48inch
Calculating the stresses is straightforward and will depend on the installation method. For acceptability of the stresses, the codes give guidelines, but you casn set more conservative criteria.
Personally, for HDD's, for installation stresses, I use calculations that are based from a variety of sources, for example DNV, Appendix B for acceptable combination of stresses, for hoop stress design factors - 49 CFR Part 192.111, acceptable shear stress - B31.4, 403.3.
You might want to look at VERITEC E305 - On Bottom Stability Design of Submarine Pipelines. Sect 5.3 is a good fundamental approach to the use of Morison's equation for on-bottom stability design calcs. This will also help determine if the pipeline weight will remain stable on the seabed with stesdy cyurrent or comnbined current & wave cases.
For concrete coated pipe, There is always a concern the concrete will fail under the bending stress. Due to its low tensile strength, the concrete will fail in tension at the interface of the steel and concrete. If the concrete has a good bond to the pipe, it will crack at the pipe surface. This will eliminate the stress in the concrete, and as long as the concrete coating thickness is thicker than the crack is deep, there will be no cracking visible on the concrete surface. If the bond to the pipe is weak, the pipe and concrete will separate which will reduce the stress in the concrete and there will be no visible cracking at the concrete surface.
If there is visible cracking on the concrete surface, the concrete can be repaired to seal the cracks. If cracking is a concern, you might want to look at the severity of the problem and look for a solution.
Greg Lamberson, BS, MBA
Consultant - Upstream Energy
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