Cathodic Protection Materials and Equipment in Plant Facilities

Cathodic Protection Materials and Equipment in Plant Facilities

1. Anodes

1.1 ICCP Anodes

1.1.1 High silicon cast iron (canister).

• This type of anodes shall be used for pipeline/piping and tank bottoms which are not requiring bottom replacement.
• The anodes shall be prepackaged in steel canisters containing carbonaceous backfill.
• The design parameter of the high silicon cast iron anode is the following:

Operating current density	0.45 kg per ampere-year
Consumption rate	1.0 Amp/ft2
Maximum current density	0.7 mA/cm2

 

     

• The impressed current anode backfill shall conform to the following specifications:

1.1.2 Mixed Metal-Oxide (MMO) Coated Titanium Ribbon (Grade 1 Titanium):

• MMO ribbon anodes shall be used for new tank bottoms and for existing tanks that are requiring bottom replacement.
• MMO ribbon anodes shall meet ASTM B-256 grade 1 titanium. The minimum width and thickness of ribbon shall be 6.35 mm and 0.6 mm respectively.
• The ribbon anodes shall be electrically continuous with each other through the current distributor, which shall be spot welded to the ribbon anode (three spots).
• The current distributor shall be a solid grade 1, uncoated titanium bar, 12.7 mm wide and 0.9 mm thick minimum.

1.1.3 Mixed Metal-Oxide (MMO) Coated Titanium Anodes:

• These types of anodes are suitable and shall only be used for submerged parts of the structure.
• They are available in solid rods, tublor or plate forms. They are fixed to the concrete either through steel channel supports or perforated PVC pipes.
• The consumption rate of these anodes shall not be more than 1.0 mg/amp-yr.
• Length, diameter, quantity and distribution pattern of these anodes shall be selected  to meet the current requirement locally, and to also conform to the anode design and the maximum anode current density.
• The MMO coating thickness shall be sufficient to provide a service life of 25 years. Calculations shall be provided to verify their service life.
• The anode cable connection to the anode shall be crimped made using 12 tons of hydraulic compression. The connection shall be appropriately covered with moisture resistance tapes and sealed with heat shrink sleeve.

1.1.4 Polymeric anodes

• Conductive polymer anodes shall be used for underground pipelines/piping in very congested areas as specified in Para. 6.10.18.
• Conductive polymer anodes shall be surrounded with a minimum coke breeze of 0.072 Ib/ft (1.15 kg/m).
• The net diameter of conductive polymer shall be 0.5 inch (13 mm) minimum and the total diameter with anode backfill shall be 1.5 inch (13 mm) minimum.
• The coke breeze, pre-packed, is high performance petroleum coke breeze serving as the active matrix in which the electrochemical reactions take place.
• The max current output of this type of anode shall be 52 mA/m.
• The coke breeze weight shall be 0.072 Ib/ft (1.15 kg/m).

1.1.5 Sacrificial Anodes

The weight of sacrificial anodes installed in soil shall be 60 Ibs excluding the anode backfill. Sacrificial anode backfill that is installed in soil shall be 75% hydrated gypsum, 20% bentonite clay and 5% hydrated gypsum. Zinc anodes can also be packaged in a backfill consisting of 50% hydrated gypsum and 50% bentonite clay.  Sacrificial anodes shall be one of the following:

1.1.6 Aluminum

Aluminum anodes shall exhibit an open circuit potential, when immersed in ASTM D1141 ’Substitute Ocean Water’ at ambient temperature, of -1050 mV or more negative with reference to a Ag/AgCl electrode.  Aluminum anodes shall conform to the following Specification:

1.1.7 Magnesium

Magnesium anodes shall exhibit an open circuit potential, when immersed in ASTM D1141 ’Substitute Ocean Water’ at ambient temperature, of -1650 mV or more negative with reference to an Ag/AgCl electrode. Magnesium anodes shall conform to the following Specification:

1.1.8 Zinc

Zinc anodes operated at 50 °C or less shall exhibit a potential of -1050 mV or more negative in reference to a Ag/AgCl electrode when tested in ASTM D1141 ‘Substitute Ocean Water’ at ambient temperature. Zinc anodes for 50 °C or less operation shall conform to the following Specification:

Zinc anodes operating at temperatures between 50 °C and 70 °C shall conform to the following Specification:

Zinc anodes shall not be used for operating temperatures above 70 °C.

2 Reference Electrodes

1. Performance and effectiveness of the CP system shall be monitored and recorded using permanently buried reference electrodes. These electrodes shall be commercially available devices, with a proven track record of use in soil or water, particularly in hot climate environments. Details of previous applications of the cells proposed by contractor shall be included as part of the technical submittal provided to SABIC prior to acceptance.
2. The reference electrodes shall be either saturated copper/copper sulphate or saturated silver/silver chloride (Sat. KCl) electrodes deposing on the applications mentioned earlier
   in this standard.
3. All permanent reference electrodes shall be supplied with a test certificate and fitted with a suitable length of cable, so that no splices are required between placement location and test stations.
4. Buried reference electrodes shall have a life expectancy of over 25 years. The half-cells shall have a predicted accuracy of +/-20mV for the 25 year electrode life expectancy and shall have a tested accuracy of +/- 5 mV against a calibrated sulphate reference electrode (same type).
5. Reference electrode shall be designed to operate in an environment between 0 oC and 60 oC. The manufacturer shall also provide the temperature coefficient and its temperature range.
6. The connection between the cable and the electrode shall only be factory fitted and completely sealed, and capable of total burial/immersion without leakage.
7. The contractor shall use reference electrodes of those manufacturers which have proven track record in use for a minimum of 10 years. Prior to procurement, contractor shall submit the details of the proposed reference electrodes for review and approval.
8. Reference electrodes shall be supplied only from approved manufacturers.

3 Cables

3.1 The positive DC feed cable from the rectifier shall feed a multi-terminal resistor controlled junction box.
3.2 Each terminal from this positive junction box shall feed an individual anode.
3.3 The negative cables from the rectifier shall be connected to the structure.
3.4 The negative from the rectifier shall be connected to the tank at two points 180 degrees apart.
3.5 All cables shall be stranded copper and shall have a minimum of seven strands.

3.6 All cables shall have a minimum of one layer of insulation and a single layer of sheathing which shall conform to SES E222-S01. DC cables shall be conductor, copper cored high molecular weight polyethylene (HMWPE) insulation. The minimum insulation thickness shall be 0.8 mm.
3.7 Single core cables shall be color coded as follows, unless otherwise directed:

Color                    System
Red                        System Positive Cables
Black                     System Negative Cables
Blue or gray         Reference Electrode Cables

3.8 Color coding shall be same for all areas.
3.9 Multi-core cables shall be color or number coded.
3.10 All cables shall be run in appropriate size conduits between the structure and the  junction box / test station and also between the junction box and the power supply or TR unit.
3.11 All cables shall be clearly labeled at termination points with permanent labels.

3.12 All underground wire attached to the positive rectifier terminal is at a positive potential  with respect to ground. If not completely insulated, the wire may discharge current (act as an anode), which will result in corrosion of the wire and rapid failure of the cathodic protection installation.

3.13 Splices in the anode lead wires, positive cable from the transformer rectifier to the junction box and negative cables from the TR to structure are not allowed. Cable insulation shall be carefully inspected prior to backfilling.

3.14 Backfill shall be sifted sand free of sharp stones or other material that could damage wire insulation. All cables between the protected structure, the junction box and /or the
transformer rectifiers shall be run in appropriately sized conduits. Cable conduits below grade level shall be rigid PVC, above grade level shall be PVC coated rigid galvanized
steel. All fittings and accessories shall meet the conduit type specification respectively.

3.15 The structure and test lead wires should be clean, dry, and free of foreign materials at points of connection. Connections of test lead wires to the structure must be installed so
that they will remain mechanically secure and electrically conductive. A preferred method is the use of a powder weld connection. However, this method is not recommended in
areas where a hazardous fire atmosphere may exist during the attachment process. Any electrical connection to a tank in a hazardous environment requires a hot-work permit.

3.16 Test lead wires should be color coded, numbered, or otherwise permanently identified.

3.17 Sufficient slack should be left to avoid strain on all wires.

3.18 Cable sizes for tanks, underground pipelines/piping and other isolated structures shall be as follows:

a. At least 16 mm² for anode tails and negative cables connected to structures.
b. At least 25 mm² from anode junction boxes to rectifiers.
c. In case if there are main positive and negative junction boxes, 35 or 50 mm² shall be used to connect between these boxes and rectifiers.

d. At least 10 mm² cables for testing.
e. At least 16 mm² for bonding between structures.
f. At least 6 mm² for buried reference electrodes and coupon cables.

3.19 Prior to procurement of multi-core cables, contractor shall submit the data sheets of the proposed cables for review and approval.

4. Test Coupon

4.1 The test coupon shall consist of a bare, cold-rolled steel cylinder head and No. 12 stranded wires, which are inserted alongside a 2-inch PVC tube. The PVC tube shall shields the reference electrode from potential gradients.

5. Test Station

5.1 All test station shall be big fink test station. Flush test station shall be used if the installation of big fink test station is impossible.
5.2 Each test station shall be visibly marked by permanent ink in red color. This shall be followed by the date of installation. Symbols and other notations compatible with the existing nomenclature, CPI, CP2, etc., shall be used for sequence of the test stations.

6. Anode & Negative Junction Boxes

6.1 Each junction box including bon box shall be complete with 316 stainless steel enclosure.
6.2 Anode (positive) junction box shall have variable resistors, current measuring shunts, and necessary appurtenances in accordance with NEMA 4X.
6.3 Each box shall be designed for outdoor installation.
6.4 Each box shall be provided with a sunshade.
6.5 Each box shall have a stainless steel permanent nameplate which shall include, as a minimum, the following items:

a. Manufacturer’s name and address
b. Model and serial numbers
c. Resistor manufacturer’s name and address
d. Resistor model and serial numbers

e. Resistor ratings
f. Ambient temperature rating
g. Nameplate shall be affixed to the outside of the door

6.6 Anode junction box shall be sized to dissipate heat generated by the variable resistors at their maximum output in an outdoor environment.
6.7 All doors shall be lockable and locks shall be capable of being opened with the same key.
6.8 Anode junction box enclosures shall be explosion proof if installed in hazardous area.
6.9 All junction boxes shall be marked clearly.

7. Power Supply, Control and Monitoring Equipment

DC power supplies or TR units, control and monitoring equipment shall conform to SES L02-S01.