Case Study on Integrated Protection for Seawater Condensers (Comments are welcome)

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Those of you who have valuable insights and practical experience are welcome to share them; I will also continue to provide examples in this area. Thank you. L B10 essentially causes \"infantile corrosion.\" For L B10 copper pipes, coating treatments are used to accelerate the formation of a protective film made of water and iron oxide on their surface. External current cathodic protection measures are applied to the pipe boxes and covers, but their effectiveness is limited and maintenance can be difficult. However, it is advisable to use sacrificial anode cathodic protection for the pipe boxes and covers. Comment by Zou Jiqiang, August 9, 2016. 1. Project Overview: The thermal power plant of a certain petrochemical complex is equipped with 4 seawater condensers; before the implementation of protective measures, these copper tubes experienced frequent leaks. B10 copper tubes begin to leak after 8-9 months of operation in seawater, and after 2 years of use it becomes necessary to replace the copper tubes in the condenser. Two of them (A and B) had 64 tons of B10 copper tubes replaced, worth 1.17 million yuan. After tube replacement, sponge ball cleaning and ferrous sulfate film-forming technology were employed. During the maintenance inspection, it was found that corrosion still existed at the inlet end of the updated copper tubes; therefore, based on the above two techniques, it was decided to first apply forced current cathodic protection to condenser A (HA177-2 copper tubes), thereby providing combined protection for the condensers. 2. Process parameters: The condenser is of the N-300II type, a split dual-flow surface-type condenser. The cooling water temperature is 15–35°C, with a flow rate of 9 kt/h; the exhaust gas temperature is 50–55°C, and the flow velocity of the cooling water inside the copper pipes is 2.3 m/s. The cooling area is 9,000 m2, with a total of 5,408 copper tubes of Φ25mm*1.25mm*7220mm. The tube sheet is made of HSn62-1 tin brass, while the water chamber is constructed from Q235 steel (lined with fiberglass). The cooling water is a mixture of seawater and fresh water; its quality differs from that of ocean water, with a lower salt content, but higher oxygen and suspended solids levels, resulting in greater corrosivity. 3. Joint protection measures: (1) Sponge ball cleaning – Every 2 days, sponge balls are placed in the cooling water; they then flow into the copper tubes of the condenser, thereby cleaning the inner walls of these tubes. 400 pieces are thrown each time (accounting for 7%-8% of the total number of copper tubes), and the cleaning time is about 30 minutes. (2) FeSO4 film formation: FeSO4 is added to cooled water, and an \"open sponge ball\" method with high flow rate and low concentration is used, consisting of a pre-film formation step and a follow-up film reinforcement step. The amount of FeSO4 added (as Fe2+) was 3–5 mg/L. During the pre-coating phase, treatment was carried out continuously for 96 hours at a flow rate of 1–3 m/s; during the re-coating phase, it was added every 2 days for 1 hour each time. (3) Forced current cathodic protection adds cathodic protection measures on top of the aforementioned two techniques. ①Determination of cathodic protection parameters: The controlled potential at the tube ends of the A condenser (HA177-2 copper tubes) is -900 to -1000 mV (Ag/AgCl). The cathodic protection current density for copper pipes is 150 mA/m2, while that for the water chamber is 10 mA/m2. The calculated cathodic protection current intensity for the entire condenser is 60A. ②The cathodic protection system mainly consists of an anode, a reference electrode, and a DC power supply. a. Anode device: The platinum-titanium anode is rod-shaped, with a diameter of 45 cm and a length of 180 cm; its effective current-carrying area is 270 cm2. It is installed on the manhole cover. b. Reference electrode device: The powder-pressed Ag/AgCl reference electrode has a diameter of Φ19mm and a length of 20mm. c. Power supply unit: Silicon rectifier low-voltage DC power supply (24V/50A) ； F potentiostat (35V/50A). ③Regarding the operation of cathodic protection, the average potential of the copper tubes in the condenser was -0.85 to -0.95 V (Ag/AgCl). The cathodic protection current was 4 to 6 A for the inlet and outlet water chambers of series B, and 1 to 2 A for the middle water chamber of series B. The average total voltage was 8 to 9 V, the average total current was 20 to 40 A, and the actual average power consumption was 600 W. 4. Protection effect: After being equipped with cathodic protection, FeSO4 film formation, and sponge ball cleaning techniques, Seawater Condenser A has been in operation for 10 years without any issues, and the lifespan of its copper tubes has increased by nearly 5 times ； The annual leakage rate decreased from 5% to 0.11% ； Annual economic benefit of 1 million yuan ； It changed the previous passive situation in which the copper tubes (5,408 pieces) had to be replaced entirely after just 2 years of operation