Offshore Lessons Learned

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Offshore accidents & lessons learned from them.

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<p>CORE Report 2007-05 Offshore Technology: Lessons Learned the Hard Way Inaugural Lloyds Register Educational Trust Lecture, Delivered by Prof Peter Marshall on 5 September 2007 in National University of Singapore</p> <p>Offshore Technology: Lessons Learned the Hard WayPeter W. Marshall Department of Civil Engineering and Centre for Offshore Research &amp; Engineering National University Singapore</p> <p>ABSTRACTPeter Marshall is an original author of many parts of the RP 2A standard for offshore platforms, and a member of the API Hurricane Evaluation &amp; Assessment Team (HEAT). When he received the OTC 2006 Distinguished Achievement Award for individuals, the five-minute acceptance speech did not allow a full expose' on how dealing with risk has been an essential part of the offshore industry in general, and his 45-year career in particular. See I-wasthere descriptions of oil spills, blowouts &amp; fires, collisions, hurricane survivals, structural failures, and technological blunders. Hear how industry-consensus standards extracted valuable lessons from these events, and continue to do so today.</p> <p>Seams are made by automatic submerged arc welding.</p> <p>KEY WORDS: Offshore technology; fixed platforms; hurricanes; blowouts; fires; collisions; tubular joints. INTRODUCTIONThe first figure shows an example of the permanent fixed offshore platform, in 40 m water depth. It supports wells, a drilling rig, and oil processing equipment. A tubular space frame extends from the sea floor to just above the surface. Steel pipe piles are driven through the legs to anchor it. A superstructure deck on top supports the equipment and keeps it out of reach of wave action. Now comes the tricky part tube-to-tube structural T- Y- and Kconnections. Notice the saddle shaped cope and carefully maintained root gap. The weld geometry and position vary around the circumference. AWS D1.1 prescribes special welder qualification for this the 6GR test.</p> <p>Platform fabricators roll their own, making structural steel pipe from plate, according to API Spec 2B.</p> <p>Tubular frames, or bents, are welded at ground level, then tilted up to make the space frame.</p> <p>1</p> <p>CORE Report 2007-05 Offshore Technology: Lessons Learned the Hard Way Inaugural Lloyds Register Educational Trust Lecture, Delivered by Prof Peter Marshall on 5 September 2007 in National University of Singapore</p> <p>The completed space frame, or jacket, is loaded onto a barge for transport and launch at sea. In the late 1960s, this technology was extended to 100m water depth</p> <p>Piles are stabbed into the jacket legs, and driven with a steam or hydraulic hammer which rides on top of the pile. Welded splices and shim connections at the top of the jacket are performed in the field.</p> <p>The deck is lifted on, here in three pieces, to complete the structure. Drilling and production modules are then placed on top.</p> <p>and to the icy waters of Alaska.</p> <p>2</p> <p>CORE Report 2007-05 Offshore Technology: Lessons Learned the Hard Way Inaugural Lloyds Register Educational Trust Lecture, Delivered by Prof Peter Marshall on 5 September 2007 in National University of Singapore</p> <p>It must be admitted that there was a lot of learning things the hard way i.e. from mistakes. Offshore pioneers had a revolutionary buccaneering spirit, and a staff of former military officers who knew how to take risks and deal with setbacks. But the 1960s were also a time when most of the basic research was done on wave forces, ice loads, laterally loaded piles, and tubular joints.</p> <p> and a more visible mess on the beach. There was a huge public outcry, and a growing distrust of technology. President Nixon signed the Environmental Protection Act into law. LESSON: Public perception is very important, and politically insensitive statements can be devastating.</p> <p>Human factors play a big role in technological disasters, from outer space to something as mundane as the failed levees at New Orleans.</p> <p>Blowouts, fires, and collisionsThese events are often beyond the control of structural designers, but nevertheless interesting to talk about. In 1969, a well being drilled from this platform (visible from shore at Santa Barbara, California) breached a fault plane which had previously been only an intermittent natural seep.</p> <p>What happens when the roughneck goes to lunch and forgets to close the master valve on a live well? Oops! doesnt quite cover it. Several men were killed in the initial explosion, but the rest got off safely, albeit some with severe burns. The authors open deck structure stood up well; this picture was taken the next day.</p> <p>Heavy crude from the undersea blowout made a big mess in the water</p> <p>3</p> <p>CORE Report 2007-05 Offshore Technology: Lessons Learned the Hard Way Inaugural Lloyds Register Educational Trust Lecture, Delivered by Prof Peter Marshall on 5 September 2007 in National University of SingaporeLESSON #1: Teflon seals are not heat resistant, allowing several other wells to begin leaking. LESSON #2: The safety devices of the day, storm chokes, stayed open at normal production rates. We now use SSSCSVs (subsurface, surface controlled safety valves) which fail shut. still far offshore. This deck was the authors first major project, requiring three lifts to install, and a world-record single lift to remove.</p> <p>Here she comes. The second black dot is the worlds first semisubmersible, Bluewater I, moored nearby.</p> <p>More oil was released here at Bay Marchand, Louisiana, than at Santa Barbara, yet there was no outcry. LESSON #3: Good Crisis management helps. Most of the oil was allowed to burn up. Too precious to waste was not yet a slogan. Skimmer booms collected much of the rest. Red Adair and his firefighting barge made good press tours. Meanwhile, rigs in the background drill relief wells to intersect the burning ones and pump them full of cement. LESSON: Drifting semi-submersibles can do serious damage.</p> <p>CollisionsWD 134A platform, in 285-ft water, briefly held the world record when completed in 1965. Hurricane Betsy flooded the eastern half of New Orleans that same year. Here, in the calm before the storm, spiraling high altitude clouds foretell her approach when she was</p> <p>Underwater inspection by the author in a mini-sub showed that heavily reinforced structural joints performed well; the upper brace buckled and severed well outside the connection.</p> <p>4</p> <p>CORE Report 2007-05 Offshore Technology: Lessons Learned the Hard Way Inaugural Lloyds Register Educational Trust Lecture, Delivered by Prof Peter Marshall on 5 September 2007 in National University of SingaporeSignature of a Hurricane Hilda, 1964</p> <p>Circle below shows source of this found art sculpture. Some of the early platforms simply disintegrated, leaving holes in the jacket legs where the braces pulled out a plug. Research showed very high shell bending stresses at the hot spot adjacent to the connecting weld. Failures were easier to explain than sister platforms which survived. Testing showed a surprising amount of reserve strength after first yielding at the hot spot. Capacity at failure was represented by punching shear on the observed rupture surface. Putting engineers in mini-subs proved risky, as the Star I got tangled up in the wreckage on the very next dive. LESSON: Do subsea inspections with ROVs (remotely operated vehicles) instead. Swimming TV cameras send back excellent close-ups.</p> <p>LESSONS FROM STORM DAMAGEThe offshore industry recently got a wake-up call from Hurricanes Ivan, Katrina, and Rita (2004-05), in which 130 or 4000 fixed platforms were lost. Hurricanes Hilda (1964), Betsy (1965), and Camille (1969) were my generations terrible trio, in which we lost 50 of 1500. LESSON (1964): A 25-year design wave has a high likelihood of being exceeded. The 100-Year Club is formed. LESSON (2007): Dj vu all over again. Those old 25-year designs should have failed.</p> <p>Punching shear design criteria allowed the use of simple tubular joints, reinforced by increasing the thickness of a joint can section of the jacket leg. The first application was that 40m platform from the Introduction, 1966. The second was the 1967 world record platform at SP 62. Details were published at the first Offshore Technology Conference.</p> <p>The SP 62 platform saw 80-ft (24m) waves in hurricane Camille two years later. The previous 100-year design wave was only 57 feet</p> <p>5</p> <p>CORE Report 2007-05 Offshore Technology: Lessons Learned the Hard Way Inaugural Lloyds Register Educational Trust Lecture, Delivered by Prof Peter Marshall on 5 September 2007 in National University of Singapore(17m). Green water caused considerable damage to deck equipment.</p> <p>Camille, 1969</p> <p>Cost-risk economics were used to justify the criteria increase, to the API reference level used in 9th to 19th editions of RP2A. LESSON: Wave height is not the whole story.</p> <p>Camille was a watershed event, stimulating a new round of research. Some 38 storms from 100 through 1969 were hindcast, with literal results from a picket line of nine sites along the edge of the continental shelf shown here in black. LESSON: The old design wave was too low. The 100-year event for anywhere in the entire NW Gulf of Mexico region was found to be 85-feet (shown in red). For a typical platform site in this region, the 100-year wave was found to be 75 feet. This increase was a hard sell. Eventually, the 9th to 19th editions, API RP2A showed a reference level wave height of 70 feet, with a guideline range of 58ft to 84-ft, and shoaling curves extending back into shallow water. This defined the modern era of platform design.</p> <p>Mudslides. Camille also created massive mudslides. The square is the 5000-acre South Pass Block 70 lease, about 4 km on a side. Changes is seafloor elevation reveal a massive mudslide. Platform B in the middle of the slide was destroyed, and Platform A on the edge moved several feet. LESSON: A 70-ft wall of mud will take out a structure designed only for shallow mudflows.</p> <p>Mud Slides</p> <p>Yet the supporting structure stood, undamaged. Ultimate collapse analysis and survival/failure experience both showed a median load at failure of at least twice the design load. LESSON: Offshore platforms have considerable reserve strength, with plastic load redistribution giving about 40% more capacity than is accounted for by safety factors and known sources of bias.</p> <p>Unstable delta muds lie in an arc 50 km east and south of Venice.</p> <p>6</p> <p>CORE Report 2007-05 Offshore Technology: Lessons Learned the Hard Way Inaugural Lloyds Register Educational Trust Lecture, Delivered by Prof Peter Marshall on 5 September 2007 in National University of SingaporeAfter Camille, a mini-industry grew up to define the problem and design slide-resistant platforms, and to route pipelines around the problem areas.. Nevertheless, after hurricane Ivan in 2004, newcomers to the Gulf of Mexico were surprised to see their pipelines swept away, and the Wall Street Journal called it Prof. Beas obscure theory. inclusions. LESSON: Ordinary steel is not isotropic, but more vulnerable to shrinkage strains in the thru-thickness direction. Fix: specify Zdirection tensile tests, sulfide shape control, or low sulfur steel for joint cans.</p> <p>Materials Problems This heavily reinforced structural connection fractured in hurricane Hilda, yet the structurally redundant 8-pile platform stood up. LESSON: Alternative load paths structural redundancy saved the day.</p> <p>Fatigue. Some of the early field failures (shown at right) appeared to be by progressive tearing, with lots of deformation, leading to an interest in low-cycle fatigue. Southwest Research Institute was investigating similar problems of plastic fatigue in pressure vessels. They tested a 40%-size structural K-connection in both ungrouted and grouted condition (shown at left).</p> <p>Several authors at the first OTC showed examples of ordinary steels with their transition temperatures on the wrong side of Gulf of Mexico, failing by brittle fracture. LESSON: Minimize stress concentrations and use tougher steel in the joint cans, e.g. API Spec 2H.</p> <p>Fatigue cracking and ultimate failure was correlated with hot spot strain gages adjacent to the weld toes. These gages measure local shell bending and membranes stresses, but not the notch effect of the weld itself. Post-mortem sectioning showed the connections to be surprisingly tolerant of weld root defects, and subsequent finite element analysis showed the highest local strains to be on the outside surface. Cracks due to lamellar tearing were also found in the late 1960s, during fabrication. Cracks initiated at microscopic sulfide</p> <p>7</p> <p>CORE Report 2007-05 Offshore Technology: Lessons Learned the Hard Way Inaugural Lloyds Register Educational Trust Lecture, Delivered by Prof Peter Marshall on 5 September 2007 in National University of SingaporeFailure in chord Crack in brace Hot spot Strain gage</p> <p>in red, is that it is all attributable to a thickness effect, and that weld profile notches do not matter. API now considers both effects.</p> <p>Fatigue test post mortem</p> <p>The hot-spot S-N curve was incorporated into AWS D1.1-1972, and relaxed reject criteria for the weld root in tubular connections was incorporated into UT (ultrasonic testing) standards, e.g. API RP 2X.</p> <p>Bigger and better. American fatigue criteria, cowboy technology, enabled the initial push into deeper water and harsher environments. This is the Shell-Esso North Sea Brent A platform, designed in 1974. By the time the more exhaustive European fatigue research was concluded in 1987, the offshore boom was over.</p> <p>Prior to the adoption of RP 2X, a new offshore platform was condemned because UT found cracks at the weld root. This provided full size specimens for fatigue testing at the University of California. External weld profiles merged smoothly with the adjoining base metal, and low cycle fatigue tests gave excellent results.</p> <p>Shells 1000-ft (300m) Cognac platform was also designed in 1974. A competitor subsequently built cheaper platforms in similar water depth, mockingly naming theirs Cerveza (beer) and Liguera (light beer).</p> <p>Subsequent large scale European tests with less desirable weld profiles showed lower results, prompting API to draw a second, lower S-N curve for this case. The European interpretation, shown</p> <p>Cognacs three piece installation was very complex, and never repeated. Two derrick barges in a common mooring system used special heave-compensated lowering devices. Acoustic transponders and a proprietary mooring adjustment algorithm allowed precise</p> <p>8</p> <p>CORE Report 2007-05 Offshore Technology: Lessons Learned the Hard Way Inaugural Lloyds Register Educational Trust Lecture, Delivered by Prof Peter Marshall on 5 September 2007 in National University of Singaporepositioning. Hydraylically adjustable mudmats were used for leveling. Skirt piles were driven through vertical sleeves with an underwater hydraulic hammer, and connected to the base by grouting the annulus. Large skirt...</p>