HDD combined stresses can be analyzed by calculating the maximum shear stress on a small element in the pipeline. Maximum shear stress should be limited to 45% of the SMYS of the pipe (ASME/ANSI B31.4). This is in accordance to PRCI report PR-227-9424 from the findings and conclusions of those companies who performed and approved the research work, However, the question comes up from time to time that the B31.4 code can be converted to B31.8’s code application.
Even if this may be true in some cases, bending loads resulting from HDD installations are not sustained. Therefore, they may be relieved by plastic deformation which operating (combined) stresses should be maintained in the elastic range to provide a conservative design regarding a HDD installation.