TITANUM Nitride-hardened alloy dramatically prolongs Snorre riser piston lifespan

Specialist titanium producer Permascand is experiencing a growing acceptance of its titanium products for offshore applications, due largely to titanium's high resistance to corrosion. The company has been working with titanium for more than 25 years. Permascand works primarily in two grades: Grade 2 titanium, which is almost pure, and the stronger alloyed Grade 5, which is the `workhorse' material for the most demanding applications (such as erospace).

Specialist titanium producer Permascand is experiencing a growing acceptance of its titanium products for offshore applications, due largely to titanium's high resistance to corrosion. The company has been working with titanium for more than 25 years. Permascand works primarily in two grades: Grade 2 titanium, which is almost pure, and the stronger alloyed Grade 5, which is the `workhorse' material for the most demanding applications (such as erospace). Site manager for process equipment Mats Melbin stresses that Grade 5 is more complex to work with, as it takes time to learn how to handle it properly. "Grade 5 titanium is much stronger than Grade 2, so we can use thinner material. But you can't just apply titanium to replace steel using the same design. You need to adapt the design to best utilize titanium's qualities." For this reason, Permascand is keen to market its engineering know-how to help customers find the best solution when using the different grades. "We don't want to be known just as fabricators," Melbin says.

Snorre pistons

To increase the service life in both erosive and corrosive environments, Permascand now offers a patented nitride-hardened titanium surface layer. The offshore industry is showing interest, with the first order for this process being for the Saga Snorre TLP to replace 53 stainless steel pistons used in the riser hydraulic system. Forty-four pistons measuring 88.9mm x 3,257 metres; four measuring 88.9mm x 3,030m; and 5 measuring 127mm x 2,751m have been made from titanium grade 5 heated in a special furnace with nitride to form a thin surface of titanium nitride. Since the nitride coating is implanted into the material, a unique adhesion and strength is achieved. The Snorre pistons are currently being changed out and Permascand is eagerly awaiting the results before going out fully to the market. However, it expects the pistons to last many times longer than the original stainless steel versions, which needed to be replaced every year. If the nitride-hardened titanium performs to expectations, a lifetime of 30 years should be reached. The cost benefits to operators will be considerable.

Fire systems

Another application of titanium offshore is to replace existing stainless steel in deluge systems which are constantly subject to corrosion and blockage from seawater. Permascand claims it is common for 40% of stainless steel deluge systems to work inadequately during tests. The company has received substantial orders over the past 12 months for replacement titanium parts including pipes, elbows, nozzles and sprinkler heads. For more information contact Mats Melbin, Permascand: telephone +46 660 295050 or fax +46 660 295051.
TITANIUMGrade 2 Grade5    Tensile strength (MPa)        275               830    Ultimate tensile      strength (MPa)            345            895    

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