How we developed technology for site stress of sphere.

In refineries and fertilizer plants liquefied petroleum gas and ethylene are stored at room temperature in spheres. These spheres are built from individual steel petals hot or cold pressed and assembled at site Depending upon the pressure and the diameter of the sphere the steel plate thickness can be as high as 65mm. The total weight of the sphere can be few hundred tons. BHPV,for some time had a monopoly in this business. After welding the sphere it has to be stress relieved. Stress relieving involves heating the sphere to a temperature of 580degC to 620degC depending on the plate thickness and composition and holding at this temperature for one two hours depending upon the thickness and cooling it slowly to room temperature. Since the sphere cannot be put in a furnace, the sphere itself is converted in to a furnace. A high velocity gas burner is fitted at the bottom of the sphere. The sphere is externally insulated and a number of thermocouples are fixed on the surface of the sphere which are used to monitor the sphere temperature.

The heart of the process is the high velocity gas burner. Initially a company from UK was contracted to carry out the stress relieving. This involved spending foreign exchange which was, before 1990 was not available easily and the logistics of getting the UK firm to come and perform stress relieving was very daunting.
The Management gave the assignment to R&D to develop the burner and stress relieving technology. We decided that chemical engineering group should handle this assignment.