Rupture of a hydrogen supply pipe in chemical plant

The explosion affected the hydrogenation unit of a isophytol plant. A pipe carrying hydrogen ruptured, releasing hydrogen, which ignited and after few seconds caused the explosion. 
The pipe belonged to the closed-loop gas line running from the top of the gas separator to the feed inlet of the hydrogenation reactor. 
The operating pressure was approximately 20 bar and the temperature 130°C. The pipe failed at approximated at 17 bar. The explosion caused the damage of other components. 
All subsystems of the isophytol plant were shut down by emergency shutdown. The building and adjacent structures were evacuated, and firefighter intervened. After extinguishing the fire, they inspected the plant with a drone and found various leaks caused by the fire in a sodium hydroxide line, a water line, and a beta-ionone line. The plant crew was able to stop immediately the leaks shut off the water and beta-ionone lines, while the sodium hydroxide leak was not stopped until later that same day. 

The INITIATING CAUSE was the rupture of a pipe carrying hydrogen. Although ZEMA report does not state this explicitly, it is possible to deduce from the corrective measures undertaken that the cause of the rupture was attributed to chloride-induced stress corrosion cracking. 
The ROOT CAUSE could be attributed to inspection tools and procedures inadequate to detect on to quantify pipe corrosion progress. 

pipes

At the moment of the rupture, the hydrogenation process was running in a closed loop. 

This means that only the closed loop of TH-GAC (tetrahydrogeranylacetone) was maintained, without producing any TH-GAC or discharging it into the pure product tank. During this process operation, the supply of pseudoionone (PSJ) was closed. To prevent a pressure drop in the hydrogenation reactor and gas separator, hydrogen was added.

From Wikipedia:
“Isophytol is a terpenoid alcohol that is used as a fragrance and as an intermediate in the production of vitamin...
It can be synthesized in six steps from pseudoionone and propargyl alcohol.[4] Total synthesis begins with the combination of acetylene and acetone to produce 3-methyl-1-butyn-3-ol. Hydrogenation by palladium catalysis results in 3-methyl-1-buten-3-ol. Reaction with diketene or acetic acid ester creates the acetoacetate; thermal reaction leads to 2-methyl-2-hepten-6-one. The steps of adding acetylene and then isopropenyl methyl ether and hydrogenating the product are done twice (this involves an intermediate of pseudoionone); then acetylene is added to create dehydroisophytol. Hydrogenation results in isophytol.”

[https://en.wikipedia.org/wiki/Isophytol ]

8 plant workers and 4 members of the fire brigades were lightly injured and treated on site. 

The fire was extinguished by plant first responders, without the intervention of external fire department. After approximately 40 minutes of firefighting, the production areas on the equipment at the 4 platforms between 9 and 18 m above ground were inspected using a drone. 

All the extinguishing water was contained within the building.

1. The exhaust gas collection system containing vinyl chloride was separated from the other exhaust gas systems. This prevented vinyl chloride from entering other subsystems that were not designed to contain it.  
2. The recirculating gas line and the exhaust gas condenser affected by the incident were constructed from nickel-based Hastelloy C (2.4602) steel. This material is resistant to chloride-induced stress corrosion cracking.
3. Corrosion samples made of stainless steel 1.4541 and Hastelloy C (2.4602) were installed in the   recirculating gas line below the exhaust gas condenser. These samples are used as corrosion indicators and are inspected for corrosion annually during shutdown procedures.