Professional Passivation and Pickling of Stainless Steel According to International and Aerospace Standards
27. 2. 2026
Professional Passivation and Pickling of Stainless Steel according to International and Aerospace Standards
Passivation of stainless steel according to AMS 2700, ASTM A380, ASTM A967, and EN 2516 is a controlled chemical process designed to remove free iron and contamination introduced by manufacturing operations and to restore a homogeneous passive layer of chromium oxide (Cr₂O₃) on the material surface.
At FK system – povrchové úpravy s.r.o., we perform passivation and pickling of stainless steels in compliance with the requirements of the aforementioned international and aerospace standards or according to specific customer requirements.
At FK system – povrchové úpravy s.r.o., we perform passivation and pickling of stainless steels in compliance with the requirements of the aforementioned international and aerospace standards or according to specific customer requirements.
What is passivation and why is it essential after machining?
Stainless steel is corrosion-resistant due to the natural formation of a thin chromium oxide layer. However, this layer is disrupted during production by:
- machining and grinding,
- welding,
- cold forming,
- handling with carbon steel tools (risk of free iron contamination).
Passivation is a chemical treatment that:
- Selectively dissolves free iron from the surface.
- Promotes the restoration of a stable passive layer.
- Reduces the risk of pitting and crevice corrosion.
Pickling vs. Passivation – Technical Difference
Pickling is a more intensive chemical process designed to remove welding scale, heavy oxide layers, and to unify the surface before further treatment. Typically, mixtures of nitric and hydrofluoric acids are used.
Passivation is a gentler process primarily focused on removing free iron from the surface layer of the material.
Media used:
Passivation is a gentler process primarily focused on removing free iron from the surface layer of the material.
Media used:
- Nitric acid: The traditional method according to older specifications.
- Citric acid: An eco-friendly alternative, increasingly specified in the aerospace industry.
Overview of Key Passivation Standards
ASTM A380
ASTM A380 is a general standard focused on cleaning, descaling, pickling, and passivation of stainless steels.
It serves as a methodological basis for correct surface preparation before subsequent passivation or final application in industrial environments.
It serves as a methodological basis for correct surface preparation before subsequent passivation or final application in industrial environments.
ASTM A967
ASTM A967 specifies particular chemical passivation procedures, including nitric and citric process variants.
It also defines methods for verifying the absence of free iron and is frequently applied in the automotive and general engineering sectors.
It also defines methods for verifying the absence of free iron and is frequently applied in the automotive and general engineering sectors.
AMS 2700 – Aerospace standard
The AMS 2700 standard defines requirements for the passivation of corrosion-resistant steels in the aerospace industry.
It specifies Types 1 to 8 (categorised by chemistry and parameters), bath concentrations, temperatures, exposure times, and testing requirements (e.g., copper sulphate test).
This standard is commonly required by aerospace component manufacturers and represents a higher level of process control.
It specifies Types 1 to 8 (categorised by chemistry and parameters), bath concentrations, temperatures, exposure times, and testing requirements (e.g., copper sulphate test).
This standard is commonly required by aerospace component manufacturers and represents a higher level of process control.
EN 2516
EN 2516 is a European aerospace standard for the passivation of corrosion-resistant steels. It is used primarily by suppliers to the European aerospace sector and harmonises requirements within the EN standard system.
Comparison of Standards
| Standard | Main Focus | Typical Application |
| ASTM A380 | Cleaning, pickling, and passivation | General engineering |
| ASTM A967 | Chemical passivation | Automotive, engineering |
| AMS 2700F | Aerospace passivation | Aerospace parts, critical components |
| EN 2516 | Aerospace passivation (EU) | European aerospace |
Frequently Asked Questions (FAQ)
What is the difference between AMS 2700 and ASTM A967?
AMS 2700 is an aerospace standard with precisely defined process types (1–8) and stricter validation requirements. ASTM A967 is a general industrial standard for chemical passivation offering broader flexibility.
AMS 2700 is an aerospace standard with precisely defined process types (1–8) and stricter validation requirements. ASTM A967 is a general industrial standard for chemical passivation offering broader flexibility.
Why is passivation necessary after machining?
Machining causes the mechanical transfer of iron particles onto the surface. These particles can initiate localised corrosion even in high-alloy steels.
Machining causes the mechanical transfer of iron particles onto the surface. These particles can initiate localised corrosion even in high-alloy steels.
Is it possible to passivate weldments without prior pickling?
Generally, this is not recommended. Welding creates heavy thermal oxides (heat tint) and localised chromium-depleted zones. These layers cannot be reliably removed by passivation alone. If pickling is omitted, a non-homogeneous structure with lower corrosion resistance may remain. In practice, the standard procedure for weldments is pickling followed by passivation according to the required standard.
Generally, this is not recommended. Welding creates heavy thermal oxides (heat tint) and localised chromium-depleted zones. These layers cannot be reliably removed by passivation alone. If pickling is omitted, a non-homogeneous structure with lower corrosion resistance may remain. In practice, the standard procedure for weldments is pickling followed by passivation according to the required standard.
Why must the material type be precisely identified before pickling and passivation?
The material type fundamentally influences surface behaviour in pickling and passivation baths. The varying compositions of stainless steels, as well as the difference between corrosion-resistant and carbon steels, require different chemical settings and process parameters. Incorrect chemistry, concentration, or exposure time can lead to excessive etching, changes in roughness, or reduced corrosion resistance. Material identification is therefore a key input for the correct setup of the technological process.
The material type fundamentally influences surface behaviour in pickling and passivation baths. The varying compositions of stainless steels, as well as the difference between corrosion-resistant and carbon steels, require different chemical settings and process parameters. Incorrect chemistry, concentration, or exposure time can lead to excessive etching, changes in roughness, or reduced corrosion resistance. Material identification is therefore a key input for the correct setup of the technological process.
Can incorrectly performed passivation impair corrosion resistance?
Yes. If prescribed bath concentrations, temperatures, or exposure times according to the relevant standard are not maintained, it can result in incomplete removal of free iron or uneven restoration of the passive layer. This may lead to localised pitting corrosion, especially in aggressive environments (chlorides, humidity, temperature cycles). For this reason, it is essential to manage the process strictly according to the required standard and technical procedure.
Yes. If prescribed bath concentrations, temperatures, or exposure times according to the relevant standard are not maintained, it can result in incomplete removal of free iron or uneven restoration of the passive layer. This may lead to localised pitting corrosion, especially in aggressive environments (chlorides, humidity, temperature cycles). For this reason, it is essential to manage the process strictly according to the required standard and technical procedure.
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In June 2025, FK system – povrchové úpravy, s.r.o. became a member of the CZECH AEROSPACE Cluster, which brings together key players in the Czech aviation industry.
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