Presently, current densities are chosen based on environmental conditions of the medium. For example, soil resistivity values, fresh water, brackish water, sea mud zone can be used to estimate current densities from established tables and nomograph. However, these estimates are for bare steel at ambient temperature. Higher and lower densities have also been reported at extreme significant changes in oxygen content with depth and sea bed current. It becomes cumbersome for corrosion engineers to make specific and accurate choice of current densities for CP design systems. Please I want a simple method to obtain this important design parameter especially for pipeline designs.
I am not sure how "simple" you expect this process to be. The process for estimating the design current requirement provided in DnV RPB401, which is available for free at:
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCAQFjAA&url=https%3A%2F%2Fexchange.dnv.com%2Fpublishing%2FCodes%2Fdownload.asp%3Furl%3D2011-04%2Frp-b401.pdf&ei=v7bpVM2XDIfaoATV34KoAw&usg=AFQjCNFNA6qsb6bybX_GHJIcmv3JpcweIg&bvm=bv.86475890,d.cGU&cad=rja
uses a procedure where the standard current requirement is estimated based upon the application and then adjustments are made for estimated coating damage and operating temperature. For offshore pipelines, similar procedures are described in ISO 15589-2 and DnV F-103.
Thank you Stephen N Smith and Salim Bousba for your comments. I am aware of the procedure in DnV RPB 401. I want anyone that has explicit method or model where the parameters of the medium such as soil resistivity, coating breakdown factors, temperature etc could be fed into such model and the results of the current density is obtained. Has anybody established such correlations?
Before I retired from a major oil company, I would periodically review CP calculations performed by quite a few engineering and design companies. In a number of these calculations, it was obvious that they had automated the DnV RPB401 calculations along with other aspects of the CP design. Usually it appeared that these calculations had been done using an Excel spreadsheet. Also, in each case, the company considered the spreadsheet as their own proprietary information since it was a design tool that they did not want to simply give to their competitors.
So, if you are looking for an automated B401 calculation, you options would be to talk with an engineering company that performs these calculations and hope that they are willing to share or else you simply write your own spreadsheet.
Thank you very much Stephen. We have actually carried out the determination of current densities requirement for few designs on pipeline transporting crude oil for major oil companies. We shall establish spreadsheet of the procedure adopted. Thank you for your advice.
- Badges
- Science topic
- Similar topics
- Biological Science
- Bioecology
- Systems Ecology
- Landscape Ecology
- Connectivity