Failure Analysis and Replacement
July 27th, 2009MarkAnderson, Principal at ThioSolv, asked us to investigate what happens over time, when pipelines see significant wear and tear.
Follow along as we conduct failure, replacement and qualitative cost analyses on an oil sands pipeline.
The Problem
Failure analysis, material selection, and qualitative cost analysis for replacement of an oil sands pipeline.
After a few years of operation, major failures are detected throughout an oil sands pipeline. It has been established that corrosion and erosion have occurred at an unexpectedly high rate due to the failure of the 5-mm thick natural rubber pipeline lining. The pipeline was operated at the slurry temperature of 90˚C. The average particle size of slurry was 0.5 mm.
It was decided that the old pipeline should be dismantled and that a new pipeline be constructed. An engineering team must address the failure by finding a replacement lining and an approximate material cost for the new lining in comparison to the old. The team also needs to provide a reasonable and quantitative explanation as to why and how the previous pipeline, made of seamless carbon steel pipes, failed. Here’s a recap of what we know.
Using Knovel
Learning why the natural rubber failed as a lining material for this pipeline
First, the team needs to find out why the natural rubber failed so quickly. Using Knovel’s basic search, the team lead enters ‘natural rubbers,’ to find information on the material. (Click on the image below to run the search yourself.)
The engineer clicks on the first title, Slurry Systems Handbook and finds sections that are relevant to his query. He selects Section ‘10.4 Natural Rubbers’:
Although the material meets the particle size requirement, the upper limit temperature of this material is clearly not high enough.
Selecting a suitable material replacement for the pipeline lining
The pipeline operates at 90˚C which is greater than the limit temperature of this material which is 65˚C. By operating at a temperature greater than the limiting temperature of the pipeline material one would expect that degradation of the pipeline would occur quite readily.
Browsing through Chapter 10 of the book, the engineer doesn’t find any of the natural rubbers viable but does come across a neoprene rubber for specific slurry handling applications at higher temperatures.
The engineer reads the description of this rubber and finds more information supporting his decision to use neoprene rubber as a lining material for new pipeline.
Performing a qualitative cost analysis
Now that a suitable material has been selected as the new lining for the steel pipeline, the engineer can begin to approximate the cost of new lining material vs. old. Using a buyer guide the engineer finds that the amount of neoprene needed for a 10-m section of the pipeline would cost about $730, compared to $1180 for the old natural rubber lining.
Now the engineer has to provide a quantitative analysis of the corrosion of the steel pipeline after the lining failed. The engineer searches Knovel for ‘corrosion rate equation’.
He clicks on Uhlig’s Corrosion Handbook (2nd Edition) then clicks through to the ‘index’ section for the index term ‘Berger-Hau Relation, erosion-corrosion rate.’ This equation will effectively describe the rate of corrosion after the rubber lining failed.
The engineer notices definitions for Re and Sc on the previous page.
Now that all of the necessary variables are known to the engineer, he is able to calculate the corrosion rate of the steel in mm/year. See his work below:
Since the wall thickness of the pipe was approximately 9.5 mm, it would corrode through in less than a year without a protective lining. Typical corrosion rates of these pipelines with undamaged lining are on the order of 1 mm/year.
The Solution
The pipeline failed because of an inappropriate pipeline lining which was not designed for higher temperatures. Neoprene is a suitable material for the pipeline lining.
With help from Knovel, the engineer finds that neoprene is not only a better lining for the steel oil sands pipeline because of its usefulness in high temperature applications, but it is also about 1.6 times cheaper than the natural rubber used in the older pipeline.
