This category encompasses any vessel designed to carry liquid cargoes and ranges from the ULCC (Ultra large crude carriers) of about 350/500,000 dwt down to the smallest estuarial tank barge.  Not only do these tankers carry crude oil but also, provided they are so equipped, are capable of carrying clean (Refined or semi-refined) petroleum products or a wide variety of other liquid cargoes.  In describing oil cargoes the term dirty refers to crude oil cargoes and clean refers refined or semi refined products.  It should, however, be noted that within the product trade itself petroleum spirit, kerosene, etc. are naturally described as ‘clean’ whilst products at the other end of the refining scale, such as heavy fuel oil, are referred to as ‘dirty’. Whereas a crude carrier will only take a very limited number of grades of oil, clean product or chemical tankers might well have the capability of taking a large number of different products at one time.  This “parcelling” of cargoes is a common feature, particularly of chemical tankers, designed to take a number of different, and often incompatible liquids carried in separate tanks.  This demands an elaborate pumping and pipe work system to prevent the intermingling of cargoes.  Also, bearing in mind that a number of liquid chemicals react with steel, chemical tankers will have some of their tanks made of stainless steel or coated with special paints such as epoxy or even with rubber.  A chemical tanker operator will always keep a careful note of which particular chemical can be carried in which particular tank, the wrong chemical in a tank with an incorrect coating could have disastrous results. Bearing in mind that liquids as far removed as liquid sulphur via hydrochloric acid and vegetable oils to wine are now carried in bulk, the range of capabilities of chemical tankers has to be wide.