The tell-tale signs of corrosion and its preventative solutions is a step toward better preservation and extended service life. The lessons by corrosion solutions company Cortec offer insights for dry and wet boiler layup success.
Dry layup means shutting down and draining the boiler. With inadequate preservation, tell-tale signs of corrosion may show up 4-6 months later when the boiler is filled up and restarted. This is seen in high iron levels of 0.5, 1.0, or 1.5ppm in the boiler water. Such high levels are bad for boilers, as they represent metal loss somewhere in the system. Further, iron can bind antiscalants, dispersants, polymers, and corrosion inhibitors from working properly.
The high iron levels could come from the boiler, steam, or condensate system where corrosion occurred during layup or oxygen pitting was triggered in the critical start-up phase. Since metal loss cannot be recovered once it has happened, prevention is a strategy. Dry layup with Cortec’s Boiler Gecko, Boiler Lizard, or Boiler Dragon depending on boiler size introduces vapour phase corrosion inhibitors into the boiler enclosure, where they form a protective molecular layer on the metal surfaces. The Boiler Gecko and Boiler Dragon can be fogged into condensate tanks or other parts of the steam system. The Boiler Egg can be added as well to protect the steam and boiler system against oxygen pitting during the critical startup phase.
Wet layup is usually done to allow faster start-up. Oxygen pitting above the water level is thus less likely to be noticed until annual inspection rolls around. If oxygen pitting has increased since the previous inspection, and extended wet layup occurred in between the two inspections, chances are that pitting arose from inadequate wet layup. This is common, as traditional sulphite chemistries used to scavenge oxygen do not work in the headspace above the water. Since maintenance and monitoring of sulphites during wet layup is challenging, corrosion can happen below the water level during wet layup, revealing itself by high iron levels in the water at start-up.
In either case, Cortec’s Boiler Iguana is a simple solution. It can be added to the feedwater or condensate system and pumped to the boiler. Due to its combination of contact and vapour phase corrosion inhibitors, Boiler Iguana protects the walls of the boiler in direct contact with the treated water and in the headspace above the water. Frequent monitoring is not required, and the product is effective up to 150°C, which means the boiler can be kept on low fire for faster return to service.
Finding high iron levels or visible corrosion damage inside boilers after start-up can be a big blow. But it can also encourage boiler operators to better protect and prevent premature failure in the future.