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US refineries commitment to safety called into question

21st February 2013


A spate of serious accidents at US refineries has led to a renewed call for a commitment to safe operations from operators. Sean Ottewell reports.

John Bresland, chairman of the US Chemical Safety Board, has urged refineries in the country to improve their commitment to safe operations.

"The frequency of accidents in US refineries is very troubling. These accidents cost lives, inflict serious injuries and can harm communities. They also earn scrutiny from government regulators; in the past few weeks a refinery in Texas drew the largest OSHA fine in history, more than US$80 million, for alleged process safety violations. I call on all refineries to redouble their commitment to safer operations and safer communities. The current rate of accidents in refineries is not sustainable and it is not acceptable."

Bresland was speaking at a meeting in Woods Cross, Utah, at which the CSB was updating the public on its investigation into the explosion at the local Silver Eagle refinery on 4th November 2009.

"Of 15 investigations, more than half involve accidents at oil refineries - even though the nation's 150 refineries account for only a small percentage of the facilities that fall under the CSB's investigative jurisdiction. Three of those eight refinery investigations are located right here in the Salt Lake City area," he noted.

Catastrophic failure

CSB investigation has revealed that at 9.11am on 4th November, the refinery experienced a catastrophic failure of a 10-inch pipe off the bottom of a reactor in the Mobil distillate dewaxing unit. The force of the rupture caused a section of the pipe to wrap itself around a steel support. At the time, the unit was undergoing a special operation to regenerate the catalyst. This involved circulating high-pressure hydrogen gas inside the piping, at a temperature of 800°F and a pressure of 630 psi.

A surveillance camera on the site shows a release and almost instantaneously the gas ignites in large fireball, which was estimated to be 100 feet high. The hydrogen contents of the reactor continue to be released through the pipe, which was then open and pointing directly east toward the housing subdivision next to the refinery.

Explosion

There were four workers near the process unit at the time of the explosion. They were blown to the ground but were not seriously injured. Another worker had been taking readings next to the pipe that failed just 1-2 minutes before the release. In addition there are commuter rail lines that frequently carry passengers on routes that are immediately adjacent to the refinery. Fortunately there was no train present during the blast.

The blast wave from the hydrogen explosion damaged over 100 homes, based on CSB investigators' survey of the neighborhood. Two of the homes were severely damaged, including one which was knocked off its foundation.

Investigations supervisor Don Holmstrom said the investigation to date indicated the Silver Eagle refinery was operating with a mechanical integrity programme that had 'serious deficiencies'.

The goal of a mechanical integrity programme is to ensure that process equipment is fabricated from the proper materials of construction and is properly installed, monitored, and maintained to prevent failures and accidental releases.

Because of the hazardous nature of the materials in a refinery - and the high temperatures and pressures that are frequently used - a robust mechanical integrity programme is essential to safe refinery operations. It is also a regulatory requirement for refineries and chemical plants under the OSHA Process Safety Management standard, enacted in 1992.

Prior to May 2009, mechanical integrity inspections - including thickness monitoring of pipes and vessels at the refinery - were completed by a contract company hired by Silver Eagle. The refinery later replaced this company with a second outside inspection company, which remains active at the site.

Revalidating readings

Witness evidence indicates that various thickness readings taken by the prior contractor are of questionable validity. The refinery is now in the process of revalidating those readings.

"Specifically, witnesses report that in 2007 the prior contractor documented the thickness of the pipe that failed on 4th November to be nearly one-half-inch. But measurements following the accident show that the pipe thickness was only one-eighth of an inch. A likely explanation is that the 2007 thickness measurement was inaccurate. This and other recent measurements call into serious question the pipe thickness readings obtained by the prior contractor," added Holmstrom.

The evidence further indicates that a significant percentage of the pipes and vessels have no documented thickness readings at all. Refinery managers have now acknowledged to CSB investigators that minimum thickness values for piping and equipment throughout the refinery have been miscalculated. These are the thicknesses at which the equipment must be retired from service due to the potential for failure. Specifically, the refinery has been using what are known as ultimate tensile strength values, rather than the industry-recommended stress tables.

"The result of these miscalculations is that these minimum thickness values may be 3-4 times too low; some of the minimum thickness values may therefore be too low for the safe operation of the equipment. In other words, there is the potential that multiple pieces of equipment have been operating at below the required thickness for safety - and creating the potential for other serious accidents," Holmstrom said.

The CSB is also conducting a full investigation of the 23rd October 2009 explosion and fire at the Caribbean Petroleum Refining facility near San Juan, Puerto Rico. At 12.23 am a large vapour cloud ignited, with the associated blast damaging homes and businesses over a mile from the facility. Since then a five-person CSB team has been conducting numerous interviews, cataloguing key pieces of evidence and collating hundreds of pages of documentation.

Caribbean Petroleum is a significant petroleum products supplier for Puerto Rico. The facility includes a tank farm and refinery that was shutdown in 2000. Prior to 23rd October the tank farm stored gasoline, diesel fuel, jet fuel, and fuel oil in about 30 operational above ground storage tanks.







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