As per API 650/ Section-5 ( ERECTION) para 5.1.3 -- "Paint or foreign material shall not be used between surfaces in contact in the construction of the tank proper, except as permitted by para 5.2.1.9." Now para 5.2.1.9 states -- "If protective coating are to be used on surfaces to be welded, the coatings shall be included in the welding procedure qualification tests for the brand formulation and maximum thickness of coating to be applied." Now I have tried weldability performance of carbon steel coated by Inorganic Zinc Silicate and it is OK. Radiography is OK. Now for Organic Coatings like high Build Coal Tar epoxy as applied soil side of bottom plate during butt or lap Joints can there be any problem if I would like to apply para 5.2.1.9. I have done a 5" length test piece and it is OK. RT Ok. Only some paint burning noticed but no weld metal porosity and RT OK. But while production welding welders are reporting that they are feeling some positive pressure which tries to lift up the weld pool and also in many areas a high-low type configurtion alongwith some underfill noticed. There is also an arguement that Bottom Plate soil side 2" edge width has to be left unpainted. But there are many to oppose this intentional non-painting approach. Paint is high build Coal Tar Epoxy. Any one having any suggestion/ comments/ operating experiences pl. share.