Question: What is the difference between NACE MR0175 and ISO 15156?
There is no technical difference. The documents are identical, NACE MR0175 and ISO 15156 is the same document and it is written and maintained by the same committee. ISO 15156 is the document number adopted by ISO while NACE MR0175 is the document number used by NACE, ANSI NACE MR0175 is the official document number within the US. In the UK the document is BS EN ISO 15156.
In terms of the technical requirements and the information presented by this document, there is no difference among them, they are identical.