Care, handling, storage and cleaning of stainless steel headboxes

Stainless steel is corrosion resistant because it has the ability to form and maintain a thin, transparent, protective film of chrome oxide. Under normal conditions, this film is self-healing should it be destroyed.

As long as the film of chrome oxide is maintained, the stainless steel behaves like gold, silver and platinum, or in other words, it has a passive behavior. Stainless steel can also develop active sites if the protective film is destroyed by scratches, nicks, stock deposits or contamination by mild steel or nonferrous inclusions.

A cell develops between the active and passive areas if a suitable electrolyte is present. In the closed loops of today's paper machines the white water system provides a very good electrolyte for these cells. The more dissolved solids and the higher the temperature of the electrolyte - the faster the rate of corrosion.

Care, handling and storage of stainless steel

• Provide clean indoor storage places such as clean racks, shelves and platforms, and using covers where possible.
• Provide storage places well removed from sources of mill dirt or other contamination. Fine particles of scale from carbon steel fabrication or fragments of other metals undergoing work should be prevented from collecting on exposed metal.
• Avoid walking over stainless material with shoes that are dirty or that may contain heavy iron hobnails.
• Handle with clean gloves or handling cloths to guard against residues of human perspiration (finger marks).
• Avoid scratching with sharp tools or abrasives containing iron.

Cleaning a stainless steel headbox

NOTE: Never use a metal instrument for cleaning.

CAUTION: Be careful not to damage the slice area in connection with cleaning and maintenance of a headbox.

Cleanliness and care in handling, storage and installation are extremely important for the prevention of corrosion to stainless steel. Among the preventive measures that should be observed are the following:

• The inside surfaces of a headbox are precision ground and electropolished. These surfaces must be handled with care as the slightest scratch can cause chemical corrosion and deposits.
• Only use equipment that will not leave scratches when working inside the headbox.
• Smooth headbox operation requires that the inside surfaces are kept as clean as possible.
• Clean the headbox with a wooden or plastic putty knife and a soft brush, as appropriate.
• Check that the temperature of the cleaning water is close to that of the headbox structures.
• Alkaline detergents or petroleum based solvents can be used for removing any dirt buildups from the inside surfaces of the headbox. Solvents are needed for removing pitch sticking to the inside surfaces, for example. Kerosene, turpentine, or Lensitil will work well. Use liquids and appropriate cleaning devices for cleaning.
• Nitric acid passivation can be performed after a thorough cleaning to prevent dirt accumulation and to improve corrosion resistance. Personnel performing a passivating operation should be protected with rain gear, rubber boots and gloves, and either a face shield or goggles. When the passivating procedure is performed on the paper machine, care should be taken to protect the fourdrinier fabric or suction breast roll so they aren't contaminated with the passivating mixture. Flush these areas thoroughly if there is any reason to believe they have been contaminated.

CAUTION: Should any of the passivating mixture get on the skin, the affected area should be flushed immediately with clear water followed by 5% of sodium bicarbonate. (Have this 5% solution readily available.)

• Store the cleaning device in its box. Make sure the plastic parts of the cleaning device are protected against sand and other coarse dirt. All hose couplings used with the cleaning device must be such that they will not scratch the flow surfaces.

Special precautions when cleaning a stainless steel headbox with chemicals

CAUTION: Do not clean the headbox with sulfuric or hydrochloric acid.

CAUTION: Never use any bromine-containing anti-slime agents or detergents during cleanups and production.

For more information on care, handling, cleaning and passivation of stainless steel, contact your Valmet representative for training options.