Cool solution for the Big Heat
15 Jan 2000
Unusual situations call for innovative thinking. When Merseyside-based Mannings Thermal and Environmental Engineers was asked to assist with the heat-treatment of a pair of 19m-diameter spheres at the Abu Dhabi National Oil Company's RPG blending facility in Ruwais, the problem was particularly knotty.
The spheres - probably the largest ever built in the Middle East - are intended to store liquefied propane. Each one weighs some 500t and is made of two-inch-thick steel. The stresses involved in fabricating these structures are colossal, and these internal stresses have to be relieved by a post-weld heat treatment. This involves heating the metal to 630 degrees C at a specific rate, maintaining that temperature for a set length of time, and cooling it back to ambient temperature.
Normally, this would be done in a precisely-controlled furnace. However, this was obviously not possible, so Mannings decided to turn the vessels themselves into a furnace, by insulating the outside of the vessels and heating them from the inside.
The outer surfaces of the vessels were covered with mineral wool insulation, and two gas-fired portable high-velocity combustion units were used to heat the inside of the vessels. These units, which incoporate a gas burner, fan and flow regulator, produce a stream of heated air.
