Technical Presentations at the July 2001 Meeting

8.1 'The performance of Titanium alloy 5111', David Peacock (The Titanium Information Group).

Titanium Alloy 5111 (ASTM Grade 32 UNS R55111), was developed specifically as a high toughness weldable alloy for sea water service. Strong interest from the US navy is supporting ongoing tests for a variety of applications for which at present Ti-6Al-4VELI would be the only notional candidate. Although 5111 is less strong than 6/4, its environmental fracture toughness is superior to 6/4, and unlike 6/4, 5111, because of its lower content in aluminium and oxygen, shows no tendency to stress corrosion cracking, nor to increased crack propagation rates with hydrogen generated by impressed potential. All fractures recorded in tests to date are ductile transgranular. Early applications are for bolting in all titanium water management systems, but wider use in high duty offshore and marine systems is confidently anticipated.

8.3 'The performance of Zeron 100 super duplex stainless steel welds in seawater', Roger Francis (Weir Materials Services)

Some corroded welds from service were presented, along with the reason for failure and the solution to prevent further attack. The suggested limits for temperature and chlorine were discussed along with some cautionary advice about measurement and interpretation. Finally some laboratory tests were described that showed the best methods of post weld treatment to optimise corrosion resistance in seawater.

The offshore oil and gas industry in the UK North Sea is now in a mature stage. Over the years there has been a distinct shift in the number of corrosion related failures. Production conditions are more highly corrosive, including the effects of corrosive species such as carbon dioxide and hydrogen sulphide, increasing water cut and sand production all contributing to internal corrosion/erosion damage. External pipework and vessel degradation has been caused by a highly corrosive marine environment, wet insulation and temperature effects.

In an attempt to counter some of these corrosion damage mechanisms, a change in materials away from carbon steel to corrosion resistant alloys and protective coatings has also taken place. During the same period, major operators have also looked to achieve increased plant up-time by looking to the inspection companies to develop inspection technologies enabling non-intrusive inspection to accurately determine the internal condition of pipework and vessels without having to shutdown plant.
The combined effects of these two factors has required the in-service inspection companies to provide more innovative NDE technology. The presentation covered a range of the latest technology available to Inspection personnel, with example applications for each of the different technologies.