Stainless Steel Pipe Fittings

Material selection for chemical pipelines

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There are many factors affecting the choice of pipeline materials: process design conditions, material properties, economy, processability, contamination of the final product, process safety, corrosion resistance, etc.

Cast iron pipe:
Ordinary cast iron pipe:

It is mainly used for water pipe, gas main pipe, sewage pipe, etc. buried in the ground, which has good corrosion resistance to soil, acid and alkali.
However, it is low in strength and brittle, so it cannot be used on pipes with high pressure or toxic or explosive media.

Ferrosilicon tube high silicon iron tube:

It can resist the corrosion of many strong acids. It has high hardness, is not easy to process, and is easily broken by vibration and impact. The anti-chlorinated iron tube is mainly resistant to corrosion of various temperatures and concentrations of hydrochloric acid.

Carbon steel pipe:

Generally not resistant to corrosion, in certain occasions, such as concentrated sulfuric acid, lye (normal temperature), can withstand certain corrosion. Not suitable for chloride ions, sensitive to stress corrosion.

stainless steel pipe:

Austenitic stainless steel:
Austenitic stainless steel is generally a corrosion-resistant steel. It is the most widely used type of steel. Among them, 18-8 stainless steel is the most representative. It has good mechanical properties and is convenient for machining, stamping and welding.
Excellent corrosion resistance and good heat resistance in an oxidizing environment. However, it is particularly sensitive to media containing chloride ions (CL-) in solution and is prone to stress corrosion.

304 stainless steel:

The most commonly used stainless steel, containing a small amount of chromium and nickel, has a low carbon content and is easy to heat treat. High temperature resistance is also good, the general use temperature limit is less than 650 °C.
304 stainless steel has excellent stainless corrosion resistance and good resistance to intergranular corrosion. For oxidizing acids, it is found in the experiment that 304 stainless steel has strong corrosion resistance in nitric acid below the boiling temperature of ≤ 65%. It also has good corrosion resistance to alkaline solutions and most organic and inorganic acids.

304L stainless steel:

The low carbon version of 304 is mainly for the carbon infiltration of 304 steel. The lower carbon content minimizes the precipitation of carbides in the heat affected zone near the weld, which may result in intergranular corrosion (weld erosion) in certain environments.

321 stainless steel:

It is a Ni-Cr-Mo type austenitic stainless steel, and its performance is very similar to that of 304. However, due to the addition of titanium metal, it has better resistance to intergranular corrosion and high temperature strength.
321 stainless steel has excellent high temperature stress breaking performance and high temperature anti-potential performance. It is used in field open-air machines for chemical, coal and petroleum industries with high resistance to intergranular corrosion, heat-resistant parts for building materials and parts with difficult heat treatment.

316 stainless steel:

Mo is added, so its corrosion resistance, atmospheric corrosion resistance and high temperature strength are particularly good, and it can be used under severe conditions. Corrosion resistance is superior to 304 stainless steel and resistant to erosion by marine and aggressive industrial atmospheres.
Due to the addition of Mo, there is some corrosion resistance to dilute sulfuric acid and chlorine ion-containing solutions. 316 is more resistant to corrosion and more resistant to corrosion than 304 in high temperature environments.

316L stainless steel:

The carbon content of 316L is much lower than 316; while the high carbon content is the main cause of intergranular corrosion of metal, so under the important working conditions of chemical industry, 316L is widely used, but the price of 316L is high, and 316L is resistant to chlorine. The ionic corrosion is better than 316.
The high alloy content of stainless steel has a nickel content of 29% to 30% and a chromium content of more than 20%. It has good corrosion resistance to acid and hydrochloric acid and is of course more expensive.

Monel tube:

Monel alloy, also known as nickel alloy, is an alloy formed by adding copper, iron, manganese and other elements to the metal nickel.
Monel alloy has good corrosion resistance and is a corrosion-resistant alloy with the largest amount, the most versatile and excellent comprehensive performance.
The alloy has excellent corrosion resistance in hydrofluoric acid and fluorine gas media, and excellent corrosion resistance to hot concentrated alkali liquor. It is also resistant to corrosion by neutral solutions, water, sea water, the atmosphere, organic compounds, etc.
An important feature of this alloy is that it generally does not produce stress corrosion cracking and has good cutting performance. Applicable temperature can be up to 500 ° C, it is more expensive than stainless steel, but in the chloride ion environment, is not sensitive to stress corrosion cracking.

Hastelloy tube:

It is a kind of nickel-based alloy. It is mainly divided into three series of B, C and G. It is mainly used in the case of iron-based Cr-Ni or Cr-Ni-Mo stainless steel, non-metallic materials and other strong corrosive media. It has been widely used in many fields such as petroleum, chemical industry and environmental protection.
Mainly resistant to wet chlorine, various oxidizing chlorides, chloride solutions, sulfuric acid and oxidizing salts, have good corrosion resistance in low temperature and medium temperature hydrochloric acid.
Therefore, in the past 30 years, in the harsh corrosive environment, such as chemical, petrochemical, flue gas desulfurization, pulp and paper, environmental protection and other industrial fields have a wide range of applications. At the earliest, Hastelloy was developed for corrosion in HCL applications.

Copper and copper alloy tubes:

Brass (copper and zinc alloy) is mainly used in the chemical industry, as well as tin bronze (tin added to brass), aluminum bronze, copper-nickel alloy (white copper) and the like.
Copper alloys have excellent resistance to atmospheric and seawater corrosion, and are mainly characterized by uniform corrosion in general media.
Brass has good corrosion resistance in the atmosphere, a variety of medium aqueous solutions, organic acids; tin bronze exhibits better corrosion resistance than brass in various corrosive media.
In the process of interaction with the atmosphere and the marine environment, the surface energy of the copper alloy forms a passive or semi-passive protective film, which inhibits various corrosion. Therefore, most copper alloys exhibit excellent corrosion resistance in the atmosphere.
Brass and tin bronze are mainly used in the chemical industry for valves and fittings, as well as tube bundles for heat exchangers. White copper is often used in tube bundle materials for heat exchangers that exchange heat with seawater.

Titanium alloy tube:

Mainly used to deal with chlorine-containing solutions, such as sea water and wet chlorine, forming an oxide film to resist corrosion. Titanium materials are used in dealing with HCL, chlorine-containing solutions, seawater, etc.

PVC tube:

Resistant to most inorganic acids, inorganic salt solutions, not resistant to strong sulfuric acid / strong nitric acid, not suitable for most organic solvents. In most cases, PVC pipes are suitable for wire and sewage pipes.

Teflon tube:

In addition to alkali, fluoride, it is resistant to almost all chemicals. The temperature can reach 250C, and the coefficient of linear expansion is 10 to 20 times that of steel; however, it is expensive, difficult to form and process, and poor in thermal conductivity.
It has the characteristics of corrosion resistance, aging resistance, low friction coefficient, non-sticking property and wide temperature range. It is commonly used in conveying pipes and exhaust pipes for transporting corrosive gases.

Glass steel pipe:

OPR has low density and light weight. The quality of glass steel pipe is only 1/6 of that of cast iron pipe. When installing the same quality pipe, the length of glass pipe is 6 times longer than that of cast iron pipe, which greatly speeds up the construction progress and saves construction costs. .
High mechanical strength, excellent impact resistance, not easily damaged by impact; Excellent durability; Excellent chemical resistance; Can withstand freezing and thawing conditions such as low temperature and thawing in cold regions, the tube will not expand and freeze and crack, nor will it produce Burst accident.
The inner wall of the pipe is smooth, the resistance to the fluid is small, and the deposit is not easy to adhere. The friction loss of the medium movement is only 30% of the steel pipe, and the conveying efficiency is much higher than that of the steel pipe and the cement pipe.
Non-conducting, non-heat transfer, good thermal insulation performance, good insulation, and the surface of the pipe is not easy to dew, so it can be used in a large number of heat transfer pipelines.
The cost of raw materials is slightly higher than that of cast iron pipes and concrete pipes, which is close to steel pipes. However, due to its many excellent characteristics and reduced transportation and construction costs, its comprehensive cost is lower than that of traditional pipes.
Large-diameter pipes are suitable for buried drainage pipes, oil pipes, etc.; small-diameter pipes are used as rainwater pipes because of their excellent impact resistance. Large-diameter glass fiber-wound glass pipes have been widely used as water supply pipes in foreign countries instead of cast iron pipes and prestressed reinforced concrete pipes.
Source: China Chemical Pipelines Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)

Article Categories:
Steel Pipe

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