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API Specification 5L

All You Need to Know: API 5L Specification for Line Pipe

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Overview of API 5L Specification for Line Pipe

The API 5L standard, published by the American Petroleum Institute (API), specifies requirements for the manufacturing of two types of steel pipes: seamless and welded, primarily used for pipelines transporting oil, gas, water, and other fluids in the oil and gas industry. The standard covers pipes for both onshore and offshore pipeline applications. API 5L Specification for Line Pipe is widely adopted for its rigorous quality controls and testing standards, which ensure the pipes meet safety, performance, and durability requirements in a range of operational environments.

Product Specification Levels (PSL) in API 5L Specification for Line Pipe

API 5L defines two distinct levels of product specification: PSL 1 and PSL 2. These levels differ in terms of mechanical properties, testing requirements, and quality control.

a) PSL1: Basic Requirements

PSL1 is the standard quality level for line pipes. It has basic requirements for chemical composition, mechanical properties, and dimensional tolerances. The pipes specified under PSL1 are used in standard pipeline projects where conditions are not extreme or corrosive.
Chemistry & Mechanical Properties: API 5L PSL1 allows for a broader range of chemical compositions and mechanical properties. The tensile and yield strength are specified, but these are typically lower than PSL2.
Testing: Basic tests, such as hydrostatic testing, are required, but PSL1 pipes do not require more advanced testing like fracture toughness or impact tests.

b) PSL2: Enhanced Requirements

PSL2 imposes stricter requirements on quality control, mechanical properties, and testing procedures. It is required in more demanding pipeline environments, such as offshore or sour service (containing hydrogen sulfide), where pipe failure could have severe consequences.
Chemistry & Mechanical Properties: PSL2 has tighter controls over chemical composition and imposes more stringent mechanical property requirements. For example, PSL2 mandates stricter limits on sulfur and phosphorus to enhance corrosion resistance.
Impact Testing: Charpy impact testing is required for PSL2, especially in low-temperature environments to ensure the pipe’s toughness and ability to resist brittle fractures.
Fracture Toughness: PSL2 specifies fracture toughness testing, especially for pipes that will be used in extreme conditions.
Additional Testing: Non-destructive testing (NDT), like ultrasonic and radiographic testing, is more common for PSL2 pipes to ensure the absence of internal defects.

Pipe Grades in API 5L Specification for Line Pipe

API 5L specifies various pipe grades that represent the strength of the material. These grades include both standard and high-strength options, with each offering different performance characteristics.

a) Grade B

Grade B is one of the most common grades for lower-pressure pipelines. It provides moderate strength and is used in projects where extreme conditions are not expected.
Yield Strength: 241 MPa (35 ksi), Tensile Strength: 414 MPa (60 ksi)

b) High-Strength Grades (X Grades)

The “X” grades in API 5L indicate higher-strength pipes, with numbers following the “X” (e.g., X42, X52, X60) corresponding to the minimum yield strength in ksi (thousands of pounds per square inch).
X42: Minimum yield strength of 42 ksi (290 MPa)
X52: Minimum yield strength of 52 ksi (358 MPa)
X60: Minimum yield strength of 60 ksi (414 MPa)
X65, X70, X80: Used in more demanding projects, such as high-pressure pipelines in offshore environments.

Higher grades like X80 provide excellent strength, allowing the use of thinner pipes to reduce material costs while maintaining safety and performance under high-pressure conditions.

Pipe Manufacturing Processes in API 5L Specification for Line Pipe

API 5L covers both seamless and welded pipe manufacturing processes, each of which has specific advantages depending on the application:

a) Seamless Pipes

Seamless pipes are manufactured through a process that involves heating a billet and piercing it to create a hollow tube. These pipes are typically used in high-pressure applications due to their uniform strength and the absence of a seam, which can be a weak point in welded pipes.
Advantages: Higher strength, no risk of seam failure, good for sour and high-pressure service.
Disadvantages: Higher cost, limited in terms of size and length compared to welded pipes.

b) Welded Pipes

Welded pipes are manufactured by rolling steel into a cylinder and welding the longitudinal seam. API 5L defines two main types of welded pipes: ERW (Electric Resistance Welded) and LSAW (Longitudinal Submerged Arc Welded).
ERW Pipes: These are manufactured by welding the seam using electric resistance, commonly used for smaller diameter pipes.
LSAW Pipes: Manufactured by welding the seam using submerged arc welding, ideal for larger diameter pipes and high-strength applications.

Dimensional Tolerances in API 5L Specification for Line Pipe

API 5L specifies dimensional tolerances for factors like pipe diameter, wall thickness, length, and straightness. These tolerances ensure that the pipes meet the required standards for fit and performance in pipeline systems.
Pipe Diameter: API 5L defines nominal outside diameters (OD) and allows specific tolerances on these dimensions.
Wall Thickness: Wall thickness is specified according to Schedule Numbers or Standard Weight categories. Thicker walls provide increased strength for high-pressure environments.

Length: Pipes can be provided in random lengths, fixed lengths, or double random lengths (typically 38-42 ft), depending on the project requirements.

Testing and Inspection in API 5L Specification for Line Pipe

Testing and inspection protocols are vital for ensuring API 5L pipes meet quality and safety requirements, particularly for PSL2 pipes where failure can lead to catastrophic consequences.

a) Hydrostatic Testing

All API 5L pipes, regardless of the specification level, must pass a hydrostatic test. This test ensures that the pipe can withstand the maximum operating pressure without failure or leaks.

b) Charpy Impact Testing (PSL2)

For PSL2 pipes, Charpy impact testing is mandatory, especially for pipes that will operate in cold environments. This test measures the toughness of the material by determining how much energy it absorbs before fracturing.

c) Fracture Toughness Testing (PSL2)

Fracture toughness testing is essential to ensure that pipes in high-stress or low-temperature environments can resist crack propagation.

d) Non-Destructive Testing (NDT)

PSL2 pipes are subjected to NDT methods, such as:
Ultrasonic Testing: Used to detect internal flaws, like inclusions or cracks, that may not be visible to the naked eye.
Radiographic Testing: Provides a detailed image of the pipe’s internal structure, identifying any potential defects.

Coating and Corrosion Protection

API 5L recognizes the need for external protection, especially for pipelines exposed to corrosive environments (e.g., offshore pipelines or buried pipelines). Common coatings and protective methods include:
3-Layer Polyethylene (3LPE) Coating: Protects against corrosion, abrasion, and mechanical damage.
Fusion-Bonded Epoxy (FBE) Coating: Commonly used for corrosion resistance, especially in underground pipelines.
Cathodic Protection: A technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell.

Applications of API 5L Pipes

API 5L pipes are used in a wide variety of pipeline applications, such as:
Crude Oil Pipelines: Transporting crude oil from production sites to refineries.
Natural Gas Pipelines: Transporting natural gas over long distances, often under high pressure.
Water Pipelines: Supplying water to and from industrial operations.
Refined Product Pipelines: Transporting finished petroleum products, such as gasoline or jet fuel, to distribution terminals.

Conclusion

The API 5L Specification for Line Pipe is fundamental to ensuring the safe, efficient, and cost-effective transportation of fluids in the oil and gas industry. By specifying stringent requirements for material composition, mechanical properties, and testing, API 5L provides the foundation for high-performance pipelines. Understanding the differences between PSL1 and PSL2, the various pipe grades, and the relevant testing protocols allows engineers and project managers to select the appropriate line pipes for their specific projects, ensuring safety and long-term durability in challenging operational environments.

Exploring the Vital Role of Steel Pipes in Oil & Gas Exploration

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Introduction

Steel pipes are critical in the oil and gas, offering unmatched durability and reliability under extreme conditions. Essential for exploration and transportation, these pipes withstand high pressures, corrosive environments, and harsh temperatures. This page explores the critical functions of steel pipes in oil and gas exploration, detailing their importance in drilling, infrastructure, and safety. Discover how selecting suitable steel pipes can enhance operational efficiency and reduce costs in this demanding industry.

I. The Basic Knowledge of the Steel Pipes for the Oil & Gas Industry

1. Terminology Explanation

API: Abbreviation of American Petroleum Institute.
OCTG: Abbreviation of Oil Country Tubular Goods, including Oil Casing Pipe, Oil Tubing, Drill Pipe, Drill Collar, Drill Bits, Sucker Rod, Pup joints, etc.
Oil Tubing: Tubing is used in oil wells for Extraction, gas extraction, water injection, and acid fracturing.
Casing: Tubing lowered from the ground surface into a drilled borehole as a liner to prevent wall collapse.
Drill Pipe: Pipe used for drilling boreholes.
Line Pipe: Pipe used to transport oil or gas.
Couplings: Cylinders used to connect two threaded pipes with internal threads.
Coupling Material: Pipe used for manufacturing couplings.
API Threads: Pipe threads specified by API 5B standard, including oil pipe round threads, casing short round threads, casing long round threads, casing partial trapezoidal threads, line pipe threads, etc.
Premium Connection: Non-API threads with unique sealing properties, connection properties, and other properties.
Failures: deformation, fracture, surface damage, and loss of original function under specific service conditions.
Primary Forms of Failure: crushing, slipping, rupture, leakage, corrosion, bonding, wear, etc.

2. Petroleum Related Standards

API Spec 5B, 17th Edition – Specification for Threading, Gauging, and Thread Inspection of Casing, Tubing, and Line Pipe Threads
API Spec 5L, 46th Edition – Specification for Line Pipe
API Spec 5CT, 11th Edition – Specification for Casing and Tubing
API Spec 5DP, 7th Edition – Specification for Drill Pipe
API Spec 7-1, 2nd Edition – Specification for Rotary Drill Stem Elements
API Spec 7-2, 2nd Edition – Specification for Threading and Gauging of Rotary Shouldered Thread Connections
API Spec 11B, 24th Edition – Specification for Sucker Rods, Polished Rods and Liners, Couplings, Sinker Bars, Polished Rod Clamps, Stuffing Boxes and Pumping Tees
ISO 3183:2019 – Petroleum and Natural Gas Industries — Steel Pipe for Pipeline Transportation Systems
ISO 11960:2020 – Petroleum and Natural Gas Industries — Steel Pipes for Use as Casing or Tubing for Wells
NACE MR0175 / ISO 15156:2020 – Petroleum and Natural Gas Industries — Materials for Use in H2S-Containing Environments in Oil and Gas Production

II. Oil Tubing

1. Classification of Oil Tubing

Oil Tubing is divided into Non-Upsetted Oil Tubing (NU), External Upsetted Oil Tubing (EU), and Integral Joint (IJ) Oil Tubing. NU oil tubing means that the end of the tubing is of average thickness, directly turns the thread, and brings the couplings. Upsetted tubing implies that the ends of both tubes are externally Upsetted, then threaded and coupled. Integral Joint tubing means that one end of the tube is Upset with external threads, and the other is Upset with internal threads connected directly without couplings.

2. Function of Oil Tubing

① Extraction of oil and gas: after the oil and gas wells are drilled and cemented, the tubing is placed in the oil casing to extract oil and gas to the ground.
② Water injection: when the downhole pressure is insufficient, inject water into the well through the tubing.
③ Steam injection: In thick oil hot recovery, steam is input into the well with insulated oil tubing.
④ Acidification and fracturing: In the late stage of well drilling or to improve the production of oil and gas wells, it is necessary to input Acidification and fracturing medium or curing material to the oil and gas layer, and the medium and the curing material are transported through the oil tubing.

3. Steel Grade of Oil Tubing

The steel grades of oil tubing are H40, J55, N80, L80, C90, T95, P110.
N80 is divided into N80-1 and N80Q, the two have the same tensile properties; the two differences are the delivery status and impact performance differences, N80-1 delivery by normalized state or when the final rolling temperature is greater than the critical temperature Ar3 and tension reduction after air cooling and can be used to find hot rolling instead of normalized, impact and non-destructive testing are not required; N80Q must be tempered (quenched and tempered) Heat treatment, impact function should be in line with the provisions of API 5CT, and should be non-destructive testing.
L80 is divided into L80-1, L80-9Cr and L80-13Cr. Their mechanical properties and delivery status are the same. Differences in use, production difficulty, and price: L80-1 is for the general type, L80- 9Cr and L80-13Cr are high corrosion resistance tubing, production difficulty, and are expensive and usually used in heavy corrosion wells.
C90 and T95 are divided into 1 and 2 types, namely C90-1, C90-2 and T95-1, T95-2.

4. The Oil Tubing Commonly Used Steel Grade, Steel Name and Delivery Status

J55 (37Mn5) NU Oil Tubing: Hot rolled instead of Normalised
J55 (37Mn5) EU Oil Tubing: Full-length Normalized after upsetting
N80-1 (36Mn2V) NU Oil Tubing: Hot-rolled instead of Normalised
N80-1 (36Mn2V) EU Oil Tubing: Full-length Normalized after upsetting
N80-Q (30Mn5) Oil Tubing: 30Mn5, Full-length Tempering
L80-1 (30Mn5) Oil Tubing: 30Mn5, Full-length Tempering
P110 (25CrMnMo) Oil Tubing: 25CrMnMo, Full-length Tempering
J55 (37Mn5) Coupling: Hot rolled on-line Normalised
N80 (28MnTiB) Coupling: Full-length Tempering
L80-1 (28MnTiB) Coupling: Full-length Tempered
P110 (25CrMnMo) Coupling: Full-length Tempering

III. Casing Pipe

1. Classification and Role of Casing

The casing is the steel pipe that supports the wall of oil and gas wells. Several layers of casing are used in each well according to different drilling depths and geological conditions. Cement is used to cement the casing after it is lowered into the well, and unlike oil pipe and drill pipe, it cannot be reused and belongs to disposable consumable materials. Therefore, the consumption of casing accounts for more than 70 percent of all oil well pipes. The casing can be divided into conductor casing, intermediate casing, production casing, and liner casing according to its use, and their structures in oil wells are shown in Figure 1.

①Conductor Casing: Typically using API grades K55, J55, or H40, conductor casing stabilizes the wellhead and isolates shallow aquifers with diameters commonly around 20 inches or 16 inches.

②Intermediate Casing: Intermediate casing, often made from API grades K55, N80, L80, or P110, is used to isolate unstable formations and varying pressure zones, with typical diameters of 13 3/8 inches, 11 3/4 inches, or 9 5/8 inches.

③Production Casing: Constructed from high-grade steel such as API grades J55, N80, L80, P110, or Q125, production casing is designed to withstand production pressures, commonly with diameters of 9 5/8 inches, 7 inches, or 5 1/2 inches.

④Liner Casing: Liners extend the wellbore into the reservoir using materials like API grades L80, N80, or P110, with typical diameters of 7 inches, 5 inches, or 4 1/2 inches.

⑤Tubing: Tubing transports hydrocarbons to the surface, using API grades J55, L80, or P110, and is available in diameters of 4 1/2 inches, 3 1/2 inches, or 2 7/8 inches.

IV. Drill pipe

1. Classification and Function of Pipe for Drilling Tools

The square drill pipe, drill pipe, weighted drill pipe, and drill collar in drilling tools form the drill pipe. The drill pipe is the core drilling tool that drives the drill bit from the ground to the bottom of the well, and it is also a channel from the ground to the bottom of the well. It has three leading roles:

① To transmit torque to drive the drill bit to drill;

② To rely on its weight to the drill bit to break the pressure of the rock at the bottom of the well;

③ To transport washing fluid, that is, drilling mud through the ground through the high-pressure mud pumps, drilling column into the borehole flow into the bottom of the well to flush the rock debris and cool the drill bit, and carry the rock debris through the outer surface of the column and the wall of the well between the annulus to return to the ground, to achieve the purpose of drilling the well.

The drill pipe is used in the drilling process to withstand a variety of complex alternating loads, such as tensile, compression, torsion, bending, and other stresses. The inner surface is also subject to high-pressure mud scouring and corrosion.
(1) Square Drill Pipe: Square drill pipes come in two types: quadrilateral and hexagonal. In China’s petroleum drill pipe, each set of drill columns usually uses a quadrilateral type drill pipe. Its specifications are 63.5mm (2-1/2 inches), 88.9mm (3-1/2 inches), 107.95mm (4-1/4 inches), 133.35mm (5-1/4 inches), 152.4mm (6 inches), and so on. The length used is usually 1214.5 m.
(2) Drill Pipe: The drill pipe is the primary tool for drilling wells, connected to the lower end of the square drill pipe, and as the drilling well continues to deepen, the drill pipe keeps lengthening the drill column one after another. The specifications of drill pipe are: 60.3mm (2-3/8 inches), 73.03mm (2-7/8 inches), 88.9mm (3-1/2 inches), 114.3mm (4-1/2 inches), 127mm (5 inches), 139.7mm (5-1/2 inches) and so on.
(3) Heavy Duty Drill Pipe: A weighted drill pipe is a transitional tool connecting the drill pipe and drill collar, which can improve the force condition of the drill pipe and increase the pressure on the drill bit. The main specifications of the weighted drill pipe are 88.9mm (3-1/2 inches) and 127mm (5 inches).
(4) Drill Collar: The drill collar is connected to the lower part of the drill pipe, which is a special thick-walled pipe with high rigidity. It exerts pressure on the drill bit to break the rock and plays a guiding role when drilling a straight well. The common specifications of drill collars are 158.75mm (6-1/4 inches), 177.85mm (7 inches), 203.2mm (8 inches), 228.6mm (9 inches), and so on.

V. Line pipe

1. Classification of Line Pipe

Line pipe is used in the oil and gas industry to transmit oil, refined oil, natural gas, and water pipelines with the abbreviation of steel pipe. Conveying oil and gas pipelines is divided into mainline, branch, and urban pipeline network pipelines. Three kinds of mainline pipeline transmission have the usual specifications of  ∅406 ~ 1219mm, a wall thickness of 10 ~ 25mm, steel grade X42 ~ X80; branch line pipeline and urban pipeline network pipelines usually have specifications for  ∅114 ~ 700mm, the wall thickness of 6 ~ 20mm, the steel grade for the X42 ~ X80. The steel grade is X42～X80. Line pipe is available in welded and seamless types. Welded Line Pipe is used more than Seamless Line Pipe.

2. Standard of Line Pipe

API Spec 5L – Specification for Line Pipe
ISO 3183 – Petroleum and Natural Gas Industries — Steel Pipe for Pipeline Transportation Systems

3. PSL1 and PSL2

PSL is the abbreviation for product specification level. The specification level of the line pipe product is divided into PSL 1 and PSL 2, and the quality level is divided into PSL 1 and PSL 2. PSL 2 is higher than PSL 1; the two specification levels not only have different test requirements, but the chemical composition and mechanical properties requirements are different, so according to API 5L order, the terms of the contract, in addition to specifying the specifications, steel grade, and other common indicators, but also must indicate the product Specification level, that is, PSL 1 or PSL 2. PSL 2 in the chemical composition, tensile properties, impact power, non-destructive testing, and other indicators are stricter than PSL 1.

4. Line Pipe Steel Grade, Chemical Composition and Mechanical Properties

Line pipe steel grades from low to high are divided into A25, A, B, X42, X46, X52, X60, X65, X70, and X80. For detailed Chemical Composition and Mechanical Properties, please refer to the API 5L Specification, 46th Edition Book.

5. Line Pipe Hydrostatic Test and Non-destructive Examination Requirements

Line pipe should be done branch by branch hydraulic test, and the standard does not allow non-destructive generation of hydraulic pressure, which is also a big difference between the API standard and our standards. PSL 1 does not require non-destructive testing; PSL 2 should be non-destructive testing branch by branch.

VI. Premium Connections

1. Introduction of Premium Connections

Premium Connection is a pipe thread with a unique structure that is different from the API thread. Although the existing API threaded oil casing is widely used in oil well exploitation, its shortcomings are clearly shown in the unique environment of some oil fields: the API round threaded pipe column, although its sealing performance is better, the tensile force borne by the threaded part is only equivalent to 60% to 80% of the strength of the pipe body, and thus it can’t be used in the exploitation of deep wells; the API biased trapezoidal threaded pipe column, although its tensile performance is much higher than that of the API round threaded connection, its sealing performance is not so good. Although the tensile performance of the column is much higher than that of the API round thread connection, its sealing performance is not very good, so it can not be used in the exploitation of high-pressure gas wells; in addition, the threaded grease can only play its role in the environment with the temperature below 95℃, so it can not be used in the exploitation of high-temperature wells.

Compared with the API round thread and partial trapezoidal thread connection, the premium connection has made breakthrough progress in the following aspects:

(1) Good sealing, through the elasticity and metal sealing structure design, makes the joint gas sealing resistant to reaching the limit of the tubing body within the yield pressure;

(2) High strength of the connection, connecting with special buckle connection of oil casing, its connection strength reaches or exceeds the strength of the tubing body, to solve the problem of slippage fundamentally;

(3) By the Material selection and surface treatment process improvement, basically solved the problem of thread sticking buckle;

(4) Through the optimization of the structure, so that the joint stress distribution is more reasonable and more conducive to the resistance to stress corrosion;

(5) Through the shoulder structure of the reasonable design, so that the operation of the buckle on the operation is more accessible.

The oil and gas industry boasts over 100 patented premium connections, representing significant advancements in pipe technology. These specialized thread designs offer superior sealing capabilities, increased connection strength, and enhanced resistance to environmental stresses. By addressing challenges such as high pressures, corrosive environments, and temperature extremes, these innovations ensure excellent reliability and efficiency in oil-healthy operations worldwide. Continual research and development in premium connections underscore their pivotal role in supporting safer and more productive drilling practices, reflecting an ongoing commitment to technological excellence in the energy sector.

VAM® Connection: Known for its robust performance in challenging environments, VAM® connections feature advanced metal-to-metal sealing technology and high torque capabilities, ensuring reliable operations in deep wells and high-pressure reservoirs.

TenarisHydril Wedge Series: This series offers a range of connections such as Blue®, Dopeless®, and Wedge 521®, known for their exceptional gas-tight sealing and resistance to compression and tension forces, enhancing operational safety and efficiency.

TSH® Blue: Designed by Tenaris, TSH® Blue connections utilize a proprietary double shoulder design and a high-performance thread profile, providing excellent fatigue resistance and ease of make-up in critical drilling applications.

Grant Prideco™ XT® Connection: Engineered by NOV, XT® connections incorporate a unique metal-to-metal seal and a robust thread form, ensuring superior torque capacity and resistance to galling, thereby extending the connection’s operational life.

Hunting Seal-Lock® Connection: Featuring a metal-to-metal seal and a unique thread profile, the Seal-Lock® connection by Hunting is renowned for its superior pressure resistance and reliability in both onshore and offshore drilling operations.

Conclusion

In conclusion, the intricate network of steel pipes crucial to the oil and gas industry encompasses a wide array of specialized equipment designed to withstand rigorous environments and complex operational demands. From the foundational casing pipes that support and protect healthy walls to the versatile tubing used in extraction and injection processes, each type of pipe serves a distinct purpose in exploring, producing, and transporting hydrocarbons. Standards like API specifications ensure uniformity and quality across these pipes, while innovations such as premium connections enhance performance in challenging conditions. As technology evolves, these critical components advance, driving efficiency and reliability in global energy operations. Understanding these pipes and their specifications underscores their indispensable role in the modern energy sector’s infrastructure.