Emergency
1-800-492-8826

Our Products

Home >> Case Study >> What is Passivation? Why do We Need to Passivate Flanged Heaters?

What is Passivation? Why do We Need to Passivate Flanged Heaters?

 
Most of the parts of flanged heaters are made of stainless steel—an alloy that is mainly comprised of iron, carbon, and chromium. Of these, chromium is the chemical element that makes the steel “stainless” i.e., resistant to rust. Chromium reacts with the oxygen in the atmosphere to form a thin oxide layer—or a passive film—on the surface of the metal. When stainless steel objects are cut or scratched, this passive film reacts with oxygen and “repairs” the exposed surface, preventing the formation of rust. See Figure 1 for the advantages.

Passivation is the process of treating the metal with acids in order to remove the free iron from the surface of the metal and coat it with this corrosion-preventing oxide layer. This passive layer gets damaged through heat or chemical damage due to high humidity levels. This may lead to rusting of the parts of the flanged heater. Therefore, passivation may need to be regularly performed to prevent damage to the parts of the heater.

Though nitric acid is usually used to passivate stainless steel products, in recent times citric acid is being used. It is safer and has many advantages over nitric acid.

  • It is more environment friendly (bio-degradable).
  • It does not require special handling equipment.
  • It does not emit harmful nitrogen oxide vapors.
  • It removes only iron (and not other elements) from the alloy.
  • Lesser quantities of citric acid are required (as compared to nitric acid), as the former is more effective at removing the corrosion.
  • It can also clean and brighten the metal.
Though the amount of acid, temperature, and duration of the passivation process depend on the type of alloy being processed, the process of passivation usually involves the following steps:
  1. Thoroughly clean the surface of the flanged heater, or other equipment. This removes oils, greases, and other deposits from the surface.
  2. Immerse the parts in a passivation solution (usually nitric-acid or citric-acid based) for a minimum of twenty minutes (up to a maximum of two hours), depending on the amount of corrosion. The solution should be at room temperature or at a maximum temperature of 160 deg. F (about 49 deg. C).
  3. Once the passivation process is completed, rinse the parts in water or a solution of sodium dichromate (Na2Cr2O7) to neutralize any remaining acid on the surface of the parts, and then drying them.
Since passivation involves the use of acids, it should be performed only by trained personnel who have experience with industrial heating, using these acids, and who have taken adequate protection such as using rubber gloves, boots, and other equipment to maintain safety during the operation. One can reference industry standards ASTM A-380 and ASTM A-967 for guidance on the procedure to be followed.

After passivation, various tests can be performed to verify whether passivation has been properly performed. This includes exposure to a salt-spray for up to two hours, or high humidity conditions for twenty-four hours. A commonly-used method of verification is to immerse the flange parts in a copper sulphate solution (CuSO4) for a period of six minutes and then rinse and examine the flange parts. If there is any pink color visible, it indicates the presence of free iron. This means the passivation process was not satisfactory.

Even though flange heaters and tanks may be made of stainless steel, the non-corrosive coating of the stainless steel often gets damaged because the flange heating equipment and the tanks are constantly exposed to hot water. Thus, flanged heaters need to be regularly passivated to maintain the non-corrosiveness of the equipment.
 

Figure 1

Latest blogs

Common Industries that Wattco works with

Case Studies View All

5 Fundamental Rules for Designing Efficient Heat Transfers
Considering these basic rules for designing thermal heat transfers will expand a project’s product...
Read More..

A Review of Industrial Heaters: Oil and Gas industry Case Study
About Industrial Heating The industrial revolution has significantly contributed to the development ...
Read More..

Advantages and Limitations of Digital Control Panels for Industries
Digital control panels are widely used in industries to monitor and control system variables. Humidi...
Read More..

Air Duct Heaters
Air duct heaters are commonly used in the HVAC industry. They provide supplementary heat to the deli...
Read More..

Alternatives to Direct Immersion Heaters
  Although immersion heaters are most often the best possible solution for tank content heating, so...
Read More..

Wattco News View All

4 Advantages of Skid Systems in Industrial Heating Processes
Many industrial heating processes involve maintaining a consistent temperature in a vessel to protec...
Read More..

4 Common Causes & Solutions of Circulation Heater Fouling
If you have noticed a decrease in the efficiency of your circulation heater, the most common culprit...
Read More..

A Closer look at Circulation Heaters
Wattco manufactures and designs circulation heaters for maximum efficiency. As a result, these heate...
Read More..

A Closer Look at Immersion Heaters for Tanks
Heating storage tanks is an important application of electric immersion heaters. Tank heating is a p...
Read More..

A Closer Look At Load Banks
Load banks are essential for applications in a variety of industrial applications, especially for te...
Read More..

Most Popular Blogs View All

Downloads

Disclaimer:

Legal

NOTE: All information in CONDEX WATTCO INC ("WATTCO") catalog was considered accurate and correct at printing time. WATTCO is committed to product research and development. WATTCO therefore has the right to make changes to specifications, designs and the Sales Terms and Conditions without prior notice. Should a conflict arise, WATTCO Sales Terms and Conditions will prevail. WATTCO is not responsible for any typographical errors.

For Any questions feel free to
call us at

1-800-492-8826

Copyright © 2021 Wattco. All Rights Reserved.