An API task group has developed a process for the assessment of existing platforms to determine their fitness for purpose. This has been released as a draft supplement to API RP 2A-WSD, 20 th edition'. Details and the background of this work are described in a companion paper 2 •
TO MEASURE AND IMPROVE yield in mixedsignal circuits, we propose a strategy that consists of observing, examining, and altering yield-influencing factors at the start of manufacturing design. We categorize yield factors as being related to defect, device mismatch, and at-speed functional problems associated with a flawed design model or load simulation. Our approach uses diagnostic circuits to supplement conventional test structure data and to highlight the device attributes that correlate to product yield. We use embedded diagnostic circuits as yield-monitoring vehicles. These structures-in conjunction with a test and analysis framework-constitute infrastructure IP that is extensible to other products within the same manufacturing process.Mixed-signal systems combine analog, memory, and logic blocks on the same semiconductor substrate. Reducing the required number of chips in the product system can lower cost and enhance functionality. Such a system on a chip can reduce chip size, form factor, packaging, and board requirements. The cost effectiveness and ultimate viability of SoCs, however, depends on their manufacturability. SoCs have to match yield levels typical of standalone analog chips, logic, and memory. The physical proximity of SoC subcircuits, howev-14 Mixed-signal systems offer advantages over multichip systems but are more difficult and complex. A comprehensive design-testing plan could increase the viability of SoCs.
This paper outlines and illustrates an engineering evaluation procedure for re-qualification of high consequence offshore platforms. The procedure is illustrated with application to a Cook Inlet patform that was damaged by a blowout. The anaPyses and evaluations documented in this paper indicate that the damage was successfully repaired, and that the structure in its repaired condition is fit for purpose. INTRODUCTION In 1985, a platform operated by Unocal (coowned by Marathon and Arco) located in Cook InIet, Alaska (Fig. 1), experienced a blowout which created a large crater encompassing three of its four legs (Fig 2.) The blowout serious y damaged the foundation (crater depth at Leg-1 was approximately 80-fi deep) and caused some damage to the superstructure. The foundation was repaired by filling the crater with 100,000 cubic yards of gravel and by driving twelve 20-in diameter insert pies into the existing piles in Leg-1. Preliminary studies of the performance of the repaired platform when it was subjectedto lateral loadings from earthquakes and ice floes indicated that a more rigorous and detailedevaluation of the serviceability of the platform during extreme conditions was necessary [1,2]. BACKGROUND The platform location is in upper Cook Inlet in a water depth (mean lower low water) of 125 ft. The maximum tidal range is approximately 30 ft. The Inlet is covered with ice during the wintermonths. Strong tidal currents move ice up and down the Inlet twice a day. Ice thickness can range from 3 fi to in excess of 6 ft (rafted, Stamuki). Cook Inlet is situated in one of the most active seismic zones in the world. Numerous majorearth shakes have occurred in this area including the 1964 Good Friday Prince William Sound earthquake (magnitude 8.5). In the last 65 years, 15 events of magnitudes greater than 6 have occurred in thisarea. Subsurface soil conditions vary greatly and ran e from soft unconsolidated clays on the west sideoft i?e Inlet to boulder-covered extremely stiff clays in the middle and east side. In the upper Inlet the soil conditions generally can be classified as deep, firm alluvium. The platform is a steel, tower-type platform that has four 17-ft diameter legs (Fig. 1). The toweris braced with horizontal and vertical X-bracing below water (Fig. 1? 3). The le s span the tidal zone (kept open to minimize ice loafing) and are joined at the deck level by 17-ft diameter horizontal beamtanks. The multi-level enclosed drilling and productiondecks are mounted on top of the beam tanks. Each of the platform?s legs contain 12, 33-inand 26-in diameter two stage piles (Fig. 3). Inside the piles are well conductors (multiples strings of casing) that are cemented to the formation and the piles. The soil conditions at the platform (Leg-1 profile, Fig. 4) consist of very strong stiff clays belowpenetrations of about 125 ft overlain b lower strength stiff clays and the gravel used to F111the blowout crater.
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