What Is Passivated Stainless Steel Tubing and Why Does It Matter?
What Is Passivated Stainless Steel Tubing?
What is Passivation Stainless Steel Tubing, and how does the passivation process work? How do I passivate stainless steel parts after machining operations? Machine shops and manufacturers of part materials such as stainless steel, titanium, and tantalum often asked these questions.
Passivation is a process that removes or neutralizes contaminants from a surface to make it more resistant to corrosion. It involves placing parts in chemical baths, which contain agents that strip away unwanted elements from the surface.
Passivated Stainless Steel Tubing is made of iron, chromium, and nickel. When these three elements come together at high temperatures (around 2200°F), they create a substance called austenite. This material is hard, durable, and non-magnetic, making it ideal for many industrial applications.
After parts have been machined, we need to clean them before using again or shipp out to customers. The cleaning process consists of several steps:
- 1) Sandblasting:
This step cleans away any dirt particles or other foreign matter on surfaces.
- 2) Degreasing:
Any remaining oils or other lubricants are removed at this stage using degreasers such as trichloroethylene (TCE).
Is Passivation Necessary?
Passivation is a widely-used metal finishing process to prevent corrosion. In stainless steel, the passivation process uses nitric acid or citric acid to remove free iron from the surface. The chemical treatment leads to a protective oxide layer or passivation film, that is less likely to chemically react with air and cause corrosion. Passivated stainless steel resists rust.
Passivated Stainless Steel Tubing:
The process of passivating stainless steel involves immersing the metal in a chemical solution called an electrolyte that contains nitric acid and sulfuric acid. The solution attacks free iron on the surface of the stainless steel, dissolving it and creating a protective coating on the surface of the metal. Nitric acid is used for low carbon content grades of stainless steel such as 304 or 316L, while for higher carbon content grades (such as 317L), citric acid is used because it does not dissolve chromium at high temperatures like nitric acid does.
Stainless Steel Passivation
Passivation can be performed using either nitric or citric acid solutions depending on which type of stainless steel you are working with: low carbon content grades (304) or high carbon content grades (317).
How Does Passivation Work?
Stainless steel is a metal alloy that resists corrosion and oxidation. The term “stainless” refers to the unique, non-reactive crystal structure of stainless steel. This structure makes it difficult for oxygen and water molecules to attach themselves to the atoms in the metal. These two elements are essential for corrosion and rust formation.
Passivation is a process that creates a protective layer on the surface of stainless steel that prevents further corrosion. In stainless steel, the passivation process uses nitric acid or citric acid to remove free iron from the surface. The chemical treatment leads to a protective oxide layer or passivation film, that is less likely to chemically react with air and cause corrosion. Passivated stainless steel resists rust.
The passivating process usually involves immersion in an acid bath followed by rinsing and drying. Passivating can be done at home with household chemicals or at a professional shop by one of our technicians who will clean your metal surfaces thoroughly before applying an appropriate passivating solution.
Is There a Specific Process for Passivated Stainless Steel Tubing?
stainless steel is a metal alloy that contains a minimum of 10.5% chromium, typically with iron, nickel, and other elements added to improve corrosion resistance and durability.
Passivation is a process that forms an oxide layer on the surface of stainless steel, protecting it from corrosion. The most common passivation process uses nitric acid or citric acid to remove free iron from the surface of the metal. In stainless steel, this leads to a protective oxide layer, or passivation film, that is less likely to chemically react with air and cause corrosion.
Passivated stainless steel resists rust when exposed to oxygen at room temperature for long periods of time. However, if moisture gets under this protective layer, it can lead to corrosion in as little as 24 hours.
Stainless Steel Passivation Processes
The two main types of passivation processes are electrochemical and chemical.
Electrochemical passivation involves the use of electricity to remove iron from the surface of stainless steel by creating an electric current between two dissimilar metals — one being stainless steel and another being either zinc or aluminum — which causes electrolysis (a chemical reaction between two substances due to an electric current passing through them).
What Will Passivating Do to the Appearance of My Parts?
Passivating is a process to improve the appearance and corrosion resistance of stainless steel parts. Common uses are in the food, pharmaceutical and medical industries to protect surgical instruments from rust and corrosion.
What Can Passivation Do?
Passivation makes stainless steel more rust-resistant by using nitric acid or citric acid to remove iron and form a protective film layer. This thin layer of chromium oxide prevents further oxidation of the base metal underneath, making it more resistant to corrosion.
The process can use for other metals such as aluminium, nickel, zinc, and copper alloys. It’s normal that we can see the combination of electroplating processes to create coatings on these materials. Some examples include:
- Chromium plating
We usually finish the passivation before chromium plating because it allows chromium to adhere better to the base material.
- Nickel plating
Before or after nickel plating depending on what’s necessary for your application, we can perform nickel passivation.
If you need a higher degree of corrosion resistance, then passivating first will produce better results than plating directly onto a passivated surface.
Will Passivating Alter the Dimensions of Parts?
The passivation of parts to EN 10305 and DIN 2391 specifications is an important process in the aerospace industry. The end finish will not change the dimension of the part or its overall performance of it.
Passivation is a process that uses chemical etching to improve corrosion resistance and prevent rusting. It also improves paint adhesion, improves surface hardness and increases lubricity. Passivating parts to SAE J524 and EN10305-4 specifications is an important process in the aerospace industry because it ensures that all parts are smooth enough for painting or plating, with no sharp edges or corners that could cause pinholes in coatings or lead to corrosion problems for metallic parts.
There are many different types of passivation available today, including those that contain nitric acid, ammonium hydroxide, and potassium hydroxide (KOH).
When electroplating copper onto aluminum alloys, we usually use nitric acid as an etch stop bath because it leaves a thin layer of copper oxide on the aluminium while preventing the copper from oxidizing at low temperatures.
This helps prevent pitting corrosion during electroplating operations and also allows copper to plate onto aluminium faster than other metals such as zinc or tin alloys.
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