Published Paper: Challenging the 10% Wall Thickness Rule For HDPE Marine Pipes

Back in 2019 me and my good friend Ilija was worked together on The Ocean Cleanup project to identify the root-cause to why Wilson 001 suffered a catastrophic fracture that required a tow-in to undergo a repair. It is easier said than done floating around in the pacific.

The Ocean Cleanup project has a pretty good understanding and supportive documentation to what the failure mechanism might be. We could support this with numerical data using FEM to show that localized stresses which was subjected to a continuous cyclic load was far from ideal. They wrote a pretty cool blog about the lessons learned here.

This was still two weeks before system 001 (Wilson) was to reach a harbor to undergo a repair before heading out again. We evaluated several options and learned a lot of the loading in such conditions. During this work Ilija started to draw parallels to the problems they sometime faced in their operations, discarding huge HPDE pipes due to scratches which could cause crack propagation due to localized stresses.

It was a fairly straight forward operation to apply the formulas from Roark’s Formulas for Stress and Strain to estimate notch stresses and perform FEM to see how the nonlinear solution would be. We were able to apply repairs which was readily available and would require low precision work to be performed to continue to use/install pipes with larger scratches than 10% wall thickness – which is the rule today.

We did not look at effects of internal pressures as we saw them to be negligible compared to bending stresses for this paper.

Hopefully this work provides an opening to review the discarding of large HDPE marine pipes which will allow faster installation time and a higher yield for produced materials.

The paper was presented at “Proceedings of the 20th Plastic Pipes Conference PPXX September 6-8, 2021, Amsterdam, Netherlands” and “Johannesburg will host the Pipes XIII Conference on 6/7 September 2022”. We were invited for the latter conference and to quote the press release: “as Zoran Davidovski (PPXX Chair) agrees: “Numerous speakers at Pipes XIII are selected from those of our Amsterdam conference on the basis of their cutting-edge experience and expertise.” Pretty cool!

This was a fun project to be a part of!

The paper is available here.