The risers are pipes through which the drill string carries out the drilling function. A marine drilling riser system provides a tubular conduit from the drilling unit to the subsea blow out preventer (BOP) and the wellbore below it. The riser assembly guides down whole tools and equipment from the surface to the wellbore, permits drilling fluids circulate back to the drilling unit, and carries the BOP stack as it is run or retrieved. The drilling riser is composed of a series of joints which are connected by couplings. Choke and kill lines for the BOP are run integrally down the outside of the riser tub along with other auxiliary lines. Typical risers are usually 75ft in length and 30t in weight.