Seamless pipe is produced by heating a round billet of steel and then piercing it with a bullet-shaped piercer, over which the steel is stretched.
Seamless pipe is a tubular section or hollow cylinder, usually but not necessarily of circular cross-section, used mainly to convey substances which can flow — liquids and gases (fluids), slurries, powders and masses of small solids.
Seamless pipes come in various types, each designed for specific applications and environments. Some of the common types of seamless pipes include:
A seamless pipe is a type of pipe that is manufactured without any welded joints or seams. It is made from a solid round steel billet or other suitable material, which is heated and pushed or pulled over a form until it takes the shape of a hollow tube. The absence of welds or joints in seamless pipes provides several advantages, including increased strength, durability, and resistance to leakage. Seamless pipes are commonly used in industries such as oil and gas, petrochemical, power generation, and construction, where reliability and performance under high pressure and temperature conditions are crucial.
Seamless pipes are formed using a process known as extrusion. Here is a general overview of how seamless pipes are formed:
The extrusion process allows for the production of seamless pipes with no seams or joints, resulting in a pipe that is stronger, more reliable, and better suited for high-pressure and high-temperature applications.
It's important to note that the specific details of the manufacturing process may vary depending on factors such as the type of seamless pipe, the material used, and the desired specifications.
Seamless pipes come in various grades, each designed for specific applications and environments. The choice of grade depends on factors like the intended use, temperature, pressure, and the type of conveyed fluid. Some common grades of seamless pipes include:
Carbon Steel Grades: Carbon steel seamless pipes are widely used for general applications. Common grades include:
Alloy Steel Grades: Alloy steel seamless pipes offer enhanced strength, corrosion resistance, and high-temperature performance. Examples include:
Stainless Steel Grades: Stainless steel seamless pipes are known for their corrosion resistance. Common grades include:
Duplex and Super Duplex Grades: These are highly corrosion-resistant and offer superior strength. Examples include:
Nickel Alloys: Seamless pipes made from nickel alloys are used in highly corrosive environments and high-temperature applications. Grades like Alloy 625, Alloy 825, and others are common.
Titanium Alloys: Seamless pipes made from titanium alloys offer exceptional corrosion resistance and are used in aerospace, chemical, and marine applications.
Copper Alloys: Seamless pipes made from copper alloys, such as C71500 and C70600, are used in marine and industrial applications due to their corrosion resistance and heat transfer properties.
High-Strength Low-Alloy (HSLA) Steel: These seamless pipes contain small alloying elements to enhance strength and toughness while maintaining good weldability. They find use in various structural and mechanical applications.
Seamless steel pipes have hollow sections and are widely used as pipes for conveying fluids, such as pipes for conveying oil, natural gas, gas, water and certain solid materials. The seamless pipe has a certain corrosion resistance, but in order to prolong the service life of the seamless pipe in some extreme environments, it is necessary to remove the oxide layer on the surface of the product. The main cleaning method is pickling. After cleaning, electrolytic cleaning is required again.
The seamless pipes stored in the warehouse waiting to be put into use need to do the following work
The warehouse shall not be piled together with acid, alkali, salt, cement and other materials that are corrosive to steel. Steel materials of different types should be stacked separately to prevent mixing and contact corrosion.
There are two types of factors that affect the quality of seamless steel pipes: steel quality and rolling process factors.
Factors in the rolling process are discussed here. The main influencing factors are: temperature, process adjustment, tool quality, process cooling and lubrication, removal and control of sundries on the surface of rolled parts, etc.
Temperature is the most important factor affecting the quality of seamless steel pipes. First of all, the uniformity of the heating temperature of the tube blank directly affects the wall thickness uniformity and inner surface quality of the perforated capillary, which in turn affects the wall thickness quality of the product. Secondly, the temperature and uniformity of the steel pipe during the rolling process (especially the final rolling temperature) are related to the mechanical properties, dimensional accuracy and surface quality of the delivered product in the hot-rolled state, especially when the steel billet or lamp tube is overheated or even When overburned, it will cause waste. Therefore, in the production process of hot-rolled seamless pipes, heating and controlling the deformation temperature in strict accordance with the process requirements are the first work that must be done.
Process adjustment and work quality mainly affect the geometric shape and appearance quality of steel pipes.
For example, the adjustment of the piercing machine and the rolling mill affects the wall thickness accuracy of the product, and the adjustment of the sizing machine is related to the accuracy and straightness of the product's outer diameter. Moreover, process adjustment also affects whether the rolling process can be carried out normally.
The quality and stability of the cutting tool are directly related to the dimensional accuracy, surface quality and cutting tool consumption of the product can be effectively controlled; the quality of the mandrel surface treatment (chrome plating) first affects the inner surface of the seamless steel pipe, and secondly affects Mandrel consumption and production costs.
The cooling quality of the piercing head and rolls not only affects their life, but also affects the quality control of the inner and outer surfaces of the finished product. The cooling and lubrication quality of the mandrel first affects the inner surface quality, wall thickness accuracy and mandrel consumption of the seamless steel pipe; it also affects the load during rolling.
5. The removal and control of sundries on the surface of rolled parts refers to the timely and effective removal of iron sheets on the inner and outer surfaces of capillaries and waste pipes, and the control of reoxidation before rolling deformation. Nitrogen blowing in the inner hole of the capillary, borax spraying, pipe rolling and high-pressure water descaling at the entrance of fixed (reduced) diameter, effectively improving and enhancing the quality of the internal and external surfaces.
The outer diameter of hot-rolled seamless pipe is generally greater than 32mm, the wall thickness is 2.5-200mm, the outer diameter of cold-rolled seamless steel pipe can be 6mm, the wall thickness can be 0.25mm, the outer diameter of thin-walled pipe can be 5mm, and the wall thickness is less than 0.25mm, cold rolling
|NPS/ DN/ OD||Permissible Variations in Outside Diameter|
|NPS 1/8 to 1½, incl
DN 6 to 40
OD 10.3 to 48.3, mm
|Over 1½ to 4, incl
DN 40 to 100
OD 48.3 to 114.3, mm
|Over 4 to 8, incl
DN 100 to 200
OD 114.3 to 219.1, mm
|Over 8 to 18, incl
DN 200 to 450
OD 219.1 to 457, mm
|Over 18 to 26, incl
DN 450 to 650
OD 457 to 660, mm
Cold drawn seamless tubing possesses a high strength-to-weight ratio and can be processed to provide a combination of desired characteristics. Cold drawn seamless mechanical tubing is used in a variety of uses, particularly when heavy wall thicknesses, specific steel alloys or both are required.
Steel Pipe & Tubing seem similar at first blush and in fact they share many characteristics but they also have some important differences.
Steel Tubing is a hollow steel shape intended for structural purposes and made from carbon, stainless, or galvanized steel further divided as:
Mechanical Tubing is used in low stress applications such as fences, kitchens, restaurants, hospitals, solar panels and made with wall thicknesses up to 10 gauge.
Structural Tubing is for high stress structural application like bridges, buildings, roll cages, and underwater platforms with wall thickness from 3/16" and up. It is often referred to as Hollow Structural Sections or just the acronym HSS.
Pipe is a hollow structure that is intended to carry material such as liquids, gasses, or even solids. Its wall thickness is described by its Schedule and it is often broken down by type using the method of manufacturing it, either ERW or Seamless
Both Tubing and Pipe are manufactured by the first two methods below. The third is reserved for Tubing only.
Electric Resistance Welded, often abbreviated as ERW, is a process that uses specific machinery to shape the pipe and tubing. A continuous steel sheet is unwound from a coil and shaped using contoured rollers, forcing the edges together under pressure. These edges are then welded together by heating the material to over 2,000 degrees. After welding, the pipe or tubing is cut into the exact size needed.
Seamless Pipe (and tubing) is made by extruding a steel block or by drilling a solid steel bar. Next, the extrusion or the drilled steel bar is cold drawn through a dye to achieve the diameter and thickness needed. Because this process can cause mechanical hardening, sometimes the material is annealed and straightened as a final process. Seamless Pipe & Tubing is subdivided as:
Cold Drawn Seamless, or CDS, exhibits precise tolerances and a good surface finish.
Hot Finished Seamless, or HFS, has less critical tolerances and somewhat scaly finish and is not as strong as CDS.
For Drawn over Mandrel, or DOM tubing, the first stages of manufacturing are identical to ones used to make electric resistance welded tubing, but in the finishing stages the entire flash weld is taken out and the tube is cold drawn over a mandrel. A mandrel is a round object against which material can be forged or shaped. The cold drawn process provides the tube with better dimensional tolerances, improved surface finish and the strongest weld strength achievable.
Pipe Size is specified with two non-dimensional numbers:
Both the size and schedule are required to accurately specify a particular piece of pipe.
Nominal Pipe Size (NPS) is the current North American Set of standard sizes for pipes used for high and low pressures and temperatures. A further discussion of this is here.
Iron Pipe Size (IPS) was an earlier standard than NPS to designate the size. The size was the approximate inside diameter of the pipe in inches. Each pipe had one thickness, named (STD) Standard or (STD.WT.) Standard Weight. There were only 3 wall thicknesses at the time. In March 1927, the American Standards Association created a system that designated wall thickness based on smaller steps between sizes and introduced Nominal Pipe Size which replaced Iron Pipe Size.
Schedule Number for wall thickness ranges from SCH 5, 5S, 10, 10S, 20, 30, 40, 40S, 60, 80, 80S, 100, 120, 140, 160, STD, XS (Extra Strong) AND XXS (Double Extra Strong).
BPE – Black Plain End Pipe
BTC – Black Threaded & Coupled
GPE – Galvanized Plain End
GTC – Galvanized Threaded & Coupled
TOE – Threaded One End
Galvanized – Covered with a protective zinc coating on steel to prevent the material from rusting. The process can be hot-dip-galvanizing where the material is dipped in molten zinc or Electro-Galvanized where the steel sheet from which the pipe is made was galvanized during production by an electro-chemical reaction.
Uncoated – Uncoated Pipe
Black Coated – Coated with a dark colored iron-oxide
Red Primed – Red Oxide Primed used as a base coat for ferrous metals, gives iron and steel surfaces a layer of protection
Seamless pipes are derived from solid steel that is in sheet or bar form and is formed into a solid round shape known as “billets” which are then heated and cast over a form such as a piercing rod to create a hollow tube or shell.
SMLS pipe is produced by heating a round billet of steel and then piercing it with a bullet-shaped piercer, over which the steel is stretched. This is followed by rolling and drawing to produce the desired dimensions. The final product is hydrostatically tested, inspected, coated if required, and stenciled with the specification. SMLS pipe is used in high-pressure, most critical locations and under most severe operating conditions. SMLS pipe is supplied according to ASTM Specifications A53, A106, A333, A312, A358, etc., and API 5L pipe
Sizes: 1/8″ (3.175 mm) nominal to 26″ (660.4 mm) OD. Less than 2 3/8″ (60.325 mm) OD is known as pressure tubing that has different dimensional standards (wall thickness and diameter). SMLS pipe, where available, is used in oil and gas production facilities both onshore and offshore (other than transmission lines) less than 26″ (660.4 mm) OD.
Mills produce two types of line pipe, seamless and welded
Seamless pipe is formed from a cylindrical bar of steel. The bar is heated to a high temperature and then a probe is inserted to create a hole through the cylinder. The cylinder is then transferred to rollers which size the cylinder to the specified diameter and wall thickness. A few mills can produce seamless pipe up to 24-in in diameter. For small diameter pipe, seamless pipe is common but unit costs are high and availability is usually limited. As pipe diameter increases, welded pipes are more economical.
In welded pipe, welding is used to close the seam after forming a steel plate or coil into a cylindrical shape. The mill uses ultrasonic and/or radiological inspection methods to ensure the quality of the weld seam and initiates pressure tests on each joint of pipe to levels that exceed the proposed operating pressure. Welded pipe is classified based on how it is formed and the type of welding technique used.
Submerged arc weld (SAW) pipe uses filler metal in welding, whereas electric resistance welded/electric fusion welding (ERW/EFW) are no-filler metal processes. SAW is further classified into longitudinal (or straight) welding (L-SAW) and S-SAW means spiral (or helical) weld tube. Normally, medium diameter straight L-SAW has a single seam, and large diameter L-SAW uses a double seam.
ERW pipe is manufactured using electric current to heat the steel to a point at which the edges melt together to form a bond. This manufacturing process was introduced in the 1920s and utilized low-frequency alternating current to heat the edges, but was found to be vulnerable to seam corrosion and inadequate bonding. Today, high-frequency alternating current is used, also known as contact welding. EFW pipe refers to a process that uses an electron beam to direct kinetic energy to melt the workpiece to form the weld.
PIPs are manufactured using two pipes separated by insulation and are used to maintain the temperature of the fluids to prevent the formation of hydrates, reduce wax deposition, or to reduce the pressure drop by reducing the viscosity of heavy crudes (Cochran, 2003).
Rigid flowlines are manufactured from carbon steel or a high-performance steel alloy, with additional coatings providing corrosion protection and insulation. Flexible flowlines have the same applications as rigid flowlines but are manufactured differently, using composite layers of steel wire and polymer sheathing that provide high flexibility (Box 1.3). A typical 8-in diameter flexible pipe, for example, can be safely bent to a radius of two meters or less. This flexibility is important for risers and flowlines laid on uneven seabeds and permits spooling on a reel or carousel in installation. The preference for using a rigid or flexible flowline is driven by design requirements, installation constraints, cost, schedule, and other factors.
A flexible pipe is a configurable product made up of several independent layers tailored to each development (Fig. 1.21). Flexible pipes are used for risers, flowlines, and jumpers in offshore operations, but because the unit cost is much more expensive than a carbon steel pipe, its use is often limited to special applications and small quantities (Tuohy et al., 2001).
Flexible pipe is manufactured by wrapping several intertwining layers of stainless steel and special polymers. The helically wound steel wires give the pipe its high-pressure resistance and bending characteristics, and since the steel wires are not in direct contact with the conveyed fluid, they do not require the same corrosion resistance as steel pipe. Variation in the choice of materials, the number and order of layers, and manufacturing process depends on the conditions and operating environment.
The components of an unbonded flexible pipe are as follows:
Carcass. The carcass forms the innermost layer and is the conduit for fluid transport. It is commonly made of a stainless steel flat strip that is spirally wound and formed into an interlocking profile. The main function of the carcass is to prevent pipe collapse due to hydrostatic pressure in the annulus.
Internal polymer sheath. The internal polymer sheath provides a barrier to maintain the bore fluid integrity. Common materials used include Polyamide-11 (Rilsan), high-density polyethylene, cross-linked polyethylene, and PVDF.
Pressure armor. The pressure armor, as its name implies, is wound around the internal polymer sheath for protection and is made of interlocking wires or wire strips. Its role is to withstand the hoop stress in the pipe wall caused by the fluid pressure.
Tensile armor. The tensile armor layers are used to resist tensile loads, to support the weight of all the pipe layers, and to transfer the load through the end fitting to the structure. The tensile armor layers are cross-wound in pairs and in high tension applications, say in a deepwater riser, may require the use of four tensile armor layers.
External polymer sheath. The main function of the external sheath is as a barrier against seawater and is often made of the same materials as the internal polymer sheath. External sheaths also provide protection against clashing with other objects during installation.
Other layers. Antifriction and antiwear tape are wound around the armor layers to reduce friction and wear of the wire layers when they rub past each other as the pipe flexes from external loads. Antiwear tapes are used to ensure that the armor layers maintain their wound shape and prevent the wires from twisting out of their configuration, a phenomenon called birdcaging that is a result of hydrostatic pressure causing axial compression in the pipe. Additional layers of material with low thermal conductivity can be applied to obtain specific thermal insulation properties.
Seamless steel pipe for the use of engineering and construction is very widely, it is a hollow steel strip no seams, it is mainly used to transport liquids pipelines, different look and general steel,one of those heavy type steel, it has a strong resistance to corrosion, resistant to general corrosion.
A Seamless steel pipe is extruded and drawn from a billet whereas a welded tube is produced from a strip that is roll formed and welded to produce a tube.
The mechanical properties of the seamless steel tube is a important indicator that ensure seamless pipe end-use properties (mechanical properties), which depends on the chemical composition and heat treatment of steel.
In steel standards, according to different requirements, it provide the tensile properties (tensile strength, yield strength or yield point elongation) and hardness.
① Tensile strength (σb)
During stretching, when pull off the bear most strongly (Fb), divided by the original cross-sectional area (So) from the stress (σ), known as the tensile strength (σb), units of N/mm2 (MPa). It said the maximum capacity resist destruction of metallic materials under tension.
② Yield point (σs)
Yield the phenomenon of metal materials, the sample does not increase during the tensile force (remains constant) and continue elongation stress is known as the yield point. If the force drop occurred, you should distinguish between upper and lower yield point. The yield point of the unit is in N/mm2 (MPa). On yield point (σsu):Sample to yield the maximum stress and force the first drop; lower yield point (σsl): yield minimum stress in the stage when excluding the initial transient effect.
③ Elongation (σ)
In the tensile test, the specimen fractured a percentage of the gauge to increase the length of the original gauge length, called elongation. Σ, said the unit is%.
(4) Cross-section contraction rate (ψ)
In the tensile test, the percentage of the specimen fractured its shrink the diameter at the cross-sectional area of the maximum reduction and the original cross-sectional area is known as section shrinkage. Ψ expressed in%.
⑤ Hardness testing
Metallic materials against hard objects indentation of the surface, known as hardness. accoring to the test method and scope of application, the hardness can be divided into brinell hardness, Rockwell hardness, Vickers hardness, Shore hardness, hardness and high temperature hardness. Commonly used for pipe, Brinell, Rockwell, Vickers hardness of three kinds.
Cold Drawn Seamless Mechanical Tubing (CDS) is a cold drawn 1018/1026 steel tube which offers uniform tolerances, enhanced machinability and increased strength and tolerances compared to hot-rolled products.
Cold drawn steel tube is with hot-rolled steel coil as raw material, and tandem cold rolling pickled to remove oxide scale, its finished rolling hard roll, rolling hard volumes due to the continuous cold deformation caused by cold hardening strength, hardness increased indicators declined tough plastic, stamping performance will deteriorate, which can only be used for simple deformation of the parts.
Rolling hard roll can be used as the raw material of the hot-dip galvanizing plant, hot dip galvanizing line set annealing line. Rolling hard roll weight is generally 6 to 13.5 tons, the coil diameter of 610mm.
Hot-rolled seamless steel pipe production base deformation process can be summarized as three stages: perforation, extension and finishing.
The main purpose of the perforation process is to become a solid round billet piercing hollow shell. Capillary in the specifications, accuracy and surface quality can not meet the requirements of the finished product, further improvements are needed to deform the metal through. The main purpose of the stretching machine is further reduced sectional view (main compression wall) for a larger axial extension, so that the capillary improved dimensional accuracy, surface quality and organizational performance.
After stretching machine rolled steel pipe shortage collectively need further molding mill in order to achieve the requirements of the finished pipe. Rolled steel due to pass in the method widely used in the production of seamless steel tubes.
So far, due to the method pass rolling steel can be divided into two categories: core pension without rolling rolling (hollow body rolling), and with the mandrel. Sizing machines, reducing mill and stretch reducing mill belonging to the hole without mandrel type continuous rolling mills are generally coffin. Its main purpose is to reduce the diameter of the deformation process or sizing get finished steel, the wall thickness of process control, can make thinning, thickening or nearly unchanged.
All the traditional hole-type rolling machine with mandrel belong to extend machine. The main purpose is to reduce the deformation process perforated capillary wall thickness and outer diameter roll passes in the deformation zone and the mandrel posed, for a larger axial extension. At the same time a certain improvement in the organization, performance, accuracy, surface quality.
Before cutting pipe and tubing
No matter the material, measure the diameter of the pipe or tube to be cut to ensure that you use the right-size tube cutter for the job. When determining how to make a straight cut, use a tape measure and a pencil or other writing instrument to mark on the surface where you want to cut. If possible, mark around the circumference of a pipe, especially when cutting with a handsaw. Ensure that a cut is as straight as possible by securing the pipe with a vise, clamp, miter box or even duct tape to keep the length from shifting out of place while cutting.
After cutting pipe and tubing
The production equipment consists of punching machine, automatic pipe rolling machine, coiling machine, sizing machine and reducing machine. The round tube is inserted into the hollow of the thick-walled tube, and the axes of the two rollers form an oblique angle with the rolling line. In recent years, the inclination angle has increased from 6° to 12° to 13° to 17°, increasing the speed of the punch. When producing structural seamless pipe with a diameter greater than 250mm, secondary perforation is used to reduce the thickness of the hollow billet wall. New technologies have also been developed to enhance the perforation process and improve the quality of the capillary.
The production equipment includes punching machine, continuous rolling mill, and tension reduction machine. The round billet is pierced into a hollow billet, then inserted into the mandrel, and continuously rolled by 7 to 9 two-roll mills. After rolling, the mandrel bar is taken out and reheated to reduce tension. In 2014, the annual output of 140mm continuous rolling mills is 0.4 to 600,000 tons, which is 2 to 4 times that of plug mills. The characteristics of this unit are suitable for the production of steel pipes with a diameter of 168mm or less. However, the equipment investment is large, the installed capacity is large, and the processing and manufacturing are complex.
Three-roll rolling production is mainly used to produce thick-walled seamless steel pipes with high dimensional accuracy. The wall thickness accuracy of the seamless steel pipe produced by this manufacturing process can reach plus or minus 5%, and the pipe accuracy is twice that of the seamless steel pipe produced by other methods. This manufacturing technique developed rapidly with the invention of the new three-high skew rolling mill in the 1960s. The new type of rolling mill is characterized by rapidly rotating the inlet rotary rack to change the expansion angle of the tail, thereby preventing the triangle from appearing at the tail, and expanding the ratio of the outer diameter to the wall thickness of the production varieties from 12 to 35, which can not only produce thin-walled seamless welded steel pipes , but also can improve production capacity.
The peeled round base is first perforated or expanded, then heated by induction heating or a salt bath, coated with lubricant, and loaded into the extruder. The metal is squeezed into the pipe through the circular gap between the mandrel and the tip of the pen. This manufacturing process is mainly used for the production of superalloy tubes, specialty tubes, composite tubes and non-ferrous metal tubes. It has a wide range of production but low volumes. The production of extruded tubes has also grown in recent years due to improvements in die materials, lubricants and extrusion speeds.
This manufacturing process is used to produce small-diameter precision-shaped thin-walled low-carbon steel pipes. It is characterized by the use of multi-stage cycle manufacturing technology. In the 1960s, it began to develop in the direction of high speed, multi-line, long stroke and long tube blank. In addition, small roller mills have also been developed, mainly for the production of precision tubes with a thickness of less than 1mm. The cold rolling equipment is complex, the tool processing is difficult, and the specification conversion is not flexible. And usually a combined process of cold rolling and cold drawing is used, that is, cold rolling is used to reduce the wall thickness to obtain larger deformation, and cold drawing technology is used to obtain various specifications.
Seamless steel pipe is regularly used in the transportation of fluids such as water, natural gas, waste and air. It is also regularly required in many high-pressure, high-corrosive environments such as in the oil & gas, power generation and pharmaceutical industries. Some common uses of seamless pipes include: