Connecting the bottom of the furnace to the boiler shell plating is a seamless Ogee ring. This ring is pressed out of thicker plating than the furnace; the greater thickness is necessary since circulation in its vicinity is not as good as elsewhere in the boiler and deposits can accumulate between it and the boiler shell plating. Hand hole cleaning doors are provided around the circumference of the boiler in the region of the ‘Ogee’ ring.
Figure above shows the method of attachment of the furnace and Ogee ring for Cochran and Clarkson welded boilers, welded to Class I Fusion Welding Regulations. ‘Tell-tale’ holes drilled at equal circumferential intervals in the boiler shell enable leakage between the ‘Ogee’ ring and the boiler shell to be detected.
“REED’S GENERAL ENGINEERING KNOWLEDGE FOR MARINE ENGINEERS”, by Leslie Jackson and Thomas D. Morton