API 5CT J55 NU Tubing

API 5CT J55 NU tubing is one of the most economical and widely used primary steel grades of tubing in petroleum drilling and production operations. J55 indicates a minimum yield strength of 55,000 psi, while NU stands for Non-Upset (non-thickened threaded connection).

J55 Grade Steel: Classified under Group 1 of the API 5CT standard, this is a low-carbon steel characterized by excellent machinability and cost-effectiveness. It is suitable for use in shallow wells, medium-depth wells, or low-pressure oil and gas wells.
NU (Non-Upset) Connection: Refers to tubing ends that have not undergone upsetting; instead, threads (typically 10 round threads per inch) are cut directly into the pipe body. Compared to EU (External Upset) connections, NU connections offer slightly lower joint strength but feature a smaller outer diameter, making them suitable for applications where annular clearance is limited.
Applications: Primarily utilized for oil production in oil wells, water injection in water wells, and as fluid discharge lines.

Request J55 NU Tubing Specification Sheet & Pricing

Color Code for API 5CT J55 NU Tubing (Color Identification Code)

To prevent errors during downhole installation operations in the field, API 5CT specifies the following color identification standards:
Pipe Body Band: One bright green band.
Coupling Color: The entire coupling is painted bright green.
Note: If J55 tubing features a white band, this typically indicates that it has undergone internal coating treatment or other special processing (please refer to the contract for details).

‌API 5CT J55 NU Tubing Specification‌

‌Dimensions and Weight Chart for API 5CT J55 NU Tubing‌

Tolerance Requirements for API 5CT Tubing‌

API 5CT imposes strict dimensional tolerance controls on tubing geometry:

‌OD Tolerance‌:

Pipe body OD < 4-1/2": ‌±0.79 mm (±0.031")‌

Pipe body OD ≥ 4-1/2": ‌+1.00% / −0.50%‌

‌Wall Thickness Tolerance‌:

Maximum allowable negative deviation: ‌-12.5%‌ (no upper limit, constrained by weight tolerance)

‌Weight Tolerance‌:

Per single joint: ‌+6.5% / -3.5%‌

‌Straightness‌:

Total length curvature shall not exceed ‌0.2%‌ of the total length

End curvature (last 1.5 m) shall not exceed ‌3.18 mm

Inspection Method

For J55 NU tubing, the inspection process is divided into mandatory factory inspections and Non-Destructive Testing (NDT):
Hydrostatic Testing:
Every length of tubing must undergo a pressure test. The standard test pressure for J55 typically ranges between 3,000 psi and 7,000 psi (depending on the outer diameter and wall thickness), with a holding time of no less than 5 seconds to ensure there are no leaks.
Drift Test:
A standard API drift mandrel is passed through the entire length of the pipe body to ensure that the internal diameter is free from flattening or protrusions, thereby guaranteeing the smooth passage of pumps and tools.
Thread Inspection:
Ring gauges and plug gauges are used to inspect the thread standoff.
The thread pitch, taper, and height are inspected.
Non-Destructive Testing (NDT):
EMI (Electromagnetic Inspection): Primarily used to detect longitudinal defects within the pipe body.
Ultrasonic Testing (UT): For J55 tubing classified as PSL-2 or PSL-3, full-body ultrasonic inspection is required.
Visual Inspection:
The internal and external surfaces of the pipe body are inspected for folds, scabs, mechanical scratches, or cracks resulting from the rolling process.
Flattening Test:
For ERW (welded) tubing, a test specimen must be cut and subjected to a flattening test to verify the integrity and ductility of the weld seam.

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GNEE API J55 NU Tubing  test equipments

GNEE API J55 NU Tubing Certificate

FAQ

What is the API standard for threads?

API thread standards are primarily governed by API Spec 5B, which defines the dimensions, tolerances, inspection methods, and marking requirements for threads used in the connections of casing, tubing, and drill pipe within the oil and gas industry, thereby ensuring interchangeability among products from different manufacturers and the reliability of field connections.

What is the difference between API thread and premium thread?

The fundamental distinction between API threads and Premium threads lies in their source standards and performance levels. API threads adhere to the API 5B standard, characterized by their high versatility and excellent interchangeability, making them suitable for standard operating conditions. Premium threads, conversely, are proprietary designs developed by manufacturers; they offer superior performance-specifically enhanced sealing capabilities as well as greater torsional and tensile strength-and are predominantly utilized in demanding environments, such as deep wells and high-pressure applications.

How to choose a tubing connection?

The selection of tubing connection types should be comprehensively evaluated based on well depth, pressure, corrosiveness, and cost. For conventional shallow to medium-depth wells, NU (Plain End) or EUE (External Upset End) connections with round threads are sufficient. For deep wells, high-pressure environments, or conditions involving H₂S, EUE or premium connections should be selected to ensure strength and sealing performance.

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