Asbestos pipes are commonly used for water and sewage pressure mains. There are very few ways of assessing the wall thickness and condition of asbestos cement pipes by non-destructive methods. Traditionally, the majority of examination was undertaken by hot tapping to remove a physical specimen (coupon) of the pipe. This procedure is time consuming, costly and risky. Alternatively, the mains have to be shut down to allow access by CCTV cameras. Advances in Surface Penetrating Radar (SPR) technology in recent years now means that defects in thin walled pipes can now be detected non-destructively.
Selected sewage pipes of different ages, diameters and thicknesses are examined in situ using SPR. In addition, some samples of damaged pipes were examined separately. These examples were used to evaluate the effectiveness and capability of existing SPR technology.
The main mechanisms for pipe deterioration is from chemical attack at the pipe obvert and scouring at the pipe invert. The results demonstrate that SPR is an effective method for detecting areas of pipe deterioration and delamination and can detect scour depths as small as 4mm.
The SPR images also show where water has infiltrated the pipe wall material and is suffering from chemical attack and material changes occurring in the asbestos cement material.
The SPR image also clearly recorded fluctuating levels of fluid within the pipes during the data collection.
SPR imaging is a quick and effective method which is now available for non-destructive evaluating asbestos cement pipes.