Nickel-based super alloy: Incoloy 825 (UNS N08825/W.Nr. 2.4858)
What is Incoloy 825?
Designated as UNS N08825 or DIN W.Nr. 2.4858, Incoloy 825 (also known as “Alloy 825”) is an iron-nickel-chromium alloy with additions of molybdenum, cooper and titanium. The molybdenum addition improves its resistance to pitting corrosion in aqueous corrosion application while copper content bestows resistance to sulfuric acid. Titanium is added for stabilization. The Alloy 825 has excellent resistance to both reducing and oxidizing acids, to stress-corrosion cracking, and to localized attack such as pitting and crevice corrosion. It is especially resistant to sulfuric and phosphoric acids. Incoloy 825 alloy is mainly used for chemical processing, petrochemical piping, pollution-control equipment, oil and gas well piping, nuclear fuel reprocessing, acid production, and pickling equipment.
Incoloy825 (N08825, 2.4858) The alloy is an all-austenitic nickel-iron-chromium alloy stabilized by titanium, with copper and molybdenum added.
Characteristics of Incoloy 825 (UNS N08825/W.Nr. 2.4858):
- (1) Good stress corrosion cracking resistance.
- (2) Good resistance to pitting and crevice corrosion.
- (3) Good oxidation resistance and non-oxidizing thermal acid performance.
- (4) Good mechanical properties at room temperature and high temperatures up to 550℃.
- (5) With the certification of the pressure vessel manufacturing temperature up to 450 ℃.
Chemical Composition Requirements
|The Chemical Composition of Incoloy 825, %|
Mechanical Properties of Incoloy 825
|Tensile Strength, min.||Yield Strength, min.||Elongation, min.||Elastic Modulus|
The properties listed in the following table are applicable to the specified specifications of Incoloy825 alloy after softening annealing (stabilizing annealing). The special properties of non-standard size materials can be provided according to the requirements of specific applications.
Mechanical properties at room temperature (minimum):
Sheet and strip/cold rolled
processing and hot processing of bars
processing and hot processing of pipes
|Condensation and heat exchanger||16-76|
High temperature mechanical properties (minimum value):
|Product||Yield strength RP0.2 N/mm2||Yield strength RP1.0 N/mm2|
|Plate, strip, tube||205||180||170||160||155||235||205||195||185||180|
Incoloy825 ISO V-notch impact test:
Average room temperature:
- Axial direction>=150J/cm2
- Radial direction>=100J/cm2
Incoloy825 (N08825, 2.4858) alloy conditional stress value:
The high conditional stress value that reaches 90% of the yield strength can be used in applications that allow a little larger deformation. The permanent stresses caused by these stresses can cause dimensional changes, so it is not recommended for flange and gasket connections.
Incoloy825 (N08825, 2.4858) alloy metallographic structure:
Incoloy825 alloy has a stable face-centered cubic structure. The chemical composition and proper heat treatment ensure that the corrosion resistance is not impaired by sensitization.
Incoloy825 (N08825, 2.4858) alloy corrosion resistance:
Incoloy825 is a general engineering alloy, which has resistance to acid and alkali metal corrosion in both oxidation and reduction environments. The high nickel content makes the alloy have effective resistance to stress corrosion cracking. It has good corrosion resistance in various media, such as sulfuric acid, phosphoric acid, nitric acid and organic acids, and alkali metals such as sodium hydroxide, potassium hydroxide and hydrochloric acid solutions. The high comprehensive performance of Incoloy825 is manifested in nuclear combustion dissolvers with various corrosive media, such as sulfuric acid, nitric acid and sodium hydroxide, which are all processed in the same equipment.
Physical Properties of Incoloy 825
|Density||Melting Range||Specific Heat||Electrical Resistivity|
- (1). Density: ρ=8.1g/cm3
- (2). Melting temperature range: 1370～1400℃
|Temperature ℃||Specific heat capacity J/Kg K||Thermal conductivity W/mK||Resistivity μΩcm||Elastic modulus KN/mm2||Coefficient of thermal expansion 10-6/K|
Product Forms and Standards of Incoloy 825
|Rods and bars||ASTM B425, DIN17752|
|Plates, sheet and strips||ASTM B906, B424|
|Seamless pipes and tubes||ASTM B423, B829|
|Welded pipes||ASTM B705, B775|
|Welded tubes||ASTM B704, B751|
|Welded pipe fittings||ASTM A366|
|Forging||ASTM B564, DIN17754|
Application areas of nickel-based alloy incoloy 825 (UNS N08825/W.Nr. 2.4858):
- Heating pipes, containers, baskets and chains used in sulfuric acid pickling plants.
- Sea water cooling heat exchanger, marine product pipeline system, acid gas environment pipeline.
- Heat exchanger, evaporator, washing, dip tube, etc. in phosphoric acid production.
- Air heat exchanger in petroleum refining.
- Food engineering, chemical process.
- Flame retardant alloy for high pressure oxygen application.
- Heat exchange tubes
- Pipe fittings
Incoloy 825 Used for Air-Cooled Heat Exchangers
In an oil refinery’s ethylene project of Indonesia, air-cooled heat exchangers are required for the gas oil hydrotreating process. The product of hydrogen cracking process is separated high-pressure hot gas which consists of hydrogen sulfide(H2S), ammonia(NH3), nitrogen(N2), etc. Considering the harsh conditions, Incoloy 825 (UNS N08825) materials are chosen for the manufacture of the air-cooled heat exchanger.
The design pressure and design temperature for tube-side pass are 15.2 MPa and 250°C respectively with flow media of hot gas(H2S+NH3+N2 ,etc). The design pressure and design temperature for shell-side pass are 0.1 MPa and 35°C respectively with flow media of air. The air-cooler dimensions are 10.5m(length) x 3m(width).
The air cooled heat exchanger mainly consists of headers, plug-type tube bundles and joint flanges. The header is made of Incoloy 825 plates (ASTM B424 UNS N08825) in solution annealed condition. The tube bundles are made of Incoloy 825 seamless tubes manufactured to ASTM B163 Gr. N08825 also in solution annealed condition. The joint flanges shall be manufactured to ASTM B564 Gr. N08825 forgings. Especially, the tube bundles are furnished with finned tubes. The extruded aluminum fins are firmly seated on the Incoloy 825 base tubes.
Incoloy 825 Quench Ring and Dip Tube for Gasifiers
Generally, a gasifier of Texaco coal gasification process consists of the upper combustion chamber and the lower cooling zone. The pressurized coal-water slurry is injected into the combustion chamber together with oxygen or air through a injection burner. A useful synthetic gas will be produced at a temperature of approx. 1400°C. Along with the hot gas, large amount of hot ash slags are generated. All the hot products shall be discharged to the cooling zone through a quench ring and dip tube structure. After been through the cooling zone, the temperature of the hot gas is reduced to about 300°C. And it is then directed to other facilities for further processing.
Both the quench ring and the dip tube are working in extremely harsh conditions: sudden temperature drop from 1400°C to 300°C; high pressures which may be as high as 25 MPa; severe corrosion and erosion caused by the hot gas & slag mixtures. Incoloy 825 is chosen for the fabrication of these components.
Function of The Incoloy 825 Quench Ring
The main body of the Incoloy 825 quench ring is made of ASTM B424 UNS N08825 plates with cooling water inlet made of ASTM B564 UNS N08825 forgings. The quench ring can be furnished in either integral or segmented pattern. It is in close contact with the combustion chamber. The holding coolant in the quench ring flows down the internal surface of the adjacent dip tube and forms a film of water over the latter.
Function of The Incoloy 825 Dip Tube
The dip tube is located below the quench ring. It is wetted by the coolant held by the quench ring. The lower serrated edge of the dip tube shall be dipped into the coolant. Hot gas and particulated slag will be passed through it and get cooled in the coolant. The dip tube shall be made from Incoloy 825 plates manufactured to ASTM B704 Gr. N08825.
Incoloy 825 Tubes Used for Distillation Column Reboiler in AlF3 Production
The distillation column reboiler is widely utilized for the production of dry aluminum fluoride (AlF3). The hydrogen fluoride (HF) is passed through the distillation column and get rectified. Then it is re-vaporized in the reboiler for further processing. Due to the corrosive and hazardous properties, hydrogen fluoride(fluid/gas) shall be properly handled. Generally, the high-temperature corrosion resistant material Incoloy 825 is chosen for the fabrication of tube pass of the reboiler.
We have supplied Incoloy 825 heat-exchanger tubes of 2″ x 2.6mm x 3m (manufactured to ASTM B163 UNS N08825) for the fabrication of a distillation-column reboiler’s tube pass.
Design temperature: 110°C
Design pressure: 0.8 MPa
Flow media: HF
The facilities belong to a reputable aluminum fluoride producer, Gulf Fluor, located in Abu Dhabi, UAE.
Pressure-Temperature Ratings for Incoloy 825 Flanges
Incoloy 825 flanges manufactured to ASME B16.5 can only be made from annealed material and its maximum applicable temperature is 538°C [1000°F]. It can be furnished in a variety of types including welding neck, slip on, blind, threaded, lap joint, long weld neck, and socket welding. The flange can be either made from ASTM B564 UNS N08825 forging or ASTM B424 Gr. N08825 plate (only for blind flange and plate flange) with nominal composition of 42Ni-21.5Cr-3Mo-2.3Cu.
Pressure-Temperature Ratings for Incoloy 825: Metric Unit
*The table lists working pressures by classes at different temperatures, in bar unit.
Pressure-Temperature Ratings for Incoloy 825: US Customary Unit
*The table lists working pressures by classes at different temperatures, in psig unit.
Incoloy 825 welding neck flanges are widely used in sour crude oil services. The primary manufacturing processes include: electric arc furnace melting → ingot casting → cogging → descaling → cutting → preheating → loose tooling forging → heat treatment → machining → inspection.
There are some difficulties in the manufacturing of Incoloy 825 flanges:
(1). The material has very high resistance to deformation: even at 980°C, its flow stress can be as high as 240 MPa.
(2). In order to prevent the intergranular corrosion and improve its resistance to hydrogen sulfide stress corrosion, fined grain is required. However, phase transformation is not available when Incoloy 825 is heated or cooled. Fined grain can only be achieved by re-crystallization or plastic deformation.
(3). The deformation on each direction shall be 15% larger than the critical values to avoid coarse grain.
Processing and heat treatment of Incoloy 825 (UNS N08825/W.Nr. 2.4858):
Incoloy825 alloy is easy to process in general industrial processes.
Incoloy825 (N08825, 2.4858) alloy preheating:
Temperature control is very important to ensure that the corrosion resistance of the alloy is not weakened by sensitization. The surface of the workpiece must be cleaned before and during the heating process to keep the surface clean. If the heating environment contains sulfur, phosphorus, lead or other low melting point metals, Nicrofer 6023/6023H alloy will become brittle. Impurities come from marking paint, chalk, lubricating oil, water, fuel, etc. The sulfur content of fuel should be low. For example, the impurity content of liquefied gas and natural gas should be less than 0.1%, the sulfur content of city gas should be less than 0.25g/m3, and the sulfur content of petroleum gas should be less than 0.5%.
The heat treatment is best carried out in a vacuum resistance furnace or an inert gas protective atmosphere, because it can control the temperature accurately and is not contaminated by impurities. If the impurity content of the gas is low, a gas heating furnace can also be considered, so that a neutral or weak oxidizing atmosphere can be obtained. It should be avoided that the composition of the furnace gas fluctuates in the oxidation and reducibility, and the combustion flame cannot directly burn the workpiece.
Incoloy825 (N08825, 2.4858) alloy thermal processing:
The suitable thermal processing temperature of Incoloy825 alloy is 1150-900℃, and the cooling method can be water quenching or rapid air cooling. During hot processing, the workpiece can be directly fed into the heated furnace. After the furnace is warm, the holding time of the material is 60 minutes per 100mm thickness. After the heat preservation reaches the specified time, it will be released immediately and processed within the specified temperature range. If the temperature of the metal drops below the minimum processing temperature, it should be heated again. It should be annealed in time after hot working to ensure the best corrosion resistance and suitable crystal structure.
Cold processing of Incoloy 825 (UNS N08825/W.Nr. 2.4858):
Cold working should be carried out after solution treatment. The work hardening rate of Incoloy825 is close to that of austenitic stainless steel, so the processing equipment should be adjusted accordingly. When the amount of cold work is large, there should be an intermediate annealing process. When the final cold deformation is greater than 15%, final stabilization is required.
Heat treatment of Incoloy 825 (UNS N08825/W.Nr. 2.4858):
The temperature range of softening annealing or stabilization treatment is 920-980℃, and the most suitable is 940±10℃. For workpieces with a thickness greater than 1.5mm, it is recommended to use water quenching or rapid air cooling to obtain the maximum creep resistance. In any heat treatment process, we must pay attention to the aforementioned matters about keeping clean.
Incoloy825 (N08825, 2.4858) alloy grinding and pickling:
The oxide near the weld of Incoloy825 workpiece is more difficult to remove than stainless steel, and it needs to be polished with a fine abrasive belt or grinding wheel. To maintain the luster of the metal, be very careful when polishing it. Before pickling in a mixed acid of nitric acid and hydrofluoric acid, sandpaper should be used to remove oxides or salt bath pretreatment. Pay special attention to the pickling time.
Machining of Incoloy 825 (UNS N08825/W.Nr. 2.4858):
Machining of incoloy825 needs to be carried out after solution treatment. The work hardening of the material must be considered. Unlike austenitic stainless steel, it needs to adopt a low surface cutting speed and heavy weight. Infeed amount.
Incoloy825 (N08825, 2.4858) alloy welding:
When welding nickel-based alloys, the following procedures should be followed:
- (1). Work site: The work site should be separated or far enough from the carbon steel processing area Keep the distance as clean as possible, with partitions and avoid ventilation between the two areas.
- (2). Work clothes and auxiliary supplies: clean fine-grained leather gloves and clean work clothes should be worn.
- (3). Tools and machinery and equipment: there should be special tools for nickel-based alloy and nickel-chromium steel. The wire brush should be made of stainless steel. The machinery and equipment such as shears, punches, rolling mills, etc. should be covered with felt, cardboard or plastic. The paper prevents iron-carbon metal from falling on the surface of the machine and sticking to the processed materials, causing corrosion. Remove oxide scale, oil stains and various marking marks, and use acetone to clean the base metal and filler alloys (such as welding rods) in the welding area. Note that trichloroethylene TRI, perchloroethylene PER and tetrachloride TETRA cannot be used.
Incoloy825 edge preparation:
It is best to use machining, such as turning, milling, planing, or plasma cutting. If the latter is used, the cutting edge (welding surface) must be ground clean and smooth, allowing fine grinding without overheating. The base material on both sides of the weld should be polished to expose the bright metal.
Incoloy825 groove angle:
Compared with carbon steel, the physical properties of nickel-based alloys and special stainless steels are mainly low thermal conductivity and high expansion coefficient. These characteristics must be considered when welding groove preparation, including Widen the bottom gap (1～3mm). At the same time, due to the viscosity of the molten metal, a larger groove angle (60～70°) should be used in butt welding to offset the shrinkage of the material.
Incoloy825 arc starting:
The arc cannot be started on the surface of the workpiece, and the arc should be started on the welding surface to prevent the arc starting point from causing corrosion.
Incoloy825 welding process:
- (1). Incoloy825 is suitable for welding with the same material or other metals using any traditional welding process, such as tungsten electrode inert gas arc welding, plasma arc welding, manual sub-arc welding, metal inert gas arc welding, MIG welding, pulse arc welding is the first choice. When using manual arc welding, it is recommended to use (Ar+He+H2+CO2) shielding gas mixed with multiple components.
- (2). The welding of Incoloy825 must be carried out in the annealed state, and a stainless steel wire brush should be used to clean up stains, dust and various marks. When welding the root of the weld, in order to obtain the best quality of the root weld, the operation must be very careful (argon 99.99), so that the weld does not produce oxides after the root is welded. The color generated in the welding heat-affected zone should be brushed off with a stainless steel brush when the weld area is not cooled.
- (3). Incoloy825 filler metal: welding rod: ENiCrMo-3, welding wire: ERNiCrMo-3.
Incoloy 825 welding parameters and influence (heat input):
Welding operation should be carried out under the low heat input specified in the heat input table, using stacked beads For welding seam technology, the temperature between layers does not exceed 120°C, and welding specifications must be followed. The heat input Q is calculated according to the following formula:
- U = arc voltage, volt
- I = welding current, ampere
- V = welding speed, cm/min.
Incoloy825 post-welding treatment (pickling, brushing to remove oxides and heat treatment):
Immediately after welding, use a stainless steel wire brush to remove oxides, that is to say, brush before the metal has no welding color, so that you can get Ideal surface quality without pickling. If there are no special requirements or regulations, pickling is usually the last process in welding. Please refer to the section on descaling and pickling.No heat treatment is required before and after welding.
Heat input per unit length (guide value):
Heat input per unit length
Heat input per unit length
|GTAW, manual/fully mechanized||≤ 10||MIG/MAG, manual/fully mechanized||≤ 11|
|Hot wire GTAW||≤ 6||Manual arc welding (SMAW)||≤ 7|
|Plasma arc||≤ 10|
ASTM G48 Method A: Ferric Chloride Pitting Test
In order to study the pitting resistance of Incoloy 825 in high chloride-ion environments, pitting test shall be conducted in accordance with ASTM G48 Method A. The specimen is a piece of Incoloy 825 plate of 30 mm x 10 mm x 3 mm manufactured to ASTM B424 UNS N08825. It is immersed into 6% FeCl3 solution at 50(±1)°C. Maintain the test solution temperature for 72 hours. Then, remove the specimen , rinse with water and scrub with a nylon bristle brush under running water to remove corrosion products, dip in acetone or methanol, and air-dry. Weigh the specimen to the accuracy of 0.0001g. Analyze corrosion products at the corrosion pit by using SEM and X-ray EDS methods respectively.
Actual Chemical Composition of Incoloy 825 Specimen
*All values are by weight percentage.
The SEM & EDS Results
The main elements remaining at the corrosion pit are Fe, Mo, Ti and O while the content of base element nickel is relatively low. It is concluded that oxidizing ions react with Cr & Ni in the corrosive solution. The product of the reaction is dissolved in the solution.
Thermal Expansion for Incoloy 825
Instantaneous Coefficient of Thermal Expansion for Incoloy 825
*TA: instantaneous coefficient of thermal expansion. Unit:10-6inch/inch/°F.
Mean Coefficient of Thermal Expansion for Incoloy 825
*TB: mean coefficient of thermal expansion. Unit: 10-6inch/inch/°F. Going from 70°F to indicated temperature.
Linear Thermal Expansion for Incoloy 825
*TC: linear thermal expansion for Incoloy 825. Unit: inch/100 ft. Going from 70°F to indicated temperature.
Design Stress Intensity of ASTM B163 UNS N08825 Tubes
The design stress intensity of ASTM B163 Gr. N08825 seamless tubes are listed in below table:
*Nominal composition: 42Ni–21.5Cr–5Mo–2.3Cu.
*A: ASTM B163 Gr. N08825 seamless tubes, annealed, P-No.: 45.
Allowable Stress & Applicable Temperature of ASTM B163 UNS N08825
Seamless tubes manufactured to ASTM B163 UNS N08825 (Incoloy Alloy 825) are primarily used for condenser and heat-exchanger service. They are applicable for piping systems designed according to ASME BPVC Section III Class 3 or ASME BPVC Section VIII Division 1 with maximum applicable temperature 800°F or 1000°F, respectively. They are also applicable for transport tanks of ASME BPVC Section XII with maximum applicable temperature 650°F.
Max. Allowable Stress Values at Different Temperatures
*Temp.: metal temperature, not exceeding.
*A: standard ASTM B163 UNS N08825 seamless tubes, annealed.
*B: ASTM B163 UNS N08825 seamless tubes, annealed; slightly greater deformation caused by stresses is acceptable.
PMI Test on Incoloy 825 Bars
Recently Yaang has procured two pieces of Incoloy 825 bars for further processing. The bars are manufactured to ASTM B425 Gr. UNS N08825, hot rolled, annealed and roughly ground. PMI test was conducted to verify its chemical composition. The specification of the bar: 200 mm(diameter) x 3.2 meter(length).
The PMI test result(actual chemical composition) is listed in below table:
*All values are in % unit and are read from the direct-reading spectrometer.
Variety specifications and supply status of Nickel-based super alloy: Incoloy 825 (UNS N08825/W.Nr. 2.4858):
Yaang Pipe Industry can produce various specifications of Incoloy825 seamless pipe, Incoloy825 steel plate, Incoloy825 round bar, Incoloy825 forgings, Incoloy825 flange, Incoloy825 pipe fittings, Incoloy825 welded pipe , Incoloy825 steel strip, Incoloy825 wire and supporting welding materials.
- Seamless pipe: solid solution + acid white, length can be set;
- Plate: solid solution, pickling, trimming;
- Welded pipe: solid solution acid white + RT% flaw detection;
- Forging: annealing + car polish; Bars are forged and rolled, surface polished or car polished;
- Strips are delivered after cold rolling, solid solution soft state, and deoxidized;
- Wire rods are finely ground in solid solution pickled disk or straight strips, solid solution straight strips Delivery in light state.
Source: China Incoloy 825 Flanges Manufcturer – Yaang Pipe Industry (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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