June 15th, 2010
Events in the Gulf of Mexico have brought home to us the hazards involved in deep water, offshore drilling. Yet it’s easy to forget that, all over the world are deep – sometimes miles deep – oil and gas wells performing perfectly efficiently. All the same, the pipes and flanges are regularly checked for signs of damage, and numerous sensors are installed to warn of possible geothermal trouble that might be brewing.
We know that deep drilling causes immense temperature and pressure stresses, as well as being a highly corrosive environment. This is why super duplex and similar high-strength alloys are widely used in deep water rig flanges.
Much of the information we have on the deep drilling environment comes from studies carried out at the Kola Borehole, in Russia. What’s been discovered has turned our dependable planet’s crust into a hostile, alien world.
Before the Kola hole was dug, researchers thought the crust was a benign series of rock interfaces. The heat and pressure started at the mantle, they thought. What they found instead was rock metamorphosed by heat and pressure so intense, it had forced out oxygen and hydrogen molecules to form water. Yet they also found intact fossil shells.
A little further, the rock turned to plastic, and the drill was so hot – way above the expected 100°C – that it had reached its tolerance. When it was withdrawn, the hole closed up. Yet the Earth’s crust had hardly been pricked.
The super duplex pipe flanges we supply at Chemipetro can stand up to most environments, although we’re not sure about changes to the laws of physics.
Tags: Flanges, pipe joints, Super Duplex, super duplex pipe fittings
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May 27th, 2010
Although duplex pipe flanges are widely used in the petrochemical industry, long-distance pipelines are still mainly built from carbon steel, which has a high level of corrosion. Currently, there is great interest in the oil and gas industry to implement duplex steel as the material of choice, owing to its strength and corrosion resistance.
One of the problems with using duplex flanges in pipelines is the increased skill required by the welder to achieve an acceptable root pass. This first layer of a multi-layer weld is the most critical, because it is the one most likely to crack or become contaminated. The preferable method for depositing root passes is GTAW (gas tungsten arc welding), which uses a specialised backing shield of inert gas, such as argon. It is tricky to use this method on duplex. Besides anything else, the gas itself causes problems at the welds.
Another disadvantage with duplex flanges is that it is difficult to achieve low-temperature toughness – essential for field welds. It is felt that if a gas-free arc welding technique could be developed, that somehow also attacked this problem, then duplex could replace carbon steel on long-distance pipelines. The benefits would be a radical improvement on corrosion of pipe flanges in pipelines, with a corresponding reduction in the tonnage of metal used each year.
We at Chemipetro supply both duplex and super duplex pipe flanges and fittings, all with excellent weldability. However, their unique and complex composition means that extra care must be taken over welding, in order not to compromise strength and corrosion resistance.
Tags: duplex pipe flanges, Flanges, super duplex pipe fittings, tungsten arc welding
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