G.S.P.L.A.J. LIBYAN IRON AND STEEL COMPANY

Transcription

1 G.S.P.L.A.J. LIBYAN IRON AND STEEL COMPANY Development of Bulk Berth No:2 and Loading Berth Cathodic Protection of Steel Piles

2 Cathodic Protection Standards: Det Norske Veritas DNV RP B401, January 2005 Recommended Practice Cathodic Protection Design BS EN Cathodic Protection for Harbour Installations. NORSOK, Standard Common Requirements, Cathodic Protection M503 September S 1997 NACE International RP , Metallurgical and Inspection Requirements for Cast Galvanic Anodes Offshore Applications. BS 7361, Part 1, CP Code of Practice for Land and Marine Applications BS EN 13509, 2003, CP Measuring Techniques TS 09 Cathodic Protection System (LISCO)

3 Cathodic Protection Method: Impressed Current Cathodic Protection will be applied to steel piles of Bulk Berth No:2 and Loading berth because of high current densities in sea water.

4 Details of Cathodic Protection System: Each Module has own independent CP system. There is total 11 modules on Bulk Berth No:2 and Loading Berth. Each of these modules will be cathodicaly separated from others. In case of any problem like T/R unit failure, cable connection failure, short circuit or etc,, only one module will stay unprotected until the problem has been resolved. This independency endency also prevents the leakage currents between anode groups connected to different T/R units, caused by different output voltages. This will increases the anode life s s and decreases the electricity consumption.

5 Each module has two(2) T/R units There will be two(2) Transformer/Rectifier units for each module.. One of the T/R units has a capacity of protecting whole module. But normally it will protect only half of the module. Other half of the module will be protected by second T/R Unit. In case of a failure of one of these two T/R units protecting one e module from any reason, other T/R unit will be able to protect the whole module temporarily. Thus any of the modules will not stay unprotected because of failure of one T/R Unit. In our project there is total 22 T/R units on Bulk Berth No:2 and Loading L Berth but normally 11 is enough for all modules developing. To prevent leakage currents between anode groups connected to different T/R units, cathode continuity c ring of one module divided into two parts. In case of a failure of one T/R T unit, these two cathode rings and two anode groups will be able to be set as one cathode ring and one anode group to let the one T/R unit to protect whole module manually inside the anode and cathode distribution boxes near the T/R units. This method also will increases the anode life s s and decreases the electricity consumption.

6 Cathodic Continuity of Piles All Piles of modules will be connected to cathodic protection system. stem. As described above there will be two independent cathode rings on each module.. These rings will be installed as meshed and connected to cathode distribution n box on each column to obtain reliable connection. In case of a failure of any y cathode cable or connection in the boxes, current will be able to flow from pile to another cathode connection. 2-2 In case of a failure of continuity rings at some points, current t will be able to flow from pile to cathode by another way on the ring because of it s meshed structure. Consequently it is prevented that any pile will l not stay unprotected because of some failures on continuity system.

7 Figure 1: Basic Diagram of Cathodic Protection System (M13)

8 Figure 2: T/R Unit & Distribution Boxes Placement

9 Anodes hanged into the Sea Anodes will be hanged into the sea from the holes located on the precast slabs with a special hanging mechanism. By this way anodes will be placed center of the piles. Thus uniform current distribution around the piles will be obtained. There will be anodes between each row (B & C, C & D, D & E) to protect whole piles uniformly. Special anode hanging mechanism consists of unique parts developed for this project. Anode hanging box, hanging rope, anode to rope fixer (spacer), deep weight, etc forms this mechanism. All forces caused by the weather conditions absorbed by this mechanism. Consequently anodes will not exposed to any external loads. It is designed for worst conditions described d in TS-02 design specifications sheet.

10 Figure 3: Anode Hanging Mechanism

11 Anode and Cathode Distribution Boxes All the cables from anode and cathode connection boxes on modules s will enter distribution boxes first. Then they will be connected to T/R units in these boxes. In anode distribution box, anode cables will be divided into two parts and each of these connected to one T/R unit. Connection diagram could be seen n on Figure 1. There is a compact switch inside the anode distribution box. This s is used for combining each two anode groups as one group to protect whole module with one T/R unit in case of other s s failure. Shunt resistances will be placed into the box for each anode ring and their currents could be measured one by one from this box. Also special resistors will be placed for each anode ring to control the current flowing on. As it is on anode distribution box, cathode cables divided d into two parts and they are connected to relevant T/R units inside the cathode distribution box. There is also compact switch inside the box to get one cathode ring on module to direct all cathode connections to one T/R unit.

12 Reference Cells placed on pile surfaces There are years life Ag/AgCl AgCl reference cells on each module. 6 of these connected to one T/R unit and other 6 to second T/R unit. Reference cells will be placed to most important points like high potential zone (near to anodes), low potential zone (far from anodes) and average potential zone to follow f cathodic protection system generally. Reference electrodes will be mounted d to pile surface s with a special apparatus. Reference electrode connection boxes will w be placed on precast slabs of modules as specified in the project. They will be provided with the original cables supplied by the manufacturer. After connection boxes, b reference cells will directly connected to relevant T/R unit. During the commissioning c all piles are going to be checked manually by diver and CP Engineer. Measurements will be reported to LISCO. In case of need, LISCO cp maintenance team could measure all the piles manually by portable reference cell with a help of diver.

13 Figure 4: Referece Fixing Mechanism

14 Details of Transformer/Rectifier Units:

15 General Properties of T/R Units TR Units will be oil cooled type. T/R units will consist of two parts. Bottom part will be oil tank. Transformer and heat generating elements (semiconductors, ctors, current transformer) will be located inside this part. There will be surface expander elements (radiator panels) on the outer surface of the oil tank to increase the heat transfer surface and rate. Silica gel breather will prevent the humidity to affect the heat transfer oil inside the tank. There will be also analog oil temperature and level indicator on the tank. Control panel will be mounted on the e oil tank. Electronic control cards, Analog to digital converters, fast circuit cuit breakers, lightning arresters, compact circuit breakers, cable glands and SCADA equipments will be placed in this panel. Front side of the control panel, there t will be user interface consisting of led indicators, Digital DC meters and adjustment buttons.

16 Technical Details of Rectifying Stack T/R unit has 3-phase 3 toroidal transformer. Transformer output enters to rectifying bridge diodes first. After diodes there are uf input capacitors. These are filtering the produced DC voltage by diodes. For driving this DC voltage to cathodic protection system, there is a module IGBT (Isolated Gate e Bipolar Transistor) consisting of two IGBTs.. PWM (Pulse Width Modulation) signals produced by the control card, drives this module IGBT to produce required voltage for the cathodic protection system. There is also a unique output t filter consisting of 2 mh current transformer and uf output capacitors to reduce the ripples caused by the rectifying operation below %1 of output voltage. These ripples can damage the mixed metal oxide coating on titanium anodes when they are not filtered well.

17 Technical Details of Control Operation There are 3 different working modes on T/R units. First one is Continuous Automatic mode. At this mode, operator can set the reference electrode voltage that kept constant. T/R unit adjusts the rectifying stack by producing proper PWM signals to keep the reference electrode set voltage constant on demand. There are 6 reference electrodes connected to T/R unit. Operator can select t one of these by step switch placed on the user panel to be kept constant. Second mode is Continuous Manual.. Control system keeps the output current determined by the operator constant. In case of reference electrode or analog to digital converter failures, operator can use this mode to protect the system. The last mode is Independent mode. At this mode T/R unit acts as adjustable voltage source (Variac). Operator can set the T/R unit s output voltage independently to current or reference electrode measurements.

18 Details of SCADA System Figure 5: M13 SCADA Diagram

19 All T/R units on Bulk Berth No: 2 and Loading Berth will be connected to SCADA system for monitoring cathodic protection system. T/R units will be connected to SCADA computer with special data cables (with spares). Data transmission between T/R units and SCADA monitoring computer will be MODBUS RTU R protocol on RS-485 serial communication method. There are two MODBUS devices on each T/R Unit. One of them transfers the data on T/R Unit s s control section (Set reference cell measurement, DC output voltage, CP current, working mode, set value, error codes and temperatures). Second device transfers 6 reference cell readings, DC output voltage and CP current. These two MODBUS devices will also be connected to different data lines. In case of a failure of one e of these two MODBUS devices in one T/R unit or one of these two different data a lines, system could be monitored continuously by this way. A special SCADA software will be developed for monitoring LISCO Port Bulk Berth No:2 and Loading Berth cathodic protection system. There will be separate windows for each module to watch cathodic protection system detailed. A Sample view of Module 13 can be seen on Figure 5. There will be one main n window to monitor whole cathodic protection system. All T/R Unit outputs, reference cell measurements, error codes will be monitored on this screen. The operator will be able to access each module s s detailed window on this screen.

20 Each cycle of readings of Bulk Berth No:2 and Loading Berth cathodic protection system will be completed about 20 seconds (44 MODBUS Devices). All A data on the windows will be automatically updated at the and of the cycles. SCADA system will record all these measurements and error codes of 11 modules in excel format minutely, daily, monthly and yearly as separate files and directories, thus the operator will be able to examine the cathodic protection system s s past historically. There will be also graphical interface to see s the changes on CP system easily displaying all measurements. SCADA system will also supply remote monitoring on LAN (Local Area Network) or internet. By this way, the operator will be able to control and monitor the cathodic protection system with another computer connected to internet or LAN.