Project name: Huaneng Guangdong Power Plant No.1/2 Condenser Water Chamber Cathodic Protection Renovation Project Case
Project affiliated unit: Huaneng Guangdong Power Plant
Construction unit: Qingdao Yinghai Corrosion and Fouling Control Technology Co.,Ltd
Huaneng Guangdong power plant no.1/2 unit, circulating water water source adopts estuary water containing salt near the seaport (sea fresh water), check in 2006, Cl-,18326mg/L. Condenser water chamber board and pipe board adopt austenitic stainless steel (pipe board and cooling pipe connection adopt casing pipe TP321 as transition, welding adopt TP316 welding stick and two adjoining plane). Condenser pipe adopts ferritic stainless steel (American SEA- CUBE). Corrosion problems and measurement is following:
Corrosion cause
There is potential different between different stainless steel materials, easy to have crevice corrosion and electrocouple corrosion. Cooling pipe end will lead to stress corrosion due to the residual stress of expansion pipe, corrosion caused by turbulent flow of pipe end and precipitation caused by impurity and so on. These factors may have caused great damage to the performance of condenser.
Anti-corrosion protection methods choice
The condenser corrosion of this system belongs to electrochemical corrosion, the solution of electrochemical corrosion is to adopt coating and cathodic protection. Condenser water chamber cathodic protection adopts sacrificial anode, and requires to adopt impressed current cathodic protection.
二、 key technology
1. Control ways choice:
sea and fresh water alternate, water resistivity alternate, under this condition, instrument work status adopts constant potential control state.
2.Auxiliary anode
The design and distribution of auxiliary anode should make anodic current reach the most remote center of the pipe plate. Only this way can get better anti-corrosion effect. Water chamber installs auxiliary anode.
3.Reference electrode
According to the water-fresh water, we choose to the high zinc reference electrode. In order to measure pipe plate potential accurately, water chamber must design and install reference electrode.
4.Electrode cable outlet sealing device
Cable outlet water chamber, the derivation must not leak, design and product should meet this demand.
三、Cathodic protection principle and system configuration (project scale)
2 sets 300MW unit, 1#,2# condenser
Main technical index
Protective potential should achieve 0.55~ 0.3V (relative high zinc reference electrode, austenitic stainless steel, NPRE<40)
Note: NPRE=%cr+3.3%(Mo+0.5W)+16%N
四、main equipment and operation management
Main equipment: auxiliary anode (model YHMOL-2225X，ø25X210 front water chamber used; YHMOL-2225X，ø25X420 back water chamber used), reference electrode (model YH-REZ-L1), potentiostat, cable and equalizer and so on.
Picture 1, electrochemical protection system circuit diagram and electrode installation drawing
五、project operation condition
Effect after protection: good operation condition for 4 years, significant protection effect.
The following pictures are shown according the before and after protection.
before protection:
There is a large area corrosion in pipe board and heat exchanger tube end, and pipe board coating edge.
Picture 2. pipe board and heat exchanger tube corrosion condition
Picture 3. coating damage and coating edge corrosion condition
after protection:
a. The water chamber is covered with protective uniform color overlay, cathodic protection effect is very good.
b. Pipe board have no obvious corrosion, coating or overlay have no damage basically, the surface is colored uniformly.
c. Rise mouth part, we use water or cloth to wash and wipe, after erasing, the most of swelling is not corroded.
Representative pictures are shown as follow:
Picture 4. 1# condenser water chamber corrosion condition (A,B condition is same basically)
Picture 5. 1# condenser A inlet pipe water picture 6. 1# condenser B inlet water pipe
plate corrosion condition plate corrosion condition
Picture 7. 1# condenser A fixed end bulge part picture 8. 1# condenser B fixed end bulge part
corrosion condition corrosion condition
