Overview
ISO 18373-1:2007 defines a laboratory method to determine the processing temperature of rigid PVC pipes using differential scanning calorimetry (DSC). The standard measures the thermal history of small samples cut from pipe walls to identify the B-onset - the temperature that indicates the maximum processing temperature experienced during extrusion. The method is suitable for all types of rigid PVC pipes and helps link processing conditions to long‑term performance.
Key topics and requirements
- Principle: Use DSC to detect small endotherms from crystallites; the B-onset corresponds closely to the pipe’s maximum processing temperature (Tp).
- Sampling: Take at least four samples from the pipe centre at 0°, 90°, 180° and 270° around the circumference to detect local temperature variations.
- Sample preparation: Test pieces mass (20 ± 10) mg; prepare thin disks to maximize contact with aluminium pans; avoid heat or mechanical stress during cutting.
- DSC setup and calibration: Calibrate instrument using at least two metals and obtain an instrumental baseline with empty pans. Use inert purge gas (e.g., N2, Ar) of suitable quality.
- Scan parameters (specified in standard):
- Start temperature: (35 ± 15) °C
- End temperature: 225 °C
- Heating rate: (20 ± 1) °C/min
- Purge gas per clause 4.3
- Result determination: Use curve magnification and tangent extrapolation at points of maximum slope to determine B-onset. Repeatability criteria and discard irregular scans; if three consecutive repeats differ by > 3 °C further tests or recalibration required.
- Sources of error: Sample inhomogeneity, movement in pan, residual stresses, additives producing spurious peaks, or frictional heat from sample cutting.
- Reporting: Include reference to ISO 18373-1, sample IDs and positions, mean and standard deviation of B-onset, number of repeats, minimum B-onset, influencing factors and test dates.
Applications and users
- Who uses it: PVC pipe manufacturers, materials and quality-control laboratories, independent testing bodies, R&D teams, and failure-analysis investigators.
- Practical value:
- Validate and control extrusion processing temperatures.
- Identify local thermal variations in pipe production.
- Correlate processing temperature with performance metrics (e.g., time to stress rupture).
- Detect formulation effects (additives can create extra DSC peaks).
Related standards
- ISO 18373-2 (DSC method - measurement of enthalpy of fusion of crystallites)
- ISO 1167-1 (resistance to internal pressure - referenced for stress‑rupture correlation)
Keywords: ISO 18373-1:2007, rigid PVC pipes, DSC method, differential scanning calorimetry, processing temperature, B-onset, PVC pipe testing, quality control, pipe manufacturing.