API 5CT sets forth standardized technical criteria for steel casing and tubing pipes employed in the petroleum and natural gas sectors for oil well operations. This specification extends its coverage beyond casing and tubing to include pup joints, coupling stock, coupling material, and accessory materials. Moreover, it delineates stringent requirements across three product specification levels (PSL-1, PSL-2, and PSL-3), with the specifications for PSL-1 forming the foundational framework of this standard.

Common Grades

  1. • J55/K55
  2. • N80/N80Q/L80
  3. • C90
  4. • R95/T95
  5. • P110/C110
  6. • Q125

Regarding connections, API 5CT is applicable to the following types, adhering to the standards outlined in API SPEC 5B:

  1. SC: Short round thread casing
  2. LC: Long round thread casing
  3. BC: Buttress thread casing
  4. NU: Non-upset tubing
  5. EU: External upset tubing
  6. IJ: Integral tubing connections
API 5CT steel pipe
Manufacture

As per the API 5CT standard, the steel material employed in crafting the pipe billet must undergo a grain-refining treatment. This steel is required to incorporate one or more grain-refining elements, such as a specified quantity of aluminum, niobium, vanadium, or titanium, to facilitate grain refinement in the austenite structure of the steel.

Key specifications include:

  1. Pipes supplied must be manufactured in either seamless or Electric Welded (EW) type.
  2. Couplings, coupling stock, and coupling materials must be seamless.
  3. Cold-drawn tubing pipes must undergo appropriate heat treatment for acceptance.
  4. Attachment materials for casing and tubing are required to be seamless pipes unless other types are explicitly specified in the order.
Heat Treatment

The differentiation between grades in API 5CT casing and tubing is significantly influenced by the employed heat treatment methods. Products necessitating heat treatment must undergo comprehensive full-body and full-length heat treatment. Specifically, heat-treated upsetting products are required to undergo treatment for their entire body and length post-upsetting.

Acceptance of a separately heat-treated coupling blank is allowed. If the finishing temperature exceeds the upper critical temperature of the treated steel, and the pipe is air-cooled, normalization is mandated.

For welding types, the weld seam must undergo heat treatment to a minimum temperature of 540 ℃ (1000°F), or an alternative treatment method must be employed to prevent the formation of untempered martensite structure in the weld.

  1. N80 Type 1 and Type Q: For N80 Type 1, the manufacturer may choose between normalization or normalization and tempering. On the other hand, N80Q steel-grade products are required to undergo quenching and tempering.
  2. R95: R95 steel grade mandates quenching and tempering.
  3. L80: Tempering grade L80 below temperatures of 620 ℃ (1150°F) may result in embrittlement, especially for grade 13 Cr.
Straightening
  1. R95: R95 casing and tubing are not allowed to undergo cold stretching or expansion after final tempering, except for cold working essential for routine straightening, and this should not exceed 3% of compression cold working.
  2. M65 and L80: Steel grade M65 and L80 products must not undergo cold working post final heat treatment, except for the cold working necessary for regular straightening.
  3. C90 and T95: C90 and T95 products can undergo cold-rotated straightening, but the pipe must be heated to a minimum temperature of 480 ℃ (1000°F) for stress relief after straightening. Light gag straightening is permitted if needed.
  4. C110: If required, the product should be cold-rotated straightened and subsequently stress-relieved at temperatures between 30℃ to 55℃ (50°F to 100°F) below the final specified tempering temperature. Alternatively, it can be hot-rotated straightened at temperatures not exceeding 165℃ (300°F) below the final specified tempering temperature. Light gag straightening is allowed if necessary.
  5. Q125: Gag-press straightening or hot-rotating straightening is permissible for straightening, but the temperature at the end of rotary straightening should not fall below 400 ℃ (750°F) (unless a higher temperature is specified in the order). If hot rotary straightening is impractical, cold-rotated straightening can be performed, but stress relief must occur at 510 ℃ (950°F) after straightening. Stress relief post cold rotary straightening is only allowed by mutual agreement between the purchaser and the manufacturer.
Chemical Composition in API 5CT Specification

The product must adhere to the chemical composition table's stipulated requirements for the designated steel grade and type. In the case of C110 steel grade, the manufacturer is obligated to provide information upon request from the purchaser regarding the lowest and highest ratios of all intentionally added elements in each batch, irrespective of the purpose of their addition.

Tensile Properties

The product must satisfy the tensile performance criteria outlined in this standard. The tensile properties of the upset casing and tubing, excluding elongation, should align with the requirements established for the pipe body. In the event of a dispute, the properties of the upset area, excluding elongation, will be determined by sampling from the upset section.

Dimension, Masses, Pipe Ends, and Defects

• API 5CT Casing dimensions and weight chart
• API 5CT Tubing dimensions and weight#

Labels and Sizes

In the dimensional table provided by this standard, pipes are identified by labels and sizes, specifically the outer diameter. For externally upset pipes, the outer diameter pertains to the pipe body and not the outer diameter of the upset section.

Dimensions and Masses

The pipe must be provided in the sizes, wall thickness, and tolerance masses as specified in the order. Additional plain end pipe sizes and wall thicknesses are available upon mutual agreement between the purchaser and the manufacturer. Coupling stock, coupling materials, and accessory materials must be supplied in the size specified in the order, or the size of the coupling material should adhere to the manufacturer's internal requirements.

The accuracy of all measuring equipment used for acceptance or rejection must be verified at least once per operating shift, excluding threaded ring gauges, plug gauges, and weighing implements.

In accordance with this standard, if a calibrated or verified measuring device is exposed to abnormal or severe conditions that may impact its accuracy, it should be recalibrated or reverified before further use.

Outside diameter tolerances

The specified tolerances for the outer diameter, denoted as D, of casing and tubing are as follows:

For upset integral tubing connection

Tolerances for the outer diameter of the pipe body directly behind the upset are applicable for approximately 127 mm (5.0 in) in sizes labeled 1: 5-1/2 and smaller, and a distance roughly equivalent to the outer diameter for sizes larger than Label 1: 5-1/2. Measurements must be taken using calipers or snap gauges.

Wall thickness：Tolerance for casing and tubing wall thickness is -12.5%.
Products end
  1. Flat-End Pipe: A flat-end pipe is supplied with unmachined threads, and it may or may not be upset. In either case, it must adhere to all the requirements specified for a particular steel grade in this standard.
  2. Product with API Threads: Steel grades H40, J55, K55, or M65 casings are available with short or long threads. However, if a long-threaded casing is desired, the purchaser must specify it in the order.
  3. Rounded Nose: The manufacturer may provide or the purchaser can specify a "round" or "bullet-nose" type of pipe end, replacing conventional corner breaks on threaded ends of external upset tubing. This enhanced end should be rounded, ensuring smooth surfaces without sharp corners or burrs, to facilitate coating application.
  4. Threading: Product threading, gauging practices, and thread inspection must conform to API Spec 5B. While the product end should not be hammered, it may be slightly shaped to meet thread machining requirements. For steel grades of C90 and higher strength, any forming must be done with the purchaser's consent.
  5. Workmanship of Ends: All product ends must be free of burrs on the inside and outside edges. Additionally, sandblasting is required for both male and female threads of C110 steel grade.
Defects

All pipes and pipe fittings are required to be free from the following defects:

  1. a. No quenching cracks.
  2. b. No arc burns.
  3. c. No surface cracking defects that reduce the net effective wall thickness to less than 87.5% of the specified wall thickness can be confirmed.
  4. d. When non-destructive inspection is specified in this standard or in an order, any non-surface cracking defects on the outer surface with an area greater than 260 mm2 (0.41 in2) must be detected.
  5. e. No non-surface cracking defect reducing the effective wall thickness to less than 87.5% of the specified wall thickness can be confirmed within 1.6 mm (1/16 in) of both sides of the weld.
  6. f. No internal upset structure on all upset products may have sharp corners or drastic changes of sections that can cause the 90 ° hook-type tool to hang up.
  7. g. No non-linear surface cracking defects on the inner surface of the externally threaded part of the sanitary tube with a depth greater than 10% of the specified wall thickness.