What are the root causes of leakage

What are the root causes of leakage in the front two body?The first three body casting processes are using large risers and large pads, The foundry wants the way that the castings will cool first and the risers cool later (We call this sequence solidification ),they think this the riser will fill the big heat junction then  Solve the problem of porosity at the big heat junction, But after casting the first and second bodies we found some defect in the bottom of the risers, The foundry thought the risers and the pads maybe too small, So they put some more bigger risers and pads at the 3nd body casting . But the defect below the riser is also bigger too, after discussion the foundry find the riser cools first and the casting is cooling after the risers this causes a lot of porosity inside the casting near the riser, this made the casting has a bad compactness just near the risers. Because the compactness inside the casting is not good ( We can also call it casting porosity ) so the body is leaking.  Why is the 3nd body more serious than the first?They put some more bigger risers and pads at the 3nd body casting Because the pads are bigger than before and the pads are on the casting body, And at the same time, the heat junction are getting bigger too. What is the current corrective action plan now?Removed the 8 Risers on flange, Use chilling iron to cool the hot junction area.( Same time solidification) Remove casting porosity caused by temperature difference. the 3nd body simulation is perfect Why does the valve body leak?Simulation software needs to collect actual production data to improve and modify to be accurate , Because of the high nickel material is special There is no such material in the simulation software system this cause a big difference between the simulation results and the actual production results. But after several time trying, the simulation software has been further improved.