Tea contains tannin compounds that naturally stain surfaces. Tea staining can occur in several places -- not only on the inside of stainless steel teapots or other cookware, but also on stainless steel utensils such as tea strainers and teaspoons, and larger surfaces such as table tops. As tea stains only the surface of stainless steel, you can remove the stains with a mild acid or slightly abrasive cleaning tool.
Unpolished stainless steel
Fill your teapot or other cookware with undiluted distilled white vinegar.
Heat the vinegar until it boils, put the teapot or cookware aside to cool and then pour out the vinegar. If you're cleaning tea stains on an unpolished stainless steel table top or other large item, skip this step.
Rub the stainless steel with a damp non-abrasive scrubbing pad in the direction of the surface grain to remove the tea stains. If you're dealing with a tough stain, sprinkle baking soda or pumice powder on the stain and scrub, using light pressure, to wear away the stain.
Rinse your stainless steel item thoroughly with warm water when finished. If you're cleaning a table top or other large surface, wipe it with damp, soft, lint-free, microfibre cloths.
Wipe the stainless steel dry with cloths to prevent spotting.
Polished stainless steel
Fill a spray bottle with distilled white vinegar. If you plan to use a commercial stainless steel cleaner, skip this step.
Cover the entire stain with vinegar or commercial cleaner. Wait 15 to 20 minutes or for a time frame recommended by the manufacturer. If you're cleaning stainless steel utensils, boil the utensils in a pot of white vinegar, put the pot aside to cool and then pour out the vinegar.
Rub the stainless steel with a cloth to remove the vinegar or cleaner and buff away the stain.
Rinse the surface with warm water or warm, damp cloths. If you used a commercial cleaner, wash the stainless steel with a warm, soapy cloth and then rinse with warm water or damp cloths.
Dry the polished stainless steel thoroughly with soft cloths to shine it.
Never use a cleaner containing chloride to remove tea stains from stainless steel, or steel wool or steel-bristled brushes to clean stainless steel as harsh abrasives and cleaners can etch stainless steel.