Why LPG Storage Tanks are Made Horizontal ?
It is said that many LPG storage tanks or vessel should be horizontal,and in general observation it is horizontal.I want to know that what is design logic behind it.
Originally for large LPG storage tanks ,the inventory control was based on measurements made by a person who had to climb up a ladder to read the gauge glasses on the tank.For large tanks,this would have meant a lot of extra climbing and would discourage the operators from do their job as well as they should.To make it easier,they used horizontal tanks which limited the amount of climbing.
Another factor is the need for NPSH for the transfer pumps,this can mean extra height for the bottom of the tank so it can be fully emptied.In some cases this could add an additional 5 to 15 feet to the skirt on a vertical LPG storage tanks.This increases wind loading and the need for a larger foundation.
For the same tank volume the vertical tank will have slightly higher pressure at low point due to static head effect.So in time from fill to empty pressure cycle will be greater for vertical tank.
Most LPG storage tanks are mass produced.Their thickness is worked out to the nearest 1/10th of a millimeter.Static head is an issue.Also,large vertical tanks are liable to additional loads and are more expensive thus less popular.