Design and reliability of pipeline rehabilitation liners

Long-term buckling experiments of liners have shown a large amount of scatter when the buckling time is plotted against the applied pressure. The presence of this scatter and other uncertainties are typically accounted for in liner design by applying a factor of safety. Moreover, an additional “factor of safety” is sometimes implied since the design equation in ASTM F1216 is generally considered to be conservative. This paper examines the scatter observed in recent cured-in-place pipe liner buckling experiments conducted at the Trenchless Technology Center to associate reliability factors with selected confidence levels. Confidence levels of 50%, 70%, 90%, 95%, 99% and 99.5% are studied. This work results in a set of reliability factors that can be directly applied to the ASTM design equation for the partially deteriorated case. The reliability factors allow a designer to quantitatively estimate the influence of observed scatter on liner design. For now, however, the traditional approach to using ASTM F1216 without the reliability factors is recommended pending the availability of buckling data obtained under test conditions more closely matching those expected in the field.