A friend has a stainless steel commercial dishwasher in his restaurant.It is 2 years odl aand rust and pitting is starting to appear.What could be the cause.The pitting is in a non welded area so I don't think disbursement of chrome is an issue.LOw grade stainless steel perhaps?

No stainless is stain-proof without exception. Low grade is probably the most likely. Does your friend dry out the dishwasher between uses? To pit, I would think long term standing water or acidic water would be needed. Stainless can also suffer chloride corrosion in higher concentrations/temperatures which may result as water droplets evaporate as the washer air dries. May want to experiment with detergents.