What is the definition of Cat. I, Cat. II and Cat. III pipe. Let me give an example to explain my question. We can say the pipe which does not need V-notch test is Cat. I pipe. Then the question is which pipes do not need impact test? Is there any specific definition of these Cat. I, II & II pipes? For example the pipe which will be used for the service..........is called Cat. X pipe. Now, from this definition, I know my pipe is Cat. I pipe or Cat. II pipe. And then from CSA Z662 we can know that as my pipe is Cat. I pipe, it does not need Charpy test or as my pipe is Cat. II pipe, it needs Charpy test. Would appreciate if someone clarify these things which I am bearing for long time.