different steel grades and different application environments require different material selections. Common steel grades are:

1. H40

Applicable to general environments, with basic tensile strength and corrosion resistance.

2. J55, K55

Applicable to environments with medium strength requirements, commonly used for casing pipe in oil wells.

3. N80, R95

Applicable to environments with higher strength requirements, commonly used for deeper oil and gas mining.

4. L80, P110

Applicable to extreme environments, L80 steel grade is often used for deep well mining, and P110 steel grade is used in high-pressure environments.

Steel pipes of each steel grade must undergo rigorous material testing to ensure their stability and reliability under conditions such as high temperature, high pressure, and corrosive environments.

End finishing and thread parameters

API Spec.5CT contains diagrams of API tubing fittings. All three fittings feature tapered and rounded threads with either 8 or 10 threads per inch, depending on size. When casing pipe is used as tubing, long thread coupling/short thread coupling and truncation thread coupling connections can be specified.

1. EUE

API External Upset End (EUE) tubing fittings are widely used because they are a good and durable connection in most wells. API EUE fittings range from 1.050 inches to 4.500 inches in outside diameter and are designed to have higher tensile and compressive strengths than the pipe body, making them considered 100% efficient fittings.

2. NUE

API Non-Upset (NUE) tubing is used much less frequently than EUE tubing. NUE costs only slightly less than EUE, but the fitting strength is much lower. NUE fittings have a smaller diameter than EUE, which is an advantage when clearances are small. The API NUE connector has an outside diameter range of 1.050 inches to 4.500 inches.

Summary

As the cornerstone of the global oil and gas industry, the API 5CT standard plays a vital role in the design, production, inspection and application of steel pipes. It ensures the safe operation of the oil and gas industry by clearly specifying the specifications, materials, performance and other requirements of steel pipes.