Elbows are used frequently in pipeline systems. Manufacturing of elbows tends to cause the primary circular sections to ovalize. Ovalization intensifies when elbows are subjected to internal hoop pressure. The total ovality in elbows comprises both manufacturing and pressurization ovality. Elbows with oval cross sections under internal pressure tend to straighten. This effect is called the Bourdon Effect. If these effects are not taken into consideration, unanticipated deformations and higher stress levels could be present at the location of elbows.
The Canadian oil and gas pipeline code (CSA Z662-11) has limited the ovality in elbows to 3 and 6 percent for progressive and non-progressive ovalizations, respectively. A mere imposition of two limits cannot determine the safety factor of pipeline. Also, consequences of using elbows with large ovality remain ambiguous as well. Understanding the influence of the Bourdon Effect and ovalization on the elbow design parameters is required.
In this paper, the influence of the Bourdon Effect on the stress and ovalization developed in the elbows are investigated. Four Nominal Pipe Sizes (12, 24, 36, and 42) are selected. Elbows and straight pipe segments connected to them are analyzed using Finite Element Analysis. Geometric dimensions of actual scanned pipeline elbows are used to represent the actual situation in the field. Under the operating pressure, the maximum stress, ovality, and the Bourdon Effect in elbows for different elbow thicknesses and straight pipe lengths connected to the elbows are monitored.
In addition, in this paper, the effect of the initial ovality was investigated for NPS 24 with constant straight pipe length. It was shown that the increase or decrease in the final ovality of the pipe is dependent on the initial ovality of the elbow cross section.
