Introduction to the welding process of Inconel 600 pipeline
For Inconel 600 pipeline working pressure, high temperature, easy to produce thermal cracking and porosity when welding characteristics, the use of manual tungsten arc welding, the choice of Inconel 62 welding wire, with appropriate welding process measures to obtain the ideal welded joints.
A production pipeline material is Inconel 600 nickel-based corrosion-resistant alloy; in normal operation, the pressure in the tube is 11MPa, the temperature is as high as 500 ℃, and the working conditions are very harsh, so the Inconel 600 nickel-based corrosion-resistant alloy of the quality of welded joints put forward higher requirements.
1. The weldability analysis
Table of Contents
The base material is imported Inconel 600 nickel-based corrosion-resistant alloy, a diameter of 33mm wall thickness of 4mm; its chemical composition and mechanical properties are shown in Table 1.
Table.1 Chemical composition and mechanical properties of Inconel 600
| Chemical composition (%) | Mechanical | |||||||||||
| C | Si | Mn | Cr | Ni | Co | Fe | S | Cu | σb(MPa) | σs(MPa) | Ψ（%） | Hardness（HV） |
| 0.05 | ≤0.5 | ≤1.0 | 140–17 | ≥72 | ≤1.0 | 6–10 | ≤0.015 | ≥0.5 | ≥560 | ≥200 | 60 | 120–160 |
Inconel 600 is a typical Ni-Cr-Fe solution-reinforced corrosion-resistant high-temperature alloy with excellent corrosion resistance, wear resistance, and oxidation resistance; weldability is good, but if the welding material or welding process is not properly selected, easy to produce cracks, and porosity, inclusions and other defects.
Thermal cracking
Weld metal containing S, P, Si, Sb, and other elements, easy to form a low melting point eutectic with Ni, resulting in thermal cracking; heat input is too large, easy to form a strong directional single-phase austenite organization, impurity bias serious, easy to produce thermal cracking; arc improperly closed, easy to produce arc pit crack; affected by the thermal cycle of welding, near the seam zone tends to produce liquefaction cracking.
Porosity
Inconel 600 alloy is prone to porosity during welding. When the weld bevel near the oil, dirt, rust, and scale is not clean, it easy to produce hydrogen porosity; in the welding, if the protection is not good, the oxygen in the air into the molten pool and the molten pool metal chemical reaction, easy to form CO porosity and water vapor porosity.
Corrosion tendency of the welded area
Inconel 600 alloy thermal conductivity is poor, and the crystallization of grains has a serious tendency to grow, resulting in coarse grains, reducing the mechanical properties of the weld and corrosion resistance.
Inclusions
Inconel 600 alloy can easily form a high oxide melting point when welding, resulting in inclusions.
2. The welding process of Inconel 600 pipeline
Welding method
Manual tungsten arc welding with concentrated heat and good protection effect.
Welding material
The welding material is Inconel 62 wire, ф2.5mm, which is similar in composition to the base material. Acetone should be used to wipe the wire before use to ensure cleanliness.
The diameter of the tungsten tip is about ф0.4mm, with an angle of 30°-45°, which is conducive to arc stability and sufficient depth of melt.
Argon gas purity should exceed 99.99%.
Pre-welding preparation
Cleaning before welding is one of the important conditions for obtaining good joints. First, degrease the inside and outside of the pipe, and then use acetone to clean the bevel on both sides of the 50mm range of oil, rust, and scale, mark with ink, cutting fluid, etc., to dry after welding.
To ensure weld penetration, consider choosing large angle small blunt edge bevel form.
Welding process parameters
Inconel 600 nickel-based corrosion-resistant alloy has a low penetration characteristic, so generally should not be used to weld large linear energy to prevent excessive alloy burnout, affecting the performance of the joint. The selected process parameters are shown in Table 2.
Table.2 Inconel 600 nickel-based corrosion-resistant alloy welding process parameters
| Number of welding layers | Welding current (A) | Arc voltage (V) | Welding speed (mm/min) | Tungsten electrode diameter (mm) | Nozzle diameter (mm) | Current attenuation (s) | Argon flow rate (L/min) front/back | Power polarity |
| 1 | 95–100 | 12–14 | 80–100 | ф2.4 | ф11 | 5–6 | 10–12/12–14 | DC direct connection |
| 2 | 100-105 | 13–15 | 100–120 | ф2.4 | ф11 | 5–6 | 10–12/12–14 | DC direct connection |
Operation points
In the premise of ensuring quality as far as possible using low current, short arc, and fast welding. In the bottoming, the front of the molten pool maintains a small hole ф2-3mm in diameter, and the wire to drop transitions to the molten pool to ensure that the root weld through. In welding, the wire does not swing laterally, and the interlayer temperature control at 50 ℃ -60 ℃. In the cover filler welding, use the angle grinder or stainless steel wire brush to clean up the interlayer and surface thoroughly; in the grinding, shall not be mixed with carbon steel; in the cover, when the weld is slightly higher than the parent material, in the closing arc when filling the arc pit.
Attention to the problem
- (1) In the application of the welding tube should first pass argon gas, a flow rate of more than 12L / min, to ensure the weld penetration and weld seam formation and to prevent oxidation; to strengthen the protection of the welding area, in the back side of the welding nozzle to add protection drag cover.
- (2) In the welding process, when the tungsten electrode such in contact with the molten pool, the tip of the tungsten electrode is contaminated, then the tungsten electrode must be ground off or replaced while grinding off the molten pool of local weld contaminants to prevent tungsten trapping defects.
- (3) In the welding process, the heating end of the wire must be in the argon gas protection, not stirring the molten pool with the wire.
- (4) Inconel 600 alloy generally does not require post-weld heat treatment.
3. Post-weld inspection
According to the above process measures welding, Inconel 600 nickel-based corrosion-resistant alloy pipe weld is well formed, the appearance of qualified. Weld by X-ray flaw detection results, according to JB4730-94 radiation flaw detection standards, as a class I film, and the weld has a good overall performance.
4. Conclusion
In short, we use manual tungsten arc welding with Inconel 62 wire with a similar composition to the base material, strict cleaning of the weld before welding; the use of smaller welding line energy in the bevel sidewall arc, the appropriate increase in current decay time, maintain a low interlayer temperature and other measures, you can get Inconel 600 pipeline quality welded joints.
Author: Gao Juan
