The Piper Alpha disaster that killed 167 workers on July 6, 1988 off the coast of Aberdeen, Scotland, remains the world’s deadliest offshore oil platform accident. The controversy around it was heightened when an investigation of the disaster by Scotland’s Department of Energy ruled the operating company, Occidental Petroleum, had used inadequate maintenance and safety procedures. The report made more than 100 recommendations about how safety could be improved in the North Sea. This report is still cited 25 years later and is regarded as the foundation of the modern safety hazard mitigation procedures that we utilize today.
Piper Alpha was once Britain’s biggest oil and gas producing platform, supplying more than 300,000 barrels of crude a day — 10 percent of the country’s total — from below the seabed 125 miles northeast of Aberdeen.
Oil was discovered at the Piper field in 1973 and was brought on stream three years later. By 1980, the steel platform was modified to also produce gas and was connected by pipeline to the Orkney Islands. When the platform exploded, 167 out of 228 workers on the rig or on one of the safety standby vessels servicing the rig died. The platform was completely destroyed and it took almost three weeks for the fire to be brought under control by famed Houston wild well controller, Red Adair.
The accident cost the Lloyd’s insurance market more than $1.6 billion, making it the largest insured man-made catastrophe in history. Occidental paid $100 million to families of the deceased but escaped any kind of criminal or civil sanction.
On the original structure the staff quarters were located well away from the most dangerous production areas of the platform. However, this safety feature became diluted when the gas compression units were installed next to the central control room.
The root cause
Further dangers arose when Occidental decided to keep the platform producing oil and gas as it set about a series of maintenance activities and production upgrades. This decision to expose workers, long term, to a combination of operations hazards in conjunction with the safety risks associated with industrial construction activities was the root cause of the Piper Alpha disaster.
Lessons learned
Following this horrific incident, the oil and gas industry looked for new ways to reduce field work under hot conditions on the platform. Early on, driving platform construction tasks into onshore fabrication shops were identified as an obvious improvement.
To effectively utilize onshore fabrication to reduce platform welding, fabricated components must be delivered dimensionally correct and ready to install. If fabrication arrives at the rig with inherent dimensional problems, rework of the spool will be required. The modification of the component as required for fit-up results in the cutting and welding activities we are attempting to eliminate. Only by reducing the construction scope of work to welding and bolting of components ready to install without modification can the identified safety benefits be realized. If our goal of ready to assemble components is achieved, the following benefits will also follow.
• The elimination of last minute unplanned rework tasks that will invariably negatively impact safety and previously well planned and scheduled activities.
• Avoiding the necessity of planning and scheduling new rework driven activities in a construction driven environment rather than a construction planning environment.
• Manpower requirements for rework activities are eliminated resulting in a reduction of man-hours on the project thereby reducing the safety exposure.
• Manpower requirements for rework activities are eliminated resulting in a reduction in the number of craftsmen on site, which reduces the manpower density of the project. Fewer people to track and monitor and fewer tasks to manage and schedule provide a definite safety advantage.
• A reduction in fabrication and laydown space on the platform where space is limited.
Where and how dimensional errors occur
This approach appears intuitive on the surface but implementation is more difficult than you might assume. Three distinct project phases were identified where dimensional errors and tolerance accumulation occur. To reduce rig construction activities to welding of bolting of dimensionally verified components without revision, all three must be addressed and controlled.
• Errors in design — These are errors that occur in the measurement of existing equipment and piping. When these errors are incorporated in the design documents, fabrication will, by definition, not be compatible with existing piping and equipment in the field.
• Errors in fabrication — Obvious errors, such as fabricating a left hand instead of the right hand that was required, are common on every project. Other more subtle errors such as errors in interpreting and following fabrication documents and material layout errors also go undetected resulting in rework in the field.
• Errors in the installation of field fabricated elements — The layout of equipment foundations, supports and structural steel on site are common sources of error. Layout of cut lines on piping and equipment on the jobsite can also be challenging. When these errors occur, the results are usually systemic and pervasive.
Traditional methods such as hand dimensions and more recently technology such as laser scans that are typically utilized for dimensional control for industrial application have inherent problems that limit their use for all three of the sources of error listed above. A comprehensive dimensional control effort requires greater precision and flexibility than laser scans can provide. This is why construction schedules and budgets are frequently overrun due to rework issues and leave-long field fits are still used for industrial construction applications.
The remedy — a new precision standard
TGC Engineers (TGCE) has a proven comprehensive work process for the elimination of rework due to fit-up problems regardless of the root cause (design, fabrication and/or platform construction activities). TGCE’s work practices are proprietary and were developed in the field while working in refineries and petrochemical plants with other engineering and construction professionals. The high level of detail and precision delivered by our measurement methodology allows TGCE, in conjunction with the project team, to provide a zero rework project. No other work process, including laser scanning technology, can make that claim.
To ensure all errors are eliminated, a new comprehensive and precise checking procedure has been developed by TGCE. Every component must be trial fit in model space to ensure fit-up before release for installation. This precision checking work process is made possible by the integration of the as-built model with the model of fabricated components as they are actually assembled (not as designed). Models of individual spools and equipment are generated during fabrication checks in the shops for the verification of these elements. By assembling these small models in conjunction with the as-built model, the entire project can be trial fit before the construction phase of the project begins. This trial fitting in model space provides a dimensional check at the connection level. A flange face deviated out of plane or a rotation out of two holing can be detected and corrected. With this technique, fabrication tolerances that accumulate with every spool are also considered, providing a complete comprehensive check of fit-up of the entire project.
Conclusion
Now 25 years after the incident that triggered the largest industrial safety campaign in history, a work process that can and does provide a zero rework project is available to meet the safety and productivity requirements of our industry. TGCE remains the leader in precision for industrial dimensional control services, delivering no rework projects for safety-driven industrial project applications.
For more information, visit www.tgcengineers.com or call (713) 477-8682.
