The equipment concerned is an overhead pipe connecting the catalytic cracking unit to a flare. It is part of the backup equipment used during the unit’s safety phases, as well as during planned shutdowns and restarts. Its function is to collect hydrocarbon gas mixtures during production so that they can be flared. With a variable diameter depending on the section from 150 to 900 mm, its design pressure is 3 bar and its design temperature is 130 °C. It is classified by the operator as safety critical equipment.
Gaseous hydrocarbons leaked out of a perforated pipe at refinery. The leak was stopped by placing an online leak sealing patch on the pipe. Thickness checks made nearby indicated that the thicknesses was sufficient.
Following a storm on 17 August, the steam cracking unit was safely shut down (ARIA 52087). This put stress on the pipe. A new perforation was discovered when the units were restarted. A second patch was put on and checked were made. The residual thickness was so fine at some points that these operations were sufficient to perforate the pipe.
The plant’s health and safety committee notified the inspection authorities for classified facilities, which visited the plant on 17 September. They saw several perforations along two 10-m-long sections of the pipe. The pipe’s condition was checked. Eleven perforations with average diameter of 2 cm were found. The operator attributed the perforations to under-deposit corrosion along the lower generating line. He made temporary repairs and continued to monitor the pipe along its entire length. The operator had detected an initial perforation on the same pipe (ARIA 53311) two months earlier. He plans to replace it in 2020.
On 21 September, the Prefect issued an emergency order requiring the operator to:
- take, within 24 hours, the necessary measures to ensure that stresses on the pipe will be minimal and leaks will be detected;
- finish inspecting and repairing the pipe within one month;
- provide documentation proving that the pipe’s safety level is maintained as well as the analysis of the incident and its impact.
On 30 October, a fire started whilst the temporary repairs were being carried out (ARIA 52555).
