The advantages of 904L stainless steel

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Super austenitic stainless steel 904L (UNS N08904, EN1.4539) is a high alloy Austenitic stainless steel with low carbon content, specially designed for harsh corrosion conditions. It has high chromium content and nickel content, the addition of copper makes it has strong acid resistance especially dilute sulfuric acid, especially high resistance to chloride gap corrosion and stress corrosion cracking, is not easy to appear erosion spots and cracks, pitting resistance is slightly better than other steel. It has good machinability and weldability, in many industrial fields have a wide range of applications: petrochemical vessels and pipelines, such as reactors, etc.; Power plant flue gas desulfurization unit; Seawater treatment plant, seawater heat exchanger; Paper industry equipment, pharmaceutical industry, food industry and other fields.

 

Metallographic structure

904L is completely austenitic. Compared with austenitic stainless steels with high molybdenum content, 904L is insensitive to the precipitation of ferrite and α phase.

 

Welding performance

As with general stainless steel,904 L can be welded in a variety of ways. The most commonly used welding methods are manual arc welding or inert gas shielded welding. The electrode or wire metal is based on the composition of the base metal and has a higher purity. The content of molybdenum is higher than that of the base metal. Preheating is generally not required before welding, except in the cold outdoors, in order to avoid the condensation of water vapor, the joint part or adjacent area can be heated evenly. Note that the local temperature should not exceed 100℃, so as not to lead to carbon accumulation and cause intergranular corrosion. Small line energy, continuity and fast welding speed should be used for welding. Generally, heat treatment is not required after welding. If heat treatment is needed, it shall be heated to 1100 ~ 1150℃ and then cooled quickly. Matching welding materials: electrode (E385-16/17), welding wire (ER385).

 

Machining performance

The machining characteristics of 904 L are similar to those of other austenitic stainless steels, and there is a tendency for cutter stickiness and work hardening during machining. Positive front Angle carbide cutting tools must be used, with vulcanization and chlorinated oil as cutting coolant, equipment and process should be to reduce work hardening as the premise. Slow cutting speed and feed should be avoided in the cutting process.

 

The corrosion resistance of 904L stainless steel

904L has good activation-passivation conversion ability, it has excellent corrosion resistance, pitting resistance, good crack corrosion resistance and stress corrosion resistance in non-oxidizing acid such as sulfuric acid, acetic acid, formic acid, phosphoric acid, has good corrosion resistance, in neutral medium containing chloride ion. It is suitable for all concentrations of sulfuric acid below 70℃ and has good corrosion resistance to acetic acid and mixture of formic acid and acetic acid at any concentration and any temperature under normal pressure.

Due to the low carbon content (Max. 0.020%) of 904L, there is no carbide precipitation under normal heat treatment and welding conditions. This eliminates the potential for intergranular corrosion that normally occurs after heat treatment and welding. The high Cr-Ni- Mo content and the addition of copper make 904L passivated even in reducing environments such as sulfuric acid and formic acid. The high nickel content makes it have a low corrosion rate in the active state. In the concentration range of 0~98% pure sulfuric acid, 904L can be used at a temperature up to 40℃. In the concentration range of 0~85% pure phosphoric acid, it still has good corrosion resistance.

904L SS is superior to ordinary stainless steel in corrosion resistance to all phosphates. In highly oxidizing nitric acid, 904L has poor corrosion resistance compared to alloy steels without molybdenum. In hydrochloric acid, the use of 904L is limited to a lower concentration of 1-2%, where its corrosion resistance is better than that of conventional stainless steel. 904L steel has strong crevice corrosion resistance in chloride solutions, concentrated hydroxide solutions and hydrogen sulfide-rich environments, due to its high nickel content which reduces corrosion rates in pits and crevices. Ordinary austenitic stainless steels may be sensitive to stress corrosion at temperatures above 60 ° C in a chloride-rich environment. This sensitivity can be reduced by increasing the nickel content of the stainless steel.

Why Precision Stainless Steel Tubes Is the Best Choice for Mechanical processing Industry

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Precision stainless steel tubes are mainly used in precision machining operations. This product is a cross-section of high performance, precision size, and high precision surface treatments. It is used to produce a variety of products for the automotive, aerospace, marine, communications, medical and food processing industries. The tubes have high tensile strength, hardness, tensile strength and dimensional stability and these features make them ideal for heavy-duty applications. Precision stainless steel tube can be used to form many different shapes including round, square, triangle, plate, tubular, rectangular and many more. It can also be custom-formed to match the exact specifications of the customer.

Precision stainless is bright or polished annealed steel tubes with precise tolerance to microscopic flaws. A perfect annealed edge can be provided on request. The internal surface roughness 0.4 mm on both the inside and outside surfaces is covered by various coatings to improve the inherent characteristics. This product has excellent heat conducting properties, which ensures that it works well for high-temperature applications and produces low friction. It has high resistance to corrosion and is capable of resisting extreme temperature fluctuations, good toughness and ductility, tensile strength and hardness. It has good resistance to wear and tear and is unaffected by the alkalis and acids. It features a tough anodized surface and a hard, wear-resistant interior.

Seamless stainless steel pipes feature a cold-rolled ligation process and an oxygen-coated interior. The cold-rolling ligation process ensures that the entire pipe remains homogenous, which ensures maximum durability. The seamless steel pipe has a precision welded finish and therefore, they require minimum welding. They have high resistance to abrasion, erosion and rust and therefore, they are suitable for use in various industries. They have good ductility and hardness and are suitable for pipe joints and other bending applications. In addition, it can also be used in the following industries:

Water transportation pipeline: corrosion resistance, high-pressure resistance, smooth inner wall characteristics make it used for the transportation of pure water pipeline, but also can be used for fire water supply, also used in sanitary appliances drainage pipeline and production equipment of non-corrosive production drainage pipeline, industrial plant rainwater pipeline, etc.

Medical instruments: such as stethoscopes, operating beds and other parts of medical instruments. Disinfectants and various chemical potions have strong corrosion performance, and 316L stainless steel has strong corrosion resistance, and in line with the medical level, safety and health.

Food field: such as stainless steel straw, beverage machine coil, juicer liner, etc., most of the 304 stainless steel and some 316 stainless steel.

For the precision engineering and mechanical processing industry, stainless steel tubes with anodized surface finish and high tensile strength are the best choices. The 304 seamless steel pipes also come with 18-8  chromium-nickel content and high rigidity. Thus, these are ideal for making pipes and tubing for these fields. If you are looking for precision-engineered and ductile stainless steel pipes, you should contact us now for fast, reliable and cost-effective service.

304L stainless steel pipe pressure rating chart

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Stainless pipes are ideal in many applications because they have a low resistance to corrosion and high strength that allows them to be used where there are varying amounts of dissolved gas and oil. 304 and 304L stainless steel pipes and tubing are used in almost every field in the world. Making up 50% of stainless steel global usage, 304L stainless steel is currently the second most widely used grade of stainless steel up to 304 steel. It’s a low carbon grade that makes it corrosion resistant and ideal for shipping and industrial use.

There are many different characteristics that come from using 304L stainless steel pipes. One of the key characteristics is that it is excellent corrosion resistance. This means that it is able to resist rusting, which is essential for shipping pipes. These pipes are also able to resist corrosion after they are exposed to moisture and water, making them ideal for use in applications where the pipes are expected to stand up against severe weather conditions. You should also note that these pipes will not corrode once they are exposed to air, meaning that they can be used effectively in places that air would normally present a problem. With all the different pressure that you can get with 304L stainless steel, which depends on the wall thickness and seamless or welded processing, you are sure to find something that will meet your needs. These types of steel pipes are also able to be used in the environment because they conduct heat well and are very durable against abrasion and impact. Here is the following pressure rating chart for 304L stainless steel pipe.

TP304L
TEMPERATUR F 100 200 300 400 500 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200 1250 1300 1350 1400 1450 1500
TEMPERATUR C 38 93 149 204 260 316 343 371 399 427 454 482 510 538 566 593 621 649 677 704 732 760 788 816
D mm

DESIGN PRESSURE(PSI)
6 1 6423 6423 6423 6077 5692 5385 5269 5192 5115 5000 4923 4577 3808 3000 2423 2040 1739 1391 1130 913 739 478 435 391
6.35 1.24 7730 7730 7730 7313 6850 6480 6341 6249 6156 6017 5925 5508 4582 3610 2916 2475 2150 1720 1397 1129 914 591 537 484
8 1 4639 4639 4639 4389 4111 3889 3806 3750 3694 3611 3556 3306 2750 2167 1750 1457 1212 970 788 636 515 333 303 273
10 1 3630 3630 3630 3435 3217 3043 2978 2935 2891 2826 2783 2587 2152 1696 1370 1133 930 744 605 488 395 256 233 209
12 1 2982 2982 2982 2821 2643 2500 2446 2411 2375 2321 2286 2125 1768 1393 1125 927 755 604 491 396 321 208 189 170
12 2 6423 6423 6423 6077 5692 5385 5269 5192 5115 5000 4923 4577 3808 3000 2423 2040 1739 1391 1130 913 739 478 435 391
15.88 1 2215 2215 2215 2095 1963 1857 1817 1790 1764 1724 1698 1578 1313 1034 836 685 552 442 359 290 235 152 138 124
14 2 5387 5387 5387 5097 4774 4516 4419 4355 4290 4194 4129 3839 3194 2516 2032 1700 1429 1143 929 750 607 393 357 321
15 1.5 3630 3630 3630 3435 3217 3043 2978 2935 2891 2826 2783 2587 2152 1696 1370 1133 930 744 605 488 395 256 233 209
15 2 4985 4985 4985 4716 4418 4179 4090 4030 3970 3881 3821 3552 2955 2328 1881 1569 1311 1049 852 689 557 361 328 295
16 2 4639 4639 4639 4389 4111 3889 3806 3750 3694 3611 3556 3306 2750 2167 1750 1457 1212 970 788 636 515 333 303 273
20 2 3630 3630 3630 3435 3217 3043 2978 2935 2891 2826 2783 2587 2152 1696 1370 1133 930 744 605 488 395 256 233 209
22 2 3275 3275 3275 3098 2902 2745 2686 2647 2608 2549 2510 2333 1941 1529 1235 1020 833 667 542 438 354 229 208 188
25 2 2855 2855 2855 2701 2530 2393 2342 2308 2274 2222 2188 2034 1692 1333 1077 887 721 577 468 378 306 198 180 162
25 2.5 3630 3630 3630 3435 3217 3043 2978 2935 2891 2826 2783 2587 2152 1696 1370 1133 930 744 605 488 395 256 233 209
38 2 1835 1835 1835 1736 1626 1538 1505 1484 1462 1429 1407 1308 1088 857 692 567 455 364 295 239 193 125 114 102
50 2.5 1740 1740 1740 1646 1542 1458 1427 1406 1385 1354 1333 1240 1031 813 656 537 430 344 280 226 183 118 108 97
60 2.5 1440 1440 1440 1362 1276 1207 1181 1164 1147 1121 1103 1026 853 672 543 443 354 283 230 186 150 97 88 80
6 1.50 10438 10438 10438 9875 9250 8750 8563 8438 8313 8125 8000 7438 6188 4875 3938 3400 3077 2462 2000 1615 1308 846 769 692
8 1.50 7368 7368 7368 6971 6529 6176 6044 5956 5868 5735 5647 5250 4368 3441 2779 2354 2034 1627 1322 1068 864 559 508 458
10 1.50 5693 5693 5693 5386 5045 4773 4670 4602 4534 4432 4364 4057 3375 2659 2148 1800 1519 1215 987 797 646 418 380 342
10 2.00 7952 7952 7952 7524 7048 6667 6524 6429 6333 6190 6095 5667 4714 3714 3000 2550 2222 1778 1444 1167 944 611 556 500
12 1.50 4639 4639 4639 4389 4111 3889 3806 3750 3694 3611 3556 3306 2750 2167 1750 1457 1212 970 788 636 515 333 303 273
18 1.50 2982 2982 2982 2821 2643 2500 2446 2411 2375 2321 2286 2125 1768 1393 1125 927 755 604 491 396 321 208 189 170
18 2.00 4073 4073 4073 3854 3610 3415 3341 3293 3244 3171 3122 2902 2415 1902 1537 1275 1053 842 684 553 447 289 263 237
14 1.50 3914 3914 3914 3703 3469 3281 3211 3164 3117 3047 3000 2789 2320 1828 1477 1224 1008 807 655 529 429 277 252 227
6.35 1.24 7730 7730 7730 7313 6850 6480 6341 6249 6156 6017 5925 5508 4582 3610 2916 2475 2150 1720 1397 1129 914 591 537 484
12.70 1.20 3414 3414 3414 3230 3026 2862 2801 2760 2719 2658 2617 2433 2024 1595 1288 1064 871 697 566 457 370 240 218 196
12.70 1.63 4777 4777 4777 4520 4234 4005 3919 3862 3805 3719 3662 3404 2832 2231 1802 1502 1252 1001 814 657 532 344 313 282
12.70 2.11 6400 6400 6400 6055 5672 5365 5250 5173 5097 4982 4905 4560 3794 2989 2414 2032 1732 1386 1126 909 736 476 433 390
12.70 2.41 7473 7473 7473 7070 6622 6264 6130 6041 5951 5817 5727 5325 4430 3490 2819 2389 2067 1654 1344 1085 879 569 517 465
15.90 1.00 2212 2212 2212 2093 1960 1854 1815 1788 1762 1722 1695 1576 1311 1033 834 685 552 441 359 290 234 152 138 124

Nickel Austenitic stainless steel grades

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Nickel is known to be an expensive alloying element and is essential in some applications where both stress corrosion resistance and austenite structure are required. For example, creep resistance is important in high temperature environments, where austenitic stainless steels are needed. Similar to the traditional austenitic stainless steels, the twin boundary is a significant feature of the nickel-rich austenitic stainless steels because of the lower stacking fault energy. Austenitic stainless steels are prone to stress corrosion cracking (SCC). However, the stress corrosion resistance is greatly improved when the nickel content exceeds 20%. The effect of nickel on the stress intensity of stress corrosion threshold (105℃, 22% NaCl aqueous solution) in Fe-Ni-Cr alloys containing 16%~21% chromium is studied. Nickel-rich austenitic stainless steel (NiASS) can be considered as a separate class of stainless steel. In fact, the stress corrosion resistance of biphasic and ferrite stainless steels is comparable to that of biphasic and ferrite stainless steels when the nickel content exceeds 30%. Several limited grades of nickel-rich austenitic stainless steels are listed in the table below. Super austenitic stainless steels 254SMO and 654SMO are designed specifically for the oil and gas industry. Typical applications are seawater cooling, pulp bleaching, and hydraulic and instrument piping equipment.

 

Ni-Austenitic stainless steels grades

Alloy C Si Mn Cr Ni Mo W Co Cu Nb N
254SMo 0.01 0.8 1.0 20 18 6.1 0.7 0.2
654SMo 0.01 3.5 24 22 7.3 0.5 0.5
Sanicro 25 0.1 0.2 0.5 22.5 25 3.6 3.5 3.0 0.5 0.23
Sanicro 28 0.02 0.6 2.0 27 31 3.5 1.0
Alloy 800 0.07 0.6 0.6 20.5 30.5
353MA 0.05 1.6 1.5 25 35 0.16
Alloy 825 0.03 0.5 0.8 20 38.5 2.6
Alloy 625 0.03 0.5 0.5 21 Bal 8.5
Alloy 690 0.02 0.5 0.5 30 60
Alloy 600 0.05 0.4 0.8 16.5 Bal 0.5

SANICRO 25, a 22Cr-25Ni alloy, is designed for use in boilers up to 700 °C. It is a material suitable for superheaters and reheaters due to its good creep fracture strength and high temperature corrosion resistance,. In fact, the creep fracture strength of SANICRO 25 is superior to that of most austenitic stainless steels in the range of 600~750℃. In a highly corrosive acidic environment, The Sanicro 28 is usually the best choice. It is used in high-intensity drilling Wells with tubing, casing and acid gas lining, and other applications include heaters, pump systems, and pumps and containers in wet phosphoric acid plants and super phosphoric acid plants.

Alloy 800 is often used in the environment range from 550 to 1100℃, which requires excellent creep resistance, good high-temperature corrosion resistance and high-temperature strength of materials. These alloys are also used in the inlet and outlet ports of the production of ammonia, methanol and civil gas, as well as in the furnace tubes used in the production of vinyl chloride and ethylene. Other applications include heat exchange tubes and radiation tubes for fluidized combustion beds and parts of heat treatment furnaces, such as muffler tubes and protective sleeves for thermocouples.

The 25Cr-35Ni alloy 353Ma is designed for use in cracking furnaces and reforming tubes where synthetic gases are treated in environments where carburizing and nitrogen absorption are potentially problematic. Although there are other alternatives that contain more chromium, 353 MA is the best choice. One reason is that it contains the element Ce, which helps form a very stable surface oxide layer.

Alloy 690 contains 60 percent nickel and is used mainly in the piping of steam generators in nuclear power plants. The operating temperature is 365℃, at which the stress corrosion crack between grains is a potential problem. Under given service conditions, alloy 690 is almost free from corrosion, making it the preferred alloy.

It is interesting to note that nickel-rich Austenitic stainless steel 254SMO is also used for art. “God, Over the Rainbow” sculpture by Carl Milles was installed in 1995 on the south coast of the Nak Strand in Stockholm. The sculpture is about 23m high and is a famous scenic spot where a large number of sailors pass by every day. The surrounding seawater contains salt, chloride is very easy to cause surface corrosion, high strength super austenitic stainless steel 254SMO is very suitable for this environment.

How to choose the right stainless steel grades?

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Stainless steel is the most popular metal used in kitchenware and other commercial applications because of its durability and resistance to corrosion. However, stainless steels are vulnerable to corrosion if exposed to saltwater and certain chemicals. When purchasing the right stainless steel grades, you should make sure that the following four terms – Corrosion-resistant, mechanical properties, machinability, weldability, surface treatments, that’s depends on the degree of resistance to wear and corrosive solutions encountered during the finishing or seasoning process. Moreover, the type of finishing used and the degree of alloying in the construction determine the composition of the final grade.

 

Corrosion-resistant

Corrosion resistance includes non-rust and acid, alkali, salt and other corrosive media performance, as well as high-temperature oxidation resistance, corrosion resistance and other properties. Selecting the stainless steel project is to solve various corrosion problems encountered in engineering, and so the corrosion resistance of stainless steel in a corrosion environment can guarantee the equipment within the service life have enough ability to resist corrosion, to ensure the safe operation of the equipment, is a priority when select material should be paid attention to the following terms: the standard of corrosion resistance is determined by people, can not be limited by it and you can not ignore it, should use the conditions of use requirements to determine the appropriate grade.

So far, there is no stainless steel that has good rust resistance in any environment , corrosion resistance, but a grade is more suitable for a specific environment. It is worth noting that the choice of stainless steel should not only consider its general corrosion resistance but also consider its local corrosion resistance. Especially in water medium and chemical medium, the latter is particularly important. The use of experience has proved that the sudden destruction of stainless steel equipment and components, local corrosion is more harmful than general corrosion. When quoting the corrosion resistance data of stainless steel in various manuals and literature, attention should be paid to the fact that many of them are test data, and there are often large differences with the actual media environment.

 

Mechanical properties

Mechanical properties include strength, hardness, plasticity, toughness, fatigue and other properties. Note that most of these properties have been measured in atmospheric environments without strong corrosive media. When in corrosive media, these mechanical properties, such as fatigue strength, are significantly reduced and sometimes break far below their strength limits under static tensile stress and media. For the equipment under frequent load, in addition to the design of strength, also required to do fatigue design, for working at low temperature, and bear impact load of stainless steel components, must consider its low-temperature toughness, brittleness, transition temperature, low-temperature fracture toughness; Sometimes the coefficient of linear expansion must be considered.

 

Machinability, weldability, surface treatment

They are so-called technology, is the ability of stainless steel to adapt to the equipment manufacturing process, such as: after processing shape, size, precision, smoothness, etc.; Welding method.

In order to determine the good resistance against acids and oxidation, it is important to note the composition of the stainless steel. A good combination of this alloy with low carbon material will result into a combination of excellent corrosion resistance and excellent ability to resist impurities. The resulting combination has been aptly referred to as 904L, which stands for high alloy austenitic. With this alloy, you are guaranteed not only a sturdy machine but also the ability to cut through any kind of surface.

Grade 904L stainless steels are a low-carbon, austenitic stainless metal with high chromium content. This high chromium content improves its resistance to acids, including sulphuric acid, reducing the risk of corrosion. In addition, it enhances the strength of the structure by increasing its toughness and preventing fatigue cracking. We are a professional supplier and processing center of high-quality 904L stainless steel sheet and pipe, any interested in us, just give us a call.

The choice of Stainless steel material for food and beverage industrial

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Most of the challenges facing the use of stainless steel in dairy and other food processing industries are related to heat exchangers and natural surface water such as well water. Like breweries, most food-related industries frequently use hot media that are heated by steam or cooled by water, which is associated with pasteurization and sterilization, and thus often encounter problems such as stress corrosion cracks. In general, food processing does not corrode standard stainless steel such as AISI304 or 316. However, the wide range of processing methods in this industry leads to many different corrosion failures. Such as:

  • Erosion/corrosion in stainless steel milk heat exchangers.
  • Uniform corrosion caused by lactic acid and other organic acids at high temperature.
  • Microbial corrosion caused by surface water or well water.
  • Stress corrosion cracks, mainly “chloride crack”.
  • Corrosion fatigue caused by vibration.

 

For plate type heat exchangers in the dairy industry, whey, milk and process water are processed through plate heat exchangers made of 1.4401 stainless steel, as shown in the table below.

Products Inlet temperature, ℃  Outlet temperature，℃ Pressure
Whey 30 10 Medium
Milk 7 30 High
Process water 57 14 Low

 

In order to avoid leaking contaminated food, the pressure of process water is kept as low as possible. Leakage occurs when the thin plates collide with each other at the pressure point, which is caused by fatigue cracks in the thin cross-section after the pressure point is eroded and corroded. Metallographic microscopic study of the section shows that no stress corrosion crack has occurred. Since the low pressure is on the process waterside, coupled with pressure fluctuations and fluid flow vibrations, erosion/corrosion occurs on this side. The way to avoid the physical collision of the plates is to change the pressure and pressure fluctuation or increase the spacing between the plates.

 

Microbial corrosion caused by well water

The food industry usually uses well water. The iron content in well water is quite high, which can activate iron-related bacteria and cause severe corrosion. One of the commonly used water treatment methods is to remove iron from well water in order to make food taste better and to avoid corrosion of packaging and processing equipment after cleaning and rinsing. Surface and well water also contain a number of types of microorganisms that are active in both aerobic and anaerobic conditions. Aerobic iron-related bacteria oxidize iron ions, while anaerobic iron-related bacteria reduce iron ions. These two reactions are ultimately classified as microbial corrosion (MIC). Other microorganisms may also be active in the water such as sulfuric acid-reducing bacteria, acid-producing bacteria. In the same biofilm, aerobic bacteria and (below) anaerobic bacteria may be active.

When using well water to treat canned vegetables (flush and cool after pasteurization). Where water does not flow for a long time, 316L manufactured pipes will leak within six months due to the high temperature of the water. The well water itself is cold (below 10 ° C), but can easily rise to 30 ° C in summer if it remains stationary in the pipe for a long period of time. Compared with Legionella, corrosive biofilms formed at higher activity rates at higher temperatures.

 

Pitting corrosion caused by chlorine disinfection and sterilization

Sodium hypochlorite is commonly used in cleaning and disinfecting stainless steel equipment. If the concentration of sodium hypochlorite is too high or the cleaning and disinfection time is too long, sodium hypochlorite will cause serious corrosion of stainless steel, especially when the temperature is above 25℃.

 

Stress corrosion fracture

There is a risk of chloride stress corrosion fracture at temperatures above 60 ° C. As cold deformation, tensile stress and chloride content increase, the risk increases. Compared with the cold-deformed pipe without annealing, the annealed pipe is insensitive to chloride stress corrosion fracture. The outside of straight-seam welded steel tubes used in the dairy industry is much more sensitive to chloride, due to tensile stresses in the section caused by bending during the manufacturing process. In other applications, tubular heat exchangers may be responsible for chloride stress corrosion cracking. Chloride stress cracks are more likely to develop on one side of the shell if the temperature exceeds 60 ° C. AISI 304 and 316 are sensitive to this problem and there is a risk of stress corrosion fracture when used in sugar evaporators where ferritic stainless steels can be used instead. Ferritic stainless steel AISI 441 has been widely used in the sugar industry, especially AISI 439. In practical use, the choice of piping is developed in 304 stainless steel and 439 stainless steel. 304 stainless steel for shorter pipes and 439 for longer pipes.

304 stainless steel: The steel can be selected when the length of the pipe is less than 3 meters. The thermal expansion coefficient of 304 stainless steel is 1.8×10-2mm/m℃, which is much larger than that of carbon steel. When the vessel is at a high temperature, the thermal stress of the pipe is high. AISI 304 stainless steel pipes were annealed after straight seam welding in the factory.

439 Stainless Steel: ASTM439 is a titanium stabilized ferritic stainless steel (17% ~ 19%Cr) used for evaporators or coils up to 5 m in length. The risk of stress corrosion fracture is greater when the length of the pipe is more than 7 m, the concentration of chloride is high, and the degree of cold deformation is high. No stress corrosion fracture occurs in ferritic stainless steels such as AISI 439. In order to avoid crevice corrosion, if corrosion resistance and sanitary conditions allow, people usually use the heat exchanger with the shell is thick carbon steel plate and the inner wall is thin thickness AISI439 steel pipe. In this way, carbon steel can provide cathodic protection for the thin-walled stainless steel pipe, and can reduce the design and production cost and prolong the service life.