SIST EN 4031:2002

Overview

SIST EN 4031:2002 is a European standard developed by the Comité Européen de Normalisation (CEN) specifically for aerospace applications. It defines the characteristics and requirements for nuts used in welded ferrules of pipe couplings with an 8°30' angle, made from titanium alloy. These precise specifications ensure reliable performance under demanding aerospace operating conditions.

Designed to withstand a nominal pressure of up to 28,000 kPa and operate within a temperature range of -55 °C to 135 °C, SIST EN 4031:2002 ensures the durability, safety, and compatibility of pipe coupling components used in aerospace fluid systems.

Key Topics

• Material Specifications
  Nuts must be manufactured from titanium alloy compliant with EN 3311 or EN 3314, ensuring high strength-to-weight ratio and corrosion resistance essential for aerospace environments.

• Dimensional Requirements
  Detailed dimensions and tolerances, including thread sizes and minor diameters, are defined to ensure precision fit and secure connections. The standard includes specific measurements for various nominal pipe diameters.

• Surface Treatment and Lubrication
  Surface finish requirements include precise roughness parameters. Before lubricant application, surfaces must be dry abrasive blasted using non-metallic grit per EN 2497. A PTFE-based coating (e.g., Tegliss 31) is specified for lubrication, minimizing friction (coefficient of friction ≤ 0.12) and enhancing wear resistance.

• Marking and Identification
  Nuts must be marked according to EN 2424, enabling traceability and quality assurance. Markings are applied on designated areas as per the standard.

• Performance Characteristics
  The standard details mechanical and hydraulic performance expectations, including pressure resistance, temperature endurance, and fluid compatibility. Lubricated nuts must withstand repeated assemblies without degradation.

Applications

SIST EN 4031:2002 applies primarily to the aerospace industry, where reliable fluid and gas transfer systems are critical. Typical applications include:

• Hydraulic and fuel line connections on aircraft
• High-pressure fluid systems in aerospace vehicles
• Welded pipe coupling assemblies requiring lightweight yet strong components
• Maintenance and replacement parts ensuring consistent quality and safety standards

The use of titanium alloy offers benefits such as corrosion resistance, light weight, and mechanical strength, making components compliant with EN 4031 ideal for harsh aerospace environments.

Related Standards

SIST EN 4031:2002 integrates and references several related European and International standards to form a comprehensive framework for aerospace pipe couplings:

• ISO 5855-3: Limits for MJ threads used in aerospace fluid system fittings
• ISO 8788: Tolerances on aerospace nuts regarding form and position
• EN 2424: Marking requirements for aerospace products ensuring traceability
• EN 2497: Dry abrasive blasting procedures for titanium and its alloys
• EN 3275: Technical specifications for pipe couplings with dynamic beam seals
• EN 3311 / EN 3314: Specifications for titanium alloy grades used in manufacturing these nuts

Together, these interconnected standards support quality control, interoperability, and safety in aerospace fluid system components.

Keywords: aerospace pipe couplings, titanium alloy nuts, welded ferrule nuts, EN 4031, aerospace fluid systems, high-pressure pipe fittings, PTFE coating, titanium pipe coupling standard, aerospace hydraulic fittings, European aerospace standards.