Inconel 600 pipelines with high working pressure and high temperatures are prone to thermal cracking and porosity during welding. Use manual tungsten arc welding, choose Inconel 62 welding wire, and use appropriate welding process measurements to obtain ideal welded joints.
A production pipeline material is Inconel 600 corrosion-resistant nickel-based alloy; In normal operation, the pressure in the tube is 11 MPa, the temperature reaches 500°C and the working conditions are very adverse. Therefore, higher requirements are imposed on the quality of welded joints from the corrosion-resistant nickel-based alloy Inconel 600.
1. Weldability analysis
The base material is an imported nickel alloy based on Inconel-600, corrosion resistant, with a diameter of 33 mm and a wall thickness of 4 mm. The chemical composition and mechanical properties are listed in Table 1.
Table 1 Chemical composition and mechanical properties of Inconel 600
| Chemical composition (%) | Mechanically | |||||||||||
| W | Yes | Mn | Cr | No | co | Faith | s | Ass | σ b (MPa) | σ S (MPa) | Ψ ( % ） | hardness ( High tension ） |
| 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 solution-strengthened, high-temperature and corrosion-resistant Ni-Cr-Fe alloy with excellent corrosion resistance, wear resistance and oxidation resistance. Weldability is good, but if the welding material or welding process is not selected correctly, cracks, porosity, inclusions and other defects are easy to occur.
Thermal cracking
Weld metals containing S, P, Si, Sb and other elements easily form a low-melting eutectic with Ni, resulting in thermal cracking. If too much heat is supplied, a strong directional organization of single-phase austenite is easily formed, with a strong tendency to contamination, which easily leads to thermal cracking. The bow is not closed properly, which easily leads to the bow breaking. Influenced by the welding thermal cycle, the seam zone tends to form liquefaction cracks.
porosity
Inconel 600 alloy is prone to porosity during welding. If the weld groove is not clean near oil, dirt, rust and scale, hydrogen porosity can easily occur. In welding, if the protection is not good, oxygen in the air will enter the weld pool and a chemical reaction of the molten metal will occur, easily forming CO porosity and water vapor porosity.
Tendency to corrode the weld
The thermal conductivity of Inconel 600 alloy is low and the crystallization grains have a strong tendency to grow, resulting in coarse grains and reducing the weld's mechanical properties and corrosion resistance.
Inclusions
During welding, Inconel 600 alloy can easily develop a high oxide melting point, resulting in inclusions.
Welding process
Manual tungsten arc welding with concentrated heat and good shielding effect.
welding material
The welding material is Inconel 62 wire, ф2.5 mm, whose composition is similar to the base material. To ensure cleanliness, the wire must be cleaned with acetone before use.
The diameter of the tungsten tip is about 0.4mm, with an angle of 30°-45°, which contributes to arc stability and sufficient melting depth.
The purity of argon gas must be greater than 99.99%.
Preparation before welding
Cleaning before welding is one of the most important requirements for good connections. First, degrease the pipe inside and outside, then clean the chamfer on both sides of the 50 mm area from oil, rust and scale with acetone. Mark them with paint, cutting fluid, etc. and let them dry after welding.
To ensure weld penetration, a chamfer shape with a large angle and small blunt edge must be chosen.
Welding process parameters
Corrosion-resistant nickel alloy Inconel 600 has a low penetration property and therefore generally should not be used for large linear energy welding to avoid excessive burning of the alloy, which would affect joint performance. The selected process parameters are listed in Table 2.
Table 2: Welding process parameters of corrosion-resistant nickel alloy Inconel 600
| Number of weld 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/rear | Energy polarity |
| 1 | 95 – 100 | 12 – 14 | 80 – 100 | ф2.4 | f11 | 5 – 6 | 10 – 12/12 – 14 | DC direct connection |
| two | 100- 105 | 13 – 15 | 100 – 120 | ф2.4 | f11 | 5 – 6 | 10 – 12/12 – 14 | DC direct connection |
Control points
Under the premise of guaranteeing the maximum possible quality, low current, short arc and fast welding are used. In bottom welding, a small hole with a diameter of 2-3 mm is left in front of the weld pool and the wire falls into the weld pool to ensure that the root weld passes through. During welding, the wire does not oscillate laterally and the temperature of the intermediate layer is controlled between 50-60°C. During deck fill welding, the interlayer and surface are carefully cleaned with an angle grinder or stainless steel brush. Carbon steel should not be added during grinding. In overlay welding, if the weld is slightly higher than the base material, when the arc closes, the arc well will be filled.
Attention to the problem
- (1) When welding, argon must first pass through the pipe at a flow rate greater than 12L/min to ensure weld penetration and weld formation and prevent oxidation. To strengthen the protection of the welding area, a protective cover must be installed on the back of the welding nozzle.
- (2) During the welding process, if the tungsten electrode comes into contact with the weld pool and the tungsten electrode tip becomes contaminated, the tungsten electrode must be ground or replaced while removing local welding impurities from the weld pool. fusion to avoid defects caused by the inclusion of tungsten.
- (3) When welding, the heating end of the wire should be in the argon gas shield and should not stir the weld pool with the wire.
- (4) Inconel 600 alloy generally does not require heat treatment after welding.
3. Check after welding
After welding according to the above process measurements, the weld of Inconel 600 nickel alloy corrosion-resistant pipes is well formed and has good appearance. The X-ray flaw detection results for the weld comply with the JB4730-94 radiation flaw detection standards and Class I layer. The weld has good overall performance.
