Pickling
& Passivation
Pickling & Passivation Services
When stainless steel is heated, such as during welding, a visible heat tint or oxide scale layer forms, depleting the underlying layer of chromium and reducing the steel’s corrosion resistance. Pickling is the process of applying an acid solution to remove these heat-affected zones and the chromium-depleted layer. This cleaning method also eliminates surface contaminants and embedded iron particles. Pickling does etch the surface of metal, preferentially attacking grain boundaries and causing slight roughening, which results in a dull matte appearance. Process control is crucial because excessive acid concentration, prolonged acid contact time, or incomplete removal and neutralization of residual acids can lead to corrosion and pitting. Typically, pickling is followed up with passivation, a process that further enhances corrosion resistance by forming a protective oxide layer.
Methodologies
Pickling and passivation can be applied through various methods such as tank immersion, spray application, circulation, and manual gel application, making it suitable for different sizes and types of components.
Spray Application
Can be performed at an Astro Pak shop facility or on-site, but requires proper acid disposal and adherence to safety procedures.
Gel Application
Pickling gel can be brushed onto specific areas, making them ideal for spot treatment of welds and other intricate areas where full immersion is impractical.
Tank Immersion
Typically performed at an Astro Pak shop facility, this process is beneficial for treating all fabrication surfaces simultaneously, ensuring uniform finish and optimal corrosion resistance.
Circulation
Chemical solution is circulated through a system of pipework and is particularly recommended for piping that will carry corrosive liquids.
Resources
Chemical descaling, or pickling, is a vital process in maintaining the integrity of stainless steel by removing tightly adhered oxide films. These films, created during high-temperature operations such as welding …
Pickling and passivation are both chemical processes used to treat metal surfaces, but they serve different purposes and involve different chemicals. Pickling Pickling is a metal treatment process primarily used …
The primary reason for self-performing pickling is time and cost savings. But in practice, the hazardous nature of the chemicals combined with the method of application make any claim of …
Project Showcase
Frequently Asked Questions
Pickling of stainless steel is the cleaning of a metal surface where actual metal removal is the result in order to remove heavy oxide films (like weld scale or heat tint). Pickling etches the surface and can affect the surface finish.
Although pickling and passivation both involve using acids to treat the surface of metals, there are some very distinct differences between the two processes.
The processes of pickling and passivating steel offer many benefits for metal products, including:
- Both pickling and passivation removes surface contamination
- Passivation maximizes corrosion resistance
- Pickling removes heavy oxidation passivation chemicals cannot, including hint tint or weld discoloration
Yes, both pickling and passivation can be performed on-site or in a controlled environment, depending on the size and type of the equipment or parts being treated.
Prior to pickling, it is necessary to clean the surface to remove foreign substances such as grease, oil, adhesives, heavy rust, etc.
The surface can be cleaned using methods such as alkaline cleaners, solvent cleaners, ultrasonic cleaning, high-pressure cleaning, and other mechanical or manual methods.
The proper cleaning solution is based on a combination of factors including:
- The material composition and configuration of the equipment/part
- The level and composition of contaminants
Process control is essential as etching can occur if the acid concentration is too high and/or if the acid contact time is too long.
Both processes involve the use of chemicals that must be handled with care. Proper safety protocols and disposal methods must be followed to minimize environmental impact and ensure worker safety.