Preventing Boiler Corrosion
is done through the removal of oxygen and maintaining appropriate alkalinity levels in the boiler water to prevent acid attack.
As shown in the chart oxygen levels are tied to the Hot well feed water temperature with nearly all oxygen gone by the time the water reaches 100oC. For this reason, we recommend keeping the temperature above 80oC and incorporating an Oxygen Scavenger such as water valley high-quality Sulphite or Tannin blends featured above. This will help maintain excellent boiler corrosion control and limit the potential for oxidation.
The other risk in an industrial boiler is acid attack which is caused by insufficient levels of alkalinity. Alkalinity naturally builds in a boiler as cycles of concentration increase and in many cases, a bespoke treatment plan will include additional alkalinity builders with a maximum recommended limit of 1200ppm (M Alkalinity) in a Shell boiler running at TDS of 3000ppm. Alkalinity Builders are available as separate chemicals or as part of our Multi-functional Boiler Treatment detailed below.
Multifunctional Products
You may also want to look at our range of Multi-functional Products which combine the oxygen scavenger with a polymer sludge conditioner & alkalinity builder to create a single easy to use liquid to simplify dosing and control.
Boiler Scale Inhibitor & Sludge Conditioning Products
WATER VALLEY
provides two kinds of scale inhibitor
– Polymer only and Polymer Phosphate,
the latter of which is the required option under the following conditions:
⦁ Phosphate must be used in boilers operating at pressures above 19 bar (150 psi)
⦁ The ‘natural’ Alkalinity of the make-up after sulphite addition is less than 20% of the TDS or make-up is dealkalised
⦁ Or when the make-up water is not efficiently softened
Polymer Phosphate treatment regimes precipitate magnesium & calcium hardness salts from boiler make-up water in the form of hydroxyapatite and serpentine. These compounds form sludge, which, when properly conditioned with polymers, is removed from the boiler during blowdown. When a significant excess of soluble orthophosphate and free hydroxide (caustic) alkalinity is maintained in the boiler water, calcium carbonate formation can be virtually eliminated. Polymeric dispersants or sludge conditioners are added with the phosphate to condition the sludge for improved removal from the boiler. boiler phosphate treatment.
Multi-Functional Treatment Products
Multi-functional Boiler Water Chemicals provide the advantage of containing a blend of essential treatments such as an Oxygen Scavenger, Polymer Treatment & Alkalinity Builder to provide a multi-treat solution, this may mean they can be dosed exclusively but in many situations, they may still need to be supplemented by
a Phosphate and Amine Treatment. If your application requires treatment with DEHA or Carbohydrazide these can be found on the Oxygen Scavenger category.
A Steam Boiler treatment program should always include an oxygen scavenger and polymer treatment. It is typical to also include a phosphate treatment especially in applications above 10 bar (150 psi). While it is always necessary to control the alkalinity, where the makeup water is reliably softened the regular use of an alkalinity builder may not be necessary.
Boiler Condensate Protection Products
Where a Condensate Return System is installed your boiler water treatment regimen will need to include preventative measures to protect the condensate line from corrosion. The two main causes of condensate line corrosion are Carbon Dioxide Attack which results in the uniform loss of metal below the water line and Oxygen Attack which results in local pitting. Both of these corrosive attacks can be prevented by the removal of these gases through effective water treatment and mitigation of their effects through the use of Amines. Be aware, the lack of suitable treatment will cause damage and failure of plant equipment.
Removing Oxygen from the boiler is done by two steps, firstly the hotwell feed water temperature should be kept above 80oC as this will remove the majority of oxygen dissolved in solution. The second step is to treat the water with an Oxygen Scavenger such as Tannin or Sulphite which will remove the remaining O2. Where oxygen removal is not possible the use of a Filming Amine will create a protective barrier against the metal within the condensate line preventing oxidation.
Removing Carbon Dioxide is more difficult which is where the dosage of a steam volatile Amine is recommended, this can be by a Filming Amine which creates a thin film barrier on the surface of the metal or a blend of Neutralising Amines which raise the pH of the steam and react with the carbonic acid neutralising it through the generation of hydroxide ions.
