API pipeline core types and standards

Pipelines play a crucial role in the transportation of oil, natural gas, and water resources. API pipelines, with their high strength, reliability, and standardized performance, have become the core foundation of global energy transmission systems.

What is an API pipeline?

API pipelines are steel pipes manufactured according to standards set by the American Petroleum Institute (API) for transporting oil, natural gas, water, and other fluid media. Their core characteristics are:

Ability to withstand complex environments such as high temperatures and high pressures;
Good toughness, corrosion resistance, and weldability;
High dimensional accuracy, stable performance, and suitability for oil and gas pipelines and long-distance transportation projects.

Main API pipeline standards

API has developed various standard systems to address different applications and performance requirements. The three core standards are: API 5L, API 5CT, and API 5D. These cover pipelines, well pipes, and drill pipe, respectively.

API 5L line pipes

API 5L line pipes can be divided into two categories: 

Seamless pipes: formed by heating and piercing round steel, hot rolling, or cold drawing, suitable for high pressure and harsh environments; 

Welded pipes: mainly made by rolling and welding steel plates, including: ERW high-frequency resistance welded pipes, LSAW straight seam submerged arc welded pipes, and SSAW spiral submerged arc welded pipes.

API 5L line pipes can also be divided according to testing requirements:
PSL1: Basic quality requirements, applicable to low-strength steel grades such as Gr.B/X42 (land-based atmospheric pressure pipelines);
PSL2: Additional performance requirements, applicable to X65/X80 high-strength steel (deep-sea/high-altitude cold-weather pipelines).

API 5L is divided into multiple grades according to steel grade to reflect tensile strength and yield strength:

Grade	Minimum Yield Strength (MPa)
Grade A / B	195–245
X42 / X46	290–320
X52 / X56	360–390
X60 / X65	415–450
X70 / X80	485–555
X90 / X100+	≥620

API 5CT casing and tubing

API 5CT is primarily used for oil well casing, production tubing, and drill pipe protective sleeves.

Common steel grades: J55, K55, N80, L80, C90, T95, P110, Q125;
Features: Must possess excellent resistance to hydrogen sulfide (H₂S) stress corrosion cracking, suitable for high-temperature and high-pressure downhole environments.

Common connection types: BTC (round thread), LTC (long thread), STC (short thread), Premium Thread (high-sealing thread).

API 5D drill pipe standard

API 5D specifies drilling pipe requirements:

Extremely high fatigue strength and torque capacity; Critical components (such as joints and weld zones) undergo special heat treatment;
Common steel grades: E75, X95, G105, S135 (numbers indicate minimum tensile strength ksi).

The special properties of drill pipes require extremely high strength, flexibility, and durability to withstand the high stresses generated during operation.

Applications of API pipelines

API pipelines, with their excellent strength, corrosion resistance, and reliability, are widely used in various energy and engineering transportation systems, including:

Long-distance oil and gas trunk lines
Submarine pipelines and offshore oil and gas gathering systems
Urban gas transmission and distribution networks
Chemical and petrochemical media transportation
High-pressure and cryogenic engineering applications
Engineering in complex geological and special environments

Summary

API pipelines, with their high strength, corrosion resistance, and stable performance, have become the primary choice for global oil, gas, and fluid transportation projects. Through stringent API standards, different types of pipelines can meet the needs of onshore, offshore, and complex environments, providing reliable guarantees for the safety and efficiency of energy transportation.