VW 13750 Surface Protection for Metal Parts - Surface Protection Types, Codes

The “VW 13750 Surface protection for metal parts - Surface protection types, codes” standard, developed by the Volkswagen automotive company, applies to the definition of general surface protection types for vehicle parts and units in drawings and technical documentation. This standard lists all invalid surface protection types included in previous versions and listed in this standard annex (Annex 1).

The basic requirements in this standard are determined as follows:

• Volkswagen's metal materials engineering department classifies vehicle parts and units according to corrosion loads and assigns them a protection class with a code number.
• When parts and units are used as intended for their intended applications, no damage should occur that would lead to functional impairment or a reduction in the anticipated corrosion protection.
• Mechanical fasteners must comply with the restrictions in the VW 60361 standard.
• Prior to surface treatment, the following standards apply to tooth dimensions: VW 11610, VW 11614, VW 11624, VW 11625, and VW 11627.
• For tooth dimensions after surface treatment, the following standards apply: VW 11611, VW 11615, and VW 11628.
• Hazardous substances must be avoided in accordance with the VW 91101 standard.

The VW 13750 standard is a long-standing group of standards that defines and standardizes types and codes of surface protection for metal parts used in vehicles. Its main purpose is to ensure consistent corrosion protection, durability, and surface treatment descriptions in technical drawings and documentation.

First published in the 1950s, the VW 13750 standard has undergone numerous revisions to accommodate environmental regulations, technological advancements, and industry needs. Key updates include:

• Phased out of coatings containing hexavalent chromium due to health and environmental concerns (e.g., restricting or banning them for new designs in later versions).
• The inclusion of modern coatings such as zinc-nickel and zinc-iron alloys.
• Compliance with broader German Automotive Industry Association standards, such as the VDA 235-104 standard.
• The latest versions include the addition of new code for advanced processes and clarification of references to relevant technical supply specifications.

This standard emphasizes the use of the latest version, as it supersedes older types of surface protection.

The VW 13750 standard applies to the following:

• General surface protection types for vehicle metal parts and components.
• Types of protection are defined in drawings and technical documents using standardized codes (i.e., with the prefix “Ofl-” meaning surface).

This standard does not cover special or bespoke surface treatments, which are covered by separate standards (e.g., VW TL 217 for zinc coatings, VW TL 244 for zinc-nickel alloys).

Parts are classified according to their corrosion load (e.g., light, medium, heavy) and assigned a protection class. The aim is to prevent functional degradation due to corrosion while maintaining properties such as weldability and friction behavior.

In surface protection coding, “Ofl-” is the fixed prefix, followed by four characters. The first character indicates the type of coating (e.g., “c” for zinc, “r” for zinc-nickel, “b” for phosphate). This is followed by numbers specifying the thickness, passivation, sealing, and additional treatments. For example, Ofl-c340 is an electrolytic zinc coating of a specific thickness and passivation. Ofl-r645 is a zinc-nickel alloy coating (without hexavalent chromium) that includes passivation, sealing, and lubricant, usually according to the VW TL 244 standard. Preferred codes for fasteners (e.g., bolts, nuts) are highlighted in bold/italic in the standard's tables.

The basic requirements of the VW 13750 standard are as follows:

• Corrosion resistance: Tested according to DIN EN ISO 9227 standard using the neutral salt spray method. Requirements vary depending on the protection class (e.g., no corrosion in the base metal after hundreds of hours).
• Threaded parts: Stricter rules for threads (referencing standards such as VW 11610 for pre-/post-coating tolerances).
• Environmental compliance: Avoidance of restricted substances according to VW 91101 standard. Options free of hexavalent chromium are preferred.
• Additional features: Coatings must not impair weldability, coefficient of friction, or storage stability (e.g., 6 months without deterioration) according to the VW 01129 standard.

VW 13750 refers to or links to numerous technical supply specifications for detailed coating requirements, such as those listed below:

• TL 217: Zinc coatings.
• TL 244: Zinc-nickel alloys.
• TL 153: Zinc-iron coatings.

This standard is also compatible with VDA standards for cross-industry compatibility.

The VW 13750 standard provides reliable corrosion protection for metal components in harsh vehicle environments (e.g., salt and moisture exposure). Suppliers must comply with this standard to deliver parts to Volkswagen Group brands. In short, this standard is a fundamental standard for standardized, environmentally friendly surface protection in automotive production, promoting longevity and consistency throughout the supply chain.

The VW 13750 standard is considered important for the following reasons:

• It ensures long-term corrosion resistance and vehicle durability: Vehicles are exposed to harsh conditions: road salt, humidity, temperature fluctuations, and chemicals. Corrosion can lead to structural failure, safety issues (e.g., in brakes, chassis, or fasteners), and costly warranty claims. This standard classifies parts according to their corrosion load (light, medium, heavy) and assigns protection classes with tested resistance levels. This prevents functional degradation, extends component life, and maintains vehicle reliability for years of use.
• It standardizes identification and communication throughout the supply chain: It uses simple, uniform codes in technical drawings and documentation. It ensures clear and explicit specification of surface treatments for thousands of metal parts (bolts, nuts, chassis components). For global suppliers, it reduces errors, misinterpretations, and production problems by ensuring that everyone, from designers to finishers, uses the same language.
• Mandatory compliance for suppliers: Companies supplying parts must comply with this standard for part approval and delivery. Non-compliance may lead to part rejection, delays, or loss of contracts.
• Beyond corrosion resistance, it supports functional properties: preserving weldability, coefficients of friction, and thread tolerances. It addresses special cases such as high-strength steels (to prevent hydrogen embrittlement) and threaded parts (with stricter rules for threads).

For many years, our organization, with its competent and experienced staff, has been understanding the needs of its customers, providing the advanced testing services they require, and assisting them in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services in accordance with the VW 13750 standard.