WorldWide Drilling Resource

63 WorldWide Drilling Resource ® JUNE 2014 Terms Part 6 by Bill Corey Pentair Water Training Institute When a vapor bubble implodes it lets off a lot of energy; and the colder the water, the larger the bubble, so more energy. In this picture, you can see the vapor b u b b l e formed at the e l b ow a n d proceeded to move to the outside of the p i pe as t he higher pres- s u r e w a s pushing it in that direction. However, when the pressure be- comes too great for the vapor bubble to remain as vapor, it will collapse and give off a shock wave that over time will cause damage. This occurred at the Hoover Dam back in 1941, and if you go to the dam’s Web site, you can see pictures of the dam and the cavitation damage that happened. I am an ex-Navy man and worked on a destroyer that dropped depth charges. When a depth charge goes off it superheats very cold water, which creates a very large vapor bubble. This bubble is not going to float to the sur- face, it is going to immediately collapse and give off a very large shock wave. Now I used to think if we didn’t hit the sub with the depth charge, we missed it; but what I found out was you only had to be close to do a lot of damage. So of course I’m thinking those at the dam must have felt the shock wave vibrations from the vapor bubble im- ploding, and that is what let them know they had a problem. But in 2004 when I visited the dam, I had the opportunity to ask one of the tour guides and he told me this story: There was a photographer on the west (Nevada) side of the dam taking pictures of the water coming out of the pipe on the east (Arizona) side of the dam. He noticed something which made him call an engineer over and ask, “Where are all those rocks coming from?” He knew there were no rocks going into the pipe, so how were there rocks coming out? The engineer realized they had a problem and told the control they had to stop the experiment. It took four hours to stop the flow of water through the pipe; and in that four hours there was cavitation damage of 115 feet long, 30 feet wide, and 45 feet deep. The walls of the pipe were made out of three-foot- thick concrete. The cavitation damage was so bad it went through the walls and 42 feet into the bedrock, a tremen- dous amount of damage. Now of course you will not have that much damage to take care of, but if you have the water moving through a pipe way too fast you can cause cavitation damage in the pipe. Let’s see what you can do next month. Bill Bill Corey may be contacted via e-mail at admin@ worldwidedrillingresource.com