What is a steel pipe?
What is a steel pipe?
A steel pipe is a round hollow section manufactured by drawing a solid billet (in carbon, alloy, stainless or nickel alloy steel) through a piercing rod. Seamless pipes are considered superior to welded pipes as they are built using monolithic steel billets, with intrinsic mechanical strength, without seam welds.
Seamless steel pipes are used for the transmission and distribution of oil, gas, steam, and chemicals. Stainless steel seamless pipes offer enhanced resistance to corrosion at high temperature and pressure.
Seamless steel pipes have a higher price per ton than welded pipes, due to their fairly complex production process and due to the oligopolistic nature of the market. For specific sizes and specifications (example 20 inch pipes or seamless high wall thickness ASTM A335 P91 pipes), the supply base is rather narrow and prices are, as a consequence, impacted.
SEAMLESS STEEL PIPE DIMENSIONS
- Carbon and low-alloy seamless pipes are manufactured according to the ASME B36.10 specification, in sizes between 1/8 and 24 inches and with multiple schedule designations, representing the wall thickness of the pipe (pipe expanders are used to reach higher nominal sizes);
- Stainless steel seamless pipes (and higher grades, as nickel-alloy) are manufactured according to the ASME B36.19 specification, generally in sizes between 1/8 and 12 inches;
- Carbon, alloy and stainless seamless pipes for upstream oil operations (OCTG pipes) are covered by the API 5CT specification.
SEAMLESS PIPE MATERIALS
The most common material specifications for seamless pipe are:
- ASTM A53 (black and galvanized pipes, seamless and welded)
- ASTM A106 (carbon seamless pipe for high-temperature service)
- ASTM A333 (carbon seamless pipe low-temperature service)
- ASTM A335 (Chrome Moly pipe, or low alloy seamless pipe)
- API 5L (carbon steel line pipes)
SEAMLESS PIPE MANUFACTURING PROCESS
Seamless pipes from 1/8 to 6 inch. are manufactured with the so-called “plug mill process” or the “extrusion process” (used for smaller diameters), whereas the “mandrel mill process” is used for larger diameters.
ERW AND LSAW Pipe
An ERW pipe (“electric resistance welding”) is manufactured by cutting, bending and welding steel coils longitudinally. The most common welding technique used for oil and gas pipes is the so-called “high-frequency induction technology” (ERW-HFI), consisting in the application of an induction current on the outer surface of the pipe able to generate a robust seam weld and join the two sides of the steel coil very tightly. No filler materials is therefore used for ERW pipes (differently from LSAW pipes).
ERW pipes are available in sizes between 1/2 and 20 inches, in carbon steel (ASTM A53 is a common grade) and stainless steel (ASTM A312). The dimensions and sizes of ERW pipes are covered by the ASME B36.10 and ASME B36.19 specifications (respectively, carbon and alloy, and stainless steel ERW pipes).
WHAT MEANS “LSAW PIPE”?
An LSAW pipe (“submerged arc welding”) is manufactured by cutting, bending and welding steel plates (JCOE process). LSAW pipes compete with seamless and ERW pipes in the size range between 16 and 24 inches but become the only option for pipe sizes above 24 inches. The two main types of LSAW pipes are the longitudinal (with a single or double straight seam weld, DSAW) and the spiral type (called, HSAW or SSAW pipe).
In the oil and gas industry, API 5L LSAW pipes are used for hydrocarbons transmission and distribution over long distances. HSAW/SSAW spiral weld pipes are used for non-critical application as water transmission and distribution (not for oil & gas).
LSAW PIPE MANUFACTURING PROCESS
LSAW pipes are manufactured with the so-called JCOE process, starting from steel plates as illustrated below.
SEAMLESS VS WELDED PIPE
The question “Shall I use seamless or a welded pipes for my project?” is coming up over and over. Each of the two has different advantages and disadvantages, which should be pondered to take a proper decision:
SEAMLESS PIPE PROS AND CONS
- Seamless pipes are manufactured out of a solid block of steel and do not have any weld seam, which may represent a weak area (subject to corrosion, erosion and, general failure)
- Seamless pipes have more predictable and precise shapes, in terms of roundness and ovality, compared to welded pipes.
- The main disadvantage of seamless pipes is that their cost per ton is higher than the cost of equivalent ERW or LSAW pipes (Seamless vs ERW pipes compete in the range 2 to 20 inches, Seamless vs LSAW in the dimensional range 16 to 24 inches)
- Delivery times may be longer, as there are fewer manufacturers of seamless pipes in the world compared to the number of welded pipe companies
- Seamless pipes may have an inconsistent wall thickness across their length, indeed the general tolerance is +/- 12.5%
WELDED PIPE PROS AND CONS
- Welded pipes are cheaper than seamless (ERW HFI type), as they are manufactured using steel coils as feedstock in simpler plants
- Welded pipes have shorter lead times than seamless pipes, as the manufacturing base is way larger
- Welded pipes have a consistent wall thickness, as they are manufactured using coils (ERW) or plates (LSAW) that have a strictly controlled thickness
- The major “defect” attributed to welded pipes is that the presence of a weld seam constitutes a weakness factor. Whereas this may have been true in the past, this is becoming less and less true with the advances of the welding technologies in the last ten years.
Conclusion: modern ERW-HFI welded pipes are absolutely a valid alternative to seamless pipes and help end users reduce prices and lead times between 20 and 25%.
As mentioned, the outside diameter of pipes of a specific NPS is constant but the inside diameter of the pipe (ID) changes depending on the pipe schedule.
The pipe ID can be easily calculated, as long as the pipe NPS and schedule are known.
The pipe ID can be calculated by deducting from the pipe NPS the pipe wall thickness multiplied by 2 (the pipe WT can be taken from the schedule). Example: for a 12 NPS pipe (DN 300 mm), schedule 40, the pipe outside diameter and the wall thickness are 12.75 inches (324 mm) and 0.406 inches (10.4 mm).
Therefore, the pipe ID (internal diameter) is 12.75 inches – 2 x 0.406 inches = 11.94 inches, or Pipe ID = 324 mm – 2 x 10.4 mm = 303.2 mm.
It should be noted that this calculation is just theoretical, as pipes have a wall thickness tolerance which is generally +/-12.5% for ASME pipes. Hence the actual ID of a given pipe may differ by +/- 12,5% from the theoretical value.
The pipe ID calculator is available on this page.
WHAT ARE OCTG PIPES
OCTG pipes are tubular products used for onshore and offshore oil & gas upstream operations. The OCTG pipe family includes casing pipes (to stabilize the wellbore), tubing pipes (to transport hydrocarbons from the reserve to the surface) and drill pipes to perforate the soil. The dimensions, tolerances, and materials for “Oil Country Tubular Goods” are covered by the API 5CT specification.
Three types of pipes belong to the OCTG family:
Drill pipes are heavyweight seamless tubular that rotates the drill bit and circulates the drilling fluid. Pipe segments of 30′ are coupled with tool joints. Drill pipe is subject to high torque by drilling, axial tension by their weight, and internal pressure due to the purging of the drilling fluid. Additionally, alternating bending loads due to non-vertical or deflected drilling may be superimposed on these basic loading patterns
API5CT CASING AND TUBING PIPES
The API 5CT specification covers seamless and welded casing and tubing pipes for upstream operations (pipes that belong to the OCTG family, as illustrated above). The application of casing and tubing pipes is shown in the picture:
API 5CT CASING PIPES
Casing pipes scope
Casing pipes are a key structural component for an oil & gas well and have the following scope:
- Keep the borehole stability in the well
- Prevent the bore contamination from water sands
- Prevent water from producing formations
- Exercise a tight control of the wellbore pressures during the drilling, production, and repair operations
Casing pipes are used to install:
- Blowout Preventers (BOP)
- Other wellhead equipment necessary to extract hydrocarbons
- Production tubing and packers
Casing pipes are also one major individual component of the overall cost of the well, therefore the correct selection of the casing size, materials, connectors, and depth shall be at the top of design engineers (for cost and efficiency reasons).
The six basic types of casing strings are:
- Conductor Casing
- Surface Casing
- Intermediate Casing
- Production Casing
- Liner tieback casing
Oilfield casing pipes are positioned into the wellbore and cemented in place to secure both subsurface formations and the wellbore from collapsing, also to enable drilling mud to circulate and extraction to take place. The strict quality requirement for steel is due to the harsh working conditions of the casing. The steel product should be produced and checked in accordance with special standards or specifications. ISO 11960 and API Spec 5CT have specified the steel product standards of the casing.
Casing pipes sizes and materials
Casing pipes are available in a diameter range 4 1/2 to 20 inches (the dimensions of API5CT casing pipes are shown in this article), and in the following materials: H-40, J-55, K-55, N-80, L-80/C, 90/T, 95, P110, Q-125. Consult this article to learn more about the materials for API5CT pipes.
Casing pipes connections
The main types of connections for casing pipes are STC (short threads), LTC (long threads), BTC (buttress threads) and premium gas-tight connections.
API 5CT TUBING PIPES
Tubing pipes scope
Tubing pipes are used to bring oil and gas from the underground reserves up to the field for further processing. Tubing pipes need resistance to mechanical stress as they are subject to very high loads and deformations during the production operations. In addition, tubing pipes sizes should be properly calculated to support the expected oil and gas flow from the ground to the surface (a too small diameter would decrease the production rate and the return on investment on the wellbore licenses, whereas too large tubing would generate non-recoverable costs due to the greater amount of steel used for the bore construction vs. the actual requirement (steel for the casing and tubing pipes).
Tubing pipes sizes and materials
Tubing pipes are manufactured in seamless and welded execution, in the size range 1.050 to 5 1/2 inches (consult this article to see the AP5CT tubing pipes sizes) and in the following material grades: H-40, J-55, K-55, N-80, L-80, C-90, T-95, P-110, Q-125 (more details about API 5CT tubing materials are in this article).
Tubing pipes connections
The main types of connections for tubing pipes are NUE (non-upset), EUE (external upset) and premium. Corrosion resistance under sour service conditions is a very important OCTG characteristic, especially for casing and tubing.
API5CT PIPE MANUFACTURING PROCESS
The manufacturing processes of casing and tubing pipes include:
API 5CT CASING COUPLINGS SHORT-THREAD
|API 5CT Casing OD||
|API Casing Couplings Short Thread||41/2||5.000||6.250|
API 5CT CASING COUPLINGS LONG-THREAD
|API 5CT Casing OD||
|Length||Weight per Coupling|
|API Casing Couplings Long Thread||41/2||5.000||6.250|
which flange or valve material matches a given pipe material?
The piping materials matching chart maps how to mate the materials of different piping products, such as pipes, valves, fittings, flanges, and stud bolts.
MOST COMMON PIPING MATERIALS
- A106: Specification for carbon steel pipe for high-temperature service. For more info about A106 pipes, read here
- A335: Specification for seamless ferritic alloy-steel pipe for high-temperature service. For more info about chrome-alloy pipes, read here
- A333: Specification for wall seamless and welded carbon and alloy steel pipe intended for use at low temperatures. For more info about LTCS pipes, read here
- A312: Standard specification for seamless, straight-seam welded, and cold worked welded austenitic stainless steel pipe intended for high-temperature and general corrosive service. For more information about stainless steel pipes, read here.
- A216: Specification for carbon steel castings for Valves, flanges, fittings, or other pressure-containing parts for high-temperature service and of the quality suitable for assembly with other castings or wrought steel parts by fusion welding. For more information about carbon steel valves, read here
- A217: Specification for steel castings, martensitic stainless steel and alloys steel castings for Valves, flanges, fittings, and other pressure-containing parts intended primarily for high-temperature and corrosive service.
- A352: Specification for steel castings for Valves, flanges, fittings, and other pressure-containing parts intended primarily for low-temperature service.
- A182: This specification covers forged or rolled alloy and stainless steel pipe flanges, forged fittings, and Valves and parts for high-temperature service. Find more information about forged body valves here.
- A105: Specification for standards for forged carbon steel piping components, that is, flanges, fittings, Valves, and similar parts, for use in pressure systems at ambient and higher-temperature service conditions. To learn more about forged flanges materials, read this article
- A182: This specification covers forged or rolled alloy and stainless steel pipe flanges, forged fittings, and Valves and parts for high-temperature service.
- A350: Specification for several grades of carbon and low alloy steel forged or ring-rolled flanges, forged fittings and Valves for low-temperature service.
PIPE FITTINGS MATERIALS
- A234: Specification for wrought carbon steel and alloy steel fittings of seamless and welded construction.
- A420: Standard specification for piping fittings of wrought carbon steel and alloy steel for low-temperature service.
- A403: Standard specification for wrought austenitic stainless steel piping fittings.
STUD BOLT MATERIALS
- A193: Standard specification for alloy and stainless steel bolting material for pressure vessels, Valves, flanges, and fittings for high temperature or high-pressure service, or other special purpose applications.
- A320: Standard Specification for Alloy-Steel and Stainless Steel Bolting Materials for Low-Temperature Service.
- A194: Standard specification for nuts in different materials
PIPE LENGTH AND PIPE ENDS
PIPE LENGTH (SRL, DRL)
The length of a pipe measures the distance in meters, or feet, between the two ends of a tubular section. Generally, pipes below 2 inches in diameter are manufactured in single random lengths (“SRL”, 5 to 7 meters), larger pipes in double random lengths (“DRL”, 11 to 13 meters).
The most common terms used to designate the length of steel pipes are:
- SRL (single random pipe length): 5-7 meters in length – generally used for pipes below 2 inches
- DRL (double random pipe length): 11-13 meters per pipe, for pipes above 2 inches
- Cut Lengths: pipes are cut at specific lengths according to project specification. Cut lengths pipes are generally more expensive than standard but may save EPC and End-Users the costs related to welding activities.
PIPE LENGTH TOLERANCE
In case of “cut lengths” pipes, the allowed tolerance is between within -0mm / +6mm.
PIPE END TYPES
The pipe end concept refers to the type of finish applied to the extremities of the tubular, and the consequent type of pipe to pipe connection that will be necessary to deploy a pipeline or a piping system.
The most common types of pipe end connections are:
- Plain ends (PE): ASME ANSI B16.5. PE ends are generally used for smaller diameters and imply the usage of slip-on flanges, and socket weld fittings.
- Beveled ends (BE): ASME ANSI B16.5. BE ends are the most common type of finish (joints are realized by welding pipes with butt weld fittings and flanges).
- Threaded ends (TE): ASME B1.20.1 NPT. TE ends require threaded fittings and flanges and are typical for small size pipelines.
- Threaded and coupled ends (T&C), generally used for gas distribution
- Grooved ends (example Victaulic pipes)
Source: China Steel Pipes Manufacturer – Yaang pipe fitting Industry Co., Limited (www.ugsteelmill.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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