API 5L line pipe - Used for the transportation of oil and gas

The API 5L specification of the American Petroleum Institute covers seamless and welded (including SAW, ERW and other processes) steel tubes and pipes. API 5L line pipe is a high-grade steel pipe, specially designed for the transportation of fluids and gases in industries such as oil and gas, water transportation and energy production. It has excellent corrosion resistance and durability, and is suitable for use in harsh environments.

The standards are divided into two quality grades: PSL1 and PSL2. PSL2 is more stringent in terms of chemical composition, mechanical properties and inspection requirements.

PSL1: Basic quality grade, allowing for relatively lenient deviations in chemical composition and mechanical properties, with fewer inspection items.
PSL2: High grade, with additional requirements for Charpy impact tests, strict chemical composition limits, and more rigorous mechanical property control.

API 5L can be classified into various steel grades according to yield strength:
Grade A/B: The lowest level, such as Grade B (minimum yield of 250 MPa).
X series: High-strength grades, such as X42 (yield 290 MPa), X46, X52, X56, X60, X65, X70, X80.

Chemical composition and mechanical properties:

The manufacturing process of API 5L line pipe is seamless pipe and welded pipe:

Seamless pipe: It is made by piercing and rolling steel billets, with no welds on the inner and outer walls. The main processes are hot rolling and cold rolling. Hot rolling: After heating the steel billet, it is perforated, drawn and rolled into tubes. Cold rolling: Rolling is carried out at room temperature to achieve more precise dimensional control and better surface quality.

There are three types of welded pipes: ERW, LSAW and SSAW

ERW: ERW pipe is a kind of resistance welded pipe, which is usually welded by high-frequency welding, such as contact welding and induction welding. Because of its good quality of steel pipes, easy transportation and low cost, it is the most recommended welded steel pipe.
Both LSAW and SSAW pipes are submerged arc welded steel pipes, suitable for the production of large-diameter steel pipes, and are widely used in structural support, liquid transportation, building structures and other fields.

Inspection and Testing

Hydrostatic Test
The pipeline must be pressurized to 125% of the rated working pressure. For small diameters (D ≤ 457mm), the pressure holding should be no less than 5 seconds, and for large diameters, it should be no less than 10 seconds.

Bend Test
To test the ductility and weld quality of the pipe material, PSL 2 has stricter requirements for bending radius and no cracking during forming than PSL 1.

Non-destructive testing methods such as ultrasonic, magnetic particle, and radiographic testing
It is implemented based on the pipe diameter and grade to eliminate defects on the inner and outer surfaces as well as weld seams.

Typical applications

Long-distance pipelines for oil and natural gas
Urban gas and water supply networks
Submarine pipelines and high-pressure wellhead pipe strings, etc.

In conclusion, API 5L pipeline steel provides systematic and quantifiable strict standards in terms of chemical composition, mechanical properties and inspection tests, to meet the comprehensive requirements of safety, durability and economy for oil and gas transportation and other fluid transportation.