Where is the pipeline located? One of the two standards you have referenced doesn't apply. RP500 uses the US “Division” standard. IP15 reflects the British implementation of the IEC “Zone” method. The two systems are not compatible. (The truth is the US “Zone” system isn’t really compatible with IEC either)
You appear to be using SI units rather than US although both are acceptable in the US. Flow rates are also relevant to the analysis.
Robert B. Alexander, P.E.
"I know that you believe you understand what you think the NEC says, but I am not sure you realize that what you read is not what it means." (Corollary to Charlie's Rule)