What is Hastelloy tube?

Hastelloy
Hastelloy is a tungsten-containing nickel-chromium-molybdenum alloy with extremely low silicon and carbon content.
one. At present, it is mainly divided into three series: B, C, and G. It is mainly used in highly corrosive media situations where iron-based Cr-Ni or Cr-Ni-Mo stainless steel, non-metallic materials, etc. cannot be used.
Hastelloy grades
In order to improve the corrosion resistance and cold and hot working properties of Hastelloy, Hastelloy has made three major improvements. The development process is as follows:
B series: B → B-2(00Ni70Mo28) → B-3
C series: C → C-276(00Cr16Mo16W4) → C-4(00Cr16Mo16) → C-22 (00Cr22Mo13W3) → C-2000(00Cr20Mo16)
G series: G → G-3 (00Cr22Ni48Mo7Cu) → G-30 (00Cr30Ni48Mo7Cu)
The most widely used ones at present are the second generation materials N10665(B-2), N10276(C-276), N06022(C-22), N06455(C-4) and N06985(G-3).
2. Typical chemical composition of Hastelloy alloy
The chemical composition of the material
Ni Cr Mo Fe C Si Co Mn P S W V Cu Nb+Ta
N10665 (B-2) Base ≤1.0 26.0~30 ≤2.0 ≤0.02 ≤0.10 ≤1.0 ≤1.0 ≤0.04 ≤0.03
N10276 (C-276) Base 14.5~16.5 15.0~ 17.0 4.0~7.0 ≤0.01 ≤0.08 ≤2.5 ≤1.0 ≤0.04 ≤0.03 3.0~ 4.5 ≤0.035
N06007 (G-3) Base 21.0~23.5 6.0~ 8.0 18.0~21 ≤0.015 ≤1.0 ≤5.0 ≤1.0 ≤0.04 ≤0.03 ≤1.5 1.5~2.5 ≤0.50
3. Mechanical properties
The mechanical properties of Hastelloy are very outstanding. It has the characteristics of high strength and high toughness, so it is difficult to machine. Moreover, its strain hardening tendency is extremely strong. When the deformation rate reaches 15%, it is about 18-8 Twice that of stainless steel. Hastelloy also has a medium-temperature sensitization zone, and its sensitization tendency increases with the increase in deformation rate. When the temperature is high, Hastelloy easily absorbs harmful elements, causing its mechanical properties and corrosion resistance to decrease.
Mechanical properties of materials
4. Commonly used Hastelloy alloys
1: Hastelloy B-2 alloy (Hastelloy B-2 alloy)
1. Corrosion resistance
Hastelloy B-2 alloy is a Ni-Mo alloy with extremely low carbon and silicon content. It reduces the precipitation of carbides and other phases in the weld and heat-affected zone, thereby ensuring that even under welding conditions Also has good corrosion resistance.
As we all know, Hastelloy B-2 alloy has excellent corrosion resistance in various reducing media and can withstand corrosion at any temperature and concentration under normal pressure. It has excellent corrosion resistance in non-aerated medium-concentration non-oxidizing sulfuric acid, various concentrations of phosphoric acid, high-temperature acetic acid, and other organic acids, acids and chlorides. At the same time, it is also resistant to corrosion by halogen catalysts. Therefore, Hastelloy B-2 alloy is usually used in a variety of harsh petroleum and chemical processes, such as distillation, concentration; alkylation and low-pressure oxo synthesis of acetic acid and other production processes.
However, in the industrial application of Hastelloy B-2 alloy for many years, it has been found that:

(1) Hastelloy B-2 alloy has two sensitization zones that have a considerable impact on the resistance to intergranular corrosion: the high temperature zone of 1200~1300°C and the 550°C sensitization zone. ~900℃ medium temperature zone;

(2) Due to dendrite segregation in the weld metal and heat-affected zone of Hastelloy B-2 alloy, intermetallic phases and carbides precipitate along the grain boundaries, making them more sensitive to intergranular corrosion ; (3) Hastelloy B-2 alloy has poor medium-temperature thermal stability. When the iron content in Hastelloy B-2 alloy drops below 2%, the alloy is sensitive to the transformation of the beta phase (Ni4Mo phase, an ordered intermetallic compound). When the alloy stays in the temperature range of 650~750℃ for a slightly longer time, the β phase is generated instantly. The existence of β phase reduces the toughness of Hastelloy B-2 alloy, making it sensitive to stress corrosion, and even causes Hastelloy B-2 alloy to be damaged during raw material production (such as hot rolling process) and equipment manufacturing process (such as Hastelloy B-2 alloy equipment post-weld overall heat treatment) and Hastelloy B-2 alloy equipment cracks in the service environment. Nowadays, the standard test methods for the intergranular corrosion resistance of Hastelloy B-2 alloy specified by our country and other countries around the world are the atmospheric pressure boiling method, and the evaluation method is the weight loss method. Since Hastelloy B-2 alloy is a corrosion-resistant alloy, the atmospheric boiling method is quite insensitive to test the intergranular corrosion tendency of Hastelloy B-2 alloy. Domestic scientific research institutions used high-temperature methods to study Hastelloy B-2 cnc machining aluminum 7075 alloy and found that the corrosion resistance of Hastelloy B-2 alloy not only depends on its chemical composition, but also depends on its thermal processing control process. When the thermal processing process is improperly controlled, the grains of Hastelloy B-2 alloy not only grow, but also the high Mo σ phase will precipitate between the grains. At this time, the intergranular corrosion resistance of Hastelloy B-2 alloy is significantly reduced. , in the high-temperature test, the grain boundary etching depth of the coarse-grained plate and the normal plate was about twice the difference.
2. Physical properties
Density: 9.2g/cm3, melting point: 1330~1380℃, magnetic permeability: (℃, RT)≤1.001
3. Chemical composition
chemical composition
Element Ni Cr Fe C Mn Si Cu Mo Co P S
Minimum margin 0.4 1.6 26.0
Maximum 1.0 2.0 0.01 1.0 0.08 0.5 30.0 1.0 0.02 0.010
5. Manufacturing and heat treatment
1: Heating
For Hastelloy B-2 alloy, it is very important to keep the surface clean and free of contaminants before and during heating. Hastelloy B-2 alloy will become brittle if heated in an environment containing sulfur, phosphorus, lead or other low melting point metal contaminants. The main sources of these contaminants include marker marks, temperature indicating paint, grease and liquids, smoke. This flue gas must have low sulfur content; for example: the sulfur content of natural gas and liquefied gas does not exceed 0.1%, the sulfur content of urban air does not exceed 0.25g/m3, and the sulfur content of fuel oil does not exceed 0.5% is qualified.
The gas environment of the heating furnace is required to be a neutral environment or a lightly reducing environment, and it cannot fluctuate between oxidizing and reducing. The flame in the furnace cannot directly impact Hastelloy B-2 alloy. At the same time, the material must be heated to the required temperature at the fastest heating speed, which means that the temperature of the heating furnace must first be raised to the required temperature, and then the material must be put into the furnace for heating.
2: Thermal processing
Hastelloy B-2 alloy can be hot processed in the range of 900~1160℃, and should be quenched with water after processing. In order to ensure the best corrosion resistance, annealing should be performed after hot working.
3: Cold working
Cold-worked Hastelloy B-2 alloy must undergo solution treatment. Since it has a much higher work hardening rate than austenitic stainless steel, the forming equipment must be carefully considered. If a cold forming process is performed, interstage annealing is necessary. When the cold working deformation exceeds 15%, solution treatment is required before use.
4: Heat treatment
The solution heat treatment temperature should be controlled between 1060~1080℃, followed by water cooling quenching or rapid air cooling when the material thickness is above 1.5mm to obtain the best corrosion resistance. During any heating operation, precautions must be taken to clean the surface of the material. The following issues should be paid attention to when heat treatment of Hastelloy materials or equipment parts: In order to prevent heat treatment deformation of equipment parts, stainless steel reinforcing rings should be used; the furnace loading temperature, heating and cooling time should be strictly controlled; before loading the furnace, heat treatment parts Pre-treatment is carried out to prevent the occurrence of thermal cracks; after heat treatment, the heat-treated parts are 100% PT; if thermal cracks occur during the heat treatment process and need to be repaired after being polished and eliminated, a special repair welding process must be used.
5: Descaling
The oxides on the surface of Hastelloy B-2 alloy and the stains near the welds must be polished away with fine grinding wheels.
Since Hastelloy B-2 alloy is relatively sensitive to oxidizing media, more nitrogen-containing gases will be produced during the pickling process.
6: Machining
Hastelloy B-2 alloy must be machined in the annealed state, and a clear understanding of its work hardening must be adopted. For example, compared with standard austenitic stainless steel, a slower surface cutting speed must be used, and the hardened layer on the surface must be used. Larger feed amount and keeping the tool in continuous working condition.
7: Welding
Hastelloy B-2 alloy weld metal and heat-affected zone are Mo-poor due to the easy precipitation of beta phase, which is prone to intergranular corrosion. Therefore, the welding process of Hastelloy B-2 alloy should be carefully formulated and strictly controlled. The general welding process is as follows: ERNi-Mo7 is used as the welding material; welding method W; the interlayer temperature is controlled to be no more than 120°C; the welding wire diameter is φ2.4, φ3.2; the welding current is 90~150A. At the same time, before welding, the welding wire, the groove of the welded parts and adjacent parts should be decontaminated and degreased.
The thermal conductivity coefficient of Hastelloy B-2 alloy is much smaller than that of steel. If a single V-shaped groove is selected, the groove angle should be about 70°, and a lower heat input should be used. Post-weld heat treatment can eliminate residual stress and improve stress corrosion cracking resistance.
2: Hastelloy C-276 alloy (Hastelloy C-276 alloy)
1. Corrosion resistance
Hastelloy C-276 alloy is a nickel-molybdenum-chromium-iron-tungsten nickel-based alloy. It is one of the most corrosion-resistant modern metal materials. Mainly resistant to wet chlorine, various oxidizing chlorides, chloride salt solutions, sulfuric acid and oxidizing salts, and has good corrosion resistance at low and medium temperatures. Therefore, in the past thirty years, it has been widely used in harsh corrosive environments, such as chemical industry, petrochemical industry, flue gas desulfurization, pulp and paper making, environmental protection and other industrial fields.
The various corrosion data of Hastelloy C-276 alloy are typical, but they cannot be used as specifications, especially in unknown environments, and materials must be selected after testing. There is not enough Cr in Hastelloy C-276 alloy to resist corrosion in strong oxidizing environments, such as hot concentrated nitric acid. The production of this alloy is mainly for chemical process environments, especially in the presence of mixed acids, such as the discharge pipe of flue gas desulfurization systems. The following table shows the comparative corrosion test results of four alloys in different environments. (All welding samples adopt autogenous tungsten arc welding)
Comparative test of corrosion of four metals in different environments
Test environment (boiling) Corrosion rate (mm/)
Typical 316 AL-6XN Inconel625 C-276
Basic metal specimen Welding specimen Basic metal specimen Welding specimen Basic metal specimen Basic metal specimen Welding specimen
20% acetic acid 0.003 0.003 0.0036 0.0018 0.0076 0.013 0.006
45% 0.277 0.262 0.116 0.142 0.13 0.07 0.049
10% oxalic acid 1.02 0.991 0.277 0.274 0.15 0.29 0.259
20% phosphoric acid 0.177 0.155 0.007 0.006 0.001 0.001 0.0006
10% 1.62 1.58 0.751 0.381 0.12 0.07 0.061
10% sulfuric acid 9.44 9.44 2.14 2.34 0.64 0.35 0.503
10% sodium bicarbonate 1.06 1.06 0.609 0.344 0.10 0.07 0.055
Hastelloy C-276 alloy can be used as flue gas desulfurization components in coal-fired systems. In this environment, C-276 is the most corrosion-resistant material. The following table shows the comparative corrosion test results of C-276 alloy and typical 316 in the “green death” solution of the flue gas simulation system.
Comparative test of corrosion in “green death” solutions
“Green death” solution (boiling) Corrosion rate (mm/a)
Typical 316 C-276
7% sulfuric acid destruction 0.67
3%
1%CuCl2
1%FeCl3
As can be seen from the above table, C-276 alloy has good corrosion resistance to mixed acid and salt solutions containing chloride ions.
The addition of Cr, Mo, and W in Hastelloy C-276 alloy greatly improves the resistance of C-276 alloy to pitting corrosion and crevice corrosion. C-276 alloy is considered inert in seawater environments, so C-276 is widely used in marine, salt water and high chlorine environments, even in strong acid and low pH conditions. The following table is a comparison of crevice corrosion of four metals in a 6% FeCl3 (per ASTM standard G-48) solution.
The occurrence of crevice corrosion
Alloy Crevice Corrosion Occurrence Temperature
°F °C
Typical 316 27 2.5
AL-6XN 113 45
Inconel625 113 45
C-276 140 60
The high content of Ni and Mo in C-276 alloy makes it highly resistant to chloride ion stress corrosion cracking. The following table shows the stress corrosion cracking test results of four metals in different chloride ion-containing solutions.
Chloride ion stress corrosion cracking test conditions
Test solution Bend U-shaped specimen test time (Hours) and test results
Typical 316 AL-6XN Inconel 625 C-276
42%MgCl2 (boiling) Failure (24 hours) Both (1000 hours) Resistance (1000 hours) Resistance (1000 hours)
33% LiCl (boiling) Failure (100 hours) Resistance (1000 hours) Resistance (1000 hours) Resistance (1000 hours)
26%NaCl (boiling) Failure (300 hours) Resistance (1000 hours) Resistance (1000 hours) Resistance (1000 hours)
2. Physical properties
Density: 8.90g/cm3, specific heat: 425J/kg/k, elastic modulus: 205Gpa (21℃)
3. Mechanical properties
Typical tensile test results of C-276 alloy are shown in the table below. The material is annealed at 1150°C and quenched with water.
Mechanical property test values
Temperature (℃) Yield strength σ0.2 (Mpa) Tensile strength σb (Mpa) Elongation δ5 (%)
-196 565 965 45
-101 480 895 50
21 415 790 50
93 380 725 50
204 345 710 50
316 315 675 55
427 290 655 60
538 270 640 60
Cold deformation processing of C-276 alloy will increase its strength. When conducting the impact test, the V-shaped groove impact sample uses a 10mm thick plate (the plate must be annealed). If the sample is a welded sample, it will show a certain temperature in the same temperature range. Flexibility, this is because of the welds. The plate impact test results are shown in the table below.
Test temperature (℃) Impact energy of V-shaped groove specimen (J)
-196 245
21 325
200 325
C-276 alloy has similar formability to ordinary austenitic stainless steel. However, because it is stronger than ordinary austenitic stainless steel, there will be greater stress during cold forming. In addition, this material works harden much faster than ordinary stainless steel, so mid-process annealing is required during extensive cold forming processes.
4. Welding and heat treatment
The welding performance of C-276 alloy is similar to that of ordinary austenitic stainless steel. Before using a welding method to weld C-276, measures must be taken to minimize the decrease in corrosion resistance of the weld and heat-affected zone, such as tungsten electrode Gas shielded welding (W), gas metal arc welding (GMAW), submerged arc welding or other welding methods that can minimize the degradation of the corrosion resistance of the weld and heat-affected zone. However, welding methods such as oxy-acetylene welding that may increase the carbon or silicon content of the material weld and heat-affected zone are not suitable.
Regarding the selection of welded joint forms, you can refer to the successful experience of C-276 welded joints in the ASME Boiler and Pressure Vessel Code.
It is best to use mechanical processing for welding grooves, but mechanical processing will cause work hardening, so it is necessary to grind the machined grooves before welding.
Appropriate heat input speed should be used during welding to prevent the occurrence of thermal cracks.
In most corrosive environments, C-276 can be used in the form of weldments. However, in very harsh environments, C-276 materials and weldments must undergo solution heat treatment to obtain the best corrosion resistance.
For the welding of C-276 alloy, you can choose to use itself as the welding material or filler metal. If certain components are required to be added to the welds of C-276, such as other nickel-based alloys or stainless steel, and these welds will be exposed to corrosive environments, then the electrodes or wires used for welding are required to have the same content as the base metal. Excellent corrosion resistance.
The solid solution heat treatment of Hastelloy C-276 alloy material includes two processes: (1) heating at 1040℃~1150℃; (2) rapid cooling to a black state (about 400℃) within two minutes, so that the treated material Has very good corrosion resistance. Therefore, it is ineffective to only perform stress relief heat treatment on Hastelloy C-276 alloy 303. Before heat treatment, it is necessary to clean the surface of the alloy from oil stains and other dirt that may produce carbon elements during the heat treatment process.
The surface of C-276 alloy will produce oxides during welding or heat treatment, which will reduce the Cr content in the alloy and affect the corrosion resistance, so the surface must be cleaned. You can use a stainless steel wire brush or grinding wheel, then immerse it in a mixture of nitric acid and nitric acid in an appropriate proportion for pickling, and finally rinse it with clean water.
(1) Haynes International, Inc., USA
The company’s predecessor, Haynes Stellite Work (Harz Cobalt Chromium Tungsten Works), was founded in Kokomo, Indiana, USA in 1921. It has a history of 91 years and has continued to innovate and invent in more than 90 years of production and research. As a result, it ranks first in the world in the field of high alloys.
Haynes International Corporation focuses on product production and development. Mainly engaged in the development and production of high-quality corrosion-resistant and high-temperature-resistant nickel-cobalt alloys. Meanwhile, the company’s expert technical staff provide further customer service and technical support worldwide. Haynes’ service centers and branches can provide customers with plates, bars, tubes, pipes, forgings, flanges and connections in a timely manner.
(2) Hastelloy alloy
Hastelloy is a type of nickel-based alloy. It is currently divided into three series: B, C, and G. It is mainly used for strong corrosion that cannot be used in iron-based Cr-Ni or Cr-Ni-Mo stainless steel, non-metallic materials, etc. It has been widely used in petroleum, chemical industry, environmental protection and many other fields abroad.
Hastelloy alloy