The report found the US-based company had failed to properly inspect and monitor the roughly 100km pipeline leading from the facility to the mainland.
It also found that the other main causes of the incident, which slashed Western Australia's domestic gas supply by one third, were ineffective anti-corrosion coating and cathodic protection of certain sections of the pipeline.
Part production was restored in August and the plant is expected to return to full production in December.
"Apache disagrees with any conclusions drawn at this time about this unforeseeable event because they are premature and misleading," managing director Tim Wall said.
"The explosion was an unforeseeable and unfortunate event, but it is important to remember that no one was injured, the environment was not damaged and through Apache's efforts, (partial) operations have been restored ahead of schedule.
"Pipeline explosions are rare and it typically takes months to determine the cause.
"Everything must be examined, from the manufacture and design of the pipe to its installation and numerous environmental factors.
"Apache only received a copy of the report yesterday.
"After we have had some time to review it thoroughly, we will provide a more detailed response.
"Apache will work to determine the root cause of this explosion thoroughly and methodically."
WA's new Mines and Petroleum Minister Norman Moore said it appeared, "on the surface", that Apache had let the state down.
Moore also expressed disappointment at the limited terms of reference of the NOPSA investigation.
