Asbestos-Cement Pipe Failure Analysis
- Date: 05/12/2017
- Project Type: Maintenance Phase
Asbestos-Cement Pipe Failure Analysis
About this Project
Asbestos-cement pipe was used extensively in the mid-1900s in potable water distribution systems, particularly in the western United States. The Chrysotile Institute estimates asbestos-cement pipe lifespan at 70 years, but actual service life depends largely on pipe condition and working environment. Because thousands of miles of asbestos-cement pipe installed in distribution systems in the U.S. is nearing the end of its useful service life, asbestos-cement pipe condition assessment and strategic replacement planning will need to be done in the coming decade.
Over time, asbestos-cement pipe undergoes gradual degradation in the form of corrosion (i.e., internal calcium leaching due to conveyed water and/or external leaching due to groundwater). Such leaching leads to reduction in effective cross-section, which results in pipe softening and loss of mechanical strength. Accordingly, as the water distribution system ages, the number of asbestos-cement pipe failures increases with time. In light of these risks, an asbestos-cement pipe condition assessment is essential to determine the remaining useful service life and develop a suitable, proactive replacement plan for the distribution system.
In this case, three pieces of a section of an asbestos-cement pipe were presented for evaluation to determine the pipe’s condition and perform a pipe failure analysis. The longest of the three which was in the worst shape was used in the evaluation and pipe failure analysis.
Note – This featured project report is an abbreviated version of the actual report prepared for the client.
Figure 1a shows three pieces of the a-c pipes
Samples
The samples were to be evaluated to determine depth of carbonation as per the phenolphthalein test, petrographic analysis according to ASTM C856 and SEM/EDX as per ASTM C1723-10.
Test
Petrographic Examination of Hardened Concrete
Examination by petrographic analysis showed three distinct carbonated areas and two uncarbonated areas. The extremities of the pipes are carbonated and about the mid-section of the pipe where a crack appears also show a band of carbonated layer.
Figure 3 (a, b, c, & d) show representative cross section of pipe.
Figure 3a shows area nearest the edge of inner wall of pipe. (Mag. 400X)
Figure 3b shows a crack in an uncarbonated layer.
Figure 3c shows an area near the outer wall of pipe.
Figure 3d shows a partially carbonated area on the outer wall of pipe. (Mag. 400X)
DISCUSSION OF RESULTS
Carbonation of a band on the pipe closer to the inner wall may have contributed to the crack formed close to the mid-section of the wall of the pipe.
Consulting Engineers
Concrete Experts
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