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In pipeline pigging, it is very necessary to understand the classification of pipes. Because only by understanding the performance and material of different pipes. So we can choose the type of pig according to this.

There are many classification methods for pipes. Which has metal pipes, non-metal pipes, and steel-lined non-metal composite pipes according to material classification.

Non-metallic pipes mainly include rubber pipes, plastic pipes, asbestos cement pipes, graphite pipes, glass steel pipes, etc. The use of non-metallic pipes is smaller than that of metal pipes. In most petrochemical plants, metal pipes account for more than 85% of all process pipeline installation projects.

So now, let me introduce you to metal pipes.



1. Welded Steel Pipe

Pipelines Pigging

Welded steel pipes, also known as seamed steel pipes, are generally formed by coil welding of steel plates or steel strips.

Classification by surface treatment of pipes

Firstly, they have galvanized pipes and non-galvanized pipes. The one with the galvanized surface is white, also known as white iron pipe or galvanized steel pipe. The non-galvanized surface is an ordinary welded steel pipe, also known as a black iron pipe.

And then, Galvanized welded steel pipes often work for pipelines that require relatively clean conveying media. Such as domestic water, purified air, instrument air, etc. Non-galvanized welded steel pipes can work for transporting steam, gas, compressed air, condensate, etc.

According to user requirements, welded steel pipes have two types when they leave the factory.

One is with threaded pipe ends and the other is with unthreaded pipe ends. The length of each pipe is 4 to 9m for welded steel pipes with threaded ends, and the length of each pipe for welded steel pipes without threads is 4 to 12m.

Welded steel pipes are classified according to the thickness of the pipe wall

Then, it has thin-walled steel pipes, thickened steel pipes, and ordinary steel pipes. The most used steel pipe is the ordinary steel pipe, and its test pressure is 2.0MPa. The test pressure of the thickened steel pipe is 3.0MPa。

There are many connection methods for welded steel pipes

It includes threaded connection, flange connection, and welding. The flange connection has a threaded flange connection and welded flange connection. Welding methods have gas welding and arc welding。

Specification range of commonly used welded steel pipes

For the nominal diameter of 6 ~ 150mm


2. Seamless Steel Pipe

Pipe and Fittings in Pipelines PiggingSeamless steel pipes are the pipes with the largest amount and the largest variety of specifications among industrial pipes.。

Classified as

There are two categories of seamless steel pipes and special seamless steel pipes for fluid transportation. The former is a steel pipe commonly working for process pipes. The latter such as boiler special steel pipe, cracking furnace pipe and heat exchanger steel pipe, etc.。

Classified by material

Carbon seamless steel pipe, chrome-molybdenum seamless steel pipe, and stainless, acid-resistant seamless steel pipe。

Classification by nominal pressure

Low pressure (0≤1.0MPa), medium pressure (1.0<10MPa=, high pressure (≥10MPa)。

Process pipelines commonly work for fluid transportation, using seamless steel pipes.

Categorized as follows

Carbon seamless steel pipe

Commonly used manufacturing material models are No. 10, No. 20, and 16Mn steel。

The specification range is: hot rolled outer diameter φ32~630mm, cold drawn outer diameter φ6~200mm, single tube length 4~12m, allowable operating temperature is -40~450℃。

It widely works to transport various media that are not corrosive to steel. Such as conveying steam, oxygen, compressed air, oil and oil, gas, etc.

Low alloy steel seamless pipe

Refers to alloy steel pipes containing a certain proportion of alloying elements。

Usually divided into two

One is the low-alloy steel pipe containing manganese, which has another name ordinary low-alloy steel pipe. Such as 16Mn, 15MnV, and so on. The other is a low-alloy steel pipe containing chromium, molybdenum, and other elements, called chrome-molybdenum steel pipe。

Commonly used are 12CrMo, 15CrMo, 12Cr2Mo, 1Cr5Mo, and so on. Its specification range is outer diameter φ10~φ273mm, single pipe length 4~12m, and the applicable temperature range of chrome-molybdenum steel pipe is -40~550℃。

Low-alloy seamless steel pipes mostly work for the transport of various high-temperature oil products, oil, and gas, less corrosive brine, low-concentration organic acids, etc.。

Stainless acid-resistant seamless steel pipe

According to the different contents of various metals such as chromium, nickel, and titanium, pipes have many varieties. There are Cr13, 00Cr17Ni14Mo2, 1Cr18Ni12Mo2Ti, 1Cr18Ni9Ti, etc.。

Among these steel grades, the most used is 1Cr18Ni9Ti, which is usually represented by the simplified material code 18-8 on the construction drawings. The applicable temperature range is -196~700℃。

In chemical production, it works to transport various highly corrosive media. Such as nitric acid, acetic acid, and urea。

High-pressure seamless steel pipe

The manufacturing material is the same as the above-mentioned seamless steel pipe. It’s just that the pipe wall is thicker than the medium and low-pressure seamless steel pipe, and the thickest pipe wall is 40mm.。

For example, the specifications of high-pressure seamless steel pipes for fertilizer equipment are φ14×4(mm)~273×40(mm). The length of a single pipe is 4~12m, the applicable pressure range is 10~32MPa, and the working temperature is -40~400℃。

In petrochemical plants, the above high-pressure seamless steel pipes are used to transport raw material gas, hydrogen nitrogen, synthesis gas, water vapor, high-pressure condensed water, and other media。

Cryogenic Steel Pipe

In the cold area of the imported project, the amount of the material is STPL-39, STPL-46, and the working temperature can reach -105 ℃。

Low-temperature steel pipes have two types: seamless steel pipes and seamed steel pipes. The nominal diameter of a seamless low-temperature steel pipe is 15-400mm, and the wall thickness is the same as that of a carbon steel pipe. The nominal diameter of the seamed cryogenic steel pipe is 400-1100mm, the wall thickness is 6-10mm, and the standard length of a single pipe is 6m。

This kind of pipeline is suitable for conveying various non-corrosive low-temperature medium pipelines. At present, there is no mass production of steel pipes corresponding to this standard in China.。


3. Steel Plate Coil Tube

Fitting in Pipelines Pigging

The main material of the coiled steel pipe is steel coiled and welded. It has two types: straight seam welded steel pipe and spiral seam welded steel pipe。

Straight seam welded steel pipe


  • Most of them are manufactured at the construction site or commissioned by processing plants。But it not produced by professional steel pipe factories。
  • Steel plate materials include Q235A, No. 10, No. 20, 16Mn, 20g, etc. Its specifications range from 200 to 3000mm in nominal diameter, the largest is 4000mm, and the wall thickness is generally 4 to 16mm.。
  • The length of a single pipe with a nominal diameter of 200-900mm is 6.4m; the length of a single pipe with a nominal diameter of 1000-3000mm is 4.8m。
  • Applicable working temperature: Q235A is -15~300℃, No. 10, No. 20, 16Mn, 20g is -40~450℃, all are suitable for low pressure range。

Spiral seam welded steel pipe


  • Produced by a steel pipe manufacturer, the materials are Q235A, 16Mn。
  • Its specifications range from 200 to 700mm in nominal diameter, 7 to 10mm in wall thickness, and 8 to 18m in length of a single tube。
  • Applicable working temperature: Q235A is -15~300℃, 16Mn is -40~450℃, operating pressure: Q235A is 2.5MPa, 16Mn is 4MPa。

The straight seam welded steel pipe and the spiral seam welded steel pipe are mostly used to transport the medium with low corrosiveness at normal temperature and low pressure. Such as low-pressure steam, underground circulating water, gas, oil, and gas. The spiral seam welded steel pipe has a long single pipe, especially suitable for long-distance transportation pipelines.。

According to the needs of the project, there are also straight seam stainless steel coil welded pipes, which are all rolled at the construction site and not produced by the manufacturer. The material used is mostly 1Cr18Ni9Ti steel plate. Its specification range has a nominal diameter of 200 to 1000mm. And a wall thickness of 4mm with a nominal diameter of 200 to 400mm. The wall thickness with a nominal diameter of 700-1000mm is 6-8mm, and the length of a single pipe is 4.5m. The applicable temperature and the range of the medium conveyed are the same as those of the low-pressure stainless steel pipe。


4. Copper pipe

Pipes and Fittings in Pipelines Pigging

Copper tubes have two types: copper tubes and brass tubes


  • Firstly, the grades of materials used in the manufacture of copper pipes are T2, T3, T4, and TUP, etc., and the copper content is relatively high, accounting for more than 99.7%;
  • Secondly, Brass pipes have H62, H68, etc., which are alloys of zinc and copper. Such as the H62 brass tube, the material composition of copper is 60.5% to 63.5%, zinc is 39.6%, and other impurities are less than 0.5%。

The manufacturing methods of copper pipes have two types: drawing and extrusion.


  • Firstly, the outer diameter of the drawn copper tube is φ3~φ200mm. The outer diameter of the extruded copper tube is φ32~φ280mm, and the wall thickness is 1.5~5mm;
  • Secondly, the specification range of copper coil welded copper tube is outer diameter φ155~φ505mm, and there are two kinds of supply methods: single and coiled。

The applicable working temperature of copper pipe is below 250℃. It mostly works for oil pipelines, thermal insulation accompanying pipes, and air separation oxygen pipelines。

5. Titanium tube

Fittings in Pipelines PiggingTitanium tube is a new type of tube material in recent years. Because of its lightweight, high strength, strong corrosion resistance, and low-temperature resistance. So it often works in process parts where other pipes are not competent。

The titanium tube is made of TA1, TA2 industrial pure titanium, and the applicable temperature range is -140 ~ 250 ℃. When the temperature exceeds 250℃, its mechanical properties decrease。

Commonly used titanium tube specifications range from 20 to 400 mm in nominal diameter. It is suitable for low and medium pressure. The wall thickness of the low-pressure pipe is 2.8 to 12.7 mm. Medium pressure pipe wall thickness 3.7~21.4mm。

Titanium tubes have many advantages though. However, due to the high price and the difficulty of welding, it has not been widely used.。




Pipe fittings are also very important for the selection of pigs in pipeline pigging. For example, when the curvature of the elbow is large, the user should choose our full polyurethane solid pig. Otherwise, the pig will easily block the pipeline. Therefore, it is also very necessary to understand pipe fittings.

Pipe fittings are required to change the direction, elevation, or pipe diameter in the pipeline network system and to lead out branch pipes from the main pipe. Due to the different shapes and complexity of the piping system, there are many types of pipe fittings.。


Commonly used Pipes and Fittings in Pipelines Pigging include elbows, tees, reducers, pipe joints, pipe caps, etc.



1. Elbow

Elbow is to change the direction of the pipe。


Common bend angles are 90°, 45°, and 180°. We can call 180° elbows U-bends. There are also elbows with special angles, but very few。


Malleable steel elbow


Malleable steel elbow, also known as the malleable iron elbow. It is the most common elbow。


The specifications of malleable steel elbows are relatively small, and the commonly used specifications range from 1/2 to 4 inches. According to their different surface treatments, they have two types: galvanized and non-galvanized.。


This kind of malleable steel pipe fittings is mainly used for heating, upper and lower water pipes, and gas pipes. In the process, except for the low-pressure pipes that need to be dismantled frequently, other material pipes are rarely used.。


❷ Pressed Elbow

Pressed elbows, also known as stamped elbows or seamless elbows. Its main parts have high-quality carbon steel, stainless acid-resistant steel, low-alloy steel seamless pipes, etc. And it is pressed and formed in a special mold.。


  • ts bending radius is one and a half times the nominal diameter (R=1.5DN). On special occasions, an elbow with a bending radius equal to the nominal diameter (R=1DN) can also be used。
  • Its specification range is within DN20~600mm。
  • Its wall thickness range is consistent with the table number of seamless steel pipe。
  • Pressed elbows are generally stamped from standard seamless steel pipes by professional manufacturers or processing plants. Both ends of the elbow should be beveled when leaving the factory。

Stamped Welded Elbow

Stamping and welding elbows are made of sheet metal stamped into half annular elbows by dying. Then the two half-ring elbows are assembled and welded to form。


Its bending radius is the same as that of seamless pipe elbows. The specification range is above the nominal diameter of 200mm。


Welding elbow


Welded elbow, also known as shrimp waist or shrimp body elbow。


There are two production methods


  • Firstly, one is to cut the steel plate in the processing plant, cut it, roll it and weld it. Most of the matching used for steel coil pipe。
  • Secondly, the other is to use pipe material to cut and form by butt welding, and its size is generally above 200mm. The operating temperature cannot be greater than 200 °C, and it can generally be produced at the construction site。


High-pressure elbow


High-pressure elbows are forged from high-quality carbon steel or low alloy steel。


According to the pipe connection form, the two ends of the elbow are processed into threads or grooves, and the processing precision is very high. This requires that the thread of the pipe mouth and the thread of the flange mouth can be tightly matched and freely screwed in without loosening.。


Suitable for petrochemical pipelines with pressures of 22.0 and 32.0MPa. Common specifications range from DN6 to 200mm。


2. Three-way pipe

The three-way pipe is a pipe fitting that connects the main pipe and the branch pipe. According to the different manufacturing materials and uses, it is divided into many types.。


Divide by specifications


It has the same diameter three-way pipe and the different diameter three-way pipe. Equal diameter tee has another name “equal diameter three-way pipe”



• The same diameter three-way pipe means that the pipe diameter of the branch pipe is the same as the pipe diameter of the main pipe


• Reducing three-way pipe means that the pipe diameter of the branch pipe is smaller than the pipe diameter of the main pipe, so it is also called unequal diameter three-way pipe, and the amount of reducing three-way pipe is more.


Malleable Steel three-way pipe


The manufacturing material and specification range of the malleable steel three-way pipe are the same as those of the malleable steel elbow. Not much is used in petrochemical process pipelines. It mainly works for indoor heating, upper and lowers water and gas pipelines。


❷ Steel three-way pipe


Before the 1970s, the development of my country’s industrial production technology was relatively slow. Engineering technology in process piping is also relatively backward。


In the design of various medium and low-pressure steel pipes, when the pipeline needs to use tee fittings, the method of gouging the pipe generally solves it. That is, on the main pipe that needs to be connected to the branch pipe. Firstly dig a hole according to the diameter of the branch pipe. And then weld the branch pipe. This method has many disadvantages, the welding quality is not easy to guarantee, the pipeline is easily deformed after welding, and impurities are easy to enter the main pipe。


But in the late 1970s, with the introduction of large-scale modern production equipment such as metallurgy and the petrochemical industry. The development of process pipeline engineering technology was promoted. At present, my country has been able to produce medium and low-pressure pipeline steel three-way pipe. And a series of products have been formed. So the specification of the seamless tee is DN20~600mm. Steel plate welded tee specification is DN150~1500mm。


So the production of stereotyped three-way pipe is made of the high-quality pipe as raw material, after cutting, digging, heating, and drawing with a mold. And then machined to become a stereotyped finished three-way pipe. The three-way pipes of medium and low-pressure steel products are all-welded on site. Then there are two situations for the Three-way Pipework for steel coil pipes. One is to use steel plate blanking in the processing plant and then roll and weld. The other is to cut holes to take over at the installation site。


High-pressure Three-way Pipe


There are two types of high-voltage tee commonly in using. One is a welded high-voltage three-way pipe. The other is the integral forging of high-pressure three-way pipe。


Welded high-pressure tee, using high-quality high-pressure steel pipe as the material. The manufacturing method is similar to the gouging tube. The hole opened on the main pipe should be consistent with the diameter of the connected branch pipe. Welding quality requirements are strict, and usually require preheating before welding and heat treatment after welding. Its specification range is DN16~200mm, pressure 22MPa, 32MPa。


So the integral forged high-pressure tee is generally connected by a threaded flange. Its specifications range from table numbers SCH160, and DN15 to 600mm, and add “XXS” to the table numbers. Its diameter range is DN15~300mm。


3. Reducer

The function of the reducer is to reduce the diameter of the pipe. Judging from the direction of fluid motion, most of them change from big to small and come from small to big. For example, the reducers of steam return pipes and sewer pipes are changed from small to large. Reducer knew as size head。


Malleable steel reducer


Malleable steel reducers generally have two types. One is the internal thread reducer, also known as the external joint. So the other is a pipe fitting with an internal thread and an external thread, which has another name core. Although it does not have the name “reducer”, it acts as a reducer。


❷ Steel Reducer


Steel reducers have seamless and slotted ones. Seamless reducers are pressed with seamless steel pipes, and slotted reducers are cut with steel plates and rolled and welded, also known as welded reducers。


These two reducers are available in concentric and eccentric sizes. There is a straight edge at the bottom of the eccentric reducer. Which can make the bottom of the pipe into a horizontal plane during use, to facilitate the discharge of materials in the pipe during shutdown and maintenance。


The specification range of seamless reducer is DN25 ~ 600mm. The specification range of seam-welded reducer is DN200 ~ 1500mm。


Steel reducers, as finished pipe fittings on pipes, were only available after the 1970s. Most of the reducing diameters on the early process pipes were made on site. If the diameter of the pipe changes greatly, the pipe end is drawn and welded. And it is directly processed into a reducer.;


At last, If the diameter of the pipe does not change much, it is directly made by heating the pipe end. Then the production of reducers by drawing strip welding requires a lot of labor, and many welds, and it is not easy to guarantee the welding quality. At present, this method has been banned for processing pipelines with high welding quality requirements.


These are some of the ways to classify pipes and fittings. So knowing the characteristics of different pipes and fittings allows us to better maintain the pipes. Because pipe cleaners are a common way of pipeline pigging. Selecting a suitable pig to clean the pipeline in daily use can prolong the service life of the pipeline. This not only reduces the cost of using pipes. It can also prevent pipeline blockage and improve pipeline transportation speed.

And our company is a professional pipeline technology company for 26 years. If you need pipe cleaning, you can click here to contact us. Then we will have professional technicians customize professional solutions for you.