Discussion Central

  • 1.  Phila Refinery Fire Due to Piping Failure

    Posted 10-16-2019 10:56
    What is the state of your process equipment?

    "Federal investigators say an aging, failed elbow pipe appears to be the cause of a June fire and subsequent explosions that left five people with minor injuries and destroyed part of the processing unit at the largest oil refinery on the East Coast," according to today's story from 6ABC Philadelphia . 

    The Chemical Safety Board released their preliminary report on the explosion and fire at the Philadelphia Energy Solutions refinery.  The report is at https://www.csb.gov/chemical-safety-board-releases-factual-update-and-new-animation-detailing-the-events-of-the-massive-explosion-and-fire-at-the-pes-refinery-in-philadelphia-pa/

    Aaron Sarafinas
    Sarafinas Process & Mixing Consulting LLC
    Warminster PA

  • 2.  RE: Phila Refinery Fire Due to Piping Failure

    Posted 10-16-2019 16:14
    5,000 lbs of hydrofluoric acid were released in this accident.  The consequences could have been a lot worse.  They used an inappropriate material for the elbow that failed and then didn't monitor its thickness.  Today is the first time I heard that this accident resulted in an HF release.


    Kirsten Rosselot
    Process Profiles
    Calabasas, CA United States

  • 3.  RE: Phila Refinery Fire Due to Piping Failure

    Posted 10-17-2019 09:56
    ​What's considered to be a small concentration of hydrofluoric acid (HF)? I haven't done much in refineries but have a good amount of experience with handling HF. I wouldn't think any concentration of HF would be OK to use with carbon steel even if it's a matter of corrosion rate and having to monitor it. I know it's a choice between using HF and H2SO4 with alkylation, and HF is more efficient, but heating up an acid that already etches metal and glass at virtually STP just seems like it would be a no brainer to not use it.

    For those not familiar with HF, it's in my opinion, the most dangerous acid to work with. If you get HF on your skin you don't really feel any burning. The fluorine in HF seeks out the calcium in bones and will work its way right through skin and muscle, liquifying it. With that amount of HF released it's miraculous that no one was injured or experienced breathing problems.

    James Burtnett-Grigsby PE
    Chemical Process Engineer
    Maumee OH

  • 4.  RE: Phila Refinery Fire Due to Piping Failure
    Best Answer

    Posted 10-17-2019 11:24
    Edited by Aaron Sarafinas 10-21-2019 08:25
    To update everyone on this incident:

    Yesterday, the CSB released a preliminary report on the June 21 PES Refinery incident. We found:

    • At about 4:00 am, a very thin piping component in the HF alkylation unit ruptured.
    • Process fluid released into the unit, forming a large ground-hugging vapor cloud. This vapor cloud was primarily propane, but also included HF. PES estimated that a total quantity of over 5,000 pounds of HF released during the incident. Most of this HF was not contained by the water spray mitigation system and released to the atmosphere, unmitigated.
    • About two minutes after the release started (4:02:06 am), the vapor cloud ignited.
    • At 4:02:37 am, the control room operator deinventoried the bulk hydrofluoric acid from the unit into the "Rapid Acid Deinventory (RAD)" drum.
    • The fire caused multiple explosions in the unit. The largest explosion occurred at 4:22 am, when a large vessel containing primarily butylene, isobutane, and butane ruptured. A 38,000 pound piece of this vessel flew about 2,300 feet and landed across the adjacent Schuylkill River. Two other large pieces landed inside the PES refinery. These pieces landed in locations where they did not impact other processes and did not cause secondary releases.

    Corroded Elbow

    • CSB performed metallurgical testing of the thin elbow. The elbow had corroded to as thin as .012 inch. The piping component adjacent to this elbow was .311 inch thick. Other piping within this piping circuit was also much thicker than the elbow that failed.
    • Composition testing found that the failed elbow had a high nickel and copper content in comparison to the adjacent piping. High nickel, copper, and chromium content has been found to cause higher corrosion rates in piping susceptible to HF corrosion.
    • The piping composition met the ASTM standard requirements applicable at the time of pipe installation (1973). Since that time, the ASTM standard has tightened requirements on nickel, copper, and chromium content.

    • This incident points to the need for refineries that use HF to perform 100% component inspection of their carbon steel piping in HF service to find similar pieces of piping that could be corroding quicker than other piping components within the same circuit. 

    • This incident is very similar to the 2012 Chevron Richmond Refinery pipe failure, which was also caused by a piping component that had corroded faster than other piping components within the same circuit, but due to sulfidation corrosion. After that incident, CSB recommended that California require refineries to perform Damage Mechanism Hazard Reviews to identify potential process damage mechanisms and consequences of failure, and to ensure safeguards are in place to control hazards presented by those damage mechanisms. (https://www.csb.gov/chevron-refinery-fire/)

    CSB Factual Update: https://www.csb.gov/assets/1/6/pes_factual_update_-_final.pdf
    CSB Press Release: https://www.csb.gov/chemical-safety-board-releases-factual-update-and-new-animation-detailing-the-events-of-the-massive-explosion-and-fire-at-the-pes-refinery-in-philadelphia-pa/
    CSB Animation: https://www.youtube.com/watch?v=J4wKjGHvs_4&feature=youtu.be

    Lauren Grim, P.E., CFEI
    Supervisory Chemical Incident Investigator
    U.S. Chemical Safety Board
    Denver, CO

  • 5.  RE: Phila Refinery Fire Due to Piping Failure

    Posted 10-17-2019 11:45

    Thank you for the thorough update, Lauren, and thank you to the CSB for the important conclusions from this incident.


    Though the incident is related to a process stream that contained HF, all process practitioners need to consider potential corrosion and erosion issues for their process streams in their equipment.  Proper corrosion studies on the appropriate process streams along with equipment inspections need to be performed in order to protect everyone (workers, neighbors, and the environment) from potentially catastrophic equipment failures.  Also be sure to consider potential process upset conditions which could create different corrosion scenarios.


    Aaron Sarafinas


    Sarafinas Process & Mixing Consulting LLC

    Email:  aaron@sarafinasprocess.com

    Phone:  +1 215.266.6473


  • 6.  RE: Phila Refinery Fire Due to Piping Failure

    Posted 10-18-2019 11:33
    Great job by an operator who just felt an ignition & I'm sure was inundated with distractions

    "About two minutes after the release started (4:02:06 am), the vapor cloud ignited"
    "At 4:02:37 am, the control room operator deinventoried the bulk hydrofluoric acid from the unit into the "Rapid Acid Deinventory (RAD)" drum"

  • 7.  RE: Phila Refinery Fire Due to Piping Failure

    Posted 10-18-2019 18:07
    Lauren, thank you for the update. The CSB Factual Update: www.csb.gov/assets/1/6/pes_factual_update_-_final.pdf contains some very interesting information. 

    Looking at Figure 2,  the process scheme for the alkylation plant, we can see that the location of the failed elbow is in the discharge of the propane recycle pump back to the depropanizer. HF is expected in the overhead of the depropanizer which is the feed source for the pump. The overhead drum also serves as a means to decant free HF from the propane before is returned to the depropanizer as reflux. So one would expect a finite amount of soluble HF in the propane stream under normal operations. 

    The piping system is stated to have been installed in 1972 and was without modification or replacement of components over a period of more than 46 years. That suggests metal loss was extremely small and the rate of corrosion was quite low for much of the life of the piping system. 

    The metallurgy of the failed elbow is uniquely different from what would be expected to be the case for a piping item conforming to the specification for the material. Perhaps this was a contributing factor. 

    One possible cause of the localized thinning may have been carryover of HF into the propane with the high HF fluid held up in a non-flowing section of the pump discharge piping. Be interesting to see if the HAZOP of the piping system contemplated the possibility of "more than" HF in the non-flowing region of the piping system. 

    Al Center

    Professor of Practice
    Robert Frederick Smith School of Chemical and Biomolecular Engineering
    Cornell University
    Ithaca, NY 14853