A Survey Of The Structural Damage Caused By Hurricane Andrew On Some Of The Platforms Located In The South Timbalier Area

Abstract

ABSTRACT This paper summarizes the results of a physical survey conducted on 30 of the platforms located in the ST131, ST135 and ST176 fields of the South Timbalier area, soon after Hurricane Andrew moved through the Gulf of Mexico. The objective of the survey was to document any consistent and defensible physical evidence of damage caused by wave forces to deck equipment or topside structural members, and to use this physical evidence to infer the maximum water elevation, or alternatively, the maximum wave height the structure may have been exposed to during Andrew. The relevance of this survey stems from the fact that there are no direct measurements of the wind, waves or currents in this area during Andrew, and the only assessment of these variables is from hindcast results [1]. INTRODUCTION On August 24-26, 1992, Hurricane Andrew moved through the Gulf of Mexico with sustained winds of 140 miles per hour. According to the most recent MMS estimates [2] approximately 2,000 out of 3,900 oil and gas facilities in the Gulf of Mexico were located within 50 miles to either side of the hurricane path. Of those, 36 major platforms and 165 satellites (most of them caissons) suffered significant damage. Of the 36 major platforms, 10 were completely toppled and 26 were leaning significantly or having significant topsides damage. Of the 165 satellites, 25 were completely toppled, 77 were leaning between 1 and 5 degrees and 43 were leaning between 5 and 45 degrees. Remarkably, and attesting to the effectiveness of the current industry practice, only 2,500 barrels of oil were reported spilled, 2,000 of which attributable to a single incident of a mobile drilling unit having dragged its anchor across a pipeline. In the three fields surveyed, three structures were toppled, and three suffered underwater damaged considered beyond economical repair and either were or will be salvaged. In addition, two other structures suffered moderate underwater damaged and were repaired, and another one had its production deck severed and was also repaired With the exception of the latter, all others were aging platforms designed, fabricated, and installed in the early to mid 1960's. The surveying crew was accompanied by operating personnel who had first-hand knowledge of the condition of each platform before and after the storm. The surveyed platforms were chosen based on their spatial separation in the fields, and the initial post-hurricane damage reports. SUMMARY AND CONCLUSIONS The survey uncovered three consistent pieces of physical evidence of topside wave force damage on many of the structure (1) bent handrails, stairways, and in some eases (bent) heavy deck support beams on the cellar deck level (2) severely bent swing rope support beams (4" S-shaped beams) installed over boat landings on the east side of many of the structure and (3) steel framed well head signs (9"x15") installed on opposite sides of each well head and bent in line with the wave direction. Less consistent, was the movement or upending of very heavy (>2000 lb.) equipment and deck hatches. For typical examples of the damage see Figures 2-13.