Analysis of failure initiation in corroded cast iron pipes under cyclic loading due to formation of through-wall cracks. (September 2019)

• Record Type: Journal Article
• Authors: Jiang, Rui; Rathnayaka, Suranji; Shannon, Benjamin; Zhao, Xiao-Ling; Ji, Jian; Kodikara, Jayantha
• Is Part Of: Engineering failure analysis. Volume 103(2019)
• Page Start: 238
• Page End: 248
• Publication Date: 2019-09
• Subjects: Cast iron pipe -- Fatigue mechanism -- Soil corrosion -- Transient pressure -- Water supply; a major radius of corrosion patch (longitudinal direction) -- AR Aspect ratio -- ASTM American Society for Testing and Materials -- Af Fatigue ratio coefficient -- Bf Fatigue ratio exponent -- b minor radius of corrosion patch (hoop direction) -- c Depth of corrosion -- c0 Corrosion pit depth -- CI Cast iron -- Cs Corrosion scaling constant -- Dcr Critical fatigue damage factor -- Di Pipe internal diameter -- k Different stress spectra -- Kfn Strength reduction factors for notched specimens -- Kfc Strength reduction factors for corrosion medium -- LDR Length-depth ratio -- Ni Number of failure cycles for a stress amplitude to cause a fracture -- ni Number of cycles for a stress amplitude -- Pmax Maximum water pressure -- R Stress ratio -- rs Long-term corrosion constant -- SCF Stress concentration factor -- t Exposure time -- t0 Wall thickness -- T0 Exposure time to form a through-wall crack by ignoring fatigue damage -- Tf Exposure time to form a through-wall crack by fatigue damage -- ΔT Reduced service lifetime due to fatigue -- σe Modified fatigue endurance limit -- σe Fatigue endurance limit -- σmin Minimum stress -- σmax Maximum stress -- σa Alternating stress -- σm Mean stress -- σu Ultimate tensile strength -- τ Corrosion transient time; System failures (Engineering) -- Periodicals; Fracture mechanics -- Periodicals; Reliability (Engineering) -- Periodicals; Pannes -- Périodiques; Rupture, Mécanique de la -- Périodiques; Fiabilité -- Périodiques; Fracture mechanics; Reliability (Engineering); System failures (Engineering); Periodicals; Electronic journals; 620.112
• DOI: 10.1016/j.engfailanal.2019.04.031
• Languages: English
• ISSNs: 1350-6307

Abstract

Abstract: The major factors contributing for the longitudinal failures in large-diameter cast iron water pipes are identified as corrosion and internal water pressure. Evidence of deteriorating pipeline integrity due to fluctuations of internal pressure loading was reported. This study aims to investigate the fatigue resistance of cast iron pipes and to identify the pipes in a water network that are at high risks of fatigue damage. Stress-controlled fatigue tests were conducted on coupons prepared from exhumed cast iron pipes. A correlation between tensile fatigue stress and cycles to failure was developed based on experimental results. A methodology was proposed to identify critical factors for initiating a through-wall crack in cast iron water pipe considering the impact of fatigue. A sensitivity analysis was conducted with relevant factors, and the relative impact of those factors to cause a premature failure was assessed. The operating pressures and stress ratios caused by pressure transients and long-term soil corrosion rate were identified as the key contributing factors for severe fatigue damage. Highlights: SN curves were developed by fatigue tests for CI pipes and the results were compared with published data from research literature The results indicate that fatigue may initiate cracks at critically corroded patches prior to limit state failure. Fatigue damage tends to be more severe in networks with high operating pressures, low stress ratios due to transient events and pipes with low tensile strength. Ageing CI pipes buried in pressure zones prone to pressure transients or /and frequent bursts may require additional condition assessment to assess the risk of fatigue damage.