Asbestos Cement Pipe
Asbestos cement (AC) pressure pipe is used primarily for potable water, as well as for sewer force mains and industrial effluent and process piping. AC pipe was first introduced in North America in the late 1920s and became a common choice for potable water main construction from the 1940s to the 1970s. The use of AC pipe was largely discontinued in North America in the early 1980s but AC pipe is still a significant portion of the water distribution systems in many North American cities.
Asbestos cement (AC) pipe is manufactured from a mixed slurry of portland cement (80-85%) and a mixture of chrysotile asbestos fibres (15-20%). The slurry is dewatered using a rotary sieve cylinder and a very thin layer of asbestos cement is produced. This thin layer is wrapped around a mandrel under pressure until a pipe with the desired wall thickness is made. After curing, the ends of the pipe lengths are cut and finished to receive couplings that are produced by cutting larger diameter pipe into sections.
Main Forms Failure in Asbestos Cement Pipes
|Form of Failure||Causes of Failure||Indicators of Failure|
|Break failure||Soil differential movement or inadequate bedding support||Circumferential cracks|
|Internal pressure and external loads (soil cover, live loads, frost)||Longitudinal cracks|
|Manufacturing defects||Cracks in body|
|Structural Failure||Movements from thermal, seismic, external loading||Joint leaks, poor bedding, and pipe movements|
|Internal pressures, external loadings, thermal stresses||Longitudinal cracks and changed internal/external loads|
|Leaks||Loss of soil support and bending failure||Leak noise, wet areas, and pressure variations|