SIST EN 2138:2001

Overview

EN 2138:1999 is a CEN aerospace series standard that specifies the characteristics of flat steel washers with cadmium plating for aerospace applications. The standard covers washers intended for use primarily underneath nuts and identifies a maximum operating temperature of 235°C. National adoptions include the Slovenian designation SIST EN 2138:2001, reflecting the same technical content.

The standard is targeted at designers, manufacturers and procurement teams who require consistent, compatible washers for aerospace fastenings where cadmium-plated steel is the specified material.

Key Topics

• Scope: Flat washers in steel with cadmium plating for aerospace service up to 235°C.
• Intended use: Primarily for placement underneath nuts; where used beneath bolt heads, compatibility must be verified.
• Material and finish: Steel washer bodies with cadmium plating (as stated in the scope). The plating is intended to provide improved surface protection appropriate for aerospace assemblies within the specified temperature limit.
• Classification: Falls under ICS 49.030.50 (washers and other locking elements) and is part of the aerospace series of fastener-related standards.

Applications

EN 2138:1999 washers are applied wherever flat steel cadmium-plated washers are required in aerospace assemblies that operate at or below 235°C. Typical practical uses include:

• Supporting nut seating to distribute load and prevent damage to mating surfaces.
• Providing a corrosion-resistant interface in bolted joints where cadmium plating is acceptable and permitted by materials and environmental regulations.
• Use in structural or equipment fastenings in aircraft assemblies, provided the operating environment does not exceed the specified temperature limit.

Practical considerations:

• Always verify compatibility if a washer from this standard is to be used under a bolt head - the standard explicitly requires this check.
• Confirm that cadmium plating is permitted for the application, considering environmental and regulatory constraints (cadmium use is controlled in many jurisdictions).

Related Standards

• National adoptions and translations (for example, SIST EN 2138:2001) reproduce the content of EN 2138:1999 for local use.
• Consult the wider suite of aerospace fastener standards for complementary guidance on nuts, bolts and locking elements when designing compatible assemblies.

Practical value

Using washers that conform to EN 2138:1999 helps ensure dimensional consistency, predictable nut seating behavior and surface protection from cadmium plating for applications within the specified temperature range. Manufacturers and maintenance organizations should reference the standard in specifications and procurement documents to maintain compatibility and performance across aerospace bolted joints.