1. Overview With the rapid development of the petrochemical industry, there is an increasing demand for materials that can withstand high temperatures and corrosive environments. Our company has been involved in the docking elbow project for Turkmenistan EPC, which involves the use of Incoloy 825, a nickel-based alloy with specifications of f355.6mm × 36.35mm. To ensure the quality and integrity of the welds, we conducted a welding procedure evaluation. 2. Material Properties and Welding Characteristics of Incoloy 825 Incoloy 825, also known as UNS N08825, is a nickel-iron-chromium based alloy renowned for its excellent resistance to both oxidizing and reducing environments. It shows strong resistance to stress corrosion cracking, pitting, and crevice corrosion. We selected ThyssenKrupp VDM sheets for this project, and their chemical composition and mechanical properties are detailed in Table 1. Table 1: Chemical Composition and Mechanical Properties of Incoloy 825 Incoloy 825 is prone to hot cracking, which includes crystal cracking, liquefaction cracking, and high-temperature plastic deformation cracking. Crystal cracks often occur in the crater of the weld bead, while liquefaction cracks appear near the fusion line. High-temperature plastic deformation cracks are typically found in the heat-affected zone. These cracks form at high temperatures and do not propagate at room temperature. The presence of impurities like sulfur and silicon in the weld metal can lead to low-melting-point eutectics, increasing the risk of cracking. Additionally, poor thermal conductivity can cause overheating, leading to coarse grains and reduced intergranular bonding. Therefore, careful welding procedures are essential to prevent hot cracks. 3. Development of the Welding Process for Incoloy 825 (1) Welding Method Selection: Manual argon arc welding was chosen due to its precision and control, especially for small components like elbows. Other methods such as submerged arc welding are unsuitable for thin plates due to high heat input, and electrode arc welding may be difficult to control during internal welding. Manual argon arc welding allows for clear observation of the weld pool and ensures good back weld quality without slag. (2) Welding Material Selection: To prevent hot cracks and intergranular corrosion, we selected ERNiCrMo-3 welding wire from TECHALLOY, which has low sulfur and silicon content and contains stabilizing elements like titanium. Its chemical composition and mechanical properties are listed in Table 2. Table 2: Chemical Composition and Mechanical Properties of ERNiCrMo-3 (3) Joint Form and Groove Preparation: Due to the high viscosity of Incoloy 825 weld metal, a proper groove angle (60°–70°) and root gap (2.5–3.0 mm) were used to improve weldability. Grooves were machined or cut using plasma arc, avoiding acetylene cutting to prevent work hardening. Surface polishing before welding was necessary to remove any work-hardened layers. (4) Pre-Weld Cleaning: Oxides and contaminants on the surface of Incoloy 825 can increase the risk of cracking. Before welding, the joint area within 50 mm was brushed with a stainless steel wire brush and cleaned with acetone to remove oxides, grease, and other impurities. (5) Welding Procedure: A small current, short arc, and fast welding technique were used to avoid excessive heat input and reduce the risk of hot cracks and porosity. The weld was performed in multiple passes, with the temperature between passes controlled to ≤808°C. Argon gas was used for protection, with a flow rate of 8–12 L/min for the front side and 15–20 L/min for the back side. After welding, the oxide layer was removed immediately with a stainless steel wire brush to ensure a clean surface. (6) Post-Weld Stabilization Treatment: Stabilization treatment at 930–950°C for 20 minutes improved the alloy’s resistance to intergranular corrosion by forming titanium carbides that reduce chromium depletion. This process ensured the long-term performance of the welded joint. 4. Mechanical Properties Testing of Incoloy 825 Testing was conducted according to ASME IX-2010ED 2011AD and customer requirements: (1) Tensile Test: The tensile strength reached 645 MPa, far exceeding the parent metal's minimum requirement, with failure occurring in the heat-affected zone, indicating good weld quality. (2) Bend Test: Two transverse plane bends and two reverse bends were performed, with no defects observed, confirming the joint's integrity. (3) Intergranular Corrosion Test: Using ASTM G28 A method, the result was 0.031 mm/month, well below the acceptable limit of 0.08 mm/month. (4) Hardness Test: The hardness value (HV10) was ≤345HV, meeting the required standards. 5. Conclusion The welding process and post-weld stabilization treatment proved effective in preventing hot cracks and ensuring the mechanical properties of the weld met the design requirements. This demonstrates the feasibility of the process and provides strong technical support for real-world applications. Sewage Pump,Sewage Pump System,Submersible Sewage Pump,A Basement Sewage Pump Shanxi Skysea Pump Lndustry Co.,Ltd. , https://www.skyseatianhai.com
