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News in Brief - March/April 2004

Connect, no. 129, March/April 2004, p.7

Protecting duplex stainless steels from localised corrosion

TWI has recently begun a Joint Industry Project evaluating the corrosion protection imparted by thermally sprayed aluminium (TSA) to 22Cr duplex stainless steel (DSS) at elevated temperatures in both subsea and topside environments.

There have been several recent incidents of identified cracking of duplex stainless steel components, and the avoidance of hydrocarbon release through chloride stress corrosion cracking is a major concern. This project aims to determine whether the application of TSA will prevent corrosion-induced failures from occurring. The programme contains a series of tests to generate industrially relevant data, including:

  • TSA coating integrity under plastic strain (to simulate pipe reeling)
  • Hydrogen embrittlement assessment versus sacrificial anodes
  • Chloride induced pitting and crevice corrosion at 130°C
  • Chloride stress corrosion cracking when immersed at 130°C
  • Chloride stress corrosion cracking under drop evaporation to simulate topside corrosion

Industry will benefit from the programme through demonstration of the suitability of such coatings to mitigate localised corrosion of 22Cr DSS and will receive guidelines on the application of TSA for subsea and topsides facilities.

Rapid adhesive bonding and cure monitoring

Two DTI-funded projects that TWI is involved with are approaching their mid-points, and are producing valuable information for industry. One project focuses on efficiency improvements in rapid bonding processes and the second is looking at cure monitoring methods. The two projects are being co-ordinated by NPL and involve other key organisations in each field.

The cure monitoring project (MMS10) has produced reports on various techniques, including dielectric, optical fibre and ultrasonic, used to monitor cure in composites and adhesives. A Review Report has also been issued, which gives information on all of the potentially viable techniques. Studio projects are on offer to industry, to help gauge the suitability of a particular monitoring technique to an organisation's processing methods. Any TWI Industrial Member interested in evaluating cure monitoring is invited to make contact to check if their production process is suitable.

The rapid bonding and efficiency improvements project (MMS9) is mainly targeted at the packaging, electronics and footwear industries. It investigates the tack properties of hot melt adhesives; the fluid and physical properties of adhesives; surface inspection methods; measurements of adhesive spread and absorption. The main reports are due at the end of 2004, with interim progress and results available at the Industrial Advisory Group (IAG).

Detecting stress corrosion cracking at temperature

Stress corrosion cracking (SCC) of austenitic and duplex stainless steels may occur at operating temperatures of up to 150°C. Recent failures have shown the need for easier, more rapid detection of the initial presence of such cracking as, under combined conditions of stress, environment and temperature, failure may be catastrophically rapid. TWI has therefore launched a Joint Industry Project to investigate the detection of SCC at elevated temperature.

A range of NDE methods will be assessed for their ability to detect SCC on as-welded surfaces at a range of temperatures. The methods include acoustic emission, eddy currents, ACFM, dye penetrant ultrasonics, thermography and shearography. The work will be carried out in stages - inspection of parent plate at low temperatures, welds at low temperatures, welds at high temperatures and a monitored pipe test. Duplex and 316 stainless steel pipe will be tested with both internal and external initiation making the work of interest to a wide range of industries.

Initial meetings have taken place and a number of companies have expressed their intention to join the project.

For more information, please contact us.

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