Gráfico de la presión de los tubos de acero inoxidable 304L

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Los tubos inoxidables son ideales en muchas aplicaciones debido a su baja resistencia a la corrosión y a su alta resistencia, lo que permite su uso en lugares donde hay variaciones en la cantidad de gas y aceite disueltos. Los tubos y tuberías de acero inoxidable 304 y 304L se utilizan en casi todos los campos del mundo. Representan el 50% del uso mundial de acero inoxidable. Acero inoxidable 304L Actualmente es la segunda clase de acero inoxidable más utilizada, después del acero 304. Es una clase de acero de bajo contenido de carbono que lo hace resistente a la corrosión y ideal para su uso en transporte y en aplicaciones industriales.

Hay muchas características diferentes que se derivan del uso de tubos de acero inoxidable 304L. Una de las características clave es que es excelente en cuanto a resistencia a la corrosión. Esto significa que es capaz de resistir la oxidación, lo cual es esencial para los tubos de transporte. Además, estos tubos son capaces de resistir la corrosión después de estar expuestos a la humedad y al agua, lo que los hace ideales para aplicaciones en las que se espera que resistan a las condiciones climáticas severas. También es importante tener en cuenta que estos tubos no se oxidarán una vez expuestos al aire, lo que los hace ideales para su uso en lugares donde el aire normalmente representaría un problema. Con todas las diferentes presiones que se pueden obtener con el acero inoxidable 304L, que dependen de la anchura de la pared y del proceso de soldadura o soldadura sin costura, seguramente encontrarás algo que se ajuste a tus necesidades. Estos tipos de tubos de acero también son aptos para el uso en el entorno debido a que transmiten bien el calor y son muy resistentes a la abrasión y a los impactos. Aquí se encuentra el siguiente cuadro de clasificación de presión para tuberías de acero inoxidable 304L.

TP304L
TEMPERATURA 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
TEMPERATURA 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

Presión de diseño (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

Grados de acero inoxidable austenítico de níquel

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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 Sí Mn Cr No 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.

 

Propiedades mecánicas

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.

La elección del material de acero inoxidable para la industria alimentaria y de bebidas

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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.

Productos 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. Acero inoxidable 304 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.

 

 

La elección del material de acero inoxidable para la cervecería

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El acero inoxidable se utiliza ampliamente en la industria alimentaria y de bebidas debido a su resistencia a altas temperaturas, su resistencia a la corrosión y sus propiedades higiénicas. En comparación con otras áreas como la producción de petróleo y gas, los recipientes y tuberías para la elaboración de cerveza se limpian regularmente mediante CIP (limpieza in situ). Para obtener los mejores resultados de limpieza, un buen tratamiento superficial de los recipientes y tuberías es fundamental. Desde la década de 1960, los procesos industriales de elaboración de cerveza han utilizado a menudo acero inoxidable AISI 304, o AISI 316, y acero inoxidable dúplex 2205. La resistencia a la corrosión de 2205 El acero inoxidable es comparable al de AISI 304 Si bien la resistencia es mayor y no es fácil producir craqueo de cloruro cuando la temperatura es superior a 60 °C. El malte troceado, la cerveza y la cerveza no corroen el acero inoxidable, incluso a punto de ebullición. Sin embargo, el acero inoxidable trabajado en frío es susceptible de craqueo de cloruro cuando se utiliza a temperaturas superiores a 60 °C. En general, la solución de elaboración de cerveza tampoco corroerá el acero inoxidable AISI 304. Solo en la elaboración de cerveza utilizando agua suave, se puede elegir el acero inoxidable AISI 316 debido al alto contenido de cloruro.

El craqueo de cloruro puede ocurrir en tubos y vasos de paredes finas debido a su susceptibilidad a la tensión de tracción. Si el vaso se atasca, suele ser debido a una calidad de soldadura inadecuada o a una carga de fatiga elevada. El CIP (limpieza en campo) no corrode el acero inoxidable, pero en condiciones extremas puede causar craqueo de cloruro en acero inoxidable con un alto grado de conformado en frío. Los mecanismos de fallo de la corrosión por fatiga y la corrosión por tensión son similares. Un ejemplo de corrosión por fatiga en un tanque de sacarificación es la apertura de un almacén de granos. Después de la molienda y el calentamiento, los granos se separan de la cerveza y se descargan a través de la abertura del almacén de granos. El impacto y la alta carga generada por el granos descargados producen fisuras de corrosión por fatura a lo largo del borde de soldadura en el área directamente opuesta a la boca del almacén. La fuga en algunos lugares se debe a una calidad deficiente. El recipiente de cerveza puede romperse desde el exterior hacia el interior debido al craqueo de cloruro y a la fatiga térmica. Si durante la soldadura de tuberías espirales calientes con vapor se produce una gran tensión interna, puede producirse una fisuración en toda la pared del recipiente de acero inoxidable.

Sensibilidad del acero inoxidable

AISI 304 o Acero inoxidable 316 Tiene un contenido de carbono < 0,08% y puede sensibilizarse si se expone a temperaturas de 500 ~ 800 °C durante un período de tiempo determinado, lo que puede ocurrir durante la soldadura. Por lo tanto, la soldadura provoca la sensibilización de la “zona afectada por el calor” a lo largo de la soldadura.

La sensibilización llevará a la formación de carburo de cromo en los límites de grano, lo que dará como resultado un bajo contenido de cromo en los límites de grano, lo cual puede causar una fácil corrosión intergranular del acero inoxidable en el caso de una pared gruesa del tubo (BBB 0,2 ~ 3 mm). Para evitar esta situación, a menudo se opta por un acero “soportable para soldar”: como el acero de grado L, como el 304L316L, cuyo contenido de carbono es inferior a 0,03%; acero estabilizado con titanio: 321,316 Ti.

 

Tratamiento superficial

Para la resistencia a la corrosión del acero inoxidable, la calidad de la soldadura y la zona afectada por el calor, la rugosidad superficial y el estado de la capa protectora de óxido son importantes. El estado superficial del acero inoxidable es particularmente importante para la industria alimentaria y de bebidas y la industria farmacéutica. Los problemas de corrosión en las cervecerías suelen ser causados por condiciones superficiales irregulares. Durante la fabricación (soldadura, tratamiento térmico, rectificado, etc.), la capa de óxido de cromo pasivada se deteriora, lo que reduce la resistencia a la corrosión. El gas protector insuficiente utilizado en la soldadura de acero inoxidable provocará la formación de un color de templado caliente. Estos colores de templado térmico porosos están compuestos por diversos óxidos que tienden a absorber iones como los iones de cloruro, lo que reduce la resistencia a la corrosión y no protege el metal base.

Si los termales o otros tipos de contaminantes son inaceptables, debe utilizarse algún tipo de acabado metálico para eliminarlos. La decapación o la pasivación pueden eliminar la antigua capa de óxido, el color de la pieza y otros contaminantes, permitiendo así que la película de óxido de cromo pasivado se recupere completamente. El proceso más común de decapado consiste en sumergir los tubos de acero inoxidable en una solución mixta de ácido nítrico y ácido fluorhídrico, que también se puede realizar mediante un sistema de lavado por pulverización o tuberías. Aunque la superficie del acero inoxidable se vuelve activa tras la decapación, una película de pasivación puede formarse en 24 horas debido a la reacción del cromo con el oxígeno del aire, pero en algunos casos la pasivación se facilita químicamente mediante el uso de ácido nítrico.

 

Soldadura

Los surcos y las zonas afectadas por el calor suelen ser la causa de la corrosión. Para las cervecerías y otras industrias alimentarias, los defectos en los surcos, como la falta de penetración, son de suma importancia, causando problemas de higiene y esterilización. Los ingenieros y los compradores suelen identificar condiciones inadecuadas de soldadura y procedimientos de soldadura que no pueden realizarse correctamente. El resultado son surcos de mala calidad y condiciones superficiales en la construcción que deben completarse.

El recalentamiento térmico se produce debido a que la luz se absorbe en una capa de óxido transparente, debido a las diferentes densidades de esta última. Debido a que los colores tienen coeficientes de refracción diferentes, la capa de óxido que parece azul solo puede reflejar la luz azul y absorber la luz de otros colores. Las capas de óxido más gruesas tienen más agujeros que las capas de óxido finas totalmente transparentes, por lo que estas últimas reducirán la resistencia a la corrosión y la no adherencia del acero inoxidable. Para la mayoría de los estándares, se acepta un color claro y escamoso de la capa de calor; todos los demás colores de capa de calor, como el rojo y el azul, son inaceptables. La industria farmacéutica no permite el templado a alta temperatura.

La geometría de la soldadura debe ser lo más regular posible. Las soldaduras bien realizadas no dañarán la superficie metálica del sustrato. La corrosión a menudo comienza en un pequeño agujero en el interior de la soldadura, en el inicio o el final de la misma.

Teóricamente, no hay pequeños agujeros, solapamientos ni otros defectos en el inicio ni en el final. Una buena penetración de la soldadura es muy importante. El tubo debe ser bien simétrico y la anchura de la soldadura debe ser fija.

 

Rugosidad superficial

La rugosidad superficial afecta las propiedades higiénicas y de corrosión del acero inoxidable. La resistencia a la corrosión de la superficie electropolida es la mejor, seguida por la superficie mecanicamente pulida. En general, la industria de la cerveza y la industria alimentaria no exigen el uso de superficies electropolidas, sin embargo, estas superficies ofrecen excelentes condiciones higiénicas y una fácil limpieza. La mayoría de los tubos se fabrican con un proceso de recocido brillante durante la fabricación. Debido a que el proceso de recocido brillante mejora considerablemente la calidad, la decapado interno de estos tubos suele ser opcional a menos que la superficie del material tenga una fuerte coloración de retorno de calor o esté contaminada con hierro. La chapa de acero inoxidable suele tener una superficie de 2B; ofrece un buen rendimiento superficial. En las cervecerías, los tubos de acero inoxidable de pared estrecha y soldados en caliente son los más utilizados, con una superficie de 2B y a veces otra superficie (cepillo o pulido) en el exterior. Los tubos extrudados de acero inoxidable no se utilizan comúnmente en las cervecerías; se utilizan para aplicaciones de alta presión.

Comparación de las chapas de acero 301, 301L y 301LN

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301 stainless steel is a type of austenitic stainless steel with a high work hardening rate. Its tensile strength can be up to 1300MPa or more. 1/16 hard to full hardening cold-rolled 301 plates are available and maintain sufficient ductility under 1/2 hardening conditions. It can be used for aircraft components, structural components of buildings, especially railway carriage components after rolling or bending. The 3/4 hardening to full hardening cold-rolled sheets should be used for simple component designs that require high wear resistance and elasticity. The 301L and 301LN are low carbon versions and high nitrogen versions of the 301. If better ductility is required or thick section profiles are to be welded, the low carbon 301L is preferred. The higher nitrogen content of 301Ln can compensate for the lower carbon content. They are specified in ASTM A666, JIS G4305, and EN 10088-2.

 

Chemical composition of 301, 301L, 301LN

Nivel C Mn Sí P S Cr No N
301 ≤0.15 2.0 1.0 0.045 0.03 16.0-18.0 6.0-8.0 0.1
301L ≤0.03 2.0 1.0 0.045 0.03 16.0-18.0 6.0-8.0 0.2
201LN ≤0.03 2.0 1.0 0.045 0.03 16.5-18.5 6.0-8.0 0.07-0.2

 

Mechanical property of 301, 301L, 301LN

301 Tempering

ASTM A666

 Resistencia a la tracción, MPa Yield strength 0.2%, Mpa Elongation (in 50mm)thick>0.76mm Hardness, Rockwell
Annealed 515 205 40 /
1/16 hard 620 310 40 /
1/8 hard 690 380 40 /
1/4 hard 860 515 25 25-32
1/2 hard 1035 760 18 32-37
3/4 hard 1205 930 12 37-41
Full hard 1275 965 9 41+

 

Specification of 301, 301L, 301LN

Nivel UNS No Euronorm JIS
No Name
301 S30100 1.4319 X5CrNi17-7 SUS 301
301L S30103 / / SUS 301L
201LN S30153 1.4318 X2CrNiN18-7 /

Resistencia a la corrosión

Similar to Acero inoxidable 304, it has good corrosion resistance in normal temperature and mild corrosion applications.

Heat resistance

Good oxidation resistance to temperatures up to 840°C (intermittent use) and 900°C (continuous use). Exposure above 400°C causes gradual loss of work hardening effect, and the strength at 800°C is equivalent to 301 of annealing. Under creep conditions, the strength of work-hardened 301 even decreases to lower than that of annealed 301.

Solution (annealing) treatment

Heated to 1010-1120°C and rapidly cooled and annealed at approximately 1020°C. Heat treatment will not harden it.

Cold working

301 stainless steel and its low carbon version 301L for the need of high strength occasions. It has a very high work hardening rate of about 14MPa/%Ra (for each 1% of cold working surface reduction, tensile strength increases by 14MPa), cold rolling and cold forming can achieve very high strength, a portion of the strain hardening austenite converted to martensite. 301 is not magnetic under annealing conditions, but strong magnetic after cold working.

Soldadura

301 can be used for all standard welding methods and mostly 308L filler metal can be used for 301 weldings. 301 stainless steel welds must be annealed for optimal corrosion resistance, whereas 301L or 301Ln welds do not require annealing. Welding and post-weld annealing both reduce the high strength caused by cold rolling, so spot welding is often used to assemble cold-rolled 301 parts which has a small heat-affected zone and the strength of the whole part is almost not reduced.

Typical applications

Rail vehicle structural parts-roll forming, bending forming, or stretch forming into profiles, also in sheet. Aircraft fuselage, road trailer, car hub cap, wiper holder, toaster spring, stove fixture, screen frame, curtain wall, etc.