The BASF Total Energies column bent down in half. ????
CBS - The U.S. Chemical Safety and Hazard Investigation Board (CSB).
“Port Artur, Texas, Sept. 5, 2023
This article provides a strategy to minimize the underlying cause and design considerations to the Column Tower Incident from the design, operation, and maintenance viewpoint, as well as to be considered before commencing any repairs.
Precedents from the CBS Report.
The CBS Chemical Safety and Hazard Investigation Board (CBS) has published the detailed-report on the distillation Tower incident leading to the collapse of the column as shown in the picture at the BASF TotalEnergies Petrochemical Facilities in Port Arthur, Texas.
During the shutdown and maintenance preparations, an internal fire caused the collapse of a distillation column tower.
- Pre-Shut Down Phase. Approximately a month before the scheduled maintenance shutdown, leaks in another process area allowed water to enter the extractive distillation unit.This water ingress led to internal corrosion, removing iron from the metal walls.The liberated iron reacted with hydrogen sulphide (H?S) present in the process equipment, forming iron sulphide (FeS), a pyrophoric material.
- Shut-down and Maintenance Preparation. A few weeks before the incident, the facility shut down its Pyrolysis Gasoline unit, including the extractive distillation tower, following standard procedures to remove solvents and hydrocarbons in preparation for maintenance.
- Incident DayOn September 5, 2023, maintenance personnel began opening manways to prepare the tower for entry. At 9:30 a.m., temperatures within the tower's stainless steel-structured packing beds began to rise.By 10:44 a.m., smoke and flames were observed emanating from the tower, prompting the activation of emergency alarms and evacuation of personnel.Despite efforts to introduce nitrogen and prevent air ingress, the tower collapsed at 11:53 a.m.
- Water ingressing and formation of corrosion.About one month before, water entered coming from a leak from another part of the process.
- The combination of water and hydrogen sulfide (H2S) caused internal corrosion in the column, with no air (O2) present so far.
- First of all, the effect was the reduction of the nominal thickness in certain areas of the column from inside to be assessed against the minimum required thickness determined by calculation, considering pressure conditions and structural loads (wind, life loads, dead loads, etc.).
- Note that sour hydrocarbons have a significant concentration of H2S.
- Additionally, due to the own corrosion process, the Iron (Fe+2) coming from the column tower shell promoted the formation of Iron Sulfide (FeS).
- Additionally, It was promoted the formation of H2(s) with additional effects coming from H2, such as:
- Iron Sulfide (FeS) Reaction: Strong Exothermic Reaction in O2 Presence. Pointed by the CBS Report as the main cause.
- H2 (g) against carbon steel material.Hydrogen
- Embrittlement (HE). Hydrogen atoms diffuse into steel, weakening its structure and making it brittle.Hydrogen-Induced Cracking (HIC). Hydrogen accumulates in steel, forming internal cracks without external stress.Hydrogen Attack (High-Temperature Hydrogen Attack-HTHA). At high temperatures, hydrogen reacts with carbon in steel, forming methane (CH?) bubblesHydrogen Blistering. Molecular hydrogen accumulates in voids, causing localized swelling or blisters.Delayed Hydrogen Cracking (Cold Cracking). Hydrogen diffuses to stressed areas after fabrication, leading to delayed cracks.Hydrogen Permeation. Hydrogen atoms diffuse through steel, reducing containment integrity.Hydrogen Delamination. Not in this case an option.Hydrogen-Induced Fatigue. Hydrogen weakens steel, accelerating crack growth under cyclic loading. Not significant for a column tower where it is not expected a significant number of cycles during life operation.Hydrogen Absorption & Decarburization. Hydrogen reacts with carbon in steel, removing it and altering mechanical properties.
Fe+H2S→FeS+H2
2. Water ingressing and formation of corrosion.
(FeS) spontaneously ignites when exposed to air (oxygen). This gas oxygen entered into the column at the time the column tower was open to proceed with its maintenance.
4FeS+7O2→2Fe2O3+4SO2+Heat
This reaction can cause localized overheating (700–900°C), ignition, and fire.
- Nitrogen or Inert Gas Purging: Before opening the Column Tower, nitrogen purge would prevent the oxygen, entering into the column and reacting with the FeS.
- Chemical cleaning and Wetting: keeping the FeS wet using water as a medium would prevent fire.
- Corrosion control and Gas Monitoring:Internal SS coating would significantly reduce the possibility of FeS formation.Continuous monitoring for H?S leaks helps detect conditions that lead to FeS formation.
- Safety: Deeply analyze from the safety standpoint the maintenance work to be done.Proper Job Hazar Analysis (JHA) & Job Safety Analysis (JSA), including:
- Task breakdown.
- Hazard identification. Refinery Maintenance shall provide the register of safety and operational incident associated to the equipment to be intervined.
- Control Measures (Eng, Process, Maintenance, Operation, Administrative, PPE).
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DIRECTOR OF SMALL-SCALE AMMONIA & UREA/DEF INDUSTRIAL PROJECTS
1 周Very informative...