I am having trouble with the fire test of big dimension floating ball valves. And I will appriciate your comments if you have an idea about the possible reasons.The testing of small diameters(DN50) were succesful for both floating and trunnion ball valves. But when we tried the DN150 floating; although the burning period was OK with very little amount of leakeage; after the burning period, During forced cooling, the valve starts leaking with a high flow rate of water. We experienced the same failure twice and I need to find a solution to be certified by a third party. Is this a soft seat or metal seated ball valve?Solid or hollow ball?The method of testing is critical for either, I've had many a failure because of the wrong methods used by a test house, there is a real 'art' to getting through these believe it or not. Will respond when I know more.Geometrically a linear increase of the diameter will give a second degree curve increase of opening area and a third degree curve increase of volume. This will to a certain degree be true for all main parts of the ball valve.This will again lead to different heat amount transferred and contained in the different parts, different amounts of material exposed to different temperatures at different time-curves, different expansion and contraction and different mechanical forces from size to size.What exactly is causing the failure is of course impossible to guess without knowing the exact construction and damage after the test, but something constructional has obviously to be altered/strengthened in the larger dimension ball valve, to compensate for the different forces working on the larger valve.

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