Energo OTC 18325

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OTC 18325

Assessment of Fixed Offshore Platform Performance in Hurricane IvanPuskar, F.J., Spong, R.E. and Ku, A., Energo Engineering; Gilbert, R.B. and Choi, Y.J., The University of Texas at Austin

Copyright 2006, Offshore Technology Conference

This paper was prepared for presentation at the 2006 Offshore Technology Conference held inHouston, Texas, U.S.A., 1–4 May 2006.

This paper was selected for presentation by an OTC Program Committee following review ofinformation contained in an abstract submitted by the author(s). Contents of the paper, aspresented, have not been reviewed by the Offshore Technology Conference and are subject tocorrection by the author(s). The material, as presented, does not necessarily reflect anyposition of the Offshore Technology Conference, its officers, or members. Papers presented atOTC are subject to publication review by Sponsor Society Committees of the OffshoreTechnology Conference. Electronic reproduction, distribution, or storage of any part of thispaper for commercial purposes without the written consent of the Offshore TechnologyConference is prohibited. Permission to reproduce in print is restricted to an abstract of notmore than 300 words; illustrations may not be copied. The abstract must contain conspicuous

acknowledgment of where and by whom the paper was presented. Write Librarian, OTC, P.O.Box 833836, Richardson, TX 75083-3836, U.S.A., fax 01-972-952-9435.

AbstractHurricane Ivan is one of several hurricanes that have

damaged or destroyed fixed offshore platforms in the Gulf of

Mexico in recent years. These events provide a unique

opportunity to determine the effectiveness of structural design

standards and regulations and develop recommendations for

changes, if needed. Specifically, Ivan provided an opportunity

to evaluate the API RP 2A (RP 2A) design process for fixed

platforms to ensure that it provides for well designed

structures.

The first part of this paper describes the general impact of

Ivan on fixed platforms in terms of survival, damage or

destruction. Specific findings and trends are reported related

to global platform performance as well as component

performance. The second part describes a quantitative

assessment to determine the adequacy of the RP 2A design

process. The approach uses a probabilistic based process that

compares analytically predicted platform damage and survival

to that actually observed during Ivan. The result is a Bias

Factor that reflects how well RP 2A predicts platform

behavior under hurricane loads. The work was funded by the

Minerals Management Service (MMS).

Introduction

Ivan was one of several hurricanes in the last dozen yearsthat have significantly damaged or destroyed fixed offshore

platforms. Prior hurricanes are Andrew in 1992 and Lili in

2002. Katrina and Rita in 2005 also caused significant

platform damage and destruction. These types of events

provide an opportunity to determine how fixed platforms in

the Gulf of Mexico perform in hurricanes on both a qualitative

and quantitative basis. The qualitative basis includes a review

of the typical types of damage to topsides and jacket, as well

as the general trends observed, such as the number and type of

platforms with wave-in-deck damage. The quantitative basis

involves the comparison of the observed damage with what

would have been predicted by RP 2A which is the basis for

design of fixed platforms in the Gulf of Mexico. This

provides a quantified assessment of the accuracy of RP 2A

and if it is adequate for design. This paper describes these

assessments for Ivan based upon an in-depth study performed

for the MMS focusing on fixed platforms (no caissons)

[Energo Engineering, 2006]. These types of assessments have

been performed previously for Andrew and Lili [Puskar, et

al., 1994 and 2004]. Recent hurricanes Katrina and Rita in

2005 provide similar opportunities, but have yet to be studied.

Ivan CharacteristicsIvan developed off the west coast of Africa in late August

2004. By September 5th it was a hurricane about 1,100 miles

east of the southern Windward Islands. The hurricane

strengthened running south of the Dominican Republic and

passed within about 20 miles of Grand Cayman on the 12th

By the late afternoon on September 15th, Ivan was in the east-

central Gulf of Mexico approaching the deepwater offshore oi

and gas facilities. During this time, the hurricane was a

Category 4 storm on the Saffir-Simpson scale, with maximum

sustained wind speeds of more than135 mph.

Figure 1 shows the storm track through the key offshore

oil and gas blocks. Also shown in the figure are the fixedplatforms that were destroyed during the hurricane. Ivan

tracked North over the deepwater facilities in the Mississippi

Canyon blocks and up into the Viosca Knoll (VK) and Main

Pass (MP) block areas. The majority of the destroyed o

damaged fixed platforms resided in the VK and MP block

areas. Ivan continued its Northerly track through the eastern

edge of the Mobile block area, making landfall as a major

hurricane with maximum winds of 130 mph on the early

morning of September 16th

just west of Gulf Shores, Alabama.

General Platform DamageA total of seven fixed platforms were destroyed in Ivan as

shown in Table 1. Figure 1 shows the location of theplatforms destroyed. One of the seven (MC 20A) was toppled

by a mudslide, while the other six failures are thought to be

attributed to metocean loads (i.e., wind, wave and current)

exceeding the capacity of the structures. The seven destroyed

platforms are from data provided by the MMS. Note tha

additional platforms may have been later decommissioned by

the operator as a result of damage sustained from Ivan.

There were also a number of other fixed platforms tha

sustained varying degrees of damage during Ivan. Some o

the damage and failures were not considered a surprise, since

the most of the platforms that failed or sustained major

damage were older facilities. These platforms were generally

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designed to lower metocean conditions and generally have

lower global strength characteristics (e.g., weaker joints, less

robust bracing patterns, etc.) than platforms designed and

constructed to newer industry practices. Additionally, these

older platforms typically have lower topside deck heights

which make them significantly more susceptible to wave-in-

deck, which can dramatically increase the loads on the

platform and cause damage. The extent of topside damage onmany of the platforms, both new and older vintage, indicated

Ivan caused extremely large waves and associated wave crest

heights.

The majority of the platforms that failed or sustained major

damage during Ivan were in water depths between 200 to 350

feet and had deck heights at or below the current RP 2A

minimum deck elevation requirements. The resulting damage

to the topsides included deck structure failures and

deformations generally as a result of wave-in-deck. Wind

damage was also observed on quarters and building structures.

The damage to the jackets included jacket leg buckles and

separations, bracing failures (e.g., parted and buckled

members), joint failures (e.g., crushed joint cans and brace

punch through) and conductor bracing failures as discussed

later.

It is important to note that even though damage and

destruction of platforms occurred during Ivan, advance

warning allowed thousands of offshore workers to be safely

evacuated from Gulf facilities prior to the storm reaching the

area [API, Hurricane Readiness Conference, 2005]. There

were also no significant environmental effects.

Although a number of platforms sustained damaged, the

majority of the platforms in the path of Ivan weathered the

storm unscathed or with only minor damage. Figure 2 shows

the percent breakdown of undamaged and damaged fixed

platforms in the path of Ivan. The path represents the

approximate boundaries of the hurricane strength winds, takenas 35 miles to each side of the storm centerline track, although

some of the damaged platforms were outside of this path.

Figure 3 shows the breakdown of the damaged and

undamaged platforms based upon year installed. It is evident

that older platforms sustained more damage than newer

platforms. This is the same observation as for prior

destructive hurricanes Andrew and Lili [Puskar, et. al., 1994 &

2004]. This clearly indicates the improvements in industry

design practices with time and those newer platforms are

much less susceptible to destruction and damage in hurricanes.

Wave Crest and Wave Height Observations

The appropriate deck height for new design as well as forstructural assessments of existing platforms used in RP 2A

Section 17 is a hotly debated topic since Ivan, as well as after

Katrina and Rita. Figure 4 shows the deck heights of the

platforms in the path of hurricane Ivan. The figure shows that

the majority of platforms with decks above the RP 2A Section

2 (new design) minimum deck elevation criteria did not

sustain major damage. The figure also shows a cluster of 200-

350 ft water depth platforms with decks lower than the RP 2A

Section 2 deck criteria that either failed or sustained major

damage during Ivan. One item to note in the figure is there

are a number of deck heights which appear to be questionable

since they are over 55 feet. The deck height data shown in the

figure was obtained from the MMS platform database. It i

suspected that some of these deck heights are the cellar deck

top of steel or in some cases the drill deck instead of the

required cellar deck bottom of steel.

Figure 5 shows the RP 2A design and Section 17

assessment wave height curves compared to the maximum

wave height at the associated platform location per the Ivan

hindcast [Oceanweather, 2004]. The comparison indicates themaximum wave heights during Ivan were generally in excess

of the current RP 2A Section 2 wave height criteria for new

design. The maximum wave heights were computed using the

maximum significant wave height (Hsig) at the site during

Ivan and then converting this to the maximum wave heigh

(Hmax) as computed by the Forrestall distribution. The figure

indicates that it is likely that the platforms in the path of Ivan

particularly the older platforms were exposed to loads in

excess of their original design. The majority of the platform

survived due to the inherent safety factors in the designs.

Additional study of the hindcast data compared to field

observations indicates that several platforms had wave-in-deck

damage, yet this would have not been predicted by the Ivan

hindcast in terms of the crest elevation. In other words, the

predicted maximum Ivan crest elevation is less than the

platform’s deck elevation, yet the platform sustained wave-in-

deck damage. This may be due to several factors including a

lower hindcast Hsig than actual Hsig, uncertainties in

converting Hsig to Hmax, uncertainties in computing the cres

elevation from Hmax, unusual wave crest shapes, or other

factors. This is a technical issue that needs to be explored

further in other studies.

Typical Ivan Fixed Platform DamageThis section provides examples of the typical types of

fixed platform damage caused by Ivan. The damage is broken

down as Topsides Damage (wave-in-deck and wind induced)and Jacket Damage

Topsides Damage -Wave-in-Deck

The majority of the fixed platforms that sustained damage

had evidence of wave-in-deck. The damage includes deflected

structural members on the underside of decks, and in many

cases, damage to equipment and support systems (piping

cable trays, etc.) on the lower decks. Wave inundation on

older platforms with lower decks is not necessarily a surprise

However, some of the newer platforms (1990’s design) also

experienced wave-in-deck, although no major jacket structure

damage occurred, but it did cause significant downtime and

repair costs.The structural damage to the topsides consisted o

distorted lower decks (plating and support under deck

structure), equipment foundation deformation, and in some

cases destroyed equipment shelters on the lower decks.

There was also non-structural damage that was in some

cases more pronounced than structural damage. This

consisted of damaged equipment (power controls, generators

etc.), cable trays, and support utilities located on the lower

decks of the platform. Displaced or missing grating, damaged

handrails and stairs and damaged quarters hampered recovery

efforts as these components need to be in good order prior to

repair activities. Getting these as well as support and safety

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OTC 18325 3

systems (power, fire water, etc.) up and running restricts the

immediate and/or permanent manning of the platform,

requiring work to often be done on a day-trip basis.

Generally, the non-structural damage associated with wave-in-

deck was one of the greatest contributors of platform

downtime following Ivan.

Topsides Damage - WindWind was also a contributor to topside damage as shown

in Figure 6. Numerous platforms exhibited signs of topside

structural failures due to wind loading including damage to

building cladding and displacement/damage of light weight

structures and equipment. One of the more significant wind

related issues was the damage to the temporary crew quarters

on the Petronius compliant tower. The quarters and heliport

toppled over into the center of the deck under wind loads,

resulting in serious damage and considerable downtime

[Wisch, 2005].

Jacket DamageThe majority of the underwater jacket damage was

confined to older platforms. Underwater jacket damage

includes jacket leg failures, joint failures, brace failures and

conductor guide frame failures. Examples are provided in the

following.

Jacket Leg FailuresLocal leg buckling was observed on four of the platforms

that sustained major damage. Three of the SP platforms are of

similar design, installed in late 1960s in approximately 230 ft

water depth. All three have an 8 pile with 8 skirt pile

configuration and are orientated in the same direction. Wave-

in-deck was observed on all three platforms and local buckles

were observed on the North/Northwest legs. Ivan approached

the platforms from the southeast and it was the leeward sidelegs under higher compression loading that buckled.

A MP platform also sustained leg buckling and separation

on the two diagonally opposed legs. The orientation of the

platform and photos of the observed damage are shown in

Figure 7. The platform is a four pile platform and the A1 and

B2 legs were separated. The X-bracing was also separated at

two locations near the leg damage. Note that the wave action

and subsequent movement of the platform caused the leg to

expand outward at the both ends, almost as if it were an

external ring stiffener, as seen in Image A. Similar damage

was observed in Lili [Puskar, et.al., 2004].

Joint FailuresJoint failures including cracks, punching and crushing

were observed on many of the platforms that sustained major

damage. Several examples are shown in Figure 8. Image A

shows a 24-inch diameter X-brace joint crushed under wave

loading from Ivan. The platform was designed in the late

1970’s. Since then, RP 2A has improved joint design

formulations. In this case, a joint can (i.e., the thicker walled

section of the through member) was present in the design.

However, it was only marginally thicker than the connecting

members and failed.

Figure 8, Image B shows an example of joint punching

failure. The brace was pushed through the chord member and

demonstrates a classic punching failure. This damage wa

located on conductor guide framing.

Brace FailuresThe majority of the platforms with major damage

sustained jacket brace failure. Most of bracing damage wa

local buckling of the bracing. Figure 9, Image A, shows

several examples, including a buckled 24” diameter X-braceNote that in this photo the marine growth was not cleaned off

instead it popped-off as the brace deformed. Marine growth

that has popped-off in this manner is often a clue during

inspections that some form of damage has occurred and

further inspection is required. Figure 9, Image B, shows an

example of a severed brace. The brace is 26-inch diameter x

½-inch wall thickness and the material yield strength is 50 ksi

Note the ends of the brace have been flattened out. This

occurred after the brace separated, and then the brace ends

came into repeated contact caused by the back and forth

motion of the jacket during the storm.

Conductor Guide Frame FailuresThis type of damage has been observed in Andrew and Lil

and is the result of fatigue damage due to the upward and

downward loads as waves pass through the structure. An

example is shown in Figure 10 including the location of the

conductor tray on the platform. In extreme storms like Ivan

these normally low-stress high-cycle fatigue issues become

high-stress low-cycle fatigue that quickly escalates to this type

of damage. The first conductor guide framing below the

waterline on many platforms is between the -20 ft to -40 f

elevation and if not properly designed can be susceptible to

this type of damage. The conductor tray may even come ou

of the water as the trough of an extreme wave like in Ivan

passes the structure, and this may in addition cause wave-slam

loads. The design characteristic typically causing this problemis the plating often found around the conductor guides, which

dramatically increases vertical wave area/load (compared to

conductor frames with tubular framing only). Another cause

is the fact that many older conductor trays are attached to the

legs via long-span horizontal bracing, often without any

vertical bracing to the tray itself, making the tray susceptible

to up-and-down vertical wave motions. This movemen

ultimately results in a fatigue problem. Note in Figure 10

Image A, how the steel coupon from the chord remains on the

end of the separated conductor guide brace. This type o

separation is characteristic of a fatigue failure where the crack

initiates at the weld toe on the chord member, and over time

the crack propagates in the chord material and around theweld. Eventually the brace completely separates from the

chord and may fall off of the platform.

Quantitative AssessmentThis provides a comparison of a platform’s actua

response to the hurricane Ivan (destroyed, damaged or

survived) versus what the load and resistance recipe in RP 2A

predicts in terms of an analytical response. In other words, i

a platform was destroyed in Ivan – would this have been

predicted by RP 2A? A probabilistic Bayesian updating

process was used based upon an approach first used in 1994

for Andrew and repeated in 2004 for Lili. Details of the

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approach can be found in the associated references [Puskar, et.

al., 1994 & 2004] and are not repeated here. The Andrew and

Lili studies show that there is about 15% conservatism

inherent in RP2A once all known factors of safety are

removed.

The approach results in what is known as a “Bias Factor,”

which indicates the ratio of the actual capacity of the platform

determined by observation to its analytical capacitydetermined using RP 2A. If a platform survives after a

hurricane, while RP 2A analyses predicted it should have been

destroyed, this platform has a Bias Factor greater than 1.0. In

this case it would imply that the RP 2A analysis recipe is

conservative. The Bias Factor is computed with all known

factors of safety (FS) in RP 2A removed (i.e., the bias is in

addition to the normal RP 2A FS).

The prior work for Andrew and Lili resulted in Bias

Factors of approximately 1.1 and 1.25 respectively. The bias

is approximately 1.15 when Andrew and Lili are combined.

These results imply that RP2A is doing a good job in terms of

fixed platform design, with an inherent conservatism of about

15%.

For this study, the Bias Factor was recomputed considering

Ivan, based upon six platforms – 2 destroyed, 3 damaged and

1 survived. The results are shown in Figure 11. The resulting

Bias Factor for Ivan is 1.0, which means the prediction

matches the observation almost exactly. The Bias Factor for

Ivan was then combined with Andrew and Lili to determine a

combined Bias Factor of 1.10 considering all three hurricanes.

Note that the combined Bias Factor was calculated through a

complicated probabilistic process and is not obtained by

simply averaging the three individual Bias Factors.

The Ivan Bias Factor is lower than for Andrew and Lili.

The lower Ivan results may be explained by the particular

selection of the specific platforms used to determine the Bias

Factor, mostly damaged or destroyed. The inclusion of moreplatforms that survived Ivan, would increase the Bias Factor,

but there was little information on survived platforms

available to this study (most operators study damaged

platforms and not those that survive). There is also a

possibility that some of the damaged platforms had prior

unknown existing damage that was not taken into account in

the assessment. Hence the Ivan Bias Factor is believed to be

conservative.

Another factor for the lower Ivan Bias Factor may be the

large number of wave-in-deck damaged and destroyed

platforms and the associated uncertainties, such as wave crest

elevation and the associated wave-in-deck loads. As noted

previously, wave-in-deck issues should be investigatedfurther.

Overall, the Quantitative Assessment for Ivan indicates

that the RP 2A fixed platform design approach has a Bias

Factor of about 1.0. When combined with Andrew and Lili,

the Bias Factor increases to 1.10. These results indicate that

RP 2A is doing a conservative job.

ConclusionsIvan provided an opportunity to evaluate fixed platform

performance in extreme storms. The results were generally as

expected, with most of the destroyed or damaged platforms of

older design. As in hurricane Andrew and Lili, most of the

destroyed platforms were thought to be the result of wave-in-

deck loads.

There were a significant amount of platforms with wave-

in-deck damage and wind damage that caused the platforms to

be shut-in for an extended period while repairs were made

There was significantly more wave-in-deck damage for Ivan

than for Lili and Andrew, indicating very large waves for

Ivan. In particular, the wave crest elevations as determinedfrom observed deck damage were exceptionally high.

The quantitative assessment indicated once again that RP

2A does a good job of predicting platform performance, with a

Bias Factor of 1.0 for Ivan and 1.10 (or about 10 percent

conservatism) when combined with prior results for Andrew

and Lili. The lower Ivan value is thought to be a combination

of the platforms selected for the assessment, which were

mostly destroyed or damaged and are thought to provide a

conservative estimate (i.e., lower Bias Factor than actual).

AcknowledgementsThe authors wish to thank their respective organizations

for the opportunity to publish this paper. We also wish to

thank the MMS for sponsoring the effort.

ReferencesABS Consulting, “ Hurricane Lili’s Impact on Fixed Platforms”

Final Report to the Minerals Management Service, June, 2004.API, " Hurricane Readiness and Recovery Conference," Sponsored by

the American Petroleum Institute, Houston, Texas, July 26-272005.

API, Recommended Practice for Planning, Designing and

Constructing Fixed Offshore Platforms, API RP 2A, Twenty

First Edition, 2nd Supplement American Petroleum Institute(API), Washington, D.C., October, 2005.

Energo Engineering, “ Assessment of Fixed Offshore Platform

Performance in Hurricanes Ivan Lili and Andrew,” Final Repor

to the Minerals Management Service, Report Number 549January, 2006.

Laurendine, T. “ Hurricane Ivan Impact to Offshore Facilities and

Status on Section 17 Assessments”, Presentation given during2005 Hurricane Readiness and Recovery Conference –Production Facilities Break-out Session, Houston, Texas, July

27, 2005.MMS, “ Impact Assessment of Offshore Facilities from Hurricanes

Katrina and Rita”, News Release #3418, January 19, 2006.Oceanweather Inc., Hindcast Study of Hurricane Ivan (2004)

Offshore Northern Gulf of Mexico, December 2004.O’Conner, P. “Observations from Pompano and Nakika”

Presentation given during Hurricane Readiness and RecoveryConference – Production Facilities Break-out Session

Presentation on Hurricane Ivan Damage Observations, Houston

Texas, July 27, 2005.Puskar, F. J., Aggarwal, R. K., Cornell, C. A., Moses, F. and

Petrauskas, C., “ A Comparison of Analytical Predicted Platform

Damage During Hurricane Andrew”, Proceedings, 26thOffshore Technology Conference, OTC No. 7473, May 1994.

Puskar, F.J., Ku, A. and Sheppard, R.E., “ Hurricane Lili’s Impact on

Fixed Platforms and Calibration of Platform Performance to

API RP 2A,” Proceedings, Offshore Technology ConferenceOTC No. 16802, May 2004.

Wisch, D. “Some Observations - Petronius and VK 900”

Presentation given during Hurricane Readiness and RecoveryConference – Production Facilities Break-out Session, HoustonTexas, July 27, 2005.

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1 MC 20 A 475 1984 L1 49 8-P destroyed

2 MP 98 A 79 1985 L1 57.5 TRI destroyed

3 MP 293 A 247 1969 L2 45 8-P destroyed

4 MP 293 SONAT 232 1972 L2 42 4-P destroyed

5 MP 305 C 244 1969 L2 46 8-P destroyed

6 MP 306 E 255 1969 L2 46 8-P destroyed

7 VK 294 A 119 1988 L2 32 B-CAS destroyed

8 MP 296 A 212 1970 L2 46 8-P major (D)

9 MP 277 A 223 2000 L2 50.3 4-P major (D)

10 MP 279 B 290 1998 L2 53.5 major (D)

11 MP 138 A 158 1991 L2 55 4-P major

12 MP 311 B 250 1980 L2 39.5 8-P major

13 MP 296 B 225 1982 L2 49.2 8-P major

14 SP 62 A 340 1967 L2 40 8-P SK major

15 SP 62 B 322 1968 L2 44 8-P SK major

16 SP 62 C 325 1968 L2 48 8-P SK major

17 VK 900 A 340 1975 L2 46.3 8-P major

18 MP 281 A 307 1999 L2 52 4-P major

19 MP 289 B 320 1968 L1 45 8-P major

20 MP 290 A 289 1968 L2 42 8-P major21 MP 305 A 180 1969 L2 45 8-P major

22 MP 305 B 241 1969 L2 46 8-P major

23 MP 306 D 255 1969 L2 46 8-P major

24 MP 306 F 271 1978 L2 49 4-P SK major

25 VK 786 A-Petronius 1754 2000 L1 55 C-TOWER major

26 VK 780 A-Spirit 722 1998 L1 49 4-P minor

27 VK 823 A-Virgo 1130 1999 L1 47 OTHER minor

28 MP 261 JP 299 2001 minor

29 MP 298 B-VALVE 222 1972 L2 43 4-P minor

30 MP 144 A 207 1968 L2 62.2 4-P minor

31 MP 252 A 277 1990 L2 50 4-P SK minor

32 MP 280 C 302 1998 L2 52 minor

33 SP 60 D 193 1971 L2 49 8-P minor

34 VK 989 A-Pompano 1290 1994 L1 55.8 4-P SK minor

Damage Category

(Note 1)

No. Area Block Year of

Installation

Exposure

Category

Deck Height

(ft)

Structure TypeWater Depth

(ft)

Note 1: Damage Categories: Destroyed – Complete Structural collapse of the platform. Major – Severe structural overload to the primary load bearing

members. Major (D) – Major damage and later decommissioned. Minor – Some structural damage but generally to secondary structures.

Table 1 – Platforms Damaged by Hurricane Ivan

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Mobile

Chandeleur Area

Viosca Knoll

Chandeleur Area, East Addition

Main Pass Area

Breton Sound Area

Main Pass Area, South and East Addition

Viosca Knoll

West Delta Area

South Pass Area

South Pass Area, South and East Addition

South Pass Area, South and East Addition

South Pass Area, South and East Additionelta Area, South Addition

MP 277'A'4-Pile in 223' Water DepthInstalled in 2000

MP 296 'A'8-Pile in 212' Water DepthInstalled in 1970

MP 279 'B'4-Pile in 290' Water DepthInstalled in 1998

MC 20'A'8-Pile in Mudslide Area475' Water DepthInstalledi n 1984

MP 305'C'8-Pile in 244' Water DepthInstalled in 196946' Bottom Deck Height

MP 306'E'8-Pile in 255' Water DepthInstalled in 196946' Bottom Deck Height

MP 293'A'8-Pile in 247' Water DepthInstalled in 196945' Bottom Deck Height

MP 293 SONAT4-Pile in 232 Water DepthInstalled in 197242' Bottom Deck Height

MP 98'A'

Tripod in 79" Water DepthInstalled in 198557' Bottom Deck Height

VK 294'A'Braced Caisson in 119' Water DepthInstalled in 198832' Bottom Deck Height

09/15/2004 6pm88.2W 28.8N135 mphmax. wind

27.49mb pressure

09/15/2004 10pm88.1W 29.3N135 mphmax. winds27.55mbpressure

09/16/2004 2am87.8W 30.2N130 mphmax. wind27.85mbpressure

MATTERHORNMATTERHORN

HORNMOUNTAINHORNMOUNTAIN

RAM POWELLRAM POWELL

NEPTUNENEPTUNE

PETRONIUSPETRONIUS

MARLINMARLIN

VIRGOVIRGO

SPIRITSPIRIT

Figure 1 – Path of Hurricane Ivan Showing the Locations of the Destroyed Fixed Base Platforms.

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6%

14%

6%

75%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Destroyed Major Damage Minor Damage No Damage

Damage Category

P e r c e n t a g e o f P l a t f o r m s i n S t o r m P

a t

h

Figure 2 - Damaged Platforms Sorted by Damage Type

2

23

62

4

11

3

4

4

3

2

1

4

0

10

20

30

40

50

60

70

80

Pre - 1978 1978 - 1991 (9th Edition) 1992 - 2000 (19th Edition) 2001 - Present (21st Edition)

Platform Vintage (year)

N u m b e r o f P l a t f o r m s

Destroyed

Major Damage

Minor DamageNo Damage

One Platform Destroyed

by Mudslide

Figure 3 - Damaged Platforms Sorted by Vintage (Year Installed)

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20

30

40

50

60

70

80

0 100 200 300 400

Water Depth (feet)

D e c k H e i g h t ( f e e t )

RP 2A - Section 2

RP 2A - Section 17 - L1



Destroyed

Major Damage

Minor Damage

No Damage

MP 98 A

Modified Caisson

Destroyed

MP 138 A

4-PileJacket Damage

VK 294 A

Braced Cassion (Designed for

wave inundation)

Destroyed

Questionable Deck Hei hts

Section 2 - L1

Section 17- L1

Section 17- L2

Section 17- L3

Figure 4 - Deck Heights of Platforms in the Path of Andrew Compared to API RP 2A Minimum Deck Elevation RequirementsThe deck heights were taken form operated supplied elevations to the MMS. As indicated, some of the deck elevations above 55’ may be

inaccurate since few platforms have decks this high.

20

30

40

50

60

70

80

0 50 100 150 200 250 300 350 400

Water Depth (ft)

I v a n H i n d c a s t W a v e H e i g h t ( f t )

Section 2 - L1

Section 2 - L2

Section 17 - L1 - DL

Section 17 - L2 - DL

Destroyed Platforms

Major Damaged Platforms

Minor Damaged Platforms

Section 2 - L1

Section 2 - L2

Section 17 - L1

Design Level

Section 17 - L2

Design Level

Figure 5 - Hindcast Maximum Wave Heights at Locations of Platforms in the Path of Andrew Compared to API RP 2A Wave Height Criteria

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Image A

Image B

Image D

Image C

Figure 6 - Topsides Wind Damage from IvanImages A to D show a variety of deck equipment damaged by wind.

B2B1

A1 A2

P l a t f o r m

N o r t h

Legseparation

Conductors

Legseparation

Leg

Leg

Pile

Image A Image B

Leg

Platform Orientation

Figure 7 - Jacket Leg Damage from IvanImage A shows the leg where it severed and was flattened due to the back and forth motion of the waves.

Image B shows a severe near a circumferential weld.

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Image A

Image B

Figure 8 - Joint Damage from IvanImage A shows a collapsed 24” joint can that was undersized.

Image B shows a brace punched completely through the chord.

Image A

Image B

Figure 9 – Brace Damage from IvanImage A shows a buckled 24” brace.

Image B shows a 26”brace that completely severed.

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Couponremains

Couponremains

Conductors

Image A

Image B

Typical Fixed Platform Framing

First elevation of

conductor bracingbelow waterline

(typically between-25’ to -40’ feet).This is theconductor framingelevation most

susceptible todamage.

Waterline Elevation

Typical boatlanding structure

ConductorsPumpCaisson

Legs

Figure 10 - Example of Conductor Guide Framing Damage from IvanThe figure on the right shows the typical location of conductor guide framing located near the water line that is prone to this type of damage.

Figure 5Bias Factor Comparison

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0.6 0.8 1.0 1.2 1.4 1.6 1.8

Bias Factor for Jacket Strength

P r o b a

b i l i t y D e n s i t y

Combined

Andrew

Lilly

Ivan

Ivan, mean=1.00

Lilly, mean=1.24

Combined, mean=1.10

Andrew, mean=1.09

Figure 11 - Comparison of Bias Factors Determined for Ivan, Lili and Andrew

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