A Quick Guide to Seamless Pipes including its Manufacturing Processes

What is the Manufacturing Process for Seamless Pipes?

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. 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.

Steel Pipe Country of Origin Steel pipe is made by mills all around the world and traded in different countries. Some of the big names in pipe industry are US Steel, Arcelor Mittal, Nucor Corp, ThyssenKrup, Vallourec, Hebei Iron and Steel Group, Posco, Jiangsu Shagang, Ulma Piping, Shultz USA and Webco, Nippon Steel & Sumitomo Metal Corporation (NSSMC), Baosteel, Wuhan Iron and Steel Group, Tata Steel Group, HYUNDAI Steel Company, JFE Steel Corporation, etc.

Types of Steel Pipes and Tubular Goods and Their Uses in the Piping Industry As manufacturing processes have evolved and become more complex, steel buyers’ options have expanded to suit many unique needs across a variety of industries.

But not all types of steel are equal. Piping industry professionals can become better buyers by examining the types of steel available today and understanding why some steels make great pipe and others do not.

There are six types of pipes and tubular goods.

Standard Pipe: There are three different types of standard metal pipes ­ welded (ERW Pipe), seamless pipe, and galvanized pipe. They represent 10% of all tubular products.

Line Pipe: Used primarily in Oil and Gas Applications. Line pipe includes ERW, FW, SAW and DSAW Pipe.

They are manufactured to API 5L Specification and are available in X42, X50, X60 etc. grades. They represent 21% of all tubular products.

Oil Country Tubular Goods (OCTG): This includes drill pipes, tubing and casing. It is used in drilling and completion of Oil and Gas wells. OCTG are produced by ERW and Seamless manufacturing. OCTG represent 35% of all tubular goods.

Pressure Tubing: used for industrial and pressure application. Pressure tubing is produced using seamless manufacturing. They represent 2% of all tubular goods.

Mechanical tubing: used for mechanical and structural application and is produced by ERW and seamless manufacturing. They conform to ASTM specification. Mechanical Tubing represents 17% of all tubular goods.

Structural Tubing: used for support or retention purpose. This tubing can be round or square and are produced by ERW manufacturing. They are used for fences, construction and other misc. support needs. They represent 15% of all tubing goods.

This rundown should also help: Carbon steel Steel is created when carbon is added to iron, which is relatively weak on its own. In modern industry, carbon is the most prominent additive to a ferrous material, but alloying elements of all sorts are common.

In fact, alloying elements are common even in piping products still considered to be carbon steel.

According to the American Iron and Steel Institute (AISI), ferrous material is designated as carbon steel when its core makeup is specified to include no more than 1.65 percent manganese, 0.60 percent silicon and 0.60 percent copper and when no minimum content is specified for other alloying elements.

Carbon steel pipe enjoys wide use across many industries due to its strength and ease of workability. Because it contains relatively few alloying elements, and in low concentrations, carbon steel pipe is relatively inexpensive.

However, it isn’t suited for extreme temperature or high­pressure service because the lack of alloying elements makes it less resistant to the accompanying stresses.

Alloy steel Alloy steels are what they sound like: Steels that include specified amounts of alloying elements. Generally, alloying elements make steels stronger and more resistant to impact or stress. While the most common alloying elements include nickel, chromium, molybdenum, manganese, silicon and copper, many others are used in the production of steel.

There are countless combinations of alloys and concentrations in use in industry, with each combination designed to achieve specific qualities.

High­alloy types of steel are favored in the piping industry for service in extreme conditions, whether it be in hot or cold conditions or subject to rough use. That’s because the combination of chemistry and proper heat treating can yield strong yet ductile pipe that can take a beating.

The oil & gas and power generation industries often favor alloy pipe due to its toughness.

Alloying elements also impart increased corrosion resistance to steel pipe. That makes it a leading choice for chemical companies as well.

Stainless steel The term is a bit of a misnomer. There’s no one combination of iron and alloying elements that makes stainless steel what it is. Instead, stainless steel refers to the fact that products made from it do not rust.

Alloys in stainless steels can include chromium, manganese, silicon, nickel and molybdenum.

These alloys work together to interact with oxygen in water and air to quickly form a thin but strong film over the steel that prevents further corrosion.

Naturally, stainless steel pipe is used in any industry where corrosion protection is necessary.

While stainless steel pipe is essentially alloy pipe by another name, it is not well suited for extreme service unless it’s been appropriately heat treated to increase strength and impact resistance.

Due to its aesthetic appeal, stainless steel is often chosen if pipe must be visible in public or professional settings.

Tool steel Tool steels are what turn other types of steel into products or equipment used in industry. They must be incredibly strong, tough, ductile and resistant to corrosion. They also must be able to retain cutting edges and maintain their shape in high temperatures. To achieve those qualities, these steels contain very high concentrations of alloying elements and are precisely heat treated.

Sometimes called super­alloys, tool steels are not well­suited for piping products. For one thing, incorporation of higher quantities of alloys makes tool steels more expensive to produce. For another, the amount of alloying elements present in tool steels makes them harder to form into piping products. Finally, pipes don’t need cutting edges.

It’s cheaper and easier to use comparatively softer, lower­alloy steels to form pipe and then heat treat up to a specified hardness.

Metallica has it all. Plus, our skilled experts are trained to gather detailed information to ensure you get exactly the pipe you need, when you need it. If you need help placing an accurate order, let us know.

DESIGN There are two types of steel pipe, one is seamless and another has a single welded seam along its length. Both have different uses. Seamless tubes are typically more light weight, and have thinner walls. They are used for bicycles and transporting liquids. Seamed tubes are heavier and more rigid. The have a better consistency and are typically straighter. They are used for things such as gas transportation, electrical conduit and plumbing. Typically, they are used in instances when the pipe is not put under a high degree of stress.

Certain pipe characteristics can be controlled during production. For example, the diameter of the pipe is often modified depending how it will be used. The diameter can range from tiny pipes used to make hypodermic needles, to large pipes used to transport gas throughout a city. The wall thickness of the pipe can also be controlled. Often the type of steel will also have an impact on pipe's strength and flexibility. Other controllable characteristics include length, coating material, and end finish.

RAW MATERIALS USED The primary raw material in pipe production is steel. Steel is made up of primarily iron. Other metals that may be present in the alloy include aluminum, manganese, titanium, tungsten, vanadium, and zirconium. Some finishing materials are sometimes used during production. For example, paint may be used if the pipe is coated. Typically, a light amount of oil is applied to steel pipes at the end of the production line. This helps protect the pipe. While it is not actually a part of the finished product, sulfuric acid is used in one manufacturing step to clean the pipe.

The integrity of a piping system depends on the considerations and principles used in design, construction and maintenance of the system. Piping systems are made of components as pipes, flanges, supports, gaskets, bolts, valves, strainers, flexible and expansion joints. The components can be made in a variety of materials, in different types and sizes and may be manufactured to common national standards or according a manufacturers proprietary item.

Some companies even publish their own internal piping standards based upon national and industry sector standards.

Quality Control A variety of measures are taken to ensure that the finished steel pipe meets specifications. For example, x­ray 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.

The ASTM standard covers various types of steel pipes, tubes and fittings for high­temperature services, ordinary use and special applications such as fire protection use.

Understanding steel grades for piping procurement

As industrial processes and applications have matured, industry organizations have developed unique classifications and specifications for the pipe destined for service in those sectors. There are lots of overlap among the organizations’ published specs, and likely lots of confusion as well.

Buyers can improve their purchasing experience by learning more about how grades of steel are designated for piping and by understanding all the information that should be included on a purchase order.

ASTM and ASME Both the American Society of Testing and Methods (ASTM) and the American Society of Mechanical Engineers (ASME) publish piping specs. ASTM and ASME pipe designations for grades of steel are very similar.

For example, A106 B is a spec published by ASTM (the ASME spec would be SA106 B). The “A” designates a ferrous material. ‘106’ is an arbitrary number that designates it as a seamless carbon steel pipe suited for high­temperature service. Then, grades (such as A, B or C) are

assigned that indicate certain characteristics of the steel based on differences in its chemical makeup and mechanical properties.

Pipe sizes are described by using a pipe chart (ANSI/ASME B36.10 and API5L) that includes the outside diameter and wall thickness. The outside diameter can be referred by the nominal pipe size (NPS) or the actual dimension in inches and the wall by stating the schedule or the actual thickness in inches.

Note that while ASTM and ASME specs are largely identical, an important difference is that pipe meant for use in pressure systems sometimes requires different or additional quality tests before it complies with the ASME standard.

American Piping Products stocks a full range of A/SA106 and A/SA 53 carbon steel pipe.

AISI and SAE The American Iron and Steel Institute (AISI) and the Society of Automotive Engineers (SAE) share a numbering system to classify steels. AISI/SAE designations only describe the chemical makeup of steel. They do not include manufacturing, heat treating or testing information.

Using 1020 steel as an example, the first digit expresses the steel as a plain carbon steel. The second digit indicates there are no added alloys. The last two digits indicate the steel has around 0.20 percent carbon content.

For another example, popular steel in the piping industry is 4130. The ’41’ indicates the steel contains chromium and molybdenum alloys. The ’30’ indicates the steel has around 0.30 percent carbon content.

Again, AISI/SAE designations only classify steels. For example, a buyer who says, “I need 100 feet of 4130” has not provided enough information. The buyer also needs to note specific production and testing information found in an ASTM or ASME spec to get exactly the pipe they need.

API Pipe for use in the oil & gas industry are classified by the American Petroleum Institute’s (API) system.

API 5L is the most common standard to which line pipe in the oil and natural gas industry is rated. Because that’s merely a standard, additional information is needed to ensure purchase orders are executed accurately.

API 5L pipe is broken down into PSL1 and PSL2 delivery conditions; those conditions are further broken down into pipe grades, i.e. Grade B, X42, X52, X65, etc. Buyers should include the combination of the overarching standard, the delivery condition and the grade for the API5L pipe they need.

Study grades of steel Buyers who place incomplete or inaccurate orders put their operations at risk of delays or cost overruns. When in doubt, consult with an engineer and refer to the industry standards that govern your application. Also be aware of other factors that play into your purchase: 

What manufacturer restrictions are in place that may impact your order?

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Are there any origins restrictions that you need to follow when buying?

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What pipe lengths and end finishes do you need?

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Are there specific chemistry requirements needed for the application?

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Are there age restrictions that may impact your order for export?

Suppliers need detailed purchase orders to ensure you get the right pipe the first time.

Grading the Pipe Pipe is graded is strength in terms of pressure. Each type of pipe is designated with a code like API5L PSL2. There are then many grades for each standard ASTM Code which determine a minimum yield strength and minimum tensile strength. The grades include grade 1, grade 2, grade 3, then grade A, grade B, grade C and continue on to grade X and there is minimum and maximum pressure rating each grade. For instance with API5L PSL2 grade 1 ASTM 252 pipe the minimum yield strength is 30,000 PSI and minimum tensile strength is 50,000 PSI. Carbon Steel Pipes Carbon steel pipes like regular steel pipes are graded using the same methods. The ratings include temperature and pressure levels for A106 Grade B carbon steel pipes, for instance.

These pipes are generally classified under the ANSI/ASME standards codes.

Each pipe has this separate code based on the ANSI/ASME standards, for instance B 31.1.

That is the ANSI code for a particular type of pipe. The grade then specifies how much pressure and the temperature the pipe is made to withstand.

PIPING CODES AND STANDARDS Piping codes and standards from standardization organizations as  ANSI  ASME  ISO  DIN And others; are the most common used.

The difference between piping codes and piping standards can be summarized: Piping Codes Piping codes defines the requirements of design, fabrication, use of materials, tests and inspection of pipes and piping systems ­ what you need to do.

A code has a limited jurisdiction defined by the code. A code is not law, but can be adopted into law.

Example: "ASME B31.1 (2007), Code for Pressure Piping, Section on Power Piping, as required by the laws of the States of Arizona, Alaska, Colorado, Illinois, Iowa, Kansas, Michigan, Missouri, Minnesota, Nebraska, Nevada, North Dakota, Ohio, Oregon, Wisconsin, et. Alia."

Piping Standards Piping standards define application design and construction rules and requirements for piping components as flanges, elbows, tees, valves etc. ­ how to do it.

A standard has a limited scope defined by the standard.

MANUFACTURING PROCESS OF SEAMLESS PIPES

Seamless pipe is Strongest amongst all pipes type as it has a Homogeneous structure throughout pipe length. Seamless pipes are manufactured in a verity of size and schedule.

However, there is a Restriction on the manufacturing of large diameter pipe. Seamless pipes are widely used in the manufacturing of pipe fittings such as bends, elbows, and tees.

Various Seamless Manufacturing process are: 1.

2.

3.

4.

Mandrel Mill Process Mannesmann Plug Mill Pipe Manufacturing Process Forged Seamless Pipe Manufacturing Process Extrusion Processes

They are explained below:­ 1. Mandrel Mill Process: ­ In the Mandrel Mill Process, a solid round (billet) is used. It is heated in a rotary hearth heating furnace and then pierced by a piercer. The pierced billet or hollow shell is rolled by a mandrel mill to reduce the outside diameter and wall thickness which forms a multiple length mother tube. The mother tube is reheated and further reduced to specified dimensions by the stretch reducer. The tube is then cooled, cut, straightened and subjected to finishing and inspection processes before shipment.

2. Mannesmann Plug Mill Process: ­ In the Plug Mill Process, a solid round (billet) is used.

It is uniformly heated in the rotary hearth heating furnace and then pierced by a Mannesmann piercer. The pierced billet or hollow shell is roll reduced in outside diameter and wall thickness. The rolled tube simultaneously burnished inside and outside by a reeling machine. The reeled tube is then sized by a sizing mill to the specified dimensions. From this step the tube goes through the straightener. This process completes the hot working of the tube. The tube (referred to as a mother tube) after finishing and inspection, becomes a finished product.

3. Forged Seamless Pipe Manufacturing Process: ­ Steel Products may be manufactured either by casting or forging steel. Forged Seamless Pipe Manufacturing Process implies the application of mechanical forces to heated solid blocks of steel (such as ingots and/or billets) that are shaped into desired products permanently. They require the application of high temperatures to steel raw materials (to liquefy or make it malleable).Once this forging is done, pipe is machined to achieve final dimension.

Forged pipes are generally used for the steam header. This process is used to manufacture large diameter seamless pipe that cannot be manufactured using traditional methods.

4. Extrusion Processes: ­ Metal extrusion is a metal forming process in which a work piece, of a certain length and cross section, is forced to flow through a die of a smaller cross sectional area, thus forming the work to the new cross section. The length of the extruded part will vary, dependent upon the amount of material in the work piece and the profile extruded. Numerous cross sections are manufactured by this method. The cross section produced will be uniform over the entire length of the metal extrusion. Starting work is usually a round billet, which may be formed into a round part of smaller diameter,

a hollow tube, or some other profile. Metal extrusion is a forming process, like other metal forming processes; it can be performed either hot or cold.

PIPE MAKING PROCESS 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 semi continuous 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 carbon­rich 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, thick­walled 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 "two­high 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 white­hot. 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.