We have a fire safe test facility and will fire safe test according to API 607_5th two weeks from now.but, we have any problem for apparatus such as upstream pipework.API 607_5th mention that "The test equipment shall be designed so that if the nominal diameter of the pipewok situated immediately upstream of the test valve is larger than DN25 or one-half the DN of the test valve"But, Inspector of the third party asserted that upstream pipe size of Large sized valves must employed to one-half the DN of the test valve.Unfortunately, our facility fixed to DN25 alreadyand we don't have any times in order to modificationpls, advice for right interpretation to above problem.In your post you state that the upstream pipe has to be 1/2 DN of the test valve with a minimum size of DN25. You evidently have fixed you upstream pipe at DN25, which will take care of any size up to DN50 without a change in up stream pipe size. I personally see no way around this requirement. But, this is sad news, if we must be size up from DN25 to 1/2DN of the test valves to upstream pipe work...I recieved any technical papers from SWRi(South West Research Institute). pls, find attached file and see Figure 1, (B)

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