Pipeline Strain and Vibration Monitoring by Smart Materials

Dielectric elastomer sensors (DESs) are a new class of mechanical strain and vibration sensors and can be used to fabricate unique intelligent elastomeric products with tailor made properties. Here, a new sensing method was developed to measure strain and vibration of pipelines using a combination of highly flexible DESs and novel polyurea coatings (intelligent coating). The structural health monitoring system described here is suitable to improve safety and maintainability of critical pipeline sections. Such system can be applied to both steel and to polymeric or composite pipes. Basically, the investigated DESs are compliant capacitors consisting of an elastomeric polyurethane film, highly flexible electrodes and surrounding polyurethane insulation. Due to the building block chemistry of polyurethane elastomers, the mechanical, electrical, thermal and chemical properties of DESs can be adapted to specific application scenarios. The versatility of the sensor concept allows the design of DESs with variable hardness (Shore A: 30 to 95), active surface (1–1500 cm²), thickness (200 μm – 1 cm) and sensitivity. Applied electrodes consist of conductive particles which are integrated in an elastomeric matrix. The capacitance of a DES is proportional to the area of overlapping electrodes (active sensor area) and it is inversely proportional to the elastomeric film thickness. In case of deformation due to tensile or pressure loading, the active sensor area expands while the thickness of the elastomeric film decreases. Both effects result in a measurable, linear increase in capacitance. When installed along the axial direction on the exterior of a pipe, the DES is sensitive to strain changes parallel to the pipe axis and allows to detect displacement or deformation that may cause the pipeline to fail. The strain sensitivity of the system depends upon the precision of the capacitance measurement. A typical setup allows a measuring accuracy of at least 0.1 % strain.