Cathodic or anodic protection system and method for independently protecting different regions of a structure

A cathodic protection system for protecting a tank structure including a bowl portion and a riser portion for containing an electrolyte using at least two protection units located adjacent to different regions of the tank structure comprising:

• a first protection unit located in the bowl portion comprising:
• first means for applying a continuously adjustable rectified alternating current voltage between the structure and at least a first positive electrode which is immersed in the electrolyte and spaced apart from the bowl portion;
• a first reference cell located in the electrolyte adjacent to said bowl portion to produce a direct current voltage between the first reference cell and the bowl portion;
• first measuring means coupled to the first reference cell to measure the potential between the first reference cell and the bowl portion;
• and
• first control means coupled between said first measuring means and said first applying means for continuously adjusting said first applying means to control the level of the rectified alternating current voltage applied by said first applying means in accordance with the level of the potential measured by said first measuring means;
• and
• a second protection unit located in the riser portion comprising:
• second means for applying a continuously adjustable rectified alternating current voltage between the structure and at least a second positive electrode which is immersed in the electrolyte and spaced apart from the riser portion;
• a second reference cell located in the electrolyte adjacent to said riser portion to produce a direct current voltage between the second reference cell and the riser portion;
• second measuring means coupled to said second reference cell to measure the potential between said second reference cell and the riser portion;
• and
• second control means coupled between said second measuring means and said second applying means for continuously adjusting said second applying means to control the level of the rectified alternating current voltage applied by said applying means in accordance with the level of potential measured by said second measuring means,
• wherein the first and second protection units are essentially independent of one another in their operation and are operated continuously and simultaneously so that the level of alternating current voltage applied between the bowl portion and the first electrode and the riser and the second electrode will be independently established by the first and second control means in accordance with the respective potentials measured by said first and second measuring means.

A method for protecting a structure immersed in an electrolyte by separately protecting at least two different regions of the structure comprising:

• protecting a first area of the structure by the steps of:
• applying a first continuously adjustable rectified alternating current voltage between the structure and at least a first electrode which is immersed in the electrolyte and spaced apart from the structure;
• producing a first direct current voltage between the structure and a first reference cell located in the electrolyte;
• measuring the potential between the first reference cell and the structure;
• and
• adjusting the level of the first rectified alternating current voltage in accordance with the level of the measured potential between the first reference cell and the structure;
• and
• protecting a second area of the structure by the steps of:
• applying a second continuously adjustable rectified alternating current voltage between the structure and at least a second electrode which is immersed in the electrolyte and spaced apart from the structure;
• producing a second direct current voltage between the structure and a second reference cell located in the electrolyte;
• measuring the potential between said second reference cell and the structure;
• and
• adjusting the level of the second rectified alternating current voltage in accordance with the level of the measured potential between the second reference cell and the structure,
• wherein the steps of protecting first and second areas of the structure are carried out essentially independently of one another so that the level of alternating current voltage applied between the structure and the first electrode and the structure and the second electrode will be independently established in accordance with the respective measured potentials between the first and second reference cells and the structure.

A cathodic protection method for protecting a tank structure including a bowl portion and a riser portion for containing an electrolyte by separately protecting the bowl portion and the riser portion of the structure comprising:

• protecting the bowl portion of the tank structure by the steps of:
• applying a first continuously adjustable rectified alternating current voltage between the bowl portion and at least a first positive electrode which is immersed in the electrolyte and spaced apart from the bowl portion;
• producing a first direct current voltage between the bowl portion and a first reference cell located in the electrolyte adjacent to said bowl portion;
• measuring the potential between the first reference cell and the bowl portion;
• and
• adjusting the level of the first rectified alternating current voltage applied by said first applying means in accordance with the level of the measured potential between the first reference cell and the bowl portion;
• and
• protecting the riser portion of the tank structure by the steps of:
• applying a second continuously adjustable rectified alternating current voltage between the riser portion and at least a second electrode which is immersed in the electrolyte and spaced apart from the riser portion;
• producing a second direct current voltage between the riser portion and a second reference cell located in the electrolyte adjacent to said riser portion;
• measuring the potential between said second reference cell and the riser portion;
• and
• adjusting the level of the second rectified alternating current voltage applied by said applying means in accordance with the level of the measured potential between the second reference cell and the riser portion,
• wherein the steps of protecting first and second areas of the structure are carried out essentially independently of one another continuously and simultaneously so that the level of alternating current voltage applied between the bowl portion and the first electrode and the riser portion and the second electrode will be independently established in accordance with the respective measured potentials between the first and second reference cells and the bowl and riser portions of the tank structure.

A system for protecting a structure immersed in an electrolyte using at least two protection units located adjacent to different regions of the structure comprising:

• a first protection unit comprising:
• first means for applying a first constant voltage between the structure and a first electrode which is immersed in the electrolyte and spaced apart from the structure;
• and
• a second protection unit comprising:
• second means for applying a second constant voltage between the structure and a second electrode which is immersed in the electrolyte and spaced apart from the structure,
• wherein the first and second protection units are essentially independent of one another in their operation and are located adjacent to different regions of the protected structure so that the level of the first and second constant voltages applied between the structure and the first electrode and the structure and the second electrode will be independently established in accordance with predetermined values.

A system for protecting a structure immersed in an electrolyte using at least two protection units located adjacent to different regions of the structure comprising:

• a first protection unit comprising:
• first means for applying a first constant current to at least a first electrode which is immersed in the electrolyte and spaced apart from the structure;
• and
• a second protection unit comprising:
• second means for applying a second constant current to at least a second electrode which is immersed in the electrolyte and spaced apart from the structure,
• wherein the first and second protection units are essentially independent of one another in their operation and are located adjacent to different regions of the protected structure so that the level of the first and second constant currents applied to the first electrode and the second electrode will be independently established in accordance with predetermined values.