ISO 13556:1998

Overview

ISO 13556:1998 specifies a standardized method and equipment requirements for locating and quantifying leaks in road vehicle exhaust systems. The standard is focused on improving the quality and repeatability of exhaust gas measurements by verifying exhaust system gas tightness prior to emission testing. It defines the pressurization system, ultrasonic detection equipment (measuring head and receiver), verification checks and test procedures for leak localization and rough quantification.

Key topics and technical requirements

• Purpose: Detect and localize exhaust system leaks to ensure reliable exhaust gas measurements.
• Pressurization system:
  • Nominal test pressure: 0.4 bar (40 kPa).
  • Clean, water- and oil-free air supply; pressure regulator and 0–1 bar manometer (±2%).
  • Calibrated leak of 1 mm diameter used for equipment checks; flexible leak‑proof adapter rated to 200 °C.
• Ultrasonic leak detection:
  • Ultrasound defined as 20–100 kHz; processing bandwidth specified 30–50 kHz.
  • Measuring head design protects the microphone from hot flow; microphone temperature handling verified with contact area exposed to 300 °C for 30 s.
  • Audio conversion device calibrated to a defined response curve; periodic verification required.
• Leak indicator scale (the device gives discrete size approximations):
  • ∅2 mm → 30 ± 5 l/min
  • ∅1.5 mm → 17 ± 3 l/min
  • ∅1 mm → 7.5 ± 1.5 l/min
  • ∅0.5 mm → 2 ± 1 l/min
• Test procedures:
  • Verify ultrasonic equipment using the 1 mm calibrated leak before testing vehicles.
  • Three test levels: operator-detectable leaks, audible-but-not-localizable leaks (use measuring head to pinpoint), and non-audible leaks (non-contact scan at ~3 m/min).
  • Quantification possible when measuring head is placed close - recommended 2 cm distance for approximate flow assessment.
• Warnings: Engines with high valve overlap may show false leaks when stopped; check national pressurization regulations before testing.

Applications

• Pre-test verification in emission testing laboratories to ensure exhaust integrity before measurement.
• Diagnostic and repair use in automotive workshops and inspection/maintenance stations for locating and repairing exhaust leaks.
• End-of-line quality control for vehicle and exhaust component manufacturers.
• Useful wherever ultrasonic leak detection, exhaust leak localization, and basic leak quantification are required to support accurate emissions measurement.

Related standards

• ISO 3929 (Measurement methods for exhaust gas emissions produced during inspection or maintenance) - ISO 13556 complements and completes requirements referenced for emission testing.
• Users should also consult applicable national regulations on test pressurization and vehicle-specific manufacturer service instructions.

Keywords: ISO 13556, exhaust system leaks, leak localization, ultrasonic detection, pressurization system, leak testing, road vehicles, emission testing, measuring head, calibrated leak.