Experimental application of heat-resistant steel material P91 solid wire

Main Products and Common Welding Consumables

Our company is a construction and engineering unit, primarily involved in the construction of chemical and petrochemical equipment, boilers, tank towers, pipelines, and structural components. Due to the nature of construction projects, the commonly used welding methods include electrode arc welding, tungsten inert gas (TIG) welding, metal inert gas (MIG) welding, submerged arc welding, and gas metal arc vertical welding. As a result, the main welding materials used are welding rods, solid wires, and flux-cored wires. The range of materials covered is extensive, including heat-resistant chromium-molybdenum steel, low-temperature steel, stainless steel, nickel alloys, titanium alloys, and aluminum alloys. Currently, due to the flexibility and high penetration rate of electrode arc and TIG welding in field applications, they are the most widely used. In contrast, MIG, submerged arc, and gas metal arc vertical welding are limited by various conditions, resulting in more restricted applications. According to incomplete statistics, welding rods account for over 50% of the total welding material used in projects, while MIG wire accounts for less than 30%, with the rest making up the remaining 20%.

Experimental Application of P91 Heat-Resistant Steel Solid Wire Gas Shielded Welding

With the development of welding technology, methods such as MIG and submerged arc welding are gradually being applied on construction sites, such as in the use of MIG welding for alloy pipelines and transverse submerged arc welding in tank engineering.

T/P91 martensitic heat-resistant steel has excellent high-temperature mechanical properties and pressure resistance. It is increasingly replacing T/P22 and T/P5 grades in petroleum and petrochemical distillation and cracking equipment, as well as refinery piping and plates. However, its weldability is poor, and it is prone to issues like cold cracking, brittle joints, and softening in the heat-affected zone (HAZ). To achieve satisfactory welds, strict adherence to technical regulations is necessary. Therefore, the common welding process involves using TIG wire for the root pass, followed by SMAW for filling and capping, with most materials still relying on imports.

P91 materials are typically thick-walled, making the low-efficiency TIG-SMAW process unsuitable for fast-track construction projects. In response, our company has focused on developing high-efficiency welding processes and materials for P91 pipelines, including MIG and submerged arc welding.

To this end, we collaborated with welding consumables manufacturers and conducted numerous tests on P91 pipeline solid wire gas shielded welding. After screening, several gas mixture tests were performed using P91 MIG solid wire, as shown in the diagram.

First, using 100% argon gas resulted in severe arc instability, minimal penetration, and poor fusion between the molten pool and base metal.

Second, a 95% Ar + 5% COâ‚‚ gas mixture reduced arc drift but still led to shallow penetration and poor fusion, making it difficult for the welder to handle.

Third, an 85% Ar + 15% COâ‚‚ gas mixture provided a stable arc, good weld appearance, and better fusion, although the penetration was still shallow, and automatic welding was not feasible.

Finally, a 80% Ar + 20% COâ‚‚ gas mixture was determined to be optimal. It provided a stable arc, moderate penetration, and good fusion, allowing for both manual and automated welding.

The key to the welding process is maintaining thin layers, generally ≤ 3mm, ensuring even side-to-side coverage, full filling, and avoiding dead zones that could cause lack of fusion. Wind protection measures must also be strengthened to prevent porosity caused by wind interference.

Additionally, heat input is strictly controlled: ≤15 kJ for TIG and ≤30 kJ for MIG. The interpass temperature is maintained between 210–230°C. After welding, the temperature is cooled to 120°C within 1 hour, followed by post-heating at 350°C for 1 hour and subsequent heat treatment.

The test weld joints were evaluated according to relevant standards, and all normal temperature bending, tensile, and impact tests passed. To ensure safety, additional high-temperature tensile and creep tests were conducted, and the results met specifications. Based on these findings, two welding procedures were established. Building on the success of P91 MIG welding, we are now conducting related tests on submerged arc welding to meet future P91 pipeline welding needs.

Future Development Ideas for Welding Materials

Modern refining and chemical engineering projects involve large-scale structures, containers, and pipelines. Increasingly, there are large, heavy, long, tall, and thick structures that require high-temperature, high-pressure, and corrosion-resistant performance. The diversity of materials is growing, with higher proportions of heat-resistant steels, low-temperature steels, stainless steels, duplex steels, and non-ferrous metals. These characteristics bring new and higher demands on welding consumables and processes. High-efficiency, eco-friendly, user-friendly, and field-adaptable welding methods and materials are urgently needed.

(1) For steel structure welding, efforts are being made to reduce or eliminate the inefficiency and high cost of electrode arc welding. MIG or self-shielded welding is currently the best alternative, but its adaptability in the field is limited, and all-position welding is challenging. Improving the performance of welding materials can enhance welder operability. Self-shielded wires offer local production and cost reduction, which could open a large market.

(2) In equipment piping, submerged arc welding without arc is ideal due to its low pollution, high efficiency, and good welder operability during factory prefabrication. However, the development of submerged arc welding wire and flux for special materials like P91 heat-resistant steel and 9% Ni low-temperature steel lags behind, affecting their application.

(3) With the increasing demand for deep chemical processing, non-ferrous metals like titanium, aluminum, and nickel alloys are becoming more common. However, their welding methods and materials are relatively limited. For example, nickel alloy MIG wire is not yet localized, aluminum alloy welding wire quality is unstable, and titanium alloy welding is mainly done via TIG. Further research and development are needed to improve welding quality and efficiency.

The product is widely used in high-end manufacturing fields such as automotive industry, mold manufacturing, engineering machinery, power generation equipment, precision machinery, aerospace, medical industry, etc.