Elsyca’s Aboveground Storage Tanks (AGST) CP Modelling

Description

Today’s AGST Cathodic Protection Market

AGST soil side corrosion even with the application of Cathodic Protection (CP) still costs the tank storage industry several tens of millions of dollars per annum. A typical tank outage incurs costs due to loss of production (storage), UT scanning and high repair costs ranging from $45,000/day up to several million dollars or more, when unscheduled shutdowns occur, and tank floors need to be replaced, excluding any environmental risks and non compliance.

Elsyca’s Groundbreaking Solution

Elsyca’s specialty engineering services enable cost-effective and reliable CP system designs and performance evaluations in line with international standards and all PHMSA requirements for corrosion and safety, or those pertaining to local government regulations, such as Seveso III Directive 2012/18/EU.

Vapor Corrosion Inhibitors (VCI) are potential considerations for AGSTs but these introduce new uncertainties in the protection performance of these hybrid systems.

Elsyca’s groundbreaking technology unlocks other potential AGST corrosion mitigation solutions.

Yesterday’s and Today’s Key Challenges

All AGSTs are defined as complex CP structures, based upon the requirements of API RP2003, API 651, NACE SP0193 and EN 14505.

The typical analytical calculations utilized to design CP systems are ineffectual when applied on AGST systems:

  • double floors and tank liners/leak detection systems affect both the CP current and potential distribution and complicate potential readings.
  • large variances in the moisture content and significant variations in both the physical and chemical sand properties are not accounted for
  • electrical calculations do not cover anodic/cathodic polarization variances
  • current may leak directly to the plant system earthing and other extraneous groundings sites.

Advantages of Computational Modelling

Elsyca’s cost effective engineering services enable the CP effectiveness to be fully visualized and verified prior to installation. The computational modelling of the tank bottom plates, CP system and foundation details, effectively account for all of the following key advantages;

  • Compliant with all NACE SP0193 Section. 4.3.1.1-3 acceptance criteria;
  • Determines the optimized anode layout, location of UT coupons, etc.;
  • Troubleshoots existing CP systems by calibrating the models based upon as-built and site gathered data and measurements;
  • Investigates the impact of broken anodes/positive connections;
  • Determines the efficacy of the proposed CP design prior to implementation;
  • Account for hybrid systems such as VCI combined with CP

Elsyca’s Key Engineering Solutions and Features

  • The potential and current distribution can be modelled for the entire tank surface area;
  • The precise CP anode, tank foundation and ring wall or annular ring construction dimensions can be replicated in the 3D models;
  • The electrolyte properties that affect the potential and current distribution and the protection levels are considered (uniform or nonuniform);
  • Tank and anode specifications (material properties, dimensions, etc.) are accurately defined and used to ensure that all voltage drops and resistive loads are accounted for;
  • The anode current distribution through the electrolyte is visualized and areas of under-protection are readily determined;
  • The net flow of current to the cathode (tank floor) from the various anodes is visualized, to ensure optimal anode placement. The number and distribution of anodes are adapted based upon the electrolyte conductivity and levels of protection;
  • The dimensions, depth and spacing of concentric ring anodes and anode grid is effectively validated and verified prior to purchasing materials and prior to any installation;

  • Full visualization of current flowing to AGST and the effect of extraneous earths on the tank potential and current distribution;
  • The anode current density and associated consumption rates are determined along the length of each anode;
  • Positive cable runs and connections to the anodes are verified and optimized from both a commercial and technical perspective;
  • Elsyca’s trusted global electrochemical expertise, cutting-edge technology and engineering proficiency provides long term industrial solutions to a complicated AGST environment;
  • Complex, confined and complicated tank floor corrosive environments are all electrochemically computed, pragmatic solutions engineered and this is visualized using powerful 3D computational modelling.

Is your AGST asset correctly protected ?

The main goal of the CP is to mitigate soil side corrosion, whilst meeting all regulatory requirements. The CP design needs to account for the anode’s internal resistance, all associated CP cabling resistances, and the soil resistance, including the current and potential distribution as per API 651/NACE SP0193.

The pictures above, highlight the IR-free potential distribution on a 122ft AGST in 5,000Ω.cm soil, with 16 anode rings. At the tank periphery, the potentials in-between the anodes, ranges from -850mV to -1000mV, thereby concluding “compliance”. However, there are non-compliant hot-spots of -700mV to -850mV in many areas. The 100mV “potential shift” is confirmed by the measurements around the tank, often ignoring these large potential variances, allowing significant equalizing currents to flow during the interruption of the CP, as the various tank potentials try to reach an equilibrium.

Has the “100mV polarization potential” and regulatory requirements actually been met?

Complex, confined and complicated tank floor corrosive environments are all electrochemically computed, pragmatic solutions engineered and this is visualized using powerful 3D computational modelling.

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