On July 23, 1984, an explosion and fire happened at a Union Oil petroleum refinery in Romeoville, Illinois, outside Chicago, killing 17 people and causing major property harm. The explosive force propelled the higher portion 14 metres (forty six ft) of the vessel a distance of 1 kilometre (0.62 mi) from its authentic location, whereas the bottom remained at the center of the resultant fire.
three Ruptured vessel
The tower was constructed from 25 millimetres (0.98 in) thick plates of sort ASTM A516 Grade 70 steel per ASME Section VIII pressure vessel code. The vessel was 18.Eight metres (62 ft) tall, 2.6 metres (eight.5 ft) in diameter.
Starting in 1970 the vessel served as an amine absorber tower, used to strip hydrogen sulfide from a process stream of propane and butane. Inspection identified hydrogen blisters and laminations and in 1974 a number of meters of the decrease shell section have been utterly replaced utilizing guide steel arc welding. After welding, no publish weld heat treatment (PWHT), a vital course of that reduces the residual stresses formed throughout welding and restores the macro construction of the steel, was carried out. Two years later, in 1976, a Monel liner was installed into the underside head to reduce corrosion; however, the previously repaired section was not coated by the liner.
Prior to the explosion, an operator tried to shut off the principle inlet valve to stop fuel leaking from a a hundred and fifty millimetres (0.Forty nine ft) horizontal crack the vessel. The crack grew to 600 millimetres (2.Zero ft) and the operator initiated evacuation. The crack continued to grow and a significant amount of flammable gasoline was released as firm fire fighters gathered at the scene. The fuel ignited, fatally wounding personnel, damaging the refinery, and launching the higher portion of the vessel to 1 kilometre (0.62 mi) from its authentic location.
Failure analysis of the vessel segments included the next non-destructive testing methods.
Magnetic particle inspection revealed “lots of” of cracks alongside the inside surfaces of the horizontal welds at each the top and bottom of the part replaced in 1974.
Ultrasonic measurements indicated delamination damage below the replaced part.
– Thickness measurements using a micrometer confirmed that the wall thickness for both sections was properly throughout the allowances for pressure vessels.[Four]
The reason for cracking didn’t become clear till metallographic results were mixed with stress corrosion cracking and hydrogen embrittlement checks, followed by fracture mechanics analysis. It appeared that an already current crack had extended by means of more than 90% of the wall thickness and was about 800 mm in size. Additional, it was determined that hydrogen embrittlement had reduced the fracture resistance of the steel by more than half. The vessel had been put into service in 1970 and had undergone a number of repairs and modifications earlier than the July 1984 incident. The vessel was fractured alongside a path that was weakened by extensive cracking adjacent to a repair weld becoming a member of a substitute section to the original vessel. These pre-current cracks initiated in areas of hard microstructure recognized to be inclined to hydrogen stress cracking. This hard microstructure formed in the course of the repair welding of the alternative part. The cracks grew by way of the vessel wall because of hydrogen pressure cracking.
When the depth of the largest of those pre-existing cracks exceeded ninety% to ninety five% of the wall thickness, the remaining thin ligament of steel within the cracked section ruptured and leakage occurred. This crack prompted an entire fracture of the vessel circumference on the working stress level of only 35 MPa (roughly 10% of the rated strength of the steel) as a result of the toughness of the vessel steel had been diminished by hydrogen embrittlement.
^ Schneidman, Dave (2 November 1985). “Welding Cracks Prompted Union Oil Blast Fatal To 17”. Chicago Tribune. Retrieved eight July 2014.
^ Zactruba, John. “Post Weld Heat Therapy – Why Is It Important?”. Bright Hub Engineering. Retrieved 28 February 2017.
^ Hayes, B. “Union Oil Amine Absorber Tower”. TWI. Retrieved 10 November 2016.
^ Siewert, Tom. “Evaluation of the Catastrophic Rupture of a Stress Vessel” (PDF). NIST Publications. NIST. Retrieved 10 November 2016.