Substituting Carbon Steel for Stainless Steel | Blog No. 90
- Keith Tyson, Senior Advisor
- Sep 2
- 2 min read
Are refrigeration materials of construction interchangeable? Can you replace carbon steel that is installed in an area prone to corrosion with stainless steel? The answer is…” depends!” The first thing that must be discussed in changing materials is “Will the new material work in the system?” That question automatically requires an engineering review and directs you to your management of change procedures. Changing carbon steel to stainless steel has not only strength considerations but also compatibility issues.
Changing carbon steel pipe to stainless steel pipe will likely be an acceptable substitution in terms of pressure and temperature. Both should work equally well in some applications. But there are other issues to watch out for following the change. If stainless steel was installed due to corrosion, likely, the process conditions that promote corrosion cannot be changed, and there will be moisture on the pipe due to process temperatures or room conditions. By adding stainless steel to the carbon steel structure, you now have all the ingredients for a type of corrosion known as galvanic. A “galvanic cell” occurs when two dissimilar metals (stainless and carbon), in direct contact via welds or threaded connections, are in the presence of moisture such as water or condensation. Corrosion can occur in the carbon steel.
When inspecting such a system, pay particular attention to the carbon pipe and look for any signs of metal loss where it is attached to stainless steel. Corrosion may occur on the carbon pipe at any point, especially if it is wet or encased in wet insulation. Also, look at other carbon steel attachments to stainless, including hangers or braces. Painting the carbon steel will help, but it is not a guarantee.
Corroded bolting is another area where stainless steel is used to replace the original carbon steel. When the bolts have corroded, an apparent answer is to replace the bolts with stainless steel ones. But this is very likely not a good answer. One of the properties of steel is its strength. Carbon steel is (usually) much stronger than stainless steel. The bolts were selected for their ability to hold the two parts together. If a weaker bolt is substituted, a failure can result. You MUST check with the manufacturer of the valve or flange to ensure the stainless bolt is a suitable product. The designer of the connection can tell you what bolting materials are suitable.
The same thing goes for pipe hangers or rods. A stainless steel rod may not hold the loads of the same-sized carbon rod; therefore, changing out to prevent future corrosion may result in other problems.
If you use your MOC procedures, then your engineering department or team should be able to determine if the substitution of stainless for carbon is acceptable. This is the best answer for changing or substituting materials; let the engineers decide.
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