GB/T 3108-2026Impressed current cathodic protection systems for ship hulls (English PDF)

5.5 Propeller Shaft Grounding Device

5.5.1 The propeller shaft grounding device mainly consists of a conductive ring, carbon brush, brush holder and brush holder support frame, as shown in Figure 1.

5.5.2 The conductive ring is generally made of brass, consisting of two semi-circular slip rings, which are then fastened with bolts.

5.5.3 Carbon brushes are typically copper-graphite. A standard propeller shaft grounding system usually has at least three sets of carbon brushes, one of which is used to measure the propeller's... Due to the potential difference of the hull, the carbon brush should be insulated from the hull.

5.6 Rudder grounding device The rudder grounding device is a single-core marine flexible cable with a cross-sectional area of not less than 25mm2, which short-circuits the rudder post to the hull.

5.7 Anode Shielding Layer The shapes of the anode shielding layer include disc-shaped and strip-shaped.

6.1 Protection Potential Range

6.1.1 For hull steel with a yield strength less than 500 MPa, the protection potential range is -0.8V to -1.1V (relative to silver/silver chloride seawater). (Reference electrode, the same below) For hull steel with a yield strength of not less than 500 MPa, the most positive protection potential is -0.8V, and the most negative protection potential should be adopted. The experiment confirmed this.

6.1.2 Structures such as shafts and rudder plates should be protected simultaneously with the hull, and the protection potential range should be the same as that of the hull structural steel.

6.1.3 The protection potential range for copper propellers is -0.45V to -1.1V.

6.2 Tracking Performance When the ship's speed changes and the given potential changes, the output voltage and output current of the potentiostat should also change accordingly, and the ship's speed should be adjusted accordingly. The body reaches the protection potential range.

6.3 Potentiostat

6.3.1 The potentiostat should be able to operate reliably under the following environmental conditions.

a) The ambient temperature is -10°C to 55°C.

b) The relative humidity of the air is not greater than 95%.

c) Condensation, salt spray, oil mist, and mold are present.

d) The power supply variation range is 6% to -10% in steady state and ±20% in transient state (recovery time 1.5s); the frequency variation range is ±5% in steady state. Transient ±10% (recovery time 5s).

e) The harmonic content of the power supply voltage is not greater than 8%.

f) Vibration. 1) 2Hz~13.2Hz, displacement ±1.0mm; 2) 13.2Hz~100Hz, acceleration ±6.9m/s2.

g) Tilting and rolling 22.5°, pitching and rolling 10°.

6.3.2 The potentiostat shall have the following performance characteristics.

a) Input impedance not less than 1MOmega;

b) The potential control error is no greater than 0.02V;

c) Continuously adjustable within a given potential range;

d) Manual and automatic control adjustment;

e) The half-load ripple factor is not greater than 5%;

6.6 Propeller Shaft Grounding Device

6.6.1 The propeller shaft shall be electrically connected to the hull using a propeller shaft grounding device, and the potential difference between the propeller and the hull shall be reduced to below 0.1V.

6.6.2 The installation location of the propeller shaft grounding device should be selected in a dry, oil-free location that is easy to observe and maintain.

6.6.3 The service life of the conductive ring, brush holder and brush holder support of the propeller shaft grounding device shall not be less than 20 years, and the service life of the carbon brush shall not be less than 5 years.

6.7 Rudder grounding device To prevent electrochemical corrosion of the rudder blades, a single-core marine flexible cable with a cross-sectional area of not less than 25 mm^2 should be used inside the rudder gear compartment to connect the rudder post to the ship. For electrical connections, the grounding resistance should be less than 0.02Omega.

6.8 Anode Shielding Layer

6.8.1 Coatings The technical specifications of the anodic shielding coating should meet the requirements of GB/T 7788.

6.8.2 Cathode Potential Value The hull potential at the edge of the anode shielding layer should not be lower than -1.1V.

6.8.3 Thickness The thickness of the anode shielding layer should be determined based on the shielding layer lifespan requirements and the performance of the anode shielding coating. Typically, the thickness near the auxiliary anode should be... It should be thicker, gradually thinning towards the edge of the shielding layer, with the edge area being as thin as 0.5mm.

6.8.4 Lifespan The design service life of the anode shielding layer should be no less than 10 years.

7.1 Calculate the protected area

7.1.1 The hull submerged area can be calculated precisely according to the line drawing, or approximately according to formula (1).

7.1.2 The surface area of the propeller is calculated according to formula (2).

7.1.3 The rudder or other attachments shall be submerged in water according to their actual dimensions.

7.2 Selecting the protection current density

7.2.1 The protective current density should be determined based on factors such as material, surface condition, ship availability, speed, dry-docking intervals, temperature, and water quality, referring to Table 3. Select.

7.2.2 For special vessels, the protection current density may be appropriately increased depending on their working conditions and the length of the allowable dry docking interval.

7.3 Total Protection Current The total protection current is calculated according to formula (3).

7.4 Selection of potentiostat, auxiliary anode, reference electrode, and carbon brush

7.4.1 The specifications of the potentiostat should be selected based on the total protection current, with a 25% design margin. When a titanium-based auxiliary anode is selected, the potentiostat... The rated output DC voltage of the potentiometer should not exceed 12V.

7.4.2 The specifications of the auxiliary anode should be selected based on factors such as the total protection current, service life, ship tonnage, and ship structure, according to Table 2 or reference. Refer to GB/T 7388 for selection. The number of auxiliary anodes is determined by rounding up the result of formula (4) to the nearest integer (generally an even number). nC = I/iC (4)

7.4.3 Fixed reference electrodes should preferably be silver/silver chloride seawater, silver/silver halide seawater, or high-purity zinc reference electrodes, depending on the ship structure and other factors. The tonnage and number of potentiostats to be installed should be determined according to Table 3 or by referring to GB/T 7387.The reference electrode type should be selected accordingly. In principle, one vessel should have [the following installed]... There should be no fewer than two reference electrodes.

7.4.4 Select the anode shielding coating according to the overall requirements of the ship and the model of the auxiliary anode. The size of the circular anode shielding layer is calculated according to formula (5), length The dimensions of the strip anode shielding layer are calculated according to formula (6).

7.4.5 Carbon brushes are usually made of copper-graphite. The number of carbon brushes should be determined by rounding up to the nearest integer according to formula (7), and should not be less than 3 sets.

7.5 Cable Selection

7.5.1 The cables used in the impressed current cathodic protection system shall be marine cables.

7.5.2 The cross-sectional area of auxiliary anode and cathode cables should be determined based on factors such as cable current carrying capacity, allowable cable voltage drop, and mechanical strength. The voltage drop of the cathode cable should be less than 2V, and the voltage drop of the cathode cable should be less than 0.1V.

7.5.3 The reference electrode cable shall be a shielded cable.

7.6 Arrangement method of auxiliary anode and reference electrode

7.6.1 General Requirements.

a) The arrangement and installation of auxiliary anodes and reference electrodes should have high resistance to mechanical damage and should be adaptable to special conditions such as navigation in ice-covered areas. Operating conditions;

b) Auxiliary anodes and reference electrodes should not be placed in locations that are prone to damage, high stress, or high fatigue loads during ship operation;

c) The overall arrangement principle of auxiliary anodes should be to ensure that the ship's potential reaches the specified protection potential range;

d) The reference electrode should be on the same horizontal plane as the auxiliary anode.

7.6.2 Longitudinal arrangement of auxiliary anodes. In principle, they should be arranged at the stern, midship, and bow, with more at the stern; however, this may vary depending on the vessel where installation is more difficult. It can be arranged bow-to-stern or only at the stern, but the port and starboard sides should be symmetrically arranged.

7.6.3 Vertical arrangement of auxiliary anodes. approximately 1/3 of the arc length from the heavy load waterline to the ship's bottom centerline, but should be 0.5m below the light load waterline. the following.

7.6.4 Longitudinal arrangement of reference electrodes. If two reference electrodes are installed throughout the ship, one should ideally be located at the stern and one at the bow or stern, preferably on either side. The reference electrodes should be installed separately on both sides; if four reference electrodes are installed, two should be installed at the fore and aft of the ship, and two on each side; the specific locations should preferably be arranged on both sides. The auxiliary anode can also be placed in the middle, near the shielding layer close to the auxiliary anode.

7.6.5 The installation positions of auxiliary anodes and reference electrodes should be optimized using computer numerical simulation technology.

a) Based on the hull shape value table, use 3D modeling software to construct a 3D structural diagram of the hull below the waterline and perform mesh generation.

b) The finite element method or boundary element method can be used to calculate the cathodic protection potential distribution of the external applied current on the ship.

c) The simulation can be repeated by manually adjusting the number and position of the auxiliary anodes, the output current, and the number, position, and control potential of the reference electrodes. The calculation method optimizes the design of impressed current cathodic protection; the auxiliary anode position and output current can also be automatically optimized using formula (8). The reference electrode controls the potential.

8.1 Inspection of Impressed Current Cathodic Protection System Components

8.1.1 Inspection of the potentiostat, auxiliary anode, reference electrode, and anode shielding coating components of the impressed current cathodic protection system includes factory inspection. And type testing.

8.1.2 Type testing shall be performed on impressed current cathodic protection components if any of the following conditions are met.

a) When the design of a new product is finalized;

b) When a product is transferred to another factory for production;

c) When the factory inspection results differ significantly from the previous type inspection results;

d) When the production stoppage period exceeds 3 years;

e) When the national quality supervision agency requests a type test.

8.1.3 The factory and type inspection items and inspection methods for potentiostats shall be performed in accordance with CB*3220.

8.1.4 The factory and type inspection items and inspection methods for auxiliary anodes shall be carried out in accordance with GB/T 7388.

8.1.5 The factory and type inspection items and inspection methods for the reference electrode shall be carried out in accordance with GB/T 7387.

8.1.6 The factory and type inspection items and inspection methods for anodic shielding coatings shall be carried out in accordance with GB/T 7788.

8.2 Shipboard Test of Impressed Current Cathodic Protection System

8.2.1 Ship trials of impressed current cathodic protection systems include mooring trials and sea trials.

8.2.2 During mooring and sea trials, the operation of the hull potential and constant potential meter shall be checked. The check items are shown in Table 4.

8.2.3 Mooring test.

a) After the ship is launched (seawater or freshwater) and before the impressed current cathodic protection system is energized, use a reference electrode installed on the hull to measure... Measure the natural electrode potential of the ship's hull;

b) After the impressed current cathodic protection system is energized, a reference electrode installed on the hull is selected as the control electrode, and the protection... Select three different given potential values within the potential range, and record the output voltage and output current of the potentiostat at different given potential values. Changes in current and hull potential;

c) After the impressed current cathodic protection system is energized, use a portable reference electrode to measure the protection of the hull at 10 selected points on both sides of the ship. Potential;

d) Measure the potential difference between the propeller shaft and the hull using a multimeter.

8.2.4 Sea Trials.

a) After the impressed current cathodic protection system is in operation, the ship's hull potential is measured at different speeds using a reference electrode installed on the ship, and the constant current is rec...