It is possible to have internal canals in an object, but there are some limitations; the canals need to be at least 5 mm on average in diameter (this size might need to be larger depending on the length and form of the object).
Should the 5 mm minimum diameter not be respected, there may be powder remaining inside the canal. Generally, if the canal has a simple form that does not twist or have right angles, the excess powder can usually be removed with a paperclip or a needle.
Should the internal canal have several 90° bends, the excess powder will be tough to remove; if this is the case, the Sculpteo customer support team will contact you before printing the object to see if you are willing to accept the risk.