A common misconception among vacuum tanker operators is that stainless steel doesn’t corrode.
Like all metals, stainless steel will corrode under certain conditions.
DPI Inspection of a Stainless Steel Vacuum Tank
Recently, we were asked by a client to inspect a stainless steel vacuum tank that was leaking through the tank wall. Internal inspection of the vacuum tank using dye penetrant inspection (DPI) revealed that the inside surface of the vacuum tank had been severely damaged by pitting corrosion.
In the image below you can see the small pin holes we found in the stainless steel wall of the vacuum tank.
Pitting is a localised form of corrosion which can occur as a result of exposure to specific environments, most notably those containing chlorides.
The passive layer on stainless steel can be attacked by certain chemicals. The chloride ion Cl- is the most common of these and is found in everyday materials such as salt and bleach. This vacuum tank was manufactured from a 304 grade stainless steel that was known to regularly carry waste liquid containing sodium chloride in solution.
It was concluded that the chloride ions present in the liquid waste most likely contributed to the pitting corrosion found inside the stainless steel vacuum tank.
The pitting corrosion was weld-repaired using a qualified weld procedure and qualified welder taking care not to damage the metallurgical properties of the original stainless steel plate.
Pitting corrosion is avoided by making sure that stainless steel does not come into prolonged contact with harmful chemicals or by choosing a grade of steel which is more resistant to attack
Take care selecting the correct grade of stainless steel for your next vacuum tank application. Please contact us if you require assistance.
