Cathodic protection applied to a waterbox can cause a non-uniform potential distribution to exist over the face of the tube sheet. These potential gradients cannot be detected by a remotely mounted reference electrode. Excessively electronegative potentials can result in hydrogen damage on titanium and ferritic stainless steel tubes while excessively electropositive potentials mean inadequate protection of the tube sheet. Model T references are the only means to verify that the actual potential at the tube sheet surface is within the acceptable range.

Typical Applications

• Condenser tube sheets

Features

• Ability to place a reference electrode in selected locations on the tube sheet
• In-line underwater connector for easy removal
• CPVC housing rated to 210^oF
• All non-metallic double tube plug for attachment
• Patented design: U.S. Patent No. 4,957,616

Electrode Housing

• Gelled Element: 1 1/16" dia. x 3" long gray CPVC housing
• Dry element: 1" dia. x 2 " long gray CPVC housing

Element Types

• AGG: Saturated gelled Ag / AgCl
• CUG: Saturated gelled Cu / CuSO₄
• AGD: Dry-type Ag / AgCl
• ZIN: 99.99% zinc

Electrode Termination

• Female underwater connector on 6" (nominal) fully encapsulated lead wire

Lead Wires

• Male underwater connector attached to #22 AWG Teflon insulated lead wires in the following colors: red, orange, yellow, green, blue, purple, brown, black, white, gray.

Typical Installation

Locate electrodes in tubes adjacent to lanes. Tubes containing reference electrodes must be plugged at both ends, either with Tube Sheet Mounted Reference Electrodes or tube plugs. Lead wires are placed along lanes and secured either by embedding in epoxy mastic or inserting in a plastic tube which is clamped to the tube sheet. Lead wires are passed through the waterbox wall via a sealing gland such as Conax MHC-062, MHM-062 or equivalent.

Typical Data

The potential across a tube sheet under cathodic protection can show large variations from one location to another. A smaller variation will also occur with time. Different waterboxes of the same apparent design can produce different potential distributions.

Data from several Model T Reference Electrodes spotted at strategic locations on the tube sheet can be used to construct iso-potential diagrams which clearly show the potential distributions. EDI can construct these diagrams from a customer's data. Experience has shown that iso-potential diagrams constructed from 30-day average data correlate very closely with inspection reports listing tubes with hydrogen damage.

The accuracy of these diagrams depends upon the number of reference electrodes used and their distribution. Six to twelve reference electrodes on each tube sheet will provide sufficient data for constructing an accurate diagram.

Dimensions

Model Designation, Electrode

• Specify as EDI Model TE-XX-SW, where XXX = element type

Model Designation, Wire

• Specify as EDI Model TW-col-LWnnn, where col = color code and nnn = wire length in feet.