In the September and October 2010 issues, POWER Contributing Editor David Daniels explored the causes and damage mechanisms of condenser tube leaks (“Taming Condenser Tube Leaks,” Part I and Part II). Dennis J. Schumerth, Valtimet’s director of business development, took issue with several of Daniels’ statements regarding the proper use of titanium condenser tubes. We have given Schumerth the opportunity to express his concerns and for Daniels to reply.
Schumerth: I believe the article does not accurately represent the track record of titanium condenser tube materials. Titanium has performed without one reported corrosion event in a surface condenser application for over 40 years. In Part II, Daniels noted that “Series 300 stainless steel alloys, such as 304 and 316L, are now fairly common in new construction in both freshwater and seawater applications.” Historically, neither of these alloys are considered appropriate for seawater applications.
Daniels: I stand corrected. I should have said that stainless steel alloys are common in freshwater condensers.
Schumerth: One paragraph in Part II states that “Titanium alloys, though typically considered immune to corrosion from the cooling water side, have failed due to impingement from saturated steam dump lines in the condenser.” Condenser tube failures can occur with any tube material but have been particularly troubling with steam dump lines in combined cycle (CCGT) plants. These cyclic fatigue failures have been classically related to improper operation or design of the plant digital control system, manufacturing deficiencies, or a suspect condenser specification.
Daniels: The theme of both articles was that, regardless of the condenser metallurgy, the plant must remain vigilant and quickly identify and correct any contamination from a condenser tube leak before it damages the rest of the steam cycle—not to recommend one type of condenser tubing over another. The intended message of this paragraph was that, just because a plant has a titanium condenser, it doesn’t mean that it will never get a condenser tube leak. Titanium tubes can fail due to erosion from poorly designed steam headers or from freezing, just like any other condenser tube material.
Schumerth: Later in the same paragraph, the article notes that “they [titanium tubes] can also suffer from failures if steel tools scratch and penetrate the protective titanium oxide layer.” The technical literature supports this concern, suggesting precautions be taken with all titanium alloys to remove or avoid surface iron contamination, but this type of pitting does not occur below 170F, well above the typical condenser operating temperatures. Indeed, carbon steel condenser tube cleaning apparatus are commonly used.
Daniels: I appreciate the enlightenment and will research that point further.
Schumerth: The author also states that “A very few cases of corrosion in titanium tubes have even been ascribed to MIC.” We disagree. The technical literature and our experience has identified many materials susceptible to MIC while titanium was identified as immune to any attack.
Daniels: I agree that titanium alloys are generally considered immune to MIC. The cases where MIC was suspected on Ti Grade 2 were under very unusual conditions where SRB bacteria destroyed the protective oxide coating on the titanium. This is certainly not a normal condition for power plant condensers, as was clearly pointed out in the article.
Schumerth: The author also states, “However, titanium tubes are still subject to biofilm accumulations that can slow the flow, etc.” This statement should include just about all tube materials rather than just titanium.
Daniels: The sentence just prior states that stainless steel tubes often have MIC issues and that MIC is an all-encompassing problem in condenser tube materials and that titanium tubes are not immune to biofilm accumulations.