The observed cracking indicates that Foretinib the axial stress perpendicular to the crack is the opening component. A worst case scenario comprising a flow rate of 1180 million standard cubic feet per day (MMSCUFD) at 69 barg was assumed. Fig. 7 and Fig. 8 illustrate the axial stress contours due to static and cyclic forces, respectively, using drag and lift coefficients in . It is evident that the most highly stressed section is the flange-to-support pipe weldment, which is consistent with the observed cracking.
Fig. 8. Static axial stress distribution in the weldment.Figure optionsDownload full-size imageDownload as PowerPoint slide
5.2. PTC19.3-2010-based assessment
The new edition of PTC19.3 standard  provides a comprehensive assessment against both lift- and drag-induced FIV damage. Due to the complex relation between Strouhal number NsNsand Reynolds numberReRe, peristalsis was first necessary to evaluate ReRe for all flow conditions using the relation:equation(8)Re=ρvDtwμwhere DtwDtw is the tip diameter of the thermowell and μμ is the dynamic viscosity, equal to 2×10-52×10-5 Pa s for dried feed gas. The values of ReRe for the current operational envelope were evaluated and found to vary between 8.6×1058.6×105 and 9.3×1059.3×105. This range of ReRe values results in a constant NsNs equal to 0.22. This value indicates similar FIV frequencies to those shown in Fig. 7, indicating that the current design violates the new standard safe operating limit for all flow rate levels at an operating pressure of 69 barg.