Technical Presentations at the July 2017 Meeting

1.1   ‘The Effect of Chlorine Dioxide on Corrosion in Seawater’, Roger Francis, RF Materials

This presentation reviews the reactions when hypochlorite or chlorine dioxide is added to seawater to control biological fouling. The active concentrations of chlorine dioxide and its products, such as chlorite, remain at significant concentrations throughout the cooling water system. The failure of four heat exchangers, tubed with aluminium brass is discussed in relation to the change from hypochlorite to chlorine dioxide dosing. The problems of monitoring the concentration of chlorite are discussed.

This presentation is a more detailed discussion of the problem published in Materials Performance 55, 12 (2016) 48.

1.2  ‘Direct Observation of Hydrogen Embrittlement in a Duplex Stainless Steel 2205 Tungsten Inert Gas (TIG) Weld’, Pierfranco Reccagni, Manchester University

Duplex stainless steels are widely used in the nuclear sector and the petrochemical industry, due to their excellent mechanical strength, outstanding corrosion resistance, and superior resistance to environmentally assisted cracking (EAC). For components fabrication, Tungsten Inert Gas (TIG) welding is frequently employed; though joining processes in general alter the microstructure of the weld regions, affecting phase balance, phase morphology, and inducing residual stresses. The formation of tertiary phases is also possible, leaving the microstructure more susceptible to both stress corrosion cracking (SCC) and hydrogen embrittlement (HE).

In order to advance our understanding of how DSS weld microstructures perform with exposure to demanding environments, a number of mini-tensile samples containing the complete weld zone and the parent material have been machined from a grade 2205 multi-pass TIG weld. Both microstructures have been characterised by electron back-scatter diffraction (EBSD), with cathodic charging applied to introduce hydrogen in to the microstructure.

The nucleation and propagation of hydrogen-induced brittle fracture was observed via low-magnification in-situ imaging during tensile straining. These observation were augmented by high resolution imaging during tensile straining hydrogen charged samples in a scanning electron microscope. The fracture path was analysed, and correlated to microstructure crystallography. The overarching goal of this study is to provide microstructure descriptors that can be applied to quantify resistance/susceptibility towards hydrogen embrittlement.

Particular attention has been paid to the crystallographic character of crack nucleation sites. The weld fusion line was identified as the preferential location for crack nucleation, which seemed to be the most HE susceptible region of the heat affected zone. The synergism between austenite and ferrite morphology in the heat affected zone, and its propensity to brittle hydrogen-induced fracture will be discussed in this presentation.

4.1    ‘The Real-Life Challenges when Protecting Marine Structures’, Lee Spoor, Sherwin-Williams

The protection of steel marine structures can cover a multitude of different types of assets, including ships/vessels, bridges, offshore installations, refineries, tanks and almost any coastal structure composed of steel. The use of anti-corrosive coating systems is one such way to protect the steel and provide the necessary longevity during service. Whilst many specifications are generated by engineers, paint manufacturers, specifiers etc., this is often done from the office. Even when site visits are performed, there can often be on-site challenges when are not foreseen prior to the painting project whether this be a "new steel" project or an "on-site" refurbishment project. There are ways that the above challenges can be tacked and methods that can be used to help ensure that a successful painting project is achieved although this may sometimes be helped by a change or modification of a specification, without any compromise of the end goal.

  • The issues outlines were salt contamination
  • The preparation of the steel including different methods of doing this with some of the advantages and disadvantages of each method
  • Obtaining good environmental conditions that are necessary for good performance of the coating system
  • The painting of corroded/pitted steel
  • Welds, edges, rivets, bolts
  • The use of stripecoats in a painting project
  • Site touch-up and repairs
  • Power tool cleaning and comparing the St3 standard
  • Tanks and the use of OAP (optically active pigmentation)
  • Corrosion in tanks

 

4.2  ‘36 Inch Pipeline Coating Recommendation Case Study’, Ramoon Ahmed, ROSEN UK

Inline inspection of a 36 inch pipeline found that widespread external corrosion was occurring. Analysis of the data identified that the corrosion distribution matched closely with the spiral welded section of the line; this had been field coated with polyethylene tape at the time of installation. Excavations revealed that the tape coating had disbonded and cathodic shielding was occurring, allowing the corrosion to take place. ROSEN performed a rehabilitation study which included a coating assessment to find alternatives to the polyethylene tape system historically used. The coating study and its results will be discussed along with the various client challenges that were faced.