DIN 50021 Salt Spray Test

The "DIN 50021 Salt Spray Test" standard, published by the German Institute for Standardization (DIN), describes the requirements that corrosion testing equipment and abrasive materials must meet. The aim of salt spray testing is to ensure that the same conditions are achieved in all cases where spray tests are performed based on standards or agreements.

This standard does not deal with sample preparation, test duration, post-test sample processing, or evaluation of results. Which of the three methods listed in this standard shall be applied in any particular case is subject to agreement between the relevant parties unless otherwise specified in the relevant standards. The tests described in this standard are used both to determine the effectiveness of corrosion protection systems and to quickly detect defects.

It is not suitable for specifically testing defects in metallic coatings where the coating is made of a base metal than the substrate (e.g., zinc or aluminum on steel), since in such cases the substrate is cathodically protected by the coating adjacent to the defect.

The tests are accelerated corrosion tests as specified in the DIN 50900-3 standard and do not provide direct information about the behavior of the tested parts in service. Similarly, since the corrosion effects in these tests differ significantly from those that may occur in service, and therefore different corrosion processes may be involved, comparing the protective values ​​of different corrosion protection systems is only possible when the similarity between them is sufficiently close.

For the purposes of this standard, spray tests are tests in which the abrasive substance is continuously sprayed with compressed air into an aqueous sodium chloride solution (main component) having a mass concentration of 5 g/100 ml.

This standard defines three different spray test methods:

• Salt spray test
• Acetic acid salt spray test
• Copper accelerated acetic acid salt spray test

DIN 50021 is a German standard that defines the neutral salt spray test, one of the most widely used accelerated corrosion tests worldwide. It has now been superseded by the "ISO 9227 Corrosion tests in artificial atmospheres - Salt spray tests" standard published by the International Organization for Standardization (ISO). However, it is still mentioned in older specifications, technical drawings, and quality documents.

The neutral salt spray (NSS) test actually involves:

• Test solution: 5% sodium chloride in distilled/deionized water.
• pH value: 6,5 to 7,2 (neutral range)
• Room temperature: 35 degrees plus/minus 2 degrees
• Continuous fine mist spraying
• Samples are exposed for a specific period of time (typically 24, 48, 96, 240, 480, 720, or 1000 hours).
• After exposure, samples are evaluated for red rust (on steel), white rust (on zinc), pitting, or blistering.

In 2016, this standard was withdrawn because a technically identical international standard (ISO 9227) had long existed. This new standard incorporates the exact same neutral salt spray (NSS) test. In practice, millions of legacy drawings, automotive specifications, and supplier requirements still refer to the DIN 50021 standard, and laboratories accept these references as equivalent to the ISO 9227 standard.

The DIN 50021 standard remains important and frequently cited today for the following reasons:

• The original global reference for salt spray testing: Long before the ISO 9227 standard in its current form, for over 50 years, the DIN 50021 standard was the most widely used and recognized standard worldwide for accelerated corrosion testing. Numerous technical drawings, specifications, and quality contracts explicitly require the DIN 50021 standard. These documents are still actively used today.
• It remains a legal and contractual requirement in many sectors: Although this standard has been withdrawn, the old specifications remain legally valid in contracts and approvals.
• Automotive original equipment manufacturers (VW, BMW, Mercedes, Porsche, Ford) still have thousands of material and coating specifications that are written according to the DIN 50021 standard.
• Type approvals and homologations (e.g. for locks, hinges, fasteners, vehicle body parts) are granted according to the DIN 50021 standard and remain valid for years.
• Therefore, suppliers are obligated under the contract to continue testing according to the DIN 50021 standard (effectively the ISO 9227 standard).
• It is a measure of how corrosive a coating is perceived to be: In many sectors, especially in German-speaking and Central European markets, corrosion resistance is still expressed in terms of DIN 50021 rating.
• Yellow chromate zinc plating: 48-120 hours until red rust appears.
• Zinc-nickel 1215% nickel + sealant: 720-1000 hours until red rust is reached.
• Hot-dip galvanizing (50-70 µm): 480-720 hours until red rust is reached.
• Geomet 321 / 500: 480-1000 hours until red rust.

The phrase "720 hours DIN 50021, free from red rust" is immediately understood by engineers as a very good level of corrosion protection.

• In Central Europe, the most common requirement remains: In some countries, for fasteners, automotive parts, construction equipment, and electroplated components, most procurement specifications, out of habit and tradition, use "DIN 50021" instead of "ISO 9227".
• Practical equivalence: Since the ISO 9227 standard is technically the same as the DIN 50021 standard (same 5% sodium chloride, same pH value 6,5-7,2 and same 35 degrees), there is no technical difference. Laboratories and certification bodies consider them 100% interchangeable.

In short, when you see the expression "DIN 50021" today, it is understood to mean "the classic neutral salt spray test according to the current ISO 9227 standard".

For many years, our organization, with its competent and experienced staff, has been understanding the needs of its clients, providing the advanced testing services they require, and assisting in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services in accordance with the "DIN 50021 Salt Spray Test" standard.