Technical Presentations at the October 2013 Meeting

1.1   Coatings to Replace Cadmium Plating for Bolts for the Marine Atmosphere’, Robin Oakley, QinetiQ (25th anniversary ‘hot’ topic)

25 years ago the elimination of cadmium plating as a protective coating for fasteners exposed to the marine atmosphere due to environmental toxicity concerns was a topic of some concern in the affected engineering communities, with various promised ‘drop-in’ replacement technologies offered as the solution to the problem.  With the benefit of 25 years more experience, the current choices to fill the technological niche once occupied by cadmium plated low alloy steel fasteners are reviewed, and the various benefits and compromises they represent considered.  Experimental evidence of the long-term marine atmospheric resistance and frictional behaviour of various fastener coatings is compared with the base-line behaviour of electroplated cadmium, and conclusions drawn on the validity of true ‘drop-in’ replacements for cadmium.

1.2  Corrosion Resistant Steel for Cargo Oil Tanks’, Kenji Katoh & Clive Tuck, Lloyd’s Register Asia and Lloyd’s Register EMEA

Several major incidents involving break up of oil tankers have taken place since the 1970s.  The primary cause of almost all of these has been found to be excessive corrosion of the structural steel plate. This has resulted in the International Maritime Organization (IMO) issuing two resolutions designed to prevent corrosion in vulnerable storage tank areas.  One resolution concerns the use of coatings for corrosion mitigation and the other deals with the application of specially developed carbon-manganese steel with reduced corrosion properties compared to standard carbon-manganese steel.  The latter is specifically for use in cargo oil tanks (COT).  The areas of rapid steel plate corrosion in COTs are the internal surface of the tank top, which encounters a typical environment of nitrogen with 4% oxygen, 13% carbon dioxide, 0.05% hydrogen sulphide, 0.01% sulphur dioxide and the tank bottom internal surface which contains brine with concentrations up to 10% sodium chloride. 

The IMO resolution MSC 289(87) for Corrosion Resistant Steel (CRT) for Cargo Oil Tanks of Crude Oil Tankers details the methods to be adopted by Classification Societies for approving such steel grades for use in ships.  Modified ship grade steels are to be used and weldability must be retained, with welding consumables requiring specific approval.  Corrosion tests are detailed which are to be used for verifying that the CRT steel plate, both in non-welded and as-welded condition, is are suitable to be approved for the application. 

To date (up to October 2013), steel manufacturers have manufactured a number of CRT products which are undergoing tests.   Difficulties which have been experienced in carrying out the required lengthy test methods have been found to be adequate control of the gas mixtures used (together with their hazardous properties), temperature control for the required temperature/time profiles and measurement of low pH values in 10% sodium chloride. Results from the current test programmes are expected to become available during the early part of 2014.

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  4.1  Keynote: Knowledge Transfer from Experienced to Novice Engineers’, Harvey Hack, Northrop Grumman Corp., USA

This presentation first looked at the reasons why Knowledge Sharing is needed: as engineers retire, knowledge and experience are lost, and there is increased competition for experienced talent.  It was noted that the most effective techniques for Knowledge Retention - Communities of practice workspaces, Engagement team databases, Decision support systems, and Collaboration tools - were not necessarily the most frequently used.  Various methods of Knowledge Sharing were considered, and the most effective techniques reviewed:

·        Face-to-face meetings

·        Communities of Practice

·        Team or department meetings

·        One-on-one consultation with expert

·        Apprenticeship/Mentoring

·        E-mail (because of frequency of use, not effectiveness) 

The ways in which retirees can contribute is dependent on organizational approach.  This can range from a policy against rehiring retirees, to encouraging the reemployment of retirees with phased retirement and flexible work arrangements. 

Successful Knowledge Sharing involves: communication, executive support, involvement of Human Resources, rewards and recognition, collaborative working environment and measurement. 

Conclusions: 

  • Build a solid business case and sell it to management so that they can begin to influence corporate culture
  • Communities of Practice and incentivizing critical experts to continue working
    • NACE online forums
    • Attending conferences and technical symposia: NACE, SSPC, ASM, ASTM
  • Mentoring, but only if corporate culture supports it
    • Expensive , time consuming
    • Frequent turnover in personnel can negate progress
  • Properly constructed web portals can be extremely effective in getting knowledge in the required detail to those who need it even if they are not experts
    • NACE/ASM/ASTM knowledge-base system “Corrosion Analysis Network”
    • Wiki-type structure to allow experts to write pages
    • Drilling up rather than drilling down
      • Start at the simple level and drill up to details and theory
  • Methods must allow novices to solve difficult technical problems

o       Experts may not exist in company

 [A pdf version of this presentation has kindly been provided for members, and can be obtained from the Secretariat].

 

4.2  Optimising the Sea Water Corrosion Resistance of Butt Welds in ZERON 100 Pipes’, Glenn Byrne, Rolled Alloys.

This paper considered how to increase superduplex stainless steel critical pitting temperature (CPT) levels to those of 6% Mo (welded with 625 filler), looking for answers to these questions:

  • What would be the applicable heat input range?

  • What would be the applicable inter pass temperature range?

  • How would phase balance and precipitation characteristics be affected?

  • Could toughness be retained?

  • Would other properties or characteristics be different?

The tests carried out were described in detail, and the resulting conclusions were as follows:

  • The use of Ar+2.5%N2 as the shielding gas or Formier as the backing gas gives an increase in critical pitting temperature compared with Ar gas shielding alone. The best results were obtained when Ar+2.5%N2 shielding gas was used with Formier as the backing gas.

  • The CPT results in seawater were more variable with Ar+2.5%N2 shielding gas compared with other results. This variation corresponds to a step type increase in corrosion resistance of the root run at a PREN of 41 (0.23% Nitrogen in the root run).

  • The CPT in seawater at +600mV SCE is much more sensitive to changes in the welding gas composition than the CPT in ferric chloride.

  • Weld heat inputs up to 2.0 kJ/mm and inter pass temperatures up to 300°C had no effect on the CPT of welds made with Ar/Ar gases tested in ferric chloride solution. In seawater at +600mV SCE the CPT of the Ar/Ar gas combination weld fell at the highest heat input, but (for welds deposited at about 1KJ/mm) there was no effect of inter pass temperatures up to 300°C.

  •  Increasing heat input or inter pass temperature reduced the CPT in ferric chloride and in seawater at +600 mV SCE for welds made with Ar+2.5%N2/ Formier (shielding/backing gases).  However, under no conditions did the CPT decrease below the values seen for welds made with Ar/Ar.

  • The impact toughness tests at minus 50°C show that there was no difference in the toughness of welds made with Ar/Ar shielding/backing gas compared with those made with Ar +2.5%N2/ Formier shielding/backing gases.

  • Hence, the use of Ar+2.5%N2/ Formier (shielding/backing gases) does not appear to decrease the welding parameter “window” available over the range of parameters considered, but the greatest improvements in corrosion resistance are seen with normal heat inputs and inter pass temperatures.

  • The use of gas combinations should be considered an optimisation process and is not a substitute for proper control of welding variables (i.e. heat input ,inter pass temperature welding sequence and technique.

[A pdf version of this presentation has kindly been provided for members, and can be obtained from the Secretariat].

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