The API Spec 5L standard is an important standard for transportation steel pipes in the petroleum and natural gas industry. In different application scenarios, there are different requirements for LSAW (submerged arc welding) steel pipes. The following is a detailed introduction for you:

Long distance onshore pipelines

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Strength requirements: Select steel pipes of appropriate grade based on the conveying distance, pressure, and pipe diameter size. For long-distance and high-pressure pipelines, high-grade LSAW Steel Pipes such as X60, X65, X70 are often used to ensure that the pipeline can withstand high pressure without rupture during long-term operation.

Resilience requirement: Considering the possible temperature changes along the pipeline, especially in cold regions, steel pipes are required to have good low-temperature toughness to prevent brittle fracture in low-temperature environments. Generally, the toughness index of steel pipes is ensured by controlling the chemical composition and adopting appropriate heat treatment processes.

dimensional accuracy

Outer diameter and wall thickness: The dimensional accuracy of the outer diameter and wall thickness of the steel pipe is strictly required to ensure the sealing of the pipeline connection and the stability of the overall structure. The outer diameter deviation is usually controlled within a small range, such as ± 0.75% - ± 1%; There are also clear regulations for wall thickness deviation, generally ranging from -3% t to+6% t (t is the nominal wall thickness).

Length: According to construction and transportation requirements, there are certain requirements for the length of steel pipes, usually standard lengths such as 12m or 18m, and the length deviation is generally controlled within ± 50mm.

welding quality

Weld strength: The weld strength needs to match the strength of the base metal, and in some cases, the weld strength may even be slightly higher than the base metal, to ensure that the weld area does not become a weak link during pipeline operation.

Weld defect control: There are strict detection and control standards for defects such as cracks, pores, and slag inclusions in the weld. Non destructive testing methods such as ultrasonic and radiographic testing are used to conduct 100% inspection of the weld to ensure that the quality of the weld meets the standard requirements.

Ocean pipeline

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Corrosion resistance: Due to the presence of a large amount of salt and corrosive substances in the marine environment, LSAW steel pipes are required to have good corrosion resistance. Usually, anti-corrosion coatings and cathodic protection are used to improve the corrosion resistance of steel pipes, while strict control is exercised over the chemical composition and microstructure of the pipes to enhance their own corrosion resistance.

High strength and toughness: Marine pipelines need to withstand complex loads such as seawater pressure, wave forces, and ocean currents, so steel pipes are required to have high strength and toughness. Generally, X70 and above grade steel pipes are selected, and their performance is guaranteed through strict production processes and quality control.

dimensional accuracy

Uniformity of outer diameter and wall thickness: In order to ensure the stability and deformation resistance of pipelines in marine environments, the uniformity of outer diameter and wall thickness of steel pipes is highly required. The control range of outer diameter deviation and wall thickness deviation is usually stricter than that of onshore pipelines.

Ellipticity and straightness: There are strict requirements for the ovality and straightness of steel pipes to ensure smooth connection and normal operation during laying and use. Ellipticity is generally controlled within a small range, and straightness deviation usually does not exceed 0.2% per meter.

welding quality

The density and fatigue resistance of welds: The welds of marine pipelines need to have good density to prevent seawater from infiltrating the interior of the pipeline and causing corrosion. At the same time, due to the alternating loads in the marine environment, welds also need to have high fatigue resistance to ensure that pipelines will not fail due to fatigue cracks during long-term use.

Acidic environment (including hydrogen sulfide)

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Resistance to sulfide stress cracking (SSC) and stress corrosion cracking (SCC): In acidic environments, steel pipes are susceptible to corrosion by hydrogen sulfide, leading to issues such as sulfide stress cracking and stress corrosion cracking. Therefore, it is required that LSAW steel pipes have good resistance to SSC and SCC, and the corrosion resistance of the steel pipes can be improved by controlling the chemical composition, reducing the sulfur and phosphorus content, and adopting appropriate heat treatment processes.

Hardness control: In order to prevent sulfide stress cracking, there are strict requirements for the hardness of steel pipes. Generally, it is stipulated that the hardness of steel pipes does not exceed a certain value to ensure their safety in acidic environments.

dimensional accuracy

The requirement for dimensional accuracy is similar to that of onshore long-distance pipelines, but due to the corrosive effect of acidic environments on pipelines, the wall thickness and outer diameter of pipelines may be affected. Therefore, a certain amount of corrosion allowance needs to be considered in the design and production process to ensure that pipelines can meet transportation requirements during their service life.

welding quality

Corrosion resistance of welds: The weld seam is one of the most susceptible parts of the pipeline to corrosion in acidic environments, so it is required that the weld seam has corrosion resistance equivalent to that of the base material. During the welding process, it is necessary to select appropriate welding materials and welding processes to ensure the quality and corrosion resistance of the weld seam.

The following are some additional requirements of API Spec 5L standard for LSAW steel pipes in different applications:

low-temperature environment

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Low temperature toughness: Steel pipes are required to have excellent low-temperature toughness to prevent brittle fracture at low temperatures. It is usually stipulated that the impact energy index at specific low temperatures, such as for certain steel grades, the Charpy impact energy at -20 ℃ or lower temperature is required to reach a certain value.

Chemical composition control: Strictly control the content of alloying elements in steel, such as nickel, manganese, etc., which can affect the low-temperature performance of steel pipes. By adjusting the content of these elements, the low-temperature toughness of steel pipes can be improved.

welding quality

Selection of welding materials: Select welding materials suitable for low-temperature environments, which should have good toughness and crack resistance at low temperatures to ensure the quality of the weld at low temperatures.

Welding process control: Optimize welding process parameters, such as controlling welding heat input, interlayer temperature, etc., to reduce the occurrence of welding defects, improve the microstructure of welds, and enhance the low-temperature performance of welds.

Urban gas transmission

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Safety requirements: There are strict requirements for the strength and reliability of steel pipes to ensure safety during urban gas transportation. Higher grade steel pipes such as X52, X60, etc. are usually selected to withstand the pressure in urban gas transmission.

Stress cracking resistance: Urban gas may contain some corrosive media, requiring steel pipes to have good stress cracking resistance to prevent pipeline cracking caused by the synergistic effect of stress and corrosive media.

dimensional accuracy

Outer diameter and wall thickness accuracy: Similar to other long-distance pipelines, there are high requirements for the outer diameter and wall thickness accuracy of steel pipes to ensure the sealing and stability of pipeline connections. At the same time, in order to meet the requirements of urban gas pipeline laying, the ovality and straightness of steel pipes are strictly controlled to ensure smooth connection and laying of pipelines during installation.

SURFACE QUALITY

Anti corrosion requirements: Urban gas pipelines usually require anti-corrosion treatment to prevent steel pipes from being corroded in underground environments. Generally, a combination of external anti-corrosion coating and internal anti-corrosion coating is used. External anti-corrosion coating can be made of materials such as polyethylene and epoxy powder, while internal anti-corrosion coating can be made of materials such as epoxy resin to improve the anti-corrosion performance of steel pipes.

Surface cleanliness: The surface of the steel pipe needs to be kept clean, free of impurities such as oil stains and rust, to ensure good adhesion between the anti-corrosion coating and the surface of the steel pipe. In the production process of steel pipes, surface treatment such as sandblasting, shot blasting, etc. is required to improve the roughness and cleanliness of the steel pipe surface.

High pressure rich gas transportation

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High strength and high pressure resistance: Due to the high pressure inside the rich gas transmission pipeline, steel pipes need to have high strength and pressure resistance. High grade LSAW steel pipes such as X70, X80, etc. are usually selected, and strict requirements are placed on the mechanical performance indicators such as yield strength and tensile strength of the steel pipes.

Resistance to hydrogen induced cracking (HIC) and stress-induced hydrogen induced cracking (SOHIC) performance: Rich gas may contain acidic gases such as hydrogen sulfide, which can easily cause hydrogen induced cracking and stress-induced hydrogen induced cracking in steel pipes. Therefore, it is required that steel pipes have good resistance to HIC and SOHIC, and the hydrogen induced cracking resistance of steel pipes can be improved by controlling the chemical composition and improving the purity of the steel.

welding quality

Crack resistance of welds: In high-pressure and gas rich environments, the weld area is easily subjected to stress and corrosive media, resulting in cracks. Therefore, it is required that the weld seam has good crack resistance, suitable welding processes and welding materials are adopted, welding defects are controlled, and the quality and crack resistance of the weld seam are improved.

Strength matching of welds: The strength of welds needs to be matched with the base material to ensure the overall strength and stability of pipelines during high-pressure rich gas transportation. Generally, it is required that the strength of the weld seam is not lower than that of the base metal, while considering the toughness and fatigue resistance of the weld seam.