Leonard LeBlanc
Houston
NASA shuttle probe affirms effectiveness of casing-type joints
Metal-to-metal sealing has been used in downhole casing for over 20 years. Simple but strong casing joint designs has been built around the technology. One of the key features of metal-to-metal sealing is the ability to withstand high variations of internal pressure and temperature without leakage or distortion.
This capability was exactly what US National Aeronautics and Space Administration (NASA) engineers were looking for in 1986, following the dramatic Challenger mid-air explosion. The accident was caused by propellant burn leakage from section joints in the Challenger shuttle's booster rockets, forcing a re-design of the joints.
The re-design team elected to use enlarged versions of metal-to metal joints developed by ABB Vetco Gray for well casing. The joints have performed successfully for NASA over the past nine years and recent problems with O-rings sealing materials in the nozzle joints were attributed to the methods by which the materials were installed rather than the joining technology.
The 150-ft long booster engine consists of a series of sections of casing with solid propellant placed circumferentially. The centers of the sections are open to allow the propellant to burn from the top down, proceeding through each section to the bottom, exiting out the nozzle at the bottom. Plates at the top of the booster take the burn thrust, but pressures of up to 6,000 psi develop against the section walls and joints.
Before 1986, the joint geometry periodically allowed thrust heat and pressure to reach the elastomer O-rings. In the case of the Challenger accident, pressure overpowered the main joint seal, swept past O-rings stiffened by cold weather, and exited the joint. The side wall exhaust jet burned a hole through the adjacent shuttle's fuel tank wall. The tank exploded during the launch.
Afterwards, ABB Vetco-Gray's Thermalok T-Seal was installed on the inside of the joints, creating a metal-to-metal seal. The T-shaped seal created something badly needed by NASA - a reasonably stiff connection that increased sealing capability with increased pressure, yet flexible enough to follow or outpace (tracking) the expansion of the section walls with high heat levels. The latter is important in maintaining the seal during conditions of maximum stress. Also, the T-shaped seal did not distort the casing walls, an important feature in re-use of the booster sections.
In addition to the joint configuration, ABB Vetco Gray helped develop a seal verification system for the booster joints. The system confirms that the joint components are working correctly.
Recent problems with the putty-like material protecting O-rings were where the nozzle joins the straight sections rather than the sections with solid propellant. Had O-rings in a nozzle joint allowed burn bypass, the shuttle would have been pushed out of control.
Wave power competing with wind and solar power offshore
The petroleum industry is a major user of alternative energy forms in low-power situations. Offshore, solar energy panels have powered data transmission and supervisory control functions on unmanned production structures offshore for a number of years. Presently, wind generators are being installed on several North Sea platforms to power electronics and data transmission functions.
The latest development for offshore power, and a competitor with the other two, is wave power. Ocean Power Technologies of Princeton, New Jersey (US) will install a 1 kW hydropiezoelectric generator on an undisclosed platform in the US Gulf of Mexico early next year. The firm expects to install and have operating a 1,000 kW unit by 1997.
Earlier efforts to develop electric power from the mechanical energy of ocean waves have been defeated by the physical and chemical impact of the ocean on rotating machinery. Ocean Power believes it has overcome these problems by using the piezoelectric effect, which is the conversion of mechanical energy to electrical energy through use of a material with piezoelectric properties.
The system uses the differential between an anchored element and a moving element. A cam moves up and down past piezoelectric elements (plastic-like polyvinyledene fluoride), creating electricity. The material can be manufactured easily in sheets and the floating generating units are simple to assemble. The units reach optimal output at 1-meter wave heights with a frequency of 0.15 Hz.
Pipelines carry data signals over 35 km
A data system being developed in the UK utilizes pipeline walls as a transmission medium. The system was developed by Flight Refueling of Wimborne (Dorset), in association with the OSO, Mobil, Enterprise Oil, British Gas, and Marathon.
The unit couples a subsea electronics module to an acoustic transmitter at one end of the pipeline. An acoustic sensor, at distances of up to 35 km away, picks up the transmitted signal. Attenuation of the signal in pipelines is considerable, but sensitive electronics can pick out the needed data.
The system eliminates use of umbilicals or water acoustics. Originally, water acoustics were the focus of considerable investigation for deepwater operations, but thermoclines and salt saturation variances created major signal distortion.
Immediate applications for pipeline signaling are subsea stepout well control and telemetry, monitoring of cathodic protection potential, integrity and thickness monitoring for pipelines and J-tubes, product transfer, anchor and mooring line monitoring.
The first trial for the system, held in Morecambe Bay, was successful. A signal was transmitting over a pipeline distance of four km.
New developments in electronics, software:
- Robot driller: Shell UK is developing a robot drilling system with real-time downhole information especially for horizontal and slim-hole drilling programs.
- High visibility: A hand-held infrared camera has been developed by Texas Instruments (Dallas, Texas) to allow expand vision capabilities at night and in conditions of smoke and fog.
- Cellular control: A system that uses cellular telephone communications to monitor and control a number of valves at non-electrified remote sites has been developed by Daniel Industries of Houston.
- Monitoring/control: An expandable Windows based monitoring and control software package that contains communications protocols for over 60 instrument manufacturers has been developed by Ci Technologies of Fairport, New York.
- Electrochemistry: A Windows-based graphical package developed by Solartron Instruments of Houston allows the simulation of electrochemical reactions, particularly for corrosion analysis.
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