API, commonly called the American Petroleum Institute, is the largest oil and natural gas industry association in the United States. It encompasses approximately 400 companies involved in oil production, refining, distribution, and many other aspects.
A tubing coupling is a short pipe or tubing with threads on both ends used to connect pipelines. So it is a type of pipe fitting that adopts a threaded connection, with the advantage of facilitating pipeline maintenance or replacement of damaged pipelines.
According to API 5CT, the grades are: K55/J55 N80 L80 P110.
What is API Coupling used for?
Simply put, they are internally threaded bodies that connect two threaded pipe sections.
For this purpose, API 5CT standard couplings play a crucial role in connecting casing and tubing. On the contrary, the most salient distinction between API steel pipe and general steel pipe couplings lies in the more stringent manufacturing process, requiring precise control at various stages, including the following:
Material selection
Mechanical testing including tensile strength
Impact testing
Chemical property control
Sulfide stress cracking test (for material grades like C90 or T95)
Dimensional tolerances, outer diameter, wall thickness, length, and straightness
Thread control, threads per inch, thread angle, etc. (higher thread options will be more stringent)
Heat treatment
Additional marking
Material certification
Product Specification Level (PSL-2 or PSL-3)
Specifications
As we have said, API couplings must be seamless, and another is the casing or tubing body from which the raw blanks are produced to be of the same grade.
The couplings shall be fabricated from blanks or stock, including hot upsetting. (except for grade C110 and Q125, hot upsetting is not permitted. These two grades of materials are typically different from other grades, so if you purchase couplings of these grades, you should pay more attention to reading the provisions in API 5CT specifications.)
Raw Material Types
The raw materials are termed or divided into:
- Couplings
- Material
- Blanks
- Accessory material
All of these can be regarded as non-threaded materials for producing a single product.
Heat Treatment or Alternate Material Grades (special requirements)
If the heat treatment type is not specified in the purchase order, J55/K55 casing or tubing connectors should be provided as rolled, normalized, normalized and tempered, or quenched and tempered.
- J55 EU tubings when specified in the order should be fitted with L80 grade 1 type.
- J55 and K55 BTC casings should be fitted with L80 grade 1 type, if specified on the order.
- N80 grade 1 normalized casing or tubing should be fitted with normalized and tempered N80 grade 1 or N80Q.
- N80 grade 1 and N80Q EU tubings should be fitted with P110, in case specified in the PO.
- N80 grade 1 and N80Q buttress casings should be fitted with P110 grade couplings, if specified in the order.
Mechanical Performance
The mechanical performance of casing or tubing couplings shall comply with the provisions of Section 7 and Section 10, including test frequency, re-test provisions, etc. These test records can be provided to the third-party inspectors specified by the customer.
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