Pressure Tank Fabrication Specifications Were Not Followed

Low-Pressure Tank Fabrication Specifications Were Not Followed 

Many vertical low-pressure storage tanks containing flammable or combustible liquids are designed with a weak weld seam on the wall-to-roof connection. This loss prevention feature allows the roof to separate and peel back if an internal fire, an internal explosion, or just a pneumatic overpressure situation occurs within the tank. If the roof relieves or is blown off, the liquid is still contained within the walls if these tanks are properly designed and fabricated. These conical roof tanks are often built to the American Petroleum Institute (API) Standard 650 Welded Steel Storage Tanks.  

There is one documented report that a welder had good intentions when he decided that the standard of welding for the roof-to-wall seam was inadequate. This well-meaning welder added a full strength weld to join the roof to the walls. [2] There were no reported problems on this tank, but the safety feature was rendered ineffective. 

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