Loss of Containment Tier 1 from Hot Vacuum Residue Tank

Tank farms are very simplistic facilities when conditions and well-done calculations are made for its design, those should include metallurgy, internal coating requirements, heat conservation (isolation and others) and venting. In refineries, they have a relevant importance due to accumulation of flammable material that is normally at low temperature to reduce risks and costs. However, in quite diverse processes where heavy and viscous material is need storage, process conditions as elevated temperature is required. That scenario implies great energy content into a place that should have more attention and priority than rest of similar facilities at softener conditions. In this case an explosion occurred from hot tank TK-12 due to undesirable light material incoming, vaporizing suddenly and creating an excessive overpressure unhandled by venting system. A root cause investigation was performed at highest level due to economic impact caused by loss this key stream and limited facilities to bypass tank TK-12, one of the most important key findings was original design HAZOP did not consider change of composition for this critical tank. Changes into design were executed, PHAs (HAZOP and SIL) for the MOC were performed, tank was rebuilt, however fourteen months after tank TK-12 was back in service, a new rupture by overpressure occurred. A new and different investigation team was composed to find out root causes, all standards were review once again, calculations suggested into API 2000 for venting were compared, and the key finding were that general rules mentioned inside this standard did not match with this kind of scenario, and they were detected that lessons learned and gaps from previous investigation were not closed. Therefore, it was performed a process simulation to reproduce conditions of the event, considering the new venting capacity and learning about this abnormal circumstance as it was light material entrance into a hot tank. Additionally, gaps from previous investigation were closed and new root cause analysis results and recommendations are being follow up. As result tank TK-12 was put back on service on September 28, 2014 and still today keep its mechanical integrity without overpressure events since then.