Explosion in a methanol synthesis unit

The accident happened in a low pressure methanol plant, commissioned in summer 1971 .
A 6 in. pipe, below the methanol synthesis gas compressor inter-stage relief valve, failed releasing hydrogen-rich synthesis gas into the methanol area. The pipe failed at the pipe-flange junction.

Syngas was ignited by an unknown ignition source and the resultant fire burned 10-20 minutes above the synthesis gas compressor. No damages to personnel are reported, even though windows were broken within a distance of 270 m, due to the explosion.
It is not known whether the pipe failure was due to fatigue or to a sudden overload. According to Lloyd (see references), a weld neck flange should have been used instead of lap-joint flange; the former shows higher fatigue life (approximately ten times) under cyclic operation.

It is not known whether the pipe failure was due to fatigue or to a sudden overload.

pipe of a methanol synthesis gas compressor

DESCRIPTION OF THE PROCESS
The Benfield process, uses a solution of potassium carbonate solution (K2CO3) as an absorbent to eliminate CO2 from a gas mixture. The gas to be cleaned is passed at high pressure (e.g., 2 MPa) countercurrently through the K2CO3 -solution in the absorber. This becomes enriched with CO2 and partially reacts to form potassium bicarbonate (KHCO3).

The recommendation of the author of the article reporting the incident was to use weld-neck flanges instead of lap-joint or stub-end flanges. The reason is the much longer lifetime under fatigue conditions of the former than the latter.

A weld-neck flange is a flange which has a pipe-formed part which is welded head-to-head to the pipe.
A lap-joint or stub-end flange use a stub-end which has to be welded on one side to the flange and to the pipe to the other side.