Foam Density Distribution Analysis in Pre-insulated Pipes Using Non-destructive X-Ray Microscopy

Pre-insulated bonded pipes used in district heating systems are engineered for a service life of at least 30 years. The longevity of these systems is primarily influenced by the properties of the polyurethane (PUR) foam insulation. While operational and installation parameters contribute to overall durability, the characterization of the foam layer is critical for service life prediction. According to EN 253, pipe manufacturers are required to maintain a minimum foam density of 55 kg/m³. However, the foaming process leads to a non-uniform density distribution across the pipe cross-section—from the steel carrier pipe to the high-density polyethylene (HDPE) casing. Determining the foam density distribution function enables normalization of measurement data, which is essential for subsequent analysis using spectroscopic techniques such as Laser Induced Breakdown Spectroscopy (LIBS) and Fourier Transform Infrared (FT-IR) Spectroscopy. Traditional methods for density determination, including liquid displacement, and the cut-and-weigh method, are often labor-intensive and prone to inaccuracies. To address these limitations, a methodology has been developed that utilizes nanoscale X-ray microscopy and computer vision techniques to analyze foam density distribution.