TWI Frequently asked questions
by Andy Knight
IR stands for
Infrared. In the field of pressure piping systems for industrial applications, high demands are placed on the mechanical stability, reproducibility and quality of the fusion joint.
The infrared fusion method is characterised by contact-free melting of the components to be fused. This eliminates the possibility of contamination or of the pipe faces sticking to the heater plate. The weld bead is also greatly reduced in size since the area of material softened is substantially smaller. Hence, the pipe bore is kept as large as possible and this minimises the possibility of a reduction in the flow rate of the media within in the pipe. Also, the probability of service-induced deposits building-up on the surface of the internal bead is lessened so that the risk of impurities, e.g. micro-organisms, in the media conveyed is significantly reduced.
BCF stands for Bead and Crevice Free. This method is used for clean-room condition applications for ultra pure PVDF piping systems. It differs from butt fusion and IR methods as no weld bead is produced. Hence, the pipe bore remains at full size for the complete system.
The pipes are placed in a clamping arrangement, which is also the heater assembly. An inflatable insert is placed inside the pipe, so that it covers the joint area. When the joint is heated, expansion of the materials takes place which applies axial loading to the pipes, aiding fusion and the formation of a high quality joint.
