Root cause thinking reveals that we are only as strong as our weakest link

A little neglect may breed great mischief

“For want of a nail, the shoe was lost.
For want of a shoe, the horse was lost.
For want of a horse, the rider was lost.
For want of a rider, the battle was lost.
For want of a battle, the kingdom was lost,
And all for the want of a horseshoe nail.”

Benjamin Franklin

A piece of pipe, long overdue for replacement, failed and spilled highly corrosive hydrocarbons mixed with a dangerous chemical at the Philadelphia Energy Solutions (PES) refinery in Pennsylvania, USA, formerly owned by Sunoco Inc, in the early morning of 21 June 2019. The result was a devastating explosion and fire, which released over 3000 pounds of dangerous hydrofluoric acid and large amounts of other hydrocarbons.

The explosions and fire destroyed a critical section of the PES refinery. At 4 am, a large amount of propane mixed with a smaller amount of hydrofluoric acid leaked, forming a large ground-hugging vapour cloud, which ignited after two minutes. Three explosions occurred, with the third causing a violent rupture of a drum containing butylenes, isobutene and butane. The largest piece, weighing about 19 tons, flew into the air and landed across the Schuylkill River.

The incident began when a 90° pipe elbow ruptured. The pipes in the PES alkylation unit were monitored at specific spots and on a frequency dependent upon the life projection of the piping. These are known as ‘condition monitoring locations’ or CMLs. The wall thickness measurement of CMLs is conducted using ultrasonic thickness technology. The ruptured elbow was not a CML and its thickness had not been monitored!

PES had a policy that any pipe thinner than 0.180" would be replaced. The Chemical Safety Board’s investigation found that the ruptured pipe was only 0.012". John Jecgura, a Professor at Colorado School of Mines, was quoted as saying that deciding where to test is based on a probability factor. As a rule of thumb, the areas most vulnerable to corrosion are places in the pipe where there is a change in the flow direction, one of which is at the elbow. Another issue is the material of the pipe.

The pipes in this alkylation unit were installed in 1973, when industry standards did not specify how much nickel or copper they should contain. In 1995, these standards were updated to specify that pipes should contain no more than 0.4% of either nickel or copper. The ruptured pipe contained 1.74% nickel and 0.84% copper.

The American Petroleum Institute (API) ‘Recommended Practice for Safe Operation of Hydrofluoric Acid Alkylation Units’ states: “HF corrosion has been found to be strongly affected by steel composition and localized corrosion rates can be subtly affected by local chemical differences”.

PES, along with the trust that is liquidating the company’s remaining assets, has sued Babcock & Wilcox Co for allegedly mislabelling the failed elbow joint and misleading the purchaser. PES was the East Coast of America’s largest refinery until the 21 June 2019 incident. The lawsuit alleges that the faulty pipe section was stamped to indicate that it was carbon steel, but also had a fainter mark showing that it was a nickel- and copper-containing alloy called Yoloy. By labelling the elbow with “misleading and inaccurate markings”, Babcock & Wilcox misled the refinery’s owner, according to the lawsuit.

If only the explosion location had been designated as a CML.

  2. A Maykuth, ‘Bankrupt Philadelphia Energy Solutions blames ‘mislabeled’ pipe for big blast that led to refinery’s closure’, Philadelphia Inquirer, 3 March 2021.

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