Storage/Loading/Unloading - Storage Tanks - Failures
November 8, 2010

Incident No. 1 Incident No. 2 Incident No. 3 Incident No. 4

Associated Links Materials of Construction

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Incident No. 1

On June 16, 1975 a 3000-ton sulphuric acid storage tank ruptured at International Minerals and Chemicals (Canada) Ltd., Port Maitland Plant, Dunnville, Ontario, Canada.  The tank was constructed of ASTM 285 Gr. C plate and had been in service for 14 years.  It was 51 ft. in diameter by 26 ft. high and was built on a thick concrete foundation.  The original side wall thickness varied from 1/2" at the bottom to 3/8" in the upper courses.  The tank was 24'-6" full at the time of failure.  The floor plate was 1/2" thick and the roof was of arch construction.

The tank ruptured vertically through steel plate (not welds) near the centre of a grooved corrosion pattern located below the acid inlet nozzle.   The rupture appears to have started about 8' from the tank floor at a horizontal weld seam which had thinned to less than 1/8" where the vertical grooves crossed the seam at right angles.  The fracture line was straight from bottom to top through plate thicknesses ranging from less than 1/8" to 3/8".  When this vertical fracture reached the 'T' weld where the side walls were attached to the floor plates, the weld sheared off around the entire tank base and roof.  With the sudden release of energy and the reaction to the acid gushing out, the side walls unrolled to an almost flat position.  This sudden push of acid moved another nearly empty tank of the same size into a third tank causing severe damage.  A concrete blockhouse was leveled at the foundation and debris was picked up over 150' away.  As the tank unrolled it struck a cast iron pipe cooler breaking or cracking about 75% of the pipe.  A 12" water main feeding the pipe cooler was sheared off and underground piping was broken.  A 5 week plant shutdown was required to cleanup and restore equipment.

The acid fill pipe was located in the roof one foot from the wall.  The corrosion was caused by acid flowing down the tank wall.  Two mechanisms combined in the removal of the protective sulphate film.   Erosion-corrosion occurred as the acid washed down the wall.  Below the liquid level, hydrogen grooving and turbulence due to the falling acid combined for a grooving corrosion phenomena.

This corrosion was missed during both an ultrasonic thickness testing and a visual inspection 10 months earlier.

After this failure, three other tanks were inspected and they all showed a similar corrosion pattern in relation to the inlet nozzle.  Two of the tanks were scrapped due to damage from the incident while the third tank was rebuilt to original specifications by removing all plates exhibiting the grooving pattern.

The grooving pattern which occurred in these tanks started on the sidewall about 3' below the inlet nozzle and extended to within one foot of the tank floor.  The grooves were straight, narrow and vertical with a spacing of about 1/8" and were cut into the plate about 1/16" deep.  The pattern extended about 4' around the tank and also showed general thinning.  At the point of failure the plate thickness was about 1/8" in the bottom of the deepest grooves.  The tank failed by simple overload.

 

 

 

 

Incident No. 2

A 50' diameter x 41'-6" high tank located at Curtis Bay near Baltimore, Maryland failed catastrophically in a brittle manner on Christmas Eve, December 24, 1983, at 9:15 pm.  The temperature was -16.6°C (2°F) and the tank was 87% full with approximately 500,000 US gallons of 87% sulphuric acid at the time.   Two empty rail cars were lifted by the rush of acid and slammed against a loading platform some 20 ft away.  An empty 20,000 gallon tank located 50 ft away was lifted and carried 100 ft.

The acid flowed over four acres of land and into Cabin Branch of Curtis Creek and then into Curtis Bay.

The tank collapsed with considerable tearing and fracture.   The main vertical crack was thick edged, (brittle) with chevrons going halfway up the tank from the bottom.  The shell-to-bottom joint was separated more than 180 degrees around the tank.  Many brittle cracks with visible chevron markings progressed from the bottom joint into the shell.  The shell-to-bottom joint had been originally made with an inside and outside fillet, and the inside fillet had been substantially removed by corrosion.  The wall thickness in the bottom course varied from 0.55 to 0.65 inches.  Original thickness was 13/16" (0.8125").   A number of samples were taken for metallurgical analysis.  Charpy impact values ranged from 3.5 ft.lbs. at 0°F to 5.5 ft.lbs. at 32°F to 13.5 ft. lbs at 68°F.   Modern steels absorb at least 10-15 ft.lbs. of energy at -20°F.  The yield strength of plates removed from the tank was 33,000 psi.  The tensile strength was measured at 63,000 psi.  The tank was built in 1941 from A-7 steel per API 12-C.

Although this tank was near minimum wall thickness for the fill height, it had enough wall thickness that an overload failure would not have occurred.  This tank failed by brittle fracture due to a critical combination of stress, poor toughness properties and cold weather.  Also, the weak shell-to-bottom joint was probably a factor on the rapid destabilization of the tank.

Incident No. 3

On July 17, 2001 at 1:22 pm, the Motiva Delaware City Refinery experienced a storage tank fire containing sulphuric acid.  Emergency personnel responded immediately and the fire was contained and extinguished at approximately 2:10 pm.

As a result of the incident, eight individuals were treated in hospital for varying injuries, including respiratory irritation.  Two individuals were admitted and all others were released.  A maintenance contractor was reported missing and a search was undertaken to locate the individual.

A temporary earthen berm measuring 5 feet high, 25 feet wide and 150 feet long was constructed at the southern end of a dike surrounding the refinery’s acid storage tanks.  The purpose of the berm was to capture and direct any potential release from the existing containment dike to an adjoining settling pond.  Approximately 671,750 US gallons of acid remained in three tanks located in the same dyked area.  Another tank thought to be holding acid was found to be empty.

Spent acid stored in tanks located elsewhere in the facility were emptied and the spent acid sent to General Chemical in Northern New Jersey for regeneration.  This freed up storage capacity for the transfer of acid from the tanks located in the dyked area affected by the July 17 incident.  By August 24, all the tanks in the dyked acid tank farm area were emptied.

The company submitted information related to the tank involved in the fire:

• Tank identification: Tank #393
• The tank was reported overdue for inspection.
• Work orders were issued to repair a hole in the tank.
• Tank has been recommended for removal from service.
• Vapour and liquid releases have occurred from the tank.  Some of these releases have been reported to governmental authorities.
• The tank was been the subject of unsafe condition reports and was noted on a joint health and safety committee’s meeting minutes.
• Consistent with the work permit issued by Motiva personnel, one test for hazardous gases was done at the beginning of the job at found to be negative.

The investigation into the cause or causes of the July 17 incident are assumed to be still underway.   This report will be updated when more information is known.

Overall Site Schematic			Tank Farm Schematic
Tank 393 History			View of Tank Farm
Emergency crews working on containment of spillage			Crane being used to clear away debris within the dyked area
Close up view of Tank 393			Close up view of Tank 393
Close up view of Tank 393 showing how tank shell has sheared away from tank bottom			Decommissioned Site of Storage Tanks

Incident No. 4

Explosion in a Sulphuric Acid Tank, November 26, 2005, Pierre-Bénite (Rhône), France