Galvanic corrsion is not just a problem with titanium. Even high alloy SS used to retube HX's with muntz tubesheets develop galvanic corrosion of the tubesheets after 20 years that threaten the life of the HX (and its the tubesheets that go bad).
Same with SS tube retubes of brass or CuNi tubed condensers with steel tube-sheets.
Getting the right metals to prevent galvanic or using other methods to control it is a huge deal for long life HXs. Titanium is far worse than other alloys - and you really have to be careful (AL6XN, SeaCure, and other super ferritics are also an issue - and I have a lot of experience using them -and desiging appropriate tubesheet, baffle, and shell materials to set down things in small enough increments to not have galvanic corrosion issues within the HX and in the attached piping system.
You cannot install sacrificial anodes on a tube-sheet to protect it or the tubes. There have been attempts to use impressed current - and if that is set wrong it destroys the tubes or the tube-sheet (as many plants can attest)
Plate HX's are fine on closed loop cooling systems. But raw water cooled heat exchangers often cannot be adequately filtered at a reasonable cost. It's quite common to have duplicate HXs and just clean the HX as the most cost effective way (you open them up and run brushes, scrapers, or hydrolance down the tubes).
We did retrofit large self cleaning rotary baskets on one set of raw water HXs for the bulk fouling that occasionally occured; and then found that at least once a year that even those plugged up and the bypass opened during major fouling events; and we had to clean the HXs anyway. When we replaced the HX's we removed those strainers as they were not helping much (and the new HX was designed to handle a lot of fouling).
Even a lot of normal industrial and power plants NDE heat exchangers to locate degraded tubes and shells. Its a lot cheaper to preventively plug and repair shells than wait for the failure.
Where there are hazardous chemicals or safety critical applications... more NDE is done, and done more often. Leaks can be very costly.
Do you prefer the metric system or the imperial system?
↑ View this comment's parent
← View full post
Galvanic corrsion is not just a problem with titanium. Even high alloy SS used to retube HX's with muntz tubesheets develop galvanic corrosion of the tubesheets after 20 years that threaten the life of the HX (and its the tubesheets that go bad).
Same with SS tube retubes of brass or CuNi tubed condensers with steel tube-sheets.
Getting the right metals to prevent galvanic or using other methods to control it is a huge deal for long life HXs. Titanium is far worse than other alloys - and you really have to be careful (AL6XN, SeaCure, and other super ferritics are also an issue - and I have a lot of experience using them -and desiging appropriate tubesheet, baffle, and shell materials to set down things in small enough increments to not have galvanic corrosion issues within the HX and in the attached piping system.
You cannot install sacrificial anodes on a tube-sheet to protect it or the tubes. There have been attempts to use impressed current - and if that is set wrong it destroys the tubes or the tube-sheet (as many plants can attest)
Plate HX's are fine on closed loop cooling systems. But raw water cooled heat exchangers often cannot be adequately filtered at a reasonable cost. It's quite common to have duplicate HXs and just clean the HX as the most cost effective way (you open them up and run brushes, scrapers, or hydrolance down the tubes).
We did retrofit large self cleaning rotary baskets on one set of raw water HXs for the bulk fouling that occasionally occured; and then found that at least once a year that even those plugged up and the bypass opened during major fouling events; and we had to clean the HXs anyway. When we replaced the HX's we removed those strainers as they were not helping much (and the new HX was designed to handle a lot of fouling).
Even a lot of normal industrial and power plants NDE heat exchangers to locate degraded tubes and shells. Its a lot cheaper to preventively plug and repair shells than wait for the failure.
Where there are hazardous chemicals or safety critical applications... more NDE is done, and done more often. Leaks can be very costly.