Seal assembly life quadrupled using titanium nitride coating

Industrial Lubrication and Tribology

ISSN: 0036-8792

Article publication date: 1 April 2000




(2000), "Seal assembly life quadrupled using titanium nitride coating", Industrial Lubrication and Tribology, Vol. 52 No. 2.



Emerald Group Publishing Limited

Copyright © 2000, MCB UP Limited

Seal assembly life quadrupled using titanium nitride coating

Seal assembly life quadrupled using titanium nitride coating

Keywords: Coatings, Surface coatings

Marshalsea Hydraulics of Taunton quadrupled the life of high pressure hydraulic pump components, destined for applications in the world's oil fields, by using ultra hard titanium nitride coating provided by Tecvac Limited of Swavesey, Cambridge, a Wallwork company (see Plate 1).

Plate 1Seal assembly life quadrupled using titanium nitride coating

Marshalsea, one of the leading suppliers of pumps and control valves to the offshore oil and gas industry, custom designs and builds hydraulic pumps to operate at pressures up to 700 bars, serving equipment submerged at sea to depths of 3,000 metres or more.

A long life and very low levels of maintenance are essential features of Marshalsea pumps. Often these pumps must operate for up to 150 million cycles without maintenance, while charging hydraulic accumulators to provide pressure for control valves, actuators and other submerged control systems. The critical pump components are the piston seal assemblies which transmit motive power from an electrically driven swash plate, operating at 25 cycles a second, to pump the water-based hydraulic fluid.

Typical Marshalsea pump designs, mostly in stainless steel, include three or six pistons. Each piston is heat treated then plasma nitrided before a final coating of titanium nitride (TiN) is applied by Tecvac. Andrew Middleton of Marshalsea commented, "At our extreme working pressures of 700 bars or more there are very high friction loads placed on the piston stem and seal surfaces, especially on the forward stroke. These loads wear the pistons and seals. We tried a number of different treatments including micropolishing the piston surface to achieve low friction levels, and thus extend life of the seal/piston assembly.

"After many lengthy trials, we identified Tecvac titanium nitride coating as the best design solution. This provides a very smooth surface finish and very low friction levels, combined with a hard surface - well above 2000 HV, to give us a dramatic increase of the piston/seal assembly life, extending average lifetimes by more than 400 per cent. The cost of the Tecvac coating amounted to less than 3 percent of the total cost of the pump assembly."

The Tecvac PVD (Physical Vapour Deposition) titanium nitride coating process achieves the fine surface finish because titanium is vaporised using an electron beam and then combined with nitrogen in a vacuum chamber to form titanium nitride. As the vapour condenses on the workpiece it gives a coating of consistent, very fine TiN particles, which allows "mirror finishes" to be faithfully replicated.

More information from: Richard Burslem, Wallwork Heat Treatment Limited, Lord Street, Bury, BL9 ORE. Tel: +44 161 797 9111; Fax: +44 161 763 1861.

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