【Daily Question 20090303】Welding issues with different materials

We experienced significant leaks in the ammonia pipelines in our facility; during the major maintenance work, the entire pipeline was replaced. However, due to inadequate planning for the maintenance, there were no spare parts available for many flow meters, flanges, and other components, so those parts remained made of the original white steel material. The pipelines were replaced section by section with white steel, and I believe that over time problems could arise due to the different expansion coefficients of the various materials. . The original poster has raised a very good question

Welding of different materials is a common occurrence; the choice of welding electrode should be based on the higher-grade material in order to ensure welding quality.

It’s not just a welding issue; the choice of welding method also has a significant impact on the pressure resistance of the material. Oxygen acetylene, sub-arc welding, and so on, will all have an impact.

I don’t understand welding; I’m learning from all of you!

The most common issue is related to the welding of the white steel material of external-threaded globe valves with carbon steel pressure guide tubes. As for the quality of this welding, it varies depending on each person’s technique, and thus the results of the welding also differ. Mainly, temperature changes can easily affect the quality of the weld joint, as the coefficients of thermal expansion differ. If cracks appear, there will definitely be leaks. :lol

The most common type of welding is that between stainless steel and carbon steel; stainless steel electrodes must be used for this purpose. Of course, the electrodes need to undergo pre-treatment such as heating before welding, in order to meet the requirements of welding and ensure its quality. Welds that are not properly selected are prone to cracking. Also, after going into operation, pipe deformation and cracking occurred due to residual stresses from the construction process.

Stainless steel electrodes must be used for welding. Of course, these electrodes need to undergo pre-treatment such as heat preservation before welding, in order to meet the welding requirements and ensure welding quality

Metals of different materials can definitely be welded together. Because elements of the same group not only have the same melting point but also possess the same electrical conductivity and thermal conductivity. In the actual welding process, it is also constrained by the dimensions of the workpieces to be welded and the requirements for the finished product. But this can usually be resolved by selecting a spot welder of the same type.

Welding of different materials is a common practice; as long as the welding process is properly managed, the expansion coefficients of various materials are taken into account, and the required heat treatment steps before and after welding are carried out, there are generally no problems. However, welding extremely rare and special materials remains challenging. In short, as long as it is done properly and in strict accordance with the welding procedures, there are generally no problems. Cracks usually appear during the welding of instrument splices, either due to insufficient attention paid to the welding process or because such areas are prone to stress concentration.

Boss, the question was posted in the wrong place.

For joints of duplex stainless steel (where improper welding methods can lead to stress corrosion, intergranular corrosion, etc.), by using an appropriate amount of heat input for multi-layer welding, and employing Ar+2%N2 as the mixed shielding gas, a combination of Shielded Metal Arc Welding (SMAW) and Tungsten Inert Gas Welding (TIG) can result in excellent corrosion resistance

When welding stainless steel to carbon steel, stainless steel electrodes must be used as the welding rods

I’ve run into a problem recently: cracks have appeared in the fillet welds between 0Cr13 with a thickness of 38 mm and 20R with a thickness of 16 mm! It was discovered during a water filling leak test.

Welding is a skill mastered by specialized workers – is it inappropriate to discuss this topic here?

Materials are selected in accordance with JB/T4709. Not only the selection of materials is important, but preheating before welding, maintaining the appropriate temperature during welding, and heat treatment after welding also need to be carried out in accordance with the specifications.

The original poster has raised a very good question. The field of instrumentation involves many different aspects of knowledge; in terms of installation, this includes welding brackets, as well as an understanding of support structures and stresses. Of course, the level of knowledge required in this field isn’t as deep as that in specialized fields, but the more we know and learn, the more it helps us in our work. Welding is a processing technique and method of joining two pieces of material, whether of the same or different types, by heating them, applying pressure, or using both methods together to achieve atomic bonding between them. Welding is widely used, applicable to both metals and non-metals. There are processes such as arc welding, TIG welding, CO2 shielded welding, oxygen-acetylene welding, laser welding, and electroslag pressure welding. During welding, the phenomenon in which the arc center deviates from the electrode axis due to the interference of air currents, the effect of magnetic fields, or the eccentricity of the welding rod is known as arc drift.

Welding of different materials is surely related to the type of welding electrode, the welding method – be it butt welding, groove welding, or socket welding – as well as the welding processes and techniques! That’s what I think; it’s just my personal opinion

The welding rod to be used for welding the material must be selected correctly