Steam generators boiling and passivation

Despite being newly built, inside the generator there are phenomena of agglomeration of residues caused by mechanical works such as rolling, wire-drawing, assembling, welding, sandblasting and possible conservation operations that could take place inside the generator through the use of protective and antioxidant oil and/or paint. In addition to this, oxidation of the pressing surfaces may be present because of hydraulic tests generally performed with untreated water without post-drying, or any condensation related to open-air storage of products before assembling them. Most of the dirt we find is usually due to:

  • Oils and fats which, due to their saponification properties in the presence of alkalines, may form foam within the generator
  • Paints, usually produced with organic products of phenolic, acrylic and epoxy nature, can create organic acidic and carbon residues through the breaking of their compounds.
  • Silica sand, processing scales, welding slag which by their hardness and the speed with which they are transported by steam through the flow of distance within the tubes, can create strong erosion through a sanding action on the crossed mechanical parts such  as curves and valves, in addition to the potential occlusion of measurement and control systems such as levels and pressure intakes.
  • Metal oxides: their layer locally reduces the heat exchange coefficient because they are not perfectly adherent and can create “permeable interspaces” where the pH can promptly rise thus creating areas of metal fragility linked to the high alkalinity (caustic fragility), as well as possible phenomena of hydrogen infiltration in the crystallographic structure of the metal.
For these reasons, it is recommended to perform an alkaline chemical wash (boil-out) on a new steam generator before it is put into operation, followed by an acid one and a passivation, necessary operation for the proper formation of a stable oxide layer on the metal

surfaces with a compact and protective crystallographic morphology against corrosion, in addition to a strong resistance to degeneration, necessary condition during start-ups/stops and any changes in production load. NPC srl oversees all the operations described above, ensuring a turnkey service, if needed also through the supply of auxiliary boilers, if it deems impossible to proceed with the ignition of the steam generator that needs to be operated.