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Nickel-based alloys have excellent corrosion resistance, good plastic toughness, and high strength, but 625 nickel-based alloys also have excellent overall performance, hot and cold deformation, smelting, casting, and welding, etc., widely used in aerospace, nuclear power, offshore oil recovery, oil and gas, and other industrial fields.

I. The properties of 625 alloy

Inconel 625 (UNS N06625), a widely used nickel-based alloy with Ni-Cr-Mo-Nb as the main additive element, has excellent all-round properties, with the following characteristics:

● High-temperature resistance

High Cr and Mo content, resulting in good resistance to high-temperature peeling and oxidation;

● Low-temperature resistance

good low-temperature toughness at -196°C due to the very high Ni content;

● High strength

High strength due to the high alloy type and content added and the multi-element compound reinforcement, which gives it a high strength, with a tensile strength of 760 MPa or more;

● Corrosion resistance

Alloy 625 exhibits excellent corrosion resistance in many media;

(1) Excellent resistance to pitting, crevice corrosion, intergranular corrosion, and erosion in chloride media;

(2) Excellent resistance to corrosion by inorganic acids such as nitric, phosphoric, sulphuric, and hydrochloric acids, as well as resistance to corrosion by alkalis and organic acids in oxidizing and reducing environments;

(3) Resistance to chloride ion corrosion and stress corrosion cracking;

(4) High Mo content, virtually corrosion free in seawater and industrial gas environments;

(5) Nb as a stabilizing alloy to reduce intergranular corrosion susceptibility;

II. Typical applications of 625 nickel-based alloys

● Pressure-bearing equipment

Nuclear power equipment, nuclear reactor components, boiler piping systems, heat exchangers, heat shields, valves, etc;

● Flue gas desulphurization systems

● Desulphurization towers, absorption towers, reheaters, flue gas inlet baffles, fans (wet) and flue pipes, etc;

● Chemical Equipment

Manufacture of equipment and components for use in acidic gas environments, e.g. sulphuric acid condensers, acetic acid reaction generators, etc;

● Aerospace

aerospace engine components, aircraft engines, structural components for astronautics, etc;

● Paper industry

Manufacturing of boilers, bleaching tanks, etc. for the pulp and paper industry;

● Seawater applications

For use in contact with seawater and subject to high mechanical stress, marine structures, and saltwater environments, especially where acidic chloride catalysts are used.

III. Welding precautions of 625 nickel-based alloys

(1) Clean weld seam is the key

The nickel content of the weld is high, and Ni can easily form low melting point eutectic with P, S, Si, Pb, etc., which can easily produce thermal cracks under the action of welding stress. Therefore, before welding, the workpiece and the surface of the wire should be thoroughly cleared of dirt, if necessary, with anhydrous alcohol or acetone wipe clean; the bevel should be used for the mechanical planing edge, clear root available sand grinding.

(2) The use of small specifications welding, to avoid coarse grain

Control welding heat input is less than 1.5 kJ/mm, the interpass temperature should be less than 100 ℃ (recommended ≤ 80 ℃), try to use small specifications, small specifications, fast welding, to prevent the weld and heat-affected zone grain growth, resulting in a decline in the toughness of welded joints.
(3) It is advisable to use low C content, low P, S and other impurities, containing Fe is not high welding consumables to avoid thermal cracking and corrosion resistance decline.

The above is all about 625 nickel-based alloys, welcome to Email: [email protected]

Nickel-based corrosion-resistant alloy Incoloy800 has been more widely used in the petrochemical industry in recent years, a corrosion-resistant material, especially in the expansion joint selection is widely used, and the welding process directly affects the service life of equipment components.
1. Incoloy800 alloy weldability analysis
Incoloy800 alloy is a small amount of aluminum and titanium Ni-Cr-Fe austenitic metal materials, with corrosion resistance, high strength, and resistance to high-temperature oxidation properties, weldability is good.
1.1 thermal cracking problem
Incoloy800 welding thermal cracking is caused by metallurgical factors and process factors, which are dominated by metallurgical factors.
Incoloy800 alloy welding, due to S, Si, and other impurities in the weld metal segregation, S and Ni form Ni-NiS low melting point eutectic, in the solidification process of the weld metal, this low melting point eutectic in the formation of a liquid film between the grain boundaries, the formation of intergranular cracking under the action of welding stress. In the welding process Si and oxygen and other complex silicates, form a layer of brittle silicate film between the grain boundaries, during the solidification of the weld metal or after solidification of the high-temperature zone, the formation of high-temperature low plasticity cracking. Therefore, S and Si are the most harmful elements in Incoloy800 alloy.
Incoloy800 alloy has poor thermal conductivity, welding heat is not easy to dissipate, there is easy to overheat, resulting in coarse grains, so that the intergranular interlayer thickens, weakening the intergranular bonding force, but also makes the weld metal liquid solid longer, promoting the formation of thermal cracks.
1.2 Pore problem
Welding Incoloy800 alloy may produce H2O pores, H2 pores, and C0 pores.
Welding Incoloy800 alloy, if the workpiece bevel and its nearby oil and dirt are not clean, a large number of H2 is into the welding pool, when the melt solidification of hydrogen gas can not escape, the formation of hydrogen pores; weldings, such as poor protection, oxygen in the air into the melt pool and the formation of carbon in the metal CO pores; welding, the liquid molten pool of nickel metal can fuse a large amount of oxygen, solidification of oxygen solubility greatly reduced, excess oxygen and nickel NiO, NiO, and nickel H2 reaction, nickel is reduced, hydrogen and oxygen H2O, H2O in the molten pool solidification too late to escape and produce H2O porosity, which is the most likely to appear when Incoloy800 alloy welding porosity.
2. welding test
2.1 test material using foreign imports of Incoloy800 alloy plate, welding test plate length 600mm, width 300mm, thickness 6mm, V-shaped single-sided bevel.
2.2 welding materials used with Incoloy800 alloy composition equivalent argon arc welding wire. Welding wire grade TEW21/33/SG.
2.3 Welding method using heat concentration, gas protection effect of manual tungsten arc argon welding.
2.4 welding process
2.4.1 Weld cleaning before welding should be welded bevel and the nearby oil cleaned, especially lead, sulfur, phosphorus, and some low melting point elements of dirt, the joint will be cleaned on both sides of the 50mm range, cleaned with acetone, and then rinsed with clean water, and so the bevel and both sides dry before welding.
2.4.2 electrode using a flat head conical electrode can ensure arc stability and obtain a sufficient depth of melt, flat head diameter of about 0.4mm, and conical top angle of 30 ~ 45 °. During the welding process, if the tungsten electrode and molten pool contact, the head is contaminated, and must be worn off or replaced with the tungsten electrode, while the molten pool metal is contaminated, the local weld should also be worn off to prevent tungsten defects.
2.4.3 Protective gas with argon as a protective gas, the purity should be more than 99.9%, the reverse side of the welding first pass argon, the flow rate of 12L/min or more, to ensure full weld penetration and weld forming, and to prevent oxidation. In order to strengthen the protection effect of the welding area, the rear side of the welding nozzle plus a protective shield.
2.4.4 operation points to choose a small current, short arc, and as fast as possible welding speed; welding process, the heating end of the wire must be in the argon protection, the wire does not swing laterally, can not stir the molten pool with the wire; multi-layer welding should be strictly controlled at 100 ℃ or less, after welding a, to be cold to the workpiece can be touched by hand and then weld the next channel; to prevent arc pit cracking, arc break to arc pit processing, the final arc break The arc pit must be filled or led out of the arc pit.
2.5 test results
2.5.1 According to technical requirements, Incoloy800 alloy welded joints according to GB150-98 “National Standard for Steel Pressure Vessels” for inspection, manufacture, and acceptance.
2.5.2 Incoloy800 welded joints test results are as follows: the appearance of the weld is checked without porosity, cracks, arc pits, slag, and other defects; weld by 100% X-ray flaw detection, all Ⅰ.
Test plate ends as required to round off 30mm, intercepted tensile specimens 2, specifications for 250 × 25 × 6; face bending, back bending specimens each 1, specifications for 150 × 30 × 6; metallographic specimens 6, specifications for 20 × 10 × 6.
After the test on the specimen, the results of the tensile specimen tensile strength of 714MPa and 720MPa, respectively; bending specimens bent 180 ° without any cracks or defects; weld, welding heat-affected zone metallographic specimens are austenite plus less than 2% of the ferrite, without any overburning organization and coarse grain composition.
Incoloy800 alloy welded joints test results and the standard requirements compared, the welded joints meet the standard requirements. This proves that the welding process is feasible.

Steel pipe appearance, seamless steel pipe, and welded steel pipe difference in the welded pipe inside the wall there are welding tendons, while the seamless no.
seamless steel pipe and welded pipe identification method: look at the inside of the tube, because the outside will be processed, welded pipe is a gap inside some can see, in some processing, it is not easy to see, you can slowly touch it with your hands, or look at the specifications, welded pipe are relatively thin, seamless steel pipe manufacturer, a welded pipe is made directly from stainless steel strip with a machine (rolled up), seamless is made from round steel or pipe billet perforated through.

Seamless steel pipe production principle

Production and manufacturing methods can be divided into hot-rolled tubes, cold-rolled tubes, cold-drawn tubes, extruded tubes, etc. according to different production methods. Hot-rolled seamless pipes are generally produced on automatic pipe-rolling units. Solid billets are inspected and cleared of surface defects, cut to the required length, centered on the perforated end face of the billet, then sent to a heating furnace for heating and perforated on a perforating machine. In the perforation, while continuously rotating and advancing, under the action of the rollers and the top, the internal cavity of the billet is gradually formed, called the hairpin. Then sent to the automatic tube rolling machine to continue rolling. The wall thickness is evenly adjusted by the equalizing machine, and the diameter is sized by the sizing machine to meet the specifications.

316 stainless steel pipe has good corrosion resistance and high-temperature resistance and is commonly used in chemical, food, light industry, mechanical instrumentation, and other industrial transmission pipelines as well as mechanical structural components. Then you know how the 316 stainless steel pipe manufacturer is produced? The following will take you to understand one by one.

1、Selected material

The use of cold-rolled stainless steel strips as raw materials, the surface state BA grade. Before the steel strip is used in the factory, the strip must be inspected in detail. Inspection items include thickness, width, edge quality state, appearance, and physical properties inspection. If necessary, the grain size of the original material is to be inspected, the inspection can be used for production only after passing.

2、Uncoiling

Before entering the welded pipe unit, the steel strip needs to be unrolled using the steel strip uncoiler, and the steel strip needs to be leveled by adding a leveling mechanism to ensure that the steel strip enters the forming part of the welded pipe unit in a straight state, so that the bending of the steel strip can be completed successfully.

3、Pipe billet forming

Continuous roll bending equipment is used to continuously roll bend the steel strip to make an open pipe billet. The steel strip needs to pass the introduction module, rough rolling module, closing module of the welded pipe unit several functional modules, each module uses different types of rolls to achieve the bending of different parts of the steel strip forming, and finally, the steel strip from the plane gradually bent to form an open billet, ready for welding into 304 stainless steel pipe.

4、Continuous welding

Steel strip after continuous roll forming unit, made of open pipe billet. Use TIG welding equipment, continuous welding, made of round tube. The welding process uses argon as a protective gas to prevent oxidation before the weld solidifies and cools in contact with oxygen. The argon gas is passed into the tube to protect the internal weld seam, and the argon gas passed into the torch is used to protect the tungsten electrode. Around the melt pool to form a protective layer of argon gas to protect the melt pool and the weld from oxidation.

5、Welding seam leveling

Due to the impact of welding current and gravity, resulting in the protrusion of the internal weld of stainless steel products tube, the external weld will also appear depressed, these problems will not have an impact if used in an ordinary low-pressure fluid environment. If used in high temperature, high pressure, and high-speed fluid environment, will cause problems in use. This defect must be eliminated by using special weld seam leveling equipment.

6、 Online heat treatment

Steel strips for the roll bending forming process will produce process hardening, which is not conducive to post-processing of the pipe, especially for the pipe bending process. During the welding process, there will be welding stress at the weld seam, which will cause cracking potential in the later use process, which requires heat treatment.

Currently commonly used heat treatment process for hydrogen protective atmosphere bright solution treatment, 304 stainless steel pipe heated to more than 1050 °, after a period of insulation, is the internal tissue morphology transformation, the formation of uniform austenite organization, under the protection of hydrogen atmosphere, no oxidation.

7、Sizing finishing

The outer diameter size of the welded pipe, in the welding and heat treatment process, will be deformed, resulting in the outer diameter size can not meet the requirements of use, and the need for sizing finishing. Usually used sizing and finishing unit consists of 4 sets of flat rollers and 4 sets of side rollers, flat rollers are designed as flat oval (or round), and side rollers are designed as oval (or round). The sizing amount is different according to the outer diameter and wall thickness of the tube, generally within the range of 0.20~0.50mm. After sizing and finishing, the outer diameter tolerance of the tube can be controlled within ±0.05mm, which can fully meet the accuracy requirements.

8、On-line flaw detection

Due to the pressure, and the need for a certain degree of reliability, the weld only relies on pressure detection is difficult to detect internal defects in the weld, you can use online eddy current flaw detection or ultrasonic flaw detection, real-time online 100% detection. The welding state can be corrected at any time according to the alarm information to reduce the production of substandard products.

9、Sizing cutting

Using online cut-to-length equipment, according to the length required by the customer, cut-to-length, you can use rotary cutting (chipless) technology, compared with chip cutting, chipless cutting has no cutting burr characteristics, at a later stage, you can not deburr the port.

10、Straightening

Roll forming unit production of welded pipe straightness can not meet the requirements of the use of the general straightness of such welded pipe needs to be controlled at 0.10/100mm. need to use a straightening machine to straighten the welded pipe to achieve the required production requirements.

11、Pressure test

The use of an automatic static water pressure test machine, the 304 stainless steel pipe pressure test, loading, flushing, and pressure testing, under the material, all automatically complete, pressure after a certain period of time through the differential pressure method to sort out an unqualified welded pipe.
12、Cleaning and drying

Welded pipe in the completion of mechanical processing, the need for the final cleaning and drying, to remove the inner wall or outer wall of the pipe residual coolant, oil and other pollutants, and then use for hot air drying to prevent rust during transport and storage. Finally, the finished stainless steel welded pipe inspection and packaging, you can leave the factory.

The above is the production process of 316 stainless steel pipe, the production process includes the selection of materials, uncoiling, billet forming, continuous welding, welding seam finishing and a series of processes.

Alloy 800 (UNS N08800), 800H (UNS N08810), 800HT (UNS N08811) is a solid solution high strength austenitic nickel-iron-chromium alloy. Nichrome is designed for resistance to oxidation and carbonization at elevated temperatures, high temperature oxidation resistance, high temperature scaling resistance and high temperature carbonization resistance. Excellent overall corrosion resistance. When the nickel content is 32%, the alloy’s resistance to corrosion cracking caused by chlorides and to embrittlement in the process of precipitation in sigma state can be enhanced. At the same time, it also has excellent resistance to uniform corrosion, and has excellent corrosion resistance in extremely high-temperature water media at 500°C. The service temperature of alloy 800 is about 590°C, and the service temperature of alloy 800H/800HT is above 590°C, which has excellent creep resistance and crack resistance. In terms of mechanical properties, it has excellent mechanical properties no matter at zero temperature, room temperature or high temperature of 600°C. Its excellent cold forming performance makes this alloy widely used in the manufacture of bellows, expansion joints and other equipment. These three Type 800 series alloy products have been widely used in ASME boilers, booster valves, first sections of electric boilers, third sections of nuclear material containers and red high pressure vessels.

Alloys 800, 800H, and 800HT are high-strength austenitic nickel-iron-chromium alloys in solid solution. Nickel-chromium-iron alloy is designed for anti-oxidation and carbonization when the temperature rises. It is resistant to high-temperature oxidation, high-temperature peeling and high-temperature carbonization, and has excellent overall corrosion resistance. These three 800 series alloy products have been widely used in ASME boilers, booster valves, the first section of electric boilers, the third section of nuclear material containers and red high pressure vessels, etc.

But what is the difference between them? Let’s describe it with data from the aspects of chemical properties and physical properties.

The grade corresponding to 1.800 is UNSN08800,

The grade corresponding to 800H is UNS N08810,

The grade corresponding to 800HT is UNS N08811;

2. In terms of chemical composition, there are some differences in the content of C, and the other requirements are the same:

C≤0.10 in 800,

0.05≤C≤0.10 in 800H,

0.06≤C≤0.10 in 800HT;

3. In terms of physical properties,

800 requires tensile strength ≥ 517MPa, yield strength ≥ 207MPa, elongation ≥ 30%;

Like 800HT, 800H requires tensile strength ≥448MPa, yield strength ≥172MPa, and elongation ≥30%.