A Refined One‐Slit‐Ring Method to Quantify Residual Hoop Stress in Chlorinated Polyvinyl Chloride Pipe—Application to Specimens After Immersion in Primer

Abstract

A refined one‐slit‐ring method is presented to characterize residual hoop stress distribution in pipe ring specimens of inhomogeneous cross section. Although the original one‐slit‐ring method enables determination of residual hoop stress distribution through slitting single ring specimen in the axial direction, its use is limited to specimens of uniform material properties. This work is to extend applicability of the method to ring specimens with a cross section of core–shell structure. Chlorinated polyvinyl chloride (CPVC) pipe is used in the study, and core–shell structure in its ring specimens is introduced through immersion in primer for 30 min. Analytical expression for the residual hoop stress distribution in these specimens is derived, and verified using finite element (FE) simulation which uses a temperature gradient field to generate stress so that diametrical change by the slitting is same as that measured experimentally. Results from the analytical expression agree well with those from the FE simulation, showing decrease of the residual hoop stress by the exposure to primer, and the extent of decrease depends on the drying time after the immersion in primer, to about half of its original value after 30 days of drying, and then remains relatively constant afterwards. POLYM. ENG. SCI., 59:E296–E309, 2019. © 2019 Society of Plastics Engineers

Evaluating the Residual Stress and Its Effect on the Quasi-Static Stress in Polyethylene Pipes

“…The cutting caused a reduction in the radius of the remaining ring specimen, due to the release of the residual hoop stress. However, due to the viscous nature of the PE pipes, the change in diameter is a function of time [ 7 ]. Thus, the diameter was measured 20 min after the cutting to ensure measurement consistency.…”

“…The nonuniform solidification process generates residual stress by causing different crystallinity distribution along the pipe wall [ 6 ]. Generally, the inner surface is under tensile residual stress while the outer surface is under compressive residual stress [ 7 ]. The compressive residual stress within the outer wall of the pipes can benefit their stretching resistance [ 7 ].…”

“…Generally, the inner surface is under tensile residual stress while the outer surface is under compressive residual stress [ 7 ]. The compressive residual stress within the outer wall of the pipes can benefit their stretching resistance [ 7 ]. However, as pointed out by many investigators [ 8 , 9 , 10 ], the presence of tensile residual stress within the pipes can accelerate the fracture process when conducting a creep rupture test, resulting in the premature failure of the PE pipes.…”

“…The slitting method was also widely used in refs. [ 2 , 6 , 7 , 12 , 13 ]. Withers and Bhadeshia [ 1 ] have a review on the measuring techniques, including electron diffraction, magnetic and electrical techniques, etc.…”

“…Based on the methodology introduced by Poduška et al [ 2 , 6 ], the magnitude and distribution of the residual hoop stress in the PE pipes can be determined by measuring the outer diameter change for one axially slit ring specimen, which was named as a one-slit-ring method for convenience in ref. [ 7 ]. The one-slit-ring method is based on the assumption that the distribution of the residual hoop stress on the cross section can be described by an exponential function, which presented to date shows a good fitting to the measured residual hoop stress distribution [ 2 , 6 ].…”