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Meaning: This is a standard specification formulated by the American Petroleum Institute, and its full name is "Pipeline Steel Pipe Specification".

Core objective: This standard specifies the manufacturing requirements, material requirements, test methods, dimensional tolerances, marking and quality assurance, etc. for seamless steel pipes and welded steel pipes used for transporting media such as petroleum and natural gas.

Importance: API 5L is a fundamental, authoritative and mandatory standard in the oil and gas pipeline industry, ensuring the safety, reliability and interchangeability of pipelines under high-pressure and long-distance transportation conditions. It has been widely adopted and applied around the world.

Meaning: This is the material Grade marking of the steel pipe. This grade corresponds to the Minimum Specified Yield Strength (SMYS) of pipeline steel.

The specific value: X52 indicates that the minimum yield strength of this grade of steel at room temperature is 52,000 pounds per square inch (psi), equivalent to 360 megapascals (MPa).

Key performance:

Yield strength (YS): ≥ 52,000 psi (360 MPa) - The ability to resist permanent deformation

Tensile strength (TS): ≥ 66,000 psi (455 MPa) - The ability to resist tensile failure

Elongation: In accordance with the standard requirements, it ensures a certain plastic deformation capacity.

Chemical composition: There are upper limit regulations on the content of elements such as carbon, manganese, phosphorus, sulfur, and silicon to ensure the weldability, toughness, and corrosion resistance of the material. X52 is usually a microalloyed steel and may require the addition of a small amount of elements (such as Nb, V, Ti) to enhance its strength.

Carbon equivalent (CE/CET) : API 5L has calculation formulas and limit requirements for the carbon equivalent that has a key impact on weldability (the requirements for PSL1 are more lenient than those for PSL2).

• Meaning: Product Specification Level 1.
• Positioning: This is the basic-level requirement defined in the API 5L standard.

• Features of PSL1:  The requirements for chemical composition are relatively lenient: the upper limit of allowable impurity elements such as sulfur and phosphorus is relatively high; The requirement for carbon equivalent is relatively low.

• The mechanical property requirements are relatively basic: mainly to ensure yield strength, tensile strength and elongation.

• Impact toughness (Charpy V-Notch) requirements: Generally, there are no mandatory requirements, unless specifically stated by the buyer in the order. This is one of the core differences between PSL1 and PSL2.

• Hardness testing requirements: Generally, there are no mandatory requirements.

• Non-destructive testing (NDT): For SSAW welded pipes, either continuous ultrasonic testing (UT) or continuous eddy current testing (ET) is required to ensure the quality of the weld seam. Full pipe body UT is not a mandatory requirement.

• Hydraulic test: Every steel pipe must undergo a hydraulic test.

• Application scenarios: It is suitable for non-harsh environments (non-low-temperature and low-stress states), non-critical or low-pressure pipeline systems, and occasions where toughness requirements are not high. The cost is usually lower than that of PSL2.

• Meaning: Spiral Submerged Arc Welding.

• Manufacturing process:

Hot-rolled steel coils (plates) that meet the requirements are used as raw materials and continuously coiled into tubes at a spiral Angle on a forming machine.

The spiral joints of the tube are welded both internally and externally in the submerged arc welding state. The welding process takes place beneath the flux layer, with the arc invisible. The flux provides protection and metallurgical effects.

• Characteristics (Compared with other welding methods such as LSAW) :

Advantages:

It can produce pipes of very large diameters (usually up to 100" or more).

The raw materials are widely available and have a relatively low cost (especially for large-diameter pipes).

It can be produced continuously and has relatively high efficiency.

Steel plates of the same width can be used to produce steel pipes of different diameters (by adjusting the helix Angle).

Disadvantages/Limitations:

The weld seam length is long (1/sin(helix Angle) times the circumference of the steel pipe).

The geometric dimensional accuracy (such as ellipticity and straightness) may be slightly inferior to that of LSAW pipes.

Possible residual stress problems (caused by the molding process).

The morphology of the heat-affected zone (HAZ) of the weld seam is complex. The weld length of it is 1.3 to 2 times that of the straight seam pipe.

The weld seam is spirally distributed. When subjected to internal pressure, the stress states in the circumferential and axial directions are different from those of straight seam pipes. The theoretical wall thickness calculation in pipeline design often needs to be appropriately increased.

PIPE:

It refers to tubular products. It is different from pipe Fittings, Flanges or other types of metal products. Here it specifically refers to the long straight pipe section used for transporting fluids.

• What's this? This is a kind of welded steel pipe manufactured in accordance with the globally common API 5L standard and used for the transportation of fluids such as oil and natural gas.

• Strength grade: It belongs to the medium strength grade (X52), with a minimum yield strength of 52,000 psi (360 MPa).

• Quality level: PSL1 belongs to the basic quality grade. Special attention should be paid to the fact that it usually does not guarantee low-temperature impact toughness. This means that this type of pipe is not suitable for cold regions or low-temperature service environments, as the risk of brittle fracture may be higher at low temperatures. The service temperature must be evaluated before application.

• How to manufacture: It is manufactured through the spiral submerged arc welding process. This means that the weld seam is a continuous long spiral line. The welds have undergone continuous UT or ET inspections and hydrostatic tests.

• Main application scenarios:

Oil and gas gathering and transportation pipelines (with average pressure)

Water source or water transmission pipeline of water treatment plant

Low-pressure large-diameter fluid transportation (chemical industry, power, etc.)

Pipe piles, pile driving, and structural pipes (At this point, more attention is paid to structural strength, and the requirements for conveying sealing performance may decrease)

• Not applicable scenarios: low-temperature environments, extremely cold regions, high-pressure critical trunk lines, and occasions with strict requirements for toughness.

• Key advantage: It is cost-effective for large-diameter pipes. Meet the basic requirements of the API 5L standard. It should be noted that the uncertainty of resilience at the PSL1 level is its core design limitation. When selecting for important projects, the service conditions must be carefully evaluated. The welding process is of vital importance, and the performance of the welded joint (especially the heat-affected zone) must be given due attention.

• Common accessories: The pipe ends usually need to be treated (such as bevels), and sometimes anti-corrosion coatings (such as FBE, 3LPE) are applied.

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