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What is stainless steel passivation?
What is passivation and how does the passivation process work? How to passivate stainless steel parts after machining? These are questions machine shops and manufacturers of component materials such as stainless steel, titanium and tantalum often ask.
Passivation is a metal surface treatment process widely used to prevent corrosion. In stainless steel, the passivation process uses nitric or citric acid to remove free iron from the surface. Chemical treatments form a protective oxide or passivation film that is less likely to chemically react with air and cause corrosion. Passivated stainless steel prevents rust.
Passivation type
Today, the industry standard for surface passivation offers three types of passivation. Each type is based on the chemicals used for passivation. The three types of passivation are:
nitric acid
Nitric acid and sodium dichromate
citric acid.
The choice of chemicals for passivation usually depends on customer requirements. Each passivation type has its own advantages and disadvantages. See our article Nitric vs. Citric passivation for more information.
Why passivate stainless steel?
Passivation is a post-fabrication best practice for newly machined stainless steel parts and assemblies. Benefits include:
Anti-rust chemical film barrier
Extend the life of the product
Remove contaminants from product surfaces
Reduced maintenance requirements.
How does passivation work?
Stainless steel is an iron-based alloy usually composed of iron, nickel and chromium. The corrosion resistance of stainless steel comes from the chromium content. When chromium is exposed to oxygen (air), it forms a thin film of chromium oxide that coats the stainless steel surface and protects the underlying iron from rust. The purpose of passivation is to enhance and optimize the formation of the chromium oxide layer.
Immersing stainless steel in an acid bath will dissolve free iron on the surface while leaving the chromium intact. The acid chemically removes free iron, leaving a uniform surface with a higher chromium content than the underlying material.
After exposure to oxygen in the air after the acid bath, the stainless steel will develop a chromium oxide layer over the next 24 to 48 hours. A higher proportion of chromium on the surface allows a thicker, more protective chromium oxide layer to form. Removing free iron from the surface eliminates the chance of corrosion starting.
The resulting passivated layer provides a chemically non-reactive surface that prevents rust.
A pump is a mechanical tool that gives enough pressure to move the liquid through the system at the desired flow rate. Therefore it is a means to change mechanical work into fluid energy. The pump can be widely classified as a centrifugal pump and positive displacement pump. So far, centrifugal pumps are the most widely used pumps.
What are Pump Housings?
Simply put, the pump housing is a cast component that holds a pump. The pump can be very miniature or massive. But regardless of size, all pumps mainly function by accepting fluid through an inlet and sending it through outlets after increasing the pressure. The housing pump is a casing that attaches all parts consisting of pump work. The pump housing is very important wherever the pump is exposed to elements. A good example where sturdy pump housing is needed is a submersible pump.
The pump housing is one of the most expensive pump parts and must be carefully chosen.
Choosing the right pump housing directly affects reliability and uptime. The pump housing that is disposed of correctly also plays an important role in improving its performance. In many systems, the pump receives a fluid that is very hot or very cold. Therefore, the choice of material is also important.
Casting of Pump Housings
Pump housing contribute to the pump fee to a large level. There are various challenges faced by casting housing pumps. One of the most important challenges is corrosion because of the fluid. While throwing pump housing, the manufacturer must ensure that the pump housing wall is sturdy enough to withstand the pressure and pressure imposed on the pump. Casting manufacturers also need to ensure that the housing casting pump is resistant to corrosion. The pump housing diameter must be large enough to accommodate pumps with enough permits for efficient installation and operation.
Material used for Pump Housings
Ductile cast iron is one of the most popular casting materials for pump housing. However, they can be made from cast iron or gray iron too. Cast iron houses mainly tend to withstand wear very well and need more rare replacement.
Usually, after the manufacturer of casting housing pumps receive CAD images, molds are made from the material needed pump housing thrown into the tolerance needed.
Housing Pump - Testing
Pumps and pump houses undergo a lot of wear because of the nature of these components. Therefore it is important to test these two entities for fatigue, corrosion, and reduction in thickness. There are regular laboratories that carry out the pump housing test.