The hub in eastern Austria is a major regional transfer node, taking gas from as far away as Russia and pumping it towards neighbours including Italy - its biggest recipient - as well as Germany, Hungary, Slovenia and Croatia.
"The investigating authorities believe that the incident was caused by the seal on the cap of the filter separator," GCA, a unit of energy company OMV, said on its website.
"The cap had come loose and was propelled with great force against another part, causing damage to this part as well. The gas which subsequently escaped was then ignited, leading to a gas fire at two points of origin."
A spokesman for GCA said investigations were ongoing.
"There is no indication of sloppiness. But there also is no indication of material failure.... We only have the information about what happened, not what caused it," he said.
GCA added that the parts in question were isolated from the rest of the site in accordance with an emergency plan, allowing gas flows to return to normal on Wednesday.