The piping equipment used in petrochemical plants generally includes pipes, fittings, valves, flanges, gaskets and fasteners, and other piping components, such as filters, separators, flame arresters, compensators, etc.

1. Tube

There are many classification methods for pipes, which can be divided into metal pipes, non-metallic pipes and steel-lined non-metallic 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, while metal pipes account for most of the petrochemical plants. To more than 85 percent of all process piping installations, this section focuses on metal piping.

(1) Welded steel pipe

Welded steel pipes, also known as seamed steel pipes, are generally formed by coil welding of steel plates or steel strips. According to the surface treatment of the pipe, it is divided into two types: galvanized and non-galvanized. The galvanized surface is whitish, also known as white iron pipe or galvanized steel pipe; the ungalvanized surface is ordinary welded steel pipe, also known as black iron pipe. Galvanized welded steel pipes are often used to transport pipes with relatively clean media, such as domestic water, purified air, instrument air, etc.; non-galvanized welded steel pipes can be used to transport steam, gas, compressed air and condensed water.

According to user requirements, welded steel pipes can be divided into two types when they leave the factory, one is threaded at the end of the pipe, and the other is unthreaded at the end of the pipe. 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 divided into thin-walled steel pipes, thickened steel pipes and ordinary steel pipes according to the thickness of the pipe wall. 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, including threaded connection, flange connection and welding. The flange connection is divided into threaded flange connection and welded flange connection, and the welding method is divided into gas welding and arc welding.

The specifications of commonly used welded steel pipes range from 6 to 150 mm in nominal diameter.

(2) Seamless steel pipe

Seamless steel pipes are the pipes with the largest amount and the largest variety of specifications in industrial pipelines. They are basically divided into two categories: seamless steel pipes for fluid transportation and special seamless steel pipes. The former is commonly used for process pipes. The latter Such as boiler special steel pipe, cracking furnace pipe and heat exchanger steel pipe. According to the material, it can be divided into carbon seamless steel pipe, chrome-molybdenum seamless steel pipe and stainless steel and acid-resistant seamless steel pipe. According to the nominal pressure, it can be divided into three categories: low pressure (0≤1.0MPa), medium pressure (1.0<10MPa=, high pressure (≥10MPa). Process pipelines are commonly used seamless steel pipes for fluid transportation.

1. Carbon seamless steel pipe, the commonly used manufacturing materials are No. 10, No. 20, and 16Mn steel, and its specification range is: hot-rolled outer diameter φ32～630mm, cold-drawn outer diameter φ6～200mm, single tube length 4～12m, allowable The operating temperature is -40～450℃, and it is widely used for conveying various media that are not corrosive to steel, such as conveying steam, oxygen, compressed air, oil and oil and gas.

2. Low-alloy steel seamless steel pipe refers to an alloy steel pipe containing a certain proportion of alloying elements. Usually divided into two types, one is low-alloy steel pipe containing manganese element, called ordinary low-alloy steel pipe, such as 16Mn, 15MnV, etc.; the other is low-alloy steel pipe containing chromium, molybdenum and other elements, called chrome-molybdenum steel pipe. Commonly used are 12CrMo, 15CrMo, 12Cr2Mo, 1Cr5Mo, etc. The specifications range from φ10 to φ273mm in outer diameter, and the length of a single pipe is 4 to 12m. The applicable temperature range of chrome molybdenum steel pipe is -40 to 550 °C. Low-alloy seamless steel pipes are mostly used to transport various high-temperature oil products, oil and gas, less corrosive brine, and low-concentration organic acids.

3. Stainless and acid-resistant seamless steel pipes have many varieties according to the different contents of chromium, nickel and titanium, including Cr13, 00Cr17Ni14Mo2, 1Cr18Ni12Mo2Ti, 1Cr18Ni9Ti and so on. Among these steel grades, the most used is 1Cr18Ni9Ti, which is usually represented by the simplified material code 18-8 on the construction drawing. The applicable temperature range is -196 ~ 700 ℃. Such as nitric acid, acetic acid and urea.

4. The high-pressure seamless steel pipe is basically the same as the above-mentioned seamless steel pipe, except 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.

In addition to the above, there are also low-temperature steel pipes, which are used in the cold area of ​​the imported projects. Pipe, at present, there is no mass production of steel pipes corresponding to this standard in China. Low-temperature steel pipes are divided into two types: seamless steel pipes and seamed steel pipes. The nominal diameter of seamless low-temperature steel pipes is 15-400mm, and the wall thickness is the same as that of carbon steel pipes; The standard length of the root canal is 6m.

(3) Steel plate coil tube

Coiled steel pipes are made of steel coils and welded, and are divided into two types: straight seam welded steel pipes and spiral seam welded steel pipes.

Most of the straight seam welded steel pipes are manufactured on the construction site or commissioned by processing plants, and professional steel pipe factories do not produce them. The steel plate materials include Q235A, No. 10, No. 20, 16Mn, 20g, etc. The specification range is 200-3000mm in nominal diameter, the largest is 4000mm, and the wall thickness is generally 4-16mm. The length of a single tube with a nominal diameter of 200 to 900mm is 6.4m; that of a nominal diameter of 1000 to 3000mm is 4.8m. Applicable working temperature: Q235A is -15~300℃, No.10, No.20, 16Mn, 20g is -40~450℃, all suitable for low pressure range.

Spiral seam coil welded steel pipe, produced by the steel pipe manufacturer, the material is Q235A, 16Mn. Its specifications range from 200 to 700 mm in nominal diameter, 7 to 10 mm in wall thickness, and 8 to 18 m in length for 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 for conveying medium at normal temperature and low pressure with low corrosiveness, such as low pressure steam, underground circulating water, gas and oil and gas. The spiral seam welded steel pipe has a long single pipe, which is 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, a wall thickness of 4mm for a nominal diameter of 200 to 400mm, a wall thickness of 6 to 8mm for a nominal diameter of 700 to 1000mm, and a single tube length of 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 tube

Copper tubes are divided into two types: copper tubes and brass tubes. The material grades used in the manufacture of red copper pipes are T2, T3, T4 and TUP, etc., with a high copper content, accounting for more than 99.7%; the material grades of brass pipes are H62, H68, etc., which are alloys of zinc and copper. Such as 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 are divided into two types: drawing and extrusion. 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; And two kinds into a plate.

The applicable working temperature of copper pipe is below 250 ℃, and it is mostly used in oil pipeline, thermal insulation accompanying pipe and air separation oxygen pipeline.

(5) Titanium tube

Titanium pipe is a new type of pipe material in recent years. Because of its light weight, high strength, strong corrosion resistance and low temperature resistance, it is often used in process parts where other pipes are not competent. Titanium tube is made of TA1, TA2 industrial pure titanium, the applicable temperature range is -140 ~ 250 ℃, when the temperature exceeds 250 ℃, its mechanical properties will decline. 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 low pressure pipe is 2.8～12.7mm, and the wall thickness of medium pressure pipe is 3.7～21.4mm. Although titanium tube has many advantages, it has not been widely used due to its high price and difficulty in welding.

2. Pipe fittings

Pipe fittings are required to change the direction, elevation or pipe diameter in the piping system, and to lead out branch pipes from the main pipe. Due to the different shapes of the piping system, simple and complex, there are many types of pipe fittings. Commonly used pipe fittings are elbows, tees, reducers, pipe joints, pipe caps, etc.

(1) Elbow

Elbow is used to change the direction of the pipe. The bending angles of commonly used elbows are 90°, 45° and 180°. 180° elbows are also called U-shaped elbows. There are also elbows with special angles, but there are very few.

1. Malleable steel elbow

Malleable steel elbow, also known as malleable iron elbow, is the most common threaded elbow. 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 low-pressure pipelines that need to be dismantled frequently, other material pipelines are rarely used. 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 are divided into two types: galvanized and non-galvanized.

2. pressed elbow

Pressed elbows, also known as stamped elbows or seamless elbows, are made of high-quality carbon steel, stainless acid-resistant steel and low-alloy steel seamless pipes, etc., and are pressed and formed in a special mold. Its bending radius is one and a half times the nominal diameter (R=1.5DN). In 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 pipes. Pressed elbows are generally stamped and processed by professional manufacturers or processing plants with standard seamless steel pipes, and both ends of the elbows should be beveled when leaving the factory.

3. Stamped Welded Elbow

Stamping and welding elbows are formed by stamping a half-ring elbow from a plate through a die, and then welding the two half-ring elbows together. Its bending radius is the same as that of seamless pipe elbow, and its specification range is more than 200mm in nominal diameter.

4. Welding elbow

Welded elbow, also known as shrimp waist or shrimp body elbow. There are two production methods. One is to cut the steel plate in the processing plant, cut it, roll it and weld it, and most of it is used for the matching of the steel plate coil. The other is to use pipe blanking, which is formed by group butt welding, and its specifications are generally above 200mm. The use temperature cannot be higher than 200℃, and it can generally be produced on the construction site.

5. High pressure elbow

High-pressure elbows are forged from high-quality carbon steel or low-alloy steel. According to the connection form of the pipe, the two ends of the elbow are processed into threads or grooves, and the processing precision is very high. It is required that the thread of the pipe mouth and the thread of the flange mouth can be tightly matched and screwed in freely without loosening. For petrochemical pipelines, the commonly used specifications range from DN6 to 200mm.

(2) Tee

The tee is a pipe fitting that connects the main pipe and the branch pipe. According to the different materials and uses, it is divided into many types. In terms of specifications, it can be divided into the same diameter tee and the different diameter tee. The same diameter tee is also called an equal diameter tee; the same diameter tee means that the pipe diameter of the branch pipe is the same as the pipe diameter of the main pipe; the different diameter The tee means that the pipe diameter of the branch pipe is smaller than that of the main pipe, so it is also called unequal diameter tee, and the amount of reducing tee is more.

1. Malleable Steel Tee

The manufacturing material and specification range of the malleable steel tee are the same as those of the malleable steel elbow.

2. steel tee

Before the 1970s, the development speed of my country's industrial production technology was relatively slow, and the engineering technology of process piping was relatively backward. In the design of various medium and low pressure steel pipes, when the pipes need to use three-way pipe fittings, they are generally solved by the method of digging holes for connecting pipes. 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. In the late 1970s, with the introduction of large-scale modern production equipment such as metallurgy and 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 custom-made tees, and a series of products have been formed. The specification of the tee is DN20～600mm, and the specification of the welded steel tee is DN150～1500mm.

The production of stereotyped tee is made of high-quality pipe as raw material, after cutting, digging, heating and drawing with a mold, and then machined to become a stereotyped finished tee. The tees of medium and low pressure steel products are all welded on site. There are two cases for the tee used for steel coil pipe, one is to use steel plate blanking in the processing plant, and it is formed by rolling and welding; the other is to cut the hole to take over at the installation site.

3. High pressure tee

There are two commonly used high-pressure tee, one is welded high-pressure tee, and the other is integral forged high-pressure tee.

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

The integral forged high-pressure tee is generally connected by a threaded flange. Its specification range is table number SCH160, DN15～600mm, the table number is added with "XXS", and its pipe diameter range is DN15～300mm.

(3) Reducer

The function of the reducer is to reduce the diameter of the pipe. From the direction of fluid movement, most of them change from large to small, and some from small to large. For example, the reducer of steam return pipes and sewer pipes changes from small to large. The reducer is commonly known as the size head.

1. Malleable steel reducer

Malleable steel reducers are generally divided into two types, one is an internal thread reducer, also known as an external joint; the other is a pipe fitting combined with an internal thread and an external thread, called a core, although it is not called a reducer, But it acts as a reducer.

2. steel reducer

The steel reducer is divided into two types: seamless and seamed. . Both types of reducers are available in both concentric and eccentric specifications. The bottom of the eccentric reducer has a straight edge, which can make the bottom of the pipe into a horizontal plane when in use, which is convenient for discharging the materials in the pipe during shutdown and maintenance.

The specification range of seamless reducer is DN25～600mm, and the specification range of seam welded reducer is DN200～1500mm.

Steel reducers, as finished pipe fittings on pipelines, have only been available since the 1970s. Most of the reducers on early process pipelines were made on site. If the diameter of the pipe changes greatly, it is welded at the pipe end and directly processed into a reducer; if the pipe diameter does not change much, the pipe end is heated and directly smashed.