EN 4552:2015

Overview

EN 4552:2015 is a European standard that defines the specifications for swivel nuts used in inch series pipe couplings with a 37° spherical profile, manufactured from heat-resisting steel, and designed specifically for aerospace applications. This vital standard ensures the quality, safety, and interoperability of pipe coupling components used in aerospace fluid systems. It supersedes the previous 2003 edition, incorporating updated dimensions, materials, and marking requirements aligned with current aerospace manufacturing and safety practices.

The standard is developed by the Aerospace and Defence Industries Association of Europe (ASD-STAN) and ratified by CEN, guaranteeing compliance across multiple European countries. It calls for compliance with nominal pressure Class D as per ISO 6771 and integrates stringent mechanical and dimensional tolerances essential for the rigorous demands of aerospace fluid systems.

Key Topics

• Scope and Application
  EN 4552:2015 covers the characteristics of swivel nuts for 37° spherical pipe couplings in the inch series, intended for welding to pipes in aerospace fluid systems. This ensures reliable joints capable of withstanding high operational pressures and temperatures.

• Material Specifications
  The components must be made from heat-resisting steel conforming to EN 3468 or EN 3487, with a minimum hardness exceeding HB 140. These materials provide corrosion resistance and mechanical strength necessary for aerospace environments.

• Dimensional Standards and Tolerances
  Detailed measurements for swivel nuts are provided, including locking wire hole options and hexagonal sizing styles (Style A and B). All dimensions and tolerances are expressed in millimeters, covering nominal diameters, wall thickness, thread size, and mass per 1,000 units.

• Marking and Designation
  Marking requirements follow EN 2424 standards to ensure traceability and identification of components. A clear designation system is given, combining standard numbers, dimensional codes, and locking wire hole options to precisely identify each part.

• Technical Compliance
  The standard refers to additional requirements from related standards such as EN 4560 for technical specifications and ISO 3161 for thread dimensions. It ensures that components comply with pressure and temperature classifications (ISO 6771 Class D).

Applications

EN 4552:2015 is primarily applied in the aerospace industry for fluid transfer systems where reliability and safety are paramount. Its practical uses include:

• Aerospace Hydraulic and Pneumatic Systems
  Ensures secure pipe coupling connections that withstand high pressure and elevated temperature conditions during flight operation.

• Military and Defense Aerospace Components
  Provides standardized components for defense aircraft fluid systems, ensuring interchangeability and dependable performance under demanding conditions.

• Spacecraft Fluid Systems
  Suitable for use in spacecraft fuel and fluid transfer lines where heat resistance and durability are critical due to extreme environmental exposure.

• Aviation Maintenance and Manufacturing
  Facilitates the production and servicing of aerospace fluid system components with consistent quality and precision, simplifying supply chain and maintenance logistics.

Related Standards

For comprehensive understanding and application, EN 4552:2015 should be used alongside these relevant standards:

• EN 4549 – Aerospace series pipe couplings in heat resisting steel or nickel alloys, focusing on welded coupling ends.
• EN 4550-1 – Aerospace 37° pipe coupling design, male sealing ends with spherical profiles in inch series.
• EN 4560 – Technical specifications for aerospace 37° pipe couplings in inch series.
• EN 2424 – Marking regulations for aerospace products to ensure clear component traceability.
• ISO 3161 – Defines UNJ thread profiles for aerospace general requirements and limits, critical for thread compatibility.
• ISO 6771 – Classifies fluid systems and components by pressure and temperature, ensuring standardized performance grading.

By adhering to EN 4552:2015, aerospace manufacturers and suppliers ensure the production of high-quality, heat-resistant swivel nuts for pipe couplings. This enhances system safety, reliability, and compatibility in sophisticated aerospace fluid transfer lines, supporting advancements in aviation and space technology.