How to get high quality steel pipes?

What are steel pipes?

Steel pipes are long, hollow tubes that are used for a variety of purposes. They are produced by two distinct methods which result in either a welded or seamless pipe. In both methods, raw steel is first cast into a more workable starting form. It is then made into a pipe by stretching the steel out into a seamless tube or forcing the edges together and sealing them with a weld. The first methods for producing steel pipe were introduced in the early 1800s, and they have steadily evolved into the modern processes we use today. Each year, millions of tons of steel pipe are produced. Its versatility makes it the most often used product produced by the steel industry.

Steel pipes are found in a variety of places. Since they are strong, they are used underground for transporting water and gas throughout cities and towns. They are also employed in construction to protect electrical wires. While steel pipes are strong, they can also be lightweight. This makes them perfect for use in bicycle frame manufacture. Other places they find utility is in automobiles, refrigeration units, heating and plumbing systems, flagpoles, street lamps, and medicine to name a few.

Materials:

The material with which a pipe is manufactured often forms as the basis for choosing any pipe. Materials that are used for manufacturing pipes include:

• Carbon steel
• ASTM A252 Spec Grade 1, Grade 2, Grade 3 Steel Pile Pipe
• Low temperature service carbon steel
• Stainless steel
• Nonferrous metals, e.g. cupro-nickel, tantalum lined, etc.
• Alloy steel

Standards of Steel Tubes and Pipes

1. ASTM
2. ASME
3. UNI
4. GOST
5. European
6. DIN
7. JIS

Our Stainless Steel Pipes meets mainly the following standards:

History

People have used pipes for thousands of years. Perhaps the first use was by ancient agriculturalists who diverted water from streams and rivers into their fields.Archeological evidence suggests that the Chinese used reed pipe for transporting water to desired locations as early as 2000 B.C. Clay tubes that were used by other ancient civilizations have been discovered. During the first century A.D. , the first lead pipes were constructed in Europe. In tropical countries, bamboo tubes were used to transport water. Colonial Americans used wood for a similar purpose. In 1652, the first waterworks was made in Boston using hollow logs.

Development of the modern day welded steel pipe can be traced back to the early 1800s. In 1815, William Murdock invented a coal burning lamp system. To fit the entire city of London with these lights, Murdock joined together the barrels from discarded muskets. He used this continuous pipeline to transport the coal gas. When his lighting system proved successful a greater demand was created for long metal tubes. To produce enough tubes to meet this demand, a variety of inventors set to work on developing new pipe making processes.

An early notable method for producing metal tubes quickly and inexpensively was patented by James Russell in 1824. In his method, tubes were created by joining together opposite edges of a flat iron strip. The metal was first heated until it was malleable. Using a drop hammer, the edges folded together and welded. The pipe was finished by passing it through a groove and rolling mill.

Russell’s method was not used long because in the next year, Comelius Whitehouse developed a better method for making metal tubes. This process, called the butt-weld process is the basis for our current pipe-making procedures. In his method, thin sheets of iron were heated and drawn through a cone-shaped opening. As the metal went through the opening, its edges curled up and created a pipe shape. The two ends were welded together to finish the pipe. The first manufacturing plant to use

this process in the United States was opened in 1832 in Philadelphia.

Gradually, improvements were made in the Whitehouse method. One of the most important innovations was introduced by John Moon in 1911. He suggested the continuous process method in which a manufacturing plant could produce pipe in an unending stream. He built machinery for this specific purpose and many pipe manufacturing facilities adopted it.

While the welded tube processes were being developed, a need for seamless metal pipes arouse. Seamless pipes are those which do not have a welded seam. They were first made by drilling a hole through the center of a solid cylinder. This method was developed during the late 1800s. These types of pipes were perfect for bicycle frames because they have thin walls, are lightweight but are strong. In 1895, the first plant to produce seamless tubes was built. As bicycle manufacturing gave way to auto manufacturing, seamless tubes were still needed for gasoline and oil lines. This demand was made even greater as larger oil deposits were found.

As early as 1840, ironworkers could already produce seamless tubes. In one method, a hole was drilled through a solid metal, round billet. The billet was then heated and drawn through a series of dies which elongated it to form a pipe. This method was inefficient because it was difficult to drill the hole in the center. This resulted in an uneven pipe with one side being thicker than the other. In 1888, an improved method was awarded a patent. In this process the solid billed was cast around a fireproof brick core. When it was cooled, the brick was removed leaving a hole in the middle. Since then new roller techniques have replaced these methods.

The Manufacturing Process of steel pipe

Steel pipes are made by two different processes. The overall production method for both processes involves three steps. First, raw steel is converted into a more workable form. Next, the pipe is formed on a continuous or semicontinuous production line. Finally, the pipe is cut and modified to meet the customer’s needs.

Ingot production

• 1 Molten steel is made by melting iron ore and coke (a carbon-rich substance that results when coal is heated in the absence of air) in a furnace, then removing most of the carbon by blasting oxygen into the liquid. The molten steel is then poured into large, thick-walled iron molds, where it cools into ingots.
• 2 In order to form flat products such as plates and sheets, or long products such as bars and rods, ingots are shaped between large rollers under enormous pressure.

Producing blooms and slabs

• 3 To produce a bloom, the ingot is passed through a pair of grooved steel rollers that are stacked. These types of rollers are called “two-high mills.” In some cases, three rollers are used. The rollers are mounted so that their grooves coincide, and they move in opposite directions. This action causes the steel to be squeezed and stretched into thinner, longer pieces. When the rollers are reversed by the human operator, the steel is pulled back through making it thinner and longer. This process is repeated until the steel achieves the desired shape. During this process, machines called manipulators flip the steel so that each side is processed evenly.
• 4 Ingots may also be rolled into slabs in a process that is similar to the bloom making process. The steel is passed through a pair of stacked rollers which stretch it. However, there are also rollers mounted on the side to control the width of the slabs. When the steel acquires the desired shape, the uneven ends are cut off and the slabs or blooms are cut into shorter pieces.

Further processing

• 5 Blooms are typically processed further before they are made into pipes. Blooms are converted into billets by putting them through more rolling devices which make them longer and more narrow. The billets are cut by devices known as flying shears. These are a pair of synchronized shears that race along with the moving billet and cut it. This allows efficient cuts without stopping the manufacturing process. These billets are stacked and will eventually become seamless pipe.
• 6 Slabs are also reworked. To make them malleable, they are first heated to 2,200° F (1,204° C). This causes an oxide coating to form on the surface of the slab. This coating is broken off with a scale breaker and high pressure water spray. The slabs are then sent through a series of rollers on a hot mill and made into thin narrow strips of steel called skelp. This mill can be as long as a half mile. As the slabs pass through the rollers, they become thinner and longer. In the course of about three minutes a single slab can be converted from a 6 in (15.2 cm) thick piece of steel to a thin steel ribbon that can be a quarter mile long.
• 7 After stretching, the steel is pickled. This process involves running it through a series of tanks that contain sulfuric acid to clean the metal. To finish, it is rinsed with cold and hot water, dried and then rolled up on large spools and packaged for transport to a pipe making facility.

Pipe making

• 8 Both skelp and billets are used to make pipes. Skelp is made into welded pipe. It is first placed on an unwinding machine. As the spool of steel is unwound, it is heated. The steel is then passed through a series of grooved rollers. As it passes by, the rollers cause the edges of the skelp to curl together. This forms an unwelded pipe.
• 9 The steel next passes by welding electrodes. These devices seal the two ends of the pipe together. The welded seam is then passed through a high pressure roller which helps create a tight weld. The pipe is then cut to a desired length and stacked for further processing. Welded steel pipe is a continuous process and depending on the size of the pipe, it can be made as fast as 1,100 ft (335.3 m) per minute.
• 10 When seamless pipe is needed, square billets are used for production. They are heated and molded to form a cylinder shape, also called a round. The round is then put in a furnace where it is heated white-hot. The heated round is then rolled with great pressure. This high pressure rolling causes the billet to stretch out and a hole to form in the center. Since this hole is irregularly shaped, a bullet shaped piercer point is pushed through the middle of the billet as it is being rolled. After the piercing stage, the pipe may still be of irregular thickness and shape. To correct this it is passed through another series of rolling mills.

Final processing

• 11 After either type of pipe is made, they may be put through a straightening machine. They may also be fitted with joints so two or more pieces of pipe can be connected. The most common type of joint for pipes with smaller diameters is threading—tight grooves that are cut into the end of the pipe. The pipes are also sent through a measuring machine. This information along with other quality control data is automatically stenciled on the pipe. The pipe is then sprayed with a light coating of protective oil. Most pipe is typically treated to prevent it from rusting. This is done by galvanizing it or giving it a coating of zinc. Depending on the use of the pipe, other paints or coatings may be used.

Quality Control

A variety of measures are taken to ensure that the finished steel pipe meets specifications. For example, x-ray gauges are used to regulate the thickness of the steel. The gauges work by utilizing two x rays. One ray is directed at a steel of known thickness. The other is directed at the passing steel on the production line. If there is any variance between the two rays, the gauge will automatically trigger a resizing of the rollers to compensate.

Pipes are also inspected for defects at the end of the process. One method of testing a pipe is by using a special machine. This machine fills the pipe with water and then increases the pressure to see if it holds. Defective pipes are returned for scrap.

How to get high quality steel pipes?

Characteristics of welded steel pipe and seamless steel pipe

Molding process of the steel pipe
1, welded steel pipe is welded, it is cut into by the steel strip narrow steel strip, and then wrapped into a tubular shape with the cold mold. And special welding then a pipe seam welding. Outside welds polished bright. Within the burr of the pipe is not to fight. The only precision welded to fight within the burr.
2, seamless steel pipe is cylindrical ingot hot pull into a tube, so can not see the weld. 

Use classification of steel pipe:
1, water gas pipe is commonly used welded steel pipes, transport fluid and gas called, to feel the pressure, so are relatively thick wall. Older know, rich from poor, a lot of it is called with the characteristics of the times, not too seriously. Original which money galvanized Yeah, two brush paint on the line. Black Well, call it black iron pipe.
2, the conduit is to wear a wire and thin-walled tube. At that time only the standard, no one production. In fact, the eighties and nineties of gas pipes with water.
3, galvanized iron pipe is galvanized welded steel pipe. Galvanized inside and outside, water can be transported. Let Electric used when threading. General are relatively thin wall. Now on the market is poor. Elbow bend angle to blast hole.

Anti-corrosion classfication of steel pipe:
Steel pipe: steel pipe is open at both ends and having a hollow cross-section and their relatively large length, and the vicinity of the steel can be divided, according to the production method of seamless and welded steel pipe, pipe specifications Dimensions (such as diameter or side length) and wall thickness, a very wide range of sizes, from a small diameter capillary tube until the large-diameter up to several meters in diameter. The steel pipe can be used for pipes, thermal equipment, industrial machinery, petroleum exploration, container, chemical industry and for special purposes.
 
Seamless steel pipe: seamless steel pipe is made from a single piece of metal on the surface of steel pipe joints. Production methods can be divided into hot-rolled pipes, cold rolled tubes, cold drawn tubes, extruded tube. Can be divided into two kinds of round and shaped cross-sectional shape. The seamless pipe of the maximum diameter of 650 mm (enlarged diameter tubes), a minimum diameter of 0.3 mm (capillary). According to different thickness can be divided into thick-walled pipes and thin-walled tube. Seamless pipe is mainly used for the petroleum exploration tube, petrochemical cracking tubes, boiler tubes, the bearing tube as well as the automotive, aerospace steel and other high-precision structure.

Welded steel pipe: welded steel pipe refers to the bending deformation of the steel strip or steel sheet as round, square and other shapes and then welded into the steel pipe, the surface of the seam. According to the different welding methods can be divided into the arc welded pipe, high or low frequency electric resistance welded pipe, gas pipe, stove pipe, Bundy tube. Weld shape can be divided into Longitudinal and spiral welded pipe. 
Welded steel pipe used for oil drilling and machinery manufacturing. The furnace can be used as a water pipe and gas pipe, large diameter welded pipe used for high-pressure oil and gas transmission; spiral welded pipe for oil and gas transmission pipe piles, piers. The welded steel pipe is lower than the cost of seamless steel, high production efficiency.

Quality testing for seamless pipe

Seamless steel pipe quality testing is a very important step, and for its detection method is also very particular to now all three – ultrasonic testing, eddy current testing, magnetic flux leakage testing, specific circumstances are as follows:

The ultrasonic testing

Ultrasonic inspection of seamless pipes

For steel quality inspection, ultrasonic testing, including for the purpose of detected defects ultrasonic testing and ultrasound to measure the dimensions for the purpose of measuring. Wider application of the former, automated testing, manually testing; latter application, generally manual measurement.

Non-destructive testing

Non-destructive testing

Nondestructive Testing, shorted for NDT, is a widely-used method in pipeline inspection. It is a process of testing, inspecting and evaluating the quality and characteristics of the material without damaging the pipeline itself or affecting the later regular work of the pipe. In other words, after NDT testing, the part can still be put into practical use. NDT utilizes the changes in heat, sound and magnets caused by abnormal inner structure or flaws to inspect the internal and external defects of the material.

The common inspection methods of NDT are visual testing (VT), ultrasonic testing (UT), radiographic testing (RT), hydrostatic testing. Anson International co, ltd uses ultrasonic testing (UT) and hydrostatic testing to inspect its line pipes.

In order to verify the mechanical properties of seamless steel pipe to meet the requirements of the standard, the test sample of seamless steel pipe mechanical performance should be prepared carefully. Mechanical property test includes tensile strength, yield strength, elongation, impact energy and so on. Process performance test includes flattening test, flaring test, hydrostatic testing, curling trials, cold bend test, perforation test. These test items are based on different standards and different uses of seamless steel tubes.

The magnetic flux leakage testing

The magnetic flux leakage testing is a non-destructive testing technology based on ferromagnetic material magnetic changes. When the ferromagnetic material is magnetized, and generates a leakage magnetic field due to the presence of defects on the workpiece surface, and therefore, through the detection of the magnetic flux leakage can be found in defects in the large caliber Seamless thermal expansion material. Steel pipe magnetic flux leakage testing technology is divided into two kinds of magnetic particle inspection method and magnetic field measurement method. The former is simple, but requires the naked eye to observe the magnetic marks, it is difficult to automate. The latter despite the device complexity, high cost and the operation is difficult, but it is picked up by sensors leakage magnetic field information, and therefore easy to automate testing suitable for the automatic inspection of large quantities of steel pipe. Therefore, under normal circumstances, no special instructions, usually refers to the magnetic field of the magnetic flux leakage testing of steel pipes assay.

Eddy current testing

ECT-620 Eddy Currentautomatic Test System

Eddy current testing method is more wide range of applications in the industrial field of non-destructive testing methods. It is based on the theory of electromagnetic induction, without any coupling agent can 100% fast automatic detection of the specimen. it is even more powerful tool for the rapid detection of bulk. Therefore, it is even not limited to the large caliber thermal expansion seamless steel pipe, has become a necessary means of various types of steel quality inspection. Automatic eddy current testing method is mainly suitable for quality inspection of steel pipes a little probe testing method and through-probe testing method two.

The former method of using the high-speed rotation of the point probe to detect longitudinal defects in the steel pipe, the detection speed is determined by the quantity of the probe and the speed of rotation, in general, is relatively slow, and the latter through the probe to detect the steel pipe transverse defects, this method is simple, and the testing speed (generally up to 60m/min), Further, since the eddy current flaw detection method is particularly sensitive pair of through holes, the related standards of the main method is to replace the pipe hydrostatic test.

Pipe connection

Pipe connection is varied, the commonly used have Butt weld, Flanged, Threaded, Socket weld, Glued, Brazed and Grooved end.

You assign connection types in the Connector Properties dialog box as you build fittings content using the Content Builder (see Adding Connectors to a Parametric Fitting). Assigned connection types are then displayed on the Connection Assignments tab of the Pipe Layout Preferences dialog box.

Unthreaded Connections are not threaded, must be either welded or bolted together. The following table shows the different orientations of pipe connection types:

Butt weld:
A butt weld is two pipes lined up with one another and welded along the contact edge to create a seal.

No extra objects are added.

Fittings and pipe segments connect directly to each other.

Flanged All types

A flange is a plate or ring that is attached to a pipe. Two flanged pipe then create a tight seal by being bolted together.

• Fitting to pipe: Flanges are typically included on fittings. A separate flange is added to the pipe segment.
• Pipe to pipe: A separate flange is added to each pipe end to create the connection.
• Fitting to fitting: Fittings with inherent flanges connect directly to each other. No separate flanges are added to the connection.

Threaded, Socket weld, Glued, Brazed

The pipe is the male fitting and the socket is equivalent to a female fitting. To provide a tight seal it is best to line the outside of the pipe and the inside of the socket with a sealant.

Socket welds require a pipe and socket connection.

• Fitting to pipe: Pipe segments typically have inherent male ends, and fittings are typically female. The pipe inserts directly into the fitting.
• Pipe to pipe: A female coupling is inserted between the pipe segments.
• Fitting to fitting: Fittings connect directly to each other.

Grooved end

A grooved end fitting has a groove or shoulder along the edge. This fittings groove allows for a seal without the need for welding.

• Fitting to pipe: Fittings and pipe segments are considered to have grooved ends that are ready to accept a coupling. A coupling is added to connect the fitting and pipe.
• Pipe to pipe: A coupling is added to connect the pipe segments.
• Fitting to fitting: A coupling is added to connect fittings.

Note:

The Piping domain includes a connection type called Same Connection. When Same Connection is configured for a pipe object that is attached to a hub, connector 1 inherits the connection type of the connection type on connector 2 of the attached hub.

Seamless pipe vs Welded pipe

Concentricity: seamless pipe manufacturing process is at a temperature of 2200 ° F in a stainless steel billet punching out a hole in this high temperature tool steel by stamping and drawing becomes soft and spirally from the Kong Zhongcheng shaped out. Such uneven wall thickness of the pipe and the eccentric high. 

Thus ASTM standard allow the wall thickness difference of seamless pipes is bigger than the welded pipes’. Slotted tube is made by precision cold-rolled plates (4-5 feet) per roll width. These cold rolled sheet is usually the maximum wall thickness of 0.002 inches. The steel sheet was cut to the width πd where d is the outer diameter of the pipe. Slit pipe wall thickness tolerances are small, and the entire circumference of the wall thickness is very uniform. 

Welding performance: general tube and seamless pipe has certain differences on the chemical composition. The production of seamless pipe steel composition is only the basic requirements to meet ASTM. While the production of the chemical composition of the steel slotted tube containing suitable for welding. For example, silicon, sulfur, manganese, oxygen and the triangle of ferrite and other elements at a certain proportion of mixed can be generated during the soldering process the solder melting and an easy transfer of heat, so that the entire weld penetration. Lack of the above chemical composition of the steel pipe, such as seamless tubes, in the welding process will produce a variety of factors of instability, is not easy to weld and welding impervious. 

Grain size: Typically, Metal grain size and heat treatment temperature and keep the same temperature is related with the time. Therefore, the annealed the same seam pipe and seamless pipe grain size. If there is a seam tube with a minimum of cold treatment, the grain size of the weld seam is less than the grain size of the weld metal, otherwise, the grain size is the same. 

Strength: the strength of the pipeline depends on the alloy composition, and thus contain the same alloy and the same heat treatment of seamless pipe and slotted tube essentially are consistent strength. After tensile testing and three-dimensional vibration test, slotted tube tear occur almost exclusively in a place away from the welding point or heated area. This is because fewer impurities and a slightly higher nitrogen content of the weld, and thus the strength of the weld at better than the other region. However, the ASME Boiler and Pressure Vessel Association seam pipe can only bear 85% of the allowable pressure, which is mainly due to the data collected as early as today has improved welding equipment. ASME regulations 100% seam tube can withstand the allowable pressure by ultrasonic testing. Similarly, Europe and Asia also provides seam pipe to ensure the quality of its welding performance by means of eddy current testing, eddy current testing require the approval of the legal procedures and licenses held by institutions. Trent eddy current testing by the permission of the Swedish Ministry of Power. ASME small current loss is based on the quality performance of the slotted tube. 

Corrosion resistance: good or bad corrosion resistance also depends on the composition of the alloy. Full heat treatment of a seamless pipe with the same chemical composition and by the corrosion resistance of the slit pipe is consistent. The ASTM provides supplementary tests proved weld corrosion resistance equal to or better than the metal being welded. In acidic chloride environment, not fully heat at the welding of the slit pipe corrosion will be accelerated, but only the needs of the corrosion test, in fact, the environment is not so bad. Bending and extension: the extension of the welding prescribed by ASTM following tests to verify: bent 45 ° bent to 90 °, flattened along the weld; then turned the seam pipe Repeat the above steps to make the weld The curved inner diameter is 180 °. Weld quality by the standards is not allowed to appear in the case of 40-fold magnification tear or intergranular separation. Pipe bending radius is controlled by the composition of the alloy, the general minimum bend radius of 2D. The ideal welding condition is a seam in a neutral or compressed state. Moreover, the pipes should be an annealing treatment in order to reduce its hardness, thereby improving the bending performance.

Source: Network Arrangement – China Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.pipelinedubai.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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References:

1. http://www.madehow.com/Volume-5/Steel-Pipe.html
2. https://en.wikipedia.org/wiki/Piping
3. https://www.yaang.com