SIST EN 3635:2015

Overview

EN 3635:2014 - Aerospace series - Weld lip - Geometrical configuration is a CEN European Standard that specifies the geometrical dimensions and tolerances for orbital‑welding fittings (weld lips) used with stainless steel fluid pipes to EN 3717. Approved in 2014 and superseding EN 3635:2008, this standard defines the form, key dimensions, tolerances and drawing designation rules required for consistent manufacture, assembly and inspection of aerospace welded tube fittings.

Key topics and requirements

• Scope: Specifies dimensions and tolerances for orbital‑welding fittings intended for stainless steel aerospace fluid pipes (EN 3717).
• Fitting dimensions: Detailed sizes are given by diameter code and thickness code with tabulated values for features such as A, B, D, S, T, W and the tube outside diameter. Nominal wall thickness is identified in a table footnote.
• Tolerance system: Includes tolerance class (h12) and specific plus/minus tolerances for critical diameters to ensure interchangeability and correct weld preparation.
• Tube end geometry: Defines the required tube end shape and permissible edge break (e.g., break edges maximum values) to ensure correct fit-up for orbital welding.
• Designation and drawing practice: Prescribes an example designation format (for example, EN3635-060-080) and shows how fittings should be identified on engineering drawings.
• Normative reference: EN 3717 (Aerospace series - Tubes - Selection for engines fluid systems) is normatively referenced and essential for application.

Applications and users

Who uses EN 3635:2014 and why:

• Aerospace component manufacturers - to produce consistent orbital‑welding fittings (weld lips) that mate correctly with EN 3717 tubes.
• Design and stress engineers - to select and specify correct fitting geometry and tolerances on assembly drawings.
• Quality, inspection and procurement teams - to verify dimensional conformity, tolerance class and correct part identification.
• Welding shops and fabricators - to prepare tube ends and set up orbital welding processes that rely on standardised geometry for reliable joints.
• Certification and regulatory bodies - to confirm compliance with aerospace fluid system standards.

Practical benefits include improved interchangeability, predictable weld fit‑up, reduced rework, and clearer procurement/specification language for aerospace fluid systems.

Related standards

• EN 3717 - Aerospace series - Tubes - Selection for engines fluid systems (normative reference).
• EN 3635:2014 supersedes EN 3635:2008 (see foreword for evolution notes).

Keywords: EN 3635:2014, aerospace series, weld lip, geometrical configuration, orbital‑welding fittings, stainless steel fluid pipes, EN 3717, dimensions and tolerances, tube end geometry, diameter code, designation.