La tolleranza di spessore della piastra in acciaio inox

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Di solito chiamiamo spessore di 4-25,0 mm per la piastra in acciaio inox al centro, spessore di 25,0-100,0 mm per la piastra spessa in acciaio inox, spessore superiore a 100,0 mm è la piastra extra spessa. Quando si cerca una piastra in acciaio inox adatta, sono disponibili diversi gradi in base alla resistenza del metallo e alla sua composizione chimica. Esiste un grado di elevata qualità realizzato con leghe Cr-Ni che vengono generalmente utilizzate in applicazioni commerciali come imbarcazioni a pressione, gusci di caldaie, ponti, automobili, cantieri navali, costruzioni e altri utilizzi industriali.

È importante considerare il tipo di utilizzo che la piastra in acciaio inossidabile dovrà avere in una determinata applicazione industriale. Alcune applicazioni richiedono una piastra rinforzata e temprata in grado di resistere a colpi di martello, abrasioni e impatti. Altre potrebbero richiedere un materiale più fragile e morbido in grado di sopportare piegature e deformazioni. Gli altri criteri da osservare sono la resistenza alla corrosione e questo determinerà quale tipo di piastra in acciaio inossidabile sia più adatto all’applicazione. I gradi più comunemente utilizzati sono: 304, 316LPlacca in acciaio inossidabile tipo 310S e 904L. Qui sono riportati i valori di tolleranza per lo spessore consentito della placca in acciaio inossidabile secondo le specifiche ASTM, JIS e GB.

 

Placca in acciaio inossidabile JIS

Spessore Larghezza
<1250 ≥1250<1600
≥0.30~<0.60 S 0,05 S 0,06
≥0.60~<0.80 S 0,07 S 0,09
≥0.80~<1.00 S 0,09 S 0,10
≥1.00~<1.25 S 0,10 S 0,12
≥1.25~<1.60 S 0,12 S 0,15
≥1.60~<2.00 S 0,15 S 0,17
≥2.00~<2.50 S 0,17 S 0,20
≥2.50~<3.15 S 0,22 S 0,25
≥3.15~<4.00 S 0,25 S 0,30
≥4.00~<5.00 S 0,35 S 0,40
≥5.00~<6.00 S 0,40 S 0,45
≥6.00~<7.00 S 0,50 S 0,50

 

Placca in acciaio inox ASTM

Spessore Tolleranza consentita Larghezza
In alto In basso ≤1000 ＞1000~≤1300
0.10 0.03 0.03
0.15 0.04 0.04
0.20 0.05 0.05
0.25 0.05 0.05
0.30 0.03 ——-
0.40 0.04 0.04
0.50 0.08 0.08
0.50 0.045 0.05
0.60 0.05 0.05
0.75 0.10 0.10
0.80 0.05 0.05
1.00 0.055 0.06
1.20 0.08 0.08
1.25 0.13 0.13
1.50 0.08 0.08
1.75 0.15 0.15
2.00 0.18 0.18
2.00 0.10 0.10
2.25 0.20 0.20
2.50 0.23 0.23
2.50 0.10 0.11
2.75 0.25 0.25
3.00 0.25 0.25
3.00 0.13 0.13
3.25 0.30 0.30
3.50 0.30 0.30
3.75 0.36 0.36
4.00 0.36 0.36
4.00 0.17 0.17
4.99 0.36 0.36
5.00 0.17 0.17
6.00 0.17 0.20
8.00 0.17 0.

 

Placca in acciaio inox GB

Spessore Tolleranza di spessore consentita
Alta precisione (A) Precisione standard (B)
>600~1000 >1000~1250 >600~1250
0.05~0.10 ——- ——- ——-
>0.10~0.15 ——- ——- ——-
>0.15~0.25 ——- ——- ——-
>0.25~0.45 S 0,040 S 0,040 S 0,040
>0.45~0.65 S 0,040 S 0,040 S 0,050
>0.65~0.90 S 0,050 S 0,050 S 0,060
>0.90~1.20 S 0,050 S 0,060 S 0,080
>1.20~1.50 S 0,060 S 0,070 S 0,110
>1.50~1.80 S 0,070 S 0,080 S 0,120
>1.50~2.00 S 0,090 S 0,100 S 0,130
>2.00~2.30 S 0,100 S 0,110 S 0,140
>2.30~2.50 S 0,100 S 0,110 S 0,140
>2.50~3.10 S 0,110 S 0,120 S 0,160
>3.10~4.00 S 0,120 S 0,130 S 0,180

Sono i tipi di acciaio inossidabile duplex 318LN?

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318LN is Nitrogen-enhanced stainless steel commonly used to address corrosion failures in 300 series stainless steel. The structure of 318LN stainless steel is composed of Austenite surrounded by continuous Ferrite phases. 318LN contains about 40-50% Ferrite in the annealed state and can be considered duplex stainless steel. The duplex structure combines ferrite alloys (stress corrosion cracking resistance and high strength) with the superior qualities of Austenitic alloys (ease of manufacture and corrosion resistance). The 318LN is resistant to H2S uniform corrosion, sulfide stress cracking, hydrogen embrittability and pitting, and reducing media corrosion. It is commonly used to manufacture sulfur-resistant wellheads, valves, stems, and fasteners for use in mining environments where H2S partial pressures exceed 1MPa. However, the use of 318LN duplex stainless steel should be limited to less than 600°F because prolonged high temperatures can brittle the 318LN stainless steel.

 

The chemical composition of 318LN steel

Cr Ni Mo C N Mn Si P S
22.0-23.0 4.50-6.50 3.00-3.50 ≤0.030 0.14-0.20 ≤2.00 ≤1.00 ≤0.030 ≤0.020
Mechanical Property
Ys (Mpa) Ts (Mpa) Elongation (%) Hv
Norme ≥ 450 ≥ 620 ≥ 18
Physical property
Density (g/cm) Specific heat(J/g.C) Conductivita termica

100C(W/m.)

 The coefficient of thermal expansion

20~100C (10/C)
7.8 0.45 19.0 13.7

 

Features of 318LNsteel

  • Excellent resistance to sulfide stress corrosion
  • Good resistance to chloride stress corrosion cracking, pitting and crevice corrosion
  • High strength,
  • Good weldability and workability

 

Applications of 318LNsteel

  • Chemical treatment containers, pipes and heat exchangers
  • Pulp mill digesters, bleach cleaners, chip presteam containers
  • Food processing equipment
  • Petrochemical pipelines and heat exchangers
  • Flue gas desulfurization equipment

 

318LN duplex stainless steel is an economical and effective solution for applications where 300 series stainless steel are susceptible to chloride stress corrosion cracking. When stainless steel is subjected to tensile stress, stress corrosion cracking will occur in contact with a solution containing chloride, and rising temperature will also increase the sensitivity of stainless steel to stress corrosion cracking. The combination of chromium, molybdenum, and nitrogen enhances the 318LN’s resistance to chloride pitting and crevice corrosion, which is critical for services such as marine environments, brackish water, bleaching operations, closed-loop water systems, and some food processing applications. In most environments, 318LN’s high chromium, molybdenum and nitrogen content provides superior corrosion resistance to ordinary stainless steels such as 316L and 317L.

Vantaggi dell'attacco a gomito in acciaio inox

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Gli accessori per tubi in acciaio inox, in particolare i tee, gli elbow e i reducers, sono sempre più comuni nell’utilizzo in ambito di ingegneria delle condotte a causa delle loro buone caratteristiche di modellazione, resistenza alla corrosione, resistenza alle alte temperature e alle alte pressioni, saldatura e altre. Rispetto agli accessori per tubi in acciaio al carbonio, gli accessori per tubi in acciaio inox sono spesso utilizzati nel trasporto di acqua potabile e nelle condotte petrolchimiche e altre con elevati requisiti ambientali. Per rendere più facile la comprensione di chi non ne conosce molto, questo articolo è pensato per illuminarvi su questa linea di prodotti e sulle sue diverse caratteristiche. Inoltre, discuteremo anche i vantaggi che potrete trarre dall’utilizzo di questi accessori. Quando avrete finito di leggere questo articolo, avrete sicuramente una buona idea di cosa siano questi prodotti e come potrete acquistarli.

Specifiche dell'anca in acciaio inox 304

DN NPS Serie A Serie B 45°Elbow 90°Elbow Orecchio 180°
DN NPS Serie A Serie B L.R L.R S.R L.R S.R L.R S.R
15 1/2 21.3 18 16 38 – 76 – 48 –
20 3/4 26.9 25 19 38 – 76 – 51 –
25 1 33.7 32 22 38 25 76 51 56 41
32 1.1/4 42.4 38 25 48 32 95 64 70 52
40 1.1/2 48.3 45 29 57 38 114 76 83 62
50 2 60.3 57 35 76 51 152 102 106 81
65 2.1/2 76.1(73) 76 44 95 64 190 127 132 100
80 3 88.9 89 51 114 76 229 152 159 121
90 3.1/2 101.6 – 57 133 89 267 178 184 140

Questi gradi comunemente utilizzati nella connessione dei tubi sono: 304Angoli in acciaio inossidabile tipo 316 e 316l. Sono ampiamente utilizzati nella produzione automobilistica, farmaceutica e alimentare. Infatti, non è raro trovare questi prodotti utilizzati nelle strutture di lavorazione alimentare. La ragione della loro ampia diffusione è molto semplice: forniscono un supporto efficace alle parti operative delle macchine, senza compromettere l’altrettanto importante qualità del lavoro. Come accennato in precedenza, utilizzano un processo di saldatura appositamente progettato, chiamato bending heat cure, per garantire che l’unione dell’angolino sia supportata da tubi in acciaio inossidabile ad alta resistenza. Ciò garantisce che i tubi possano essere sostituiti in qualsiasi momento necessario.

Un altro importante vantaggio dell'utilizzo di accessori in acciaio inox è la sua resistenza alla corrosione. Poiché l'acciaio inox è un acciaio legato con l'aggiunta di Cr e Mo, ha la possibilità di diventare parte integrante di molti processi industriali, dove la conduttività elettrica è fondamentale. Ciò significa che un guasto elettrico può compromettere il funzionamento di un impianto e potrebbe non essere sufficiente spegnere la corrente. Ad esempio, quando si verifica un guasto elettrico in un impianto chimico, il personale di emergenza deve accedere autonomamente alla zona, cosa che potrebbe rivelarsi molto difficile se i punti di distribuzione della corrente non sono adeguatamente posizionati.

 

WLD steel è un 304 Fornitore e produttore di gomiti a 90 gradi in acciaio inox. In primo luogo, vengono realizzati con l’obiettivo di garantire prestazioni di altissima qualità. Ciò significa che sono dotati di accessori per tubi in acciaio inox con il diametro e la lunghezza corretti per l’applicazione, indipendentemente dalla dimensione o dalla forma del tubo. Ad esempio, potrebbe essere necessario montare tubi di diverse larghezze, che variano da un incremento di due pollici a uno di quattro pollici. Un prodotto ben progettato sarà in grado di soddisfare queste esigenze senza alcun problema.

 

 

La prevenzione della corrosione delle condotte sotterranee

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The corrosion of above-ground pipelines is caused by the combined action of corrosive ions (Cl-, S2-), CO2, bacteria and dissolved oxygen. Dissolved oxygen is a strong oxidant, it is easy to oxidize iron ions to form precipitation, and the relationship between dissolved oxygen and corrosion rate is linear. Sulfate-reducing bacteria will the existence of the sulfate-reducing hydrogen sulphide in the water, may lead to pipe hydrogen induced cracking and stress corrosion cracking, corrosion products generated ferrous sulfide and adhere on the surface of the steel is poor, easy to fall off, is potential, as the cathode constitute an active micro battery and steel matrix, and continue to produce corrosion to the steel substrate. Saprophytic bacteria adhere to the pipeline and cause fouling blockage, and also produce oxygen concentration cells and cause pipeline corrosion. The oil-water mixture in the surface pipeline may enter the sewage tank after separation. Therefore, when choosing anti-corrosion measures for the above-ground pipelines in the oil fields, the protection effect, construction difficulty, cost and other factors should be considered. Some commonly used anti-corrosion measures are for oil field above-ground pipelines:

 

Coating

There are many anticorrosive coatings on pipelines, and their performance is different. Choosing appropriate coatings can greatly extend the service life of pipelines. According to the corrosive environment, transport media and other conditions to choose the appropriate coating. The outer protective coating is the first and most important barrier of the above-ground steel pipe, mainly organic coating and metal coating (or coating). Organic coatings can be divided into epoxy resin, modified phenolic epoxy, asphalt, coal tar and other coatings. The experimental results show that the surface of the coating does not bubble when soaked in brine and oil, and the coating meets the requirements of API RP 5L2 adhesion and peel test, indicating that the coating has good adhesion. The coating is heated at 250℃ for 30min and then cooled by water at room temperature. The coating surface has no peeling, no cracking, no bubble, no adhesion loss, etc., that is, the coating has good heat resistance. According to ASTM D522, ASTM D968 and other standards to carry out bending and wear tests, the coating also has good bending and wear resistance.

 

Cathodic protection

It is not easy to coat the internal surface for small diameter pipelines (pipe diameter less than 60mm), even if the coating is completed indoors, it is difficult to achieve 100% pinhole free. In addition, the inner wall coating is often subjected to wear in the process of use, so the use of cathodic protection can effectively reduce corrosion perforation. Sacrificial anode protection is the earliest cathodic protection method, which is simple to operate and does not require power supply. The sacrificial anode materials commonly used in China include magnesium, zinc, aluminum and their alloys.

The output current of the sacrificial anode depends on its shape and size. In the laboratory test of magnesium, zinc, an aluminum alloy of cathodic protection potential (relative to the copper/copper sulfate reference electrode), three types of alloy are accord with the requirement of oil and gas station cathodic protection specification (cathodic protective potential is 0.85 V or more), including aluminum alloy anode protective effect is best, magnesium anode and zinc alloy anode is poorer.

 

Special joint

The special joint is designed to solve the damage to the interface coating caused by pipe welding after coating. Methods include: using refractory insulation material and high-temperature coating; Or use a new type of high temperature heat insulation ceramic joint, which has good heat insulation performance and corrosion resistance, as well as in the temperature of drastic changes in the performance of the burst and permeability resistance, but the disadvantage is that the strength and toughness is poor. Laboratory tests show that under the conditions of drastic changes in temperature, the crack resistance and penetration resistance of the joint can meet the requirements. However, under the premise of ensuring the strength and toughness, the joint wall thickness is too thick, and the change of inner diameter will affect the normal construction of the pipeline. The use of refractory insulation materials and high-temperature coating joints can fully meet the requirements of use.

 

The heat treatments of U stainless steel heat exchanger

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When talking about the heat treatment of austenitic U-shaped stainless steel tubes, most people think it’s not necessary because of sensitization and high solution treatment temperature, it is easy to cause deformation of the pipe. In fact, the heat treatment of Austenitic stainless steel is inevitable, heat treatment can not change the structure of stainless steel tubes, but can change the processability.

For example, due to low carbon content, 304 stainless steel heat exchange tube is difficult when normalizing to make the surface roughness of the gear shaping cutter to meet the requirements, reduce the tool life. The low carbon martensite and iron cable structure obtained after incomplete quenching can greatly improve the hardness and surface roughness, and the service life of the pipe can also be increased by 3 ~ 4 times. In addition, the u-shaped heat exchange tube bending part has a small bending radius and obvious work hardening phenomenon, heat treatment is necessary, and compared with the whole equipment for heat treatment, austenitic stainless steel pipe solution heat treatment, pickling passivation is much simpler. In this paper, a series of tests have been taken on U-shaped tubes with different specifications, bending radius and heat treatment conditions, and the necessity of heat treatment for U-shaped tubes made of austenitic stainless steel has been analyzed.

 

Experimental materials:

304 stainless steel U-tube

Size: 19*2mm, bending radius: 40, 15, 190, 265, 340mm

Size: 25*2.5mm Bending radius: 40, 115, 190, 265, 340,mm

Heat treatment: untreated, subsolid solution treatment, solid solution treatment

 

Hardness Testing

The bending section of u-shaped heat exchange tube without heat treatment and subsolid solution treatment: with the decrease of bending radius, the hardness value increases. The hardness value of heat exchange tube after solution treatment (compared with that before bending) has no obvious change. This indicates that Austenitic stainless steel work hardening effect is obvious, and with the increase of deformation, the trend of work hardening increases.

 

Microscopic inspection

For the u-shaped bend section with a bending radius of 40mm: there are a lot of martensite and slip lines in the microstructure without heat treatment, and the equiaxed shape of austenite in the microstructure has completely disappeared (too much martensite will make the steel brittle). Most of the martensite in the subsolid solution treated tissue has been transformed, but a small amount of martensite still exists.

After solution treatment, the austenite grains were equiaxed and no martensite was found. The slip bands and martensite also existed in the unheated microstructure of u-shaped tubes with bending radius R of 115, 190, 265 and 340mm after bending, but the content decreased gradually with the increase of bending radius. When the bending radius R of the U-shaped tube is greater than or equal to 265mm, the effect on the microstructure before and after heat treatment is not significant. When the bending radius R is less than 265mm, there is martensite in the microstructure of unheated U-shaped tubes, and the content of martensite decreases with the increase of heat treatment temperature (subsolid solution treatment and solid solution treatment).

 

Intergranular corrosion test

By microscopic examination, it was found that the presence of martensite did not affect intergranular corrosion. Although there is a large amount of martensite in the absolutized microstructure, there is no tendency of intergranular corrosion along with the distribution of martensite. Some grain boundaries widened before and after solution treatment, and the distribution of grain boundaries widened was independent of the distribution of martensite. On the basis of microscopic examination after the corrosion test, the bending test was carried out for u-shaped tubes in various states according to the test standard. No intergranular corrosion cracks were found in the tubes after bending 180°.

 

Solution treatment temperature

The effect of solution treatment is affected by the low solution temperature, and the results of microstructure and hardness can not be obtained. If the temperature is slightly higher, defects such as concave or crack may appear inside the U-shaped segment.

 

From the experiment, it is known that the martensite transformation of stainless steel after cold processing, the influence of corrosion resistance is far greater than the stress. When the bending radius of the u-shaped tube is less than 115mm, the microstructure of the u-shaped tube before and after solution treatment is significantly different. For this small radius U-shaped pipe bend segment, solid solution treatment should be performed after cold forming. If there is no requirement for higher intergranular corrosion resistance, it is recommended that the u-shaped bending section with a bending radius less than or equal to 265mm be treated with solution treatment (note to eliminate residual stress). For u-shaped heat exchange tubes with large radius curvature, the bending section may not be treated with solution, except for stress corrosion sensitive environments. Because the small pipe diameter fluid resistance is large, it is inconvenient to clean and easy to block the structure, and the large diameter stainless steel pipe fluid resistance is not as large as the small pipe diameter, easy to clean, more used for viscous or dirty fluid.

 

WLD Company can provide 304/316 stainless steel heat exchange tubes from 10mm to 114mm, the thickness of 0.6mm to 3.0mm; The length can be customized according to your actual working conditions. If you need it please contact us today.

The polishing treatment on stainless steel tube

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The polishing treatment of stainless steel tubes is actually a surface grinding process, through the instrument and stainless steel tube surface friction to obtain a bright surface. Stainless steel tube outside polishing is used to cut the surface with different coarse particle size linen wheel to obtain the bright surface, and the internal polishing is in the stainless steel tube inside the reciprocating or selective movement of the internal grinding with plastic grinding head. It is worth noting that polishing can not improve the original machining accuracy but only change the surface flatness, the surface roughness value of polished stainless steel tube can reach 1.6-0.008um. According to the processing process, can be divided into mechanical abandonment and chemical polishing.

 

Mechanical polishing

Wheel polishing: The use of the flexible polishing wheel and fine abrasive on the surface of the steel pipe roll and micro-cutting to achieve the polishing process. The polishing wheel is made of overlapping layers of canvas, felt or leather, used for polishing large workpieces.

Roller polishing and vibration polishing is to put the workpiece, abrasive and polishing fluid into the drum or vibration box, the drum slowly rolling or vibration box vibration makes the workpiece and abrasive friction, polishing liquid chemical reaction can remove the steel pipe surface stains, corrosion, and burr to obtain a smooth surface. It’s suitable for large workpieces. The grinding resistance is related to the grinding machinery, the rigidity of the workpiece, and also has a relationship with the grinding vibration amplitude or grinding temperature, which affects the life of the grinding tool and the character of the grinding surface. The grinding temperature will cause the thermal deformation of the workpiece, reduce the dimensional accuracy, and also affect the processing metamorphic layer of the grinding surface.

Chemical polishing

The stainless steel tube is immersed in a special chemical solution. The phenomenon that the raised part of the metal surface dissolves faster than the concave part is used to achieve the process of polishing.

Chemical polishing is less investment, fast speed, high efficiency, good corrosion resistance; However, there are also brightness differences, gas overflow needs ventilation equipment, heating difficulties, suitable for complex parts and small parts of the light intensity requirements are not high products.

Electrolytic polishing

Electrolytic anode polishing on stainless steel tube is the process insoluble metal as the cathode, the poles into the electrochemical trough at the same time, through direct current (dc) and selective anodic dissolution, so stainless steel tube surface to achieve high brightness and luster appearance, and form – a sticky film on the surface, enhance the corrosion resistance of the pipe, applicable to occasions with higher requirements for surface quality.

Mirror polishing

Stainless steel mirror processing is actually a kind of polishing process, to the stainless steel pipe through the grinder counterclockwise rotation, correction wheel drive workpiece rotation, pressure on the pipe in the way of gravity pressure, In the matching grinding emulsion (mainly metal oxide, inorganic acid, organic lubricant and weak alkaline cleaning agent melt), stainless steel decorative tube and grinding disk for relative operation friction to achieve the purpose of grinding and polishing. The grade of polishing is divided into ordinary polishing, 6K, 8K, 10K, of which 8K grinding has been widely used because of the low process cost.