Corrosion Simulation Newsletter
An article in December 2014's MP magazine looked at the effect of grounding on the cathodic protection (CP) potential distribution at an oil station, which had been studied using BEASY's corrosion and cathodic protection simulation software.
Influences from four factors were analysed: grounding system material, relative position between the grounding conductor and the pipeline, and length and buried depth of the grounding conductors. CP designs with and without grounding were compared.
Corrosion Modeling Solutions Showcased at NACE 2014
BEASY participated in a very busy NACE Corrosion Conference in San Antonio last month. We were active in the conference program and exhibition hall, highlighting corrosion modeling services and software. It was good to see many friends and interested engineers visiting us at our booth. There were a number of papers presented during the Technical Program which featured some engineering projects carried out by the BEASY engineering services team and by customers.
Improved Effectiveness Of Direct Assessment Field Surveys Through The Application Of Boundary Element Analysis (BEA) To Simulate Electrical Field Interference Between Collocated Pipelines. Katurah Hansen, Angel R. Kowalski, Shane Finneran, Jason Land. Det Norske Veritas (USA), Inc.
Direct Assessment above ground surveys are often time consuming, laborious, expensive and require operational knowledge of NACE Standard TM0109-2009. The use of boundary element analysis (BEA) software allows for a more comprehensive re-creation of different possible conditions and can provide additional analysis to validate survey results when conditions, such as buried metallic structures adjacent to the pipeline being assessed limit the sensitivity of the survey tools. This combined use approach offers the benefit that a simulation model can be developed that fits well to the actual conditions of the pipeline, with minimal assumptions.
To evaluate the effectiveness of the designed CP System, a boundary element analysis (BEA) was performed to analyze the predicted potential distribution and current density for the natural gas pipeline collocation. The interfering current makes it difficult to accurately calculate these distributions by other methods. Results from the BEA allow for current shielding, over potential hot spots, and other critical areas where the CP is least effective, to be identified.
ICCP System Design on the Hull of an Ice Breaker by Computational Analysis. Min-Jung Lee, Chae-Seon Lim. Samsung Heavy Industries Co., Ltd
Impressed current cathodic protection (ICCP) systems have been employed with coatings to prevent corrosion on the hulls of ice breakers. Many ICCP systems used for commercial vessels are designed based on the designer's experiences rather than by analytical method. The purpose of this paper is to simulate the performance of ICCP systems on hulls under Arctic conditions by a computational analysis based on boundary element methods (BEM) and to deduce an optimized design. For this purpose, an Arctic shuttle tanker that will travel across the Barents Sea was investigated. The coating breakdown factors at the end of the design life were assumed to range from 1% to 5% depending on the ice strengthening areas of the hull. The design optimization process consisted of a series of calculations of the structure potential with several cases of ICCP system arrangements and reference cell target potentials. The effects of these factors were studied under Arctic conditions.
The model predicted the potential distributions on the hull and the results were used to determine the optimized design of the ICCP systems under the service conditions.
Image: Coating damage on the hull of an Arctic vessel after 2.5 years under Arctic Sea
The Application Of Computer Modeling To Improve The Integrity Of Ballast Tanks. Robert Adey, Guy Bishop, John Baynham, CM BEASY Ltd
Generally additional cathodic protection (CP) systems are installed in ballast tanks to provide protection to the areas that may become unprotected by degraded coatings. Because of the complex geometry of the tanks and the presence of pipework, equipment and in some cases ladders and walkways the correct placement of both sacrificial & ICCP anodes is essential to get a good potential distribution that ensures no areas are either under or over protected.
Computer modeling has become widely used in the maritime corrosion industry to predict the performance of CP designs and to ensure adequate protection is provided to the structure over its life. In this paper a case study is presented where computer modeling is used to verify and optimize the design of the corrosion control system of a ballast tank and to predict how it will perform over the service life of the tank. Case studies are presented for both a sacrificial CP system and ICCP design.
Image: Optimized anode layout showing initial consumption rates
An interesting article was published in the September 2014 issue of the NACE Materials Performance magazine. The article presents design considerations and some of the challenges a corrosion engineer encounters while designing a cathodic protection (CP) system for offshore wind turbine foundations. The authors were Sameer Ayyar, Jacob Jansson and Ruth Sorenson from COWI A/S Copenhagen, Denmark.
The study was supported by computer modelling where a number of options were evaluated. In the figure shown here the model results for an anode cage attached to a monopile structure at a level of -5 to -10m can be seen. The immersed surface of the monopile is bare. Corrosion protection is extended to all the external immersed surfaces and 5m below the mudline.
Project: London Array Offshore Wind Farm. Image source. COWI.
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Once a structure is commissioned information on the condition of the structure and the performance of the CP system is obtained by surveying the structure to obtain data on the potentials and in some cases field gradients. The number of locations where data is collected and the frequency of such surveys are very much dependent upon the operator and can vary significantly. Data is typically provided in tabular form and has to be assessed by the CP engineer along with other integrity data to identify anomalies (i.e. where the potential is outside the expected range) and to identify trends which may indicate that the design is not performing as expected.
Physical scale modeling (PSM) has been used for many years, in particular for naval applications to validate the corrosion control measures such as cathodic protection systems installed on ships. Tom Curtin based in BEASY's US Office has recently used PSM as part of a project where the aim was to investigate the CP provided to ballast tanks to verify that the computer modeling results were providing accurate predictions.
The design verification of CP systems applied to underground facilities including storage tanks, buried piping, equipment bases, grounding systems, reinforced concrete and other underground structures is complex challenge. Space limitations may restrict installation of anodes in certain areas and shielding effects from buried structures may affect the distribution of the protective current. Modelling provides a tool to ensure adequate protection by evaluating ground bed design options and locations to mitigate the effect of interference and shielding.
A recent study investigated the impact of interference between nearby storage tanks and pipelines on the performance of the CP system and the potentials achieved.
The modelling study aimed to verify the protection provided including the interference between the CP systems for the underground infrastructure comprising three tank bases, pipelines with different quality coatings, ICCP Anodes, grounding rods, tank bottom ICCP Grid and sacrificial anodes.