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Petrobras 36

Coordinates: 22°03′42″S 39°33′15″W / 22.06167°S 39.55417°W / -22.06167; -39.55417
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The platform listing prior to its sinking in March 2001
History
Name
  • Spirit of Columbus (1994–2000)
  • Petrobras 36 (P-36) (2000–2001)
Owner
  • Spirit of Columbus:
    • Società Armamento Navi Appoggio
  • P-36:
    • Petro-Deep
    • Brasoil (bareboat charter purchase agreement)
Operator
  • P-36:
Builder
Cost
  • Conversion to P-36:
    • US$500 million
Out of service20 March 2001
IdentificationIMO number: 8916566
FateSunk
General characteristics
Class and type
  • Spirit of Columbus:
  • P-36:
    • RINA (hull)
    • ABS (topsides)
Type
  • Spirit of Columbus:
    • Semi-sub drilling rig and production platform
  • P-36:
    • Semi-sub production platform, self-propelled
Tonnage
  • P-36:
    • 34,481 GT
Length112.78 m
Beam77.72 m
Height120 m (42.67 m to main deck)
Capacity
  • Spirit of Columbus:
    • Oil production: 100,000 bbl/d (16,000 m3/d)
    • Gas production: 2,000,000 m3/d (71,000,000 cu ft/d)
  • P-36:
    • Oil production: 180,000 bbl/d (29,000 m3/d)
    • Gas production: 7,200,000 m3/d (250,000,000 cu ft/d)

Petrobras 36 (P-36) was a semi-submersible oil platform. Prior to its sinking on 20 March 2001, it was the largest in the world.[1] It was operated by Petrobras,[2][3] a semi-public Brazilian oil company headquartered in Rio de Janeiro.[4][5]

Vessel

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The unit was built at the Fincantieri shipyard in Genoa, Italy between 1984 and 1994 as Spirit of Columbus, an oil production unit integrated with a drilling rig.[6][7] It was then owned by Società Armamento Navi Appoggio S.p.A.[3] The rig was converted into a 31,400-tonnes oil production platform (with no drilling capacity) by Davie Shipbuilding in Lévis, Quebec,[8][9][10] starting in September 1997. It was delivered to Petrobras in late 1999.[11][7] The cost of the platform conversion was over US$500 million[12] (currently over US$888 million[13]). After completion of the conversion works, the semi-sub was loaded onboard the Mighty Servant 1, which had to undergo dedicated structural works to accommodate the large rig. After an 18-day passage, the platform reached Guanabara Bay, where it stayed for a few months.[12] P-36 went on to operate for Petrobras on the Roncador oil field in the Campos Basin, 150 kilometers (90 mi) off the Brazilian coast. Production started on 16 May 2000.[9][14][7]

The unit had two pontoons, four columns, and three decks.[7] Each column was retrofitted with a "stability box" that provided extra buoyancy. Additional stability boxes were installed on the pontoons.[15]

Its nominal oil production capacity was 180,000 barrels (29,000 m3) per day, which at the time of construction was nearly twice the average production of the largest floating facility in operation.[11] By the time of the accident, production had ramped up to about 84,000 barrels (13,400 m3) of crude and 45,000,000 cubic feet (1,300,000 m3) of gas per day.[9][14][7]

Columns

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The starboard column at aft of the hull housed an emergency drain tank, ballast tanks, a waste oil tank, a deareator for pretreatment of injected water, a fresh water tank, and associated pumps and piping. The tanks were not standalone but integrated in the column outer shell. The spaces were ventilated through a dedicated set of ducts.[16]

The emergency drain system also included another tank, housed in the port aft column. The tanks were connected to the production facilities on the topsides and between each other. Fluid transfer capacity to and from the tanks was provided by dedicated pumps, one in each column.[17]

Accident

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In the early hours of 15 March 2001 there were two explosions in the starboard aft column.[18] The first explosion was caused by an overpressure event, the second by the ignition of leaking hydrocarbon vapors.[19]

The first event was the burst of the starboard aft emergency drain tank. This had been mechanically isolated because its pump had been removed for maintenance. The atmospheric vent pipe of the tank was isolated with a blind flange to prevent water intake from other equipment on upper decks. However, a valve exposed to the discharge side of the port aft emergency drain pump was leaking. When this pump was started, fluids began to flow through the valve into the starboard aft emergency drain tank.[20] The pump had been started in the late evening of 14 March. It took about two hours for the pressure in the tank to reach about 10 bar(g).[20][21] At 12:22 am the tank shell gave way. As a result, water mixed with oil spilled into the column from the tank and an 18-inch (460 mm) seawater line failed, resulting in flooding of the column space. Additionally, the firewater system lost pressure due to the pipe failure in the column. Because of the logic programmed in the control and safety system, this resulted in the platform shutdown and the activation of the firewater pump in the starboard aft column, which was trying to compensate for the loss of pressure. This further exacerbated the flooding.[20] The passage of water between different compartments within the column was facilitated by the ventilation dampers failing to close automatically. These remained open, thus allowing a path for the flooding to extend to other levels. Some manholes in the lower part of the column had been left open. This furthered the flooding in lower spaces including one of the stability boxes.[21] After the firewater pumps were stopped, flooding continued because the sea chest valves allowing inflow of seawater from the ocean failed in their set position, i.e., they remained open. The flammable vapors from the emergency drain tank dispersed and climbed to the decks above the column through watertight doors and ventilation ducts that had been left open in preparation for unrelated maintenance activities. The presence of the vapors was revealed by the gas detection system.[20]

At 12:39 am the vapors ignited. The ensuing explosion killed eleven people – all Petrobras employees – who were in the area taking part in the emergency response.[22][23]

The rig started developing a list. Operators tried to contain it by flooding the port fore column, i.e., the one diametrically opposite the one affected by the explosions. However, this operation was unsuccessful and probably contributed to make the situation even worse.[24][21] At the time of the accident, there were 175 people on the rig, of whom 85 crew members.[25] Evacuation of non-essential personnel started at 1:44 am. In about two hours and a half 138 non-essential workers were evacuated using a crane and a personnel transfer basket. When all options to level the platform seemed exhausted, it was decided to evacuate all remaining personnel onboard. This was completed by 6:03 am.[26][21] Meanwhile, the list increased and by 8:15 am was about 20°. This was sufficient to allow further down-flooding through openings to the chain locker.[26] This event made the later sinking of the platform inevitable.[24]

A team of close to 350 engineers worked to reduce the listing in the following days.[27] Marine salvage teams tried over the weekend to save the platform by pumping nitrogen and compressed air into the tanks to expel the water, but they abandoned the rig due to bad weather.[28][21] The platform sank at 11:40 am on 20 March in 1360 m (4460 ft) of water with an estimated 1200 m3 of diesel oil and 350 m3 of crude oil remaining on board.[29] About 350 m3 of hydrocarbons surfaced in the hours after the sinking. These were either recovered or dispersed using chemicals.[30]

Aftermath

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A dedicated commission was formed from members of the National Agency of Petroleum, Natural Gas and Biofuels (ANP) and the Directorate of Ports and Coasts [pt] (DPC), an agency of the Brazilian Navy, with the mandate of investigating the causes of the accident and propose recommendations for the offshore oil and gas industry.[25]

P-36 was replaced by FPSO Brasil, a ship-shaped floating platform leased from SBM Offshore. The FPSO started its lease contract with Petrobras in December 2002. It was demobilized in 2014. In 2007, the semi-submersible platform P-52, built in Singapore and Brazil, came into operation to further supplement production.[citation needed]

Impact on process safety

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The accident stressed the importance of upholding key elements of process safety management. It is now commonly used as a case history to illustrate the criticality of the process safety elements that failed on the occasion of the accident, among which were:

  • Safe work practices, in particular in terms of safe isolation of the starboard aft emergency drain tank. The accident proximate cause was a valve passing that allowed the tank to become pressurized beyond its mechanical limits. The tank should not have been isolated by only closing its valves, but positive isolation should have been achieved by placing a blind flange in the flow path from the port aft emergency drain pump.[31]
  • Process knowledge management: The failure of this process safety element was manifested by the emergency response team not understanding how a designated safe space (the column internals) could become unsafe due to the presence of hydrocarbon-containing vessels. A gas test should have been carried out before entering the space, which would have prevented the ignition of the flammable cloud.[31]
  • Emergency management.[32]

See also

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References

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  1. ^ Fachetti et al. (2000), p. 7.
  2. ^ Furlow & Murillo (2001).
  3. ^ a b Petromec Inc. v Petroleo Brasileiro S.A. Petrobras and Others (2008).
  4. ^ Hilyard (2012), p. 229.
  5. ^ Petrobras (n.d.).
  6. ^ Fachetti et al. (2000), p. 2.
  7. ^ a b c d e Barusco (2002), p. 1.
  8. ^ Petterson (2008), pp. 4–5.
  9. ^ a b c Laverty Wilson (2002), p. 9.
  10. ^ Fachetti et al. (2000).
  11. ^ a b Hawrylyshyn (1999).
  12. ^ a b Petterson (2008), p. 4.
  13. ^ Federal Reserve Bank of Minneapolis (n.d.).
  14. ^ a b Atherton & Gil (2008), p. 160.
  15. ^ Barusco (2002), p. 9.
  16. ^ Barusco (2002), pp. 1, 10–11.
  17. ^ Barusco (2002), pp. 2, 10.
  18. ^ ANP–DPC Commission of Investigation (2001), p. 5.
  19. ^ ANP–DPC Commission of Investigation (2001), pp. 9–10.
  20. ^ a b c d Atherton & Gil (2008), p. 161.
  21. ^ a b c d e Vinnem (2014), p. 150.
  22. ^ ANP–DPC Commission of Investigation (2001), p. 10.
  23. ^ Atherton & Gil (2008), pp. 161–162.
  24. ^ a b Atherton & Gil (2008), p. 162.
  25. ^ a b ANP–DPC Commission of Investigation (2001), p. 6.
  26. ^ a b ANP–DPC Commission of Investigation (2001), p. 13.
  27. ^ FABIG (2001), p. 21.
  28. ^ Gibb (2001).
  29. ^ ANP–DPC Commission of Investigation (2001), pp. 5, 14.
  30. ^ Atherton & Gil (2008), p. 163.
  31. ^ a b CCPS (2021), p. 113.
  32. ^ ALNabani (2018), p. 46.

Sources

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22°03′42″S 39°33′15″W / 22.06167°S 39.55417°W / -22.06167; -39.55417

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