Application cases and solutions for welding materials for pressure vessel manufacturing

Our company is a specialized manufacturer and designer of pressure vessels, serving industries such as energy, chemicals, petrochemicals, coal chemicals, fine chemicals, fertilizers, paper, clean energy, and offshore engineering. We produce various equipment including towers, heat exchangers, reactors, and converters.

Commonly used welding consumables include carbon steel, chrome-molybdenum steel, low-temperature steel (2.5Ni, 3.5Ni), low-alloy high-strength steel, stainless steel (including duplex and urea-grade), and nickel-based alloys. Carbon steel, chrome-molybdenum steel, low-temperature steel, and low-alloy high-strength steel are typically used with welding rods and submerged arc welding wires, while stainless steel and nickel-based alloys are mainly used with welding rods and strips.

In recent years, with the improvement in equipment capacity and technological advancements, the degree of welding automation has increased. As a result, the use of welding rods has gradually decreased, while the proportion of welding wires and strips has risen. This shift has led to improved production efficiency and better welding quality.

In actual production, the recommended welding consumables based on standards may not always meet additional performance requirements, such as mechanical properties after normalizing and tempering or when using new welding methods for the first time. Below are some examples from our factory for reference.

According to GB713-2008 and National Standard No. 1, the tensile strength of Q345R steel plates with thickness >60~100mm is ≥490MPa, and for >100~150mm it is ≥480MPa. Different welding consumables were tested, and results showed that by upgrading the welding rod grade and customizing the flux, the tensile strength at room temperature could meet or exceed the standard's lower limit.

First, reducing the surfacing thickness can help save costs, especially when the surface is not processed afterward.

For a project involving eight sets of equipment requiring a 5mm thick stainless steel layer, we used submerged arc welding with about 8mm thickness. The cost was approximately 1.6 million yuan. By reducing the thickness by 1mm, we saved 200,000 yuan. The goal was to reduce by at least 2mm, and after testing, the results were promising. The second test also showed good outcomes.

From Table 3, increasing the CrNi content and adjusting the flux allowed us to achieve a 5.5mm surfacing layer that met both the minimum thickness requirement and acceptable test results.

The dilution rate for submerged arc electrode surfacing is 18%–25%, while for electroslag it is 7%–10%. Reducing the dilution rate is crucial for corrosion-resistant surfacing, and electroslag surfacing excels in this area. Simply from the perspective of consumables, we saved at least 400,000 yuan.

Second, replacing the nickel-based flux improved the appearance and quality of the surfacing, especially when the surface was processed afterward. For an ammonia synthesis tower casing made from 12Cr2Mo1IV forging material, initial tests with flux and submerged arc welding showed poor fusion. Even after adjusting parameters, the results were unsatisfactory. Eventually, switching to electroslag flux from Jingqun consumables resulted in a much better surface finish, as shown in the images below.

As a non-standard pressure vessel manufacturer, we still face challenges with certain special welding materials in China, such as nickel-based alloys, duplex steels, urea-grade stainless steel, and 12Cr2Mo1 CrMo steel. Some domestic manufacturers’ test samples do not meet technical requirements, and their weldability is not as good as imported materials. However, importing these materials comes with long lead times and high costs, which affect production cycles and increase expenses.

We hope to see more domestic welding consumables rise to compete with imported products. Additionally, some manufacturers do not produce steel wire or strips themselves, so we encourage the government to support the development of self-produced steel wire and strips for better compatibility and performance.

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