Technical Presentations at the July 2008 Meeting

2.1  ZERON 21 CLD - a Cast Lean Duplex Stainless Steel, Roger Francis, Weir Materials & Foundries 

Zeron 21 CLD is a cast lean duplex stainless steel developed by Weir materials and Foundries in Manchester.  It was designed as a lower cost alternative to CF8M (cast 316).  The driving force for the development was the high price of nickel, which has made austenitic stainless steels increasingly expensive compared with low nickel alternatives. 

The nominal composition of Zeron 21 CLD is Fe/21Cr/4Ni/2Mo/0.17N/0.3Cu/0.3W with an austenite/ ferrite phase balance of 50/50.  The pitting resistance equivalent number, or PREN, (given by PREN = %Cr + 3.3x%Mo + 16x%N) is designed to be always greater than 30, compared with a typical PREN of 24 for 316 stainless steel.  The alloy has a minimum 0.2% proof stress of 420MPa and a tensile strength of 650MPa.  These are much greater than those of CF8M and equivalent to those for cast 22%Cr duplex.  This enables further cost savings to be made by designing to the strength of the alloy to reduce wall thickness.  Zeron 21 CLD meets the NORSOK M-630 requirements for impact toughness. 

The alloy is fully weldable by all common arc methods and type 2209 filler is recommended.  This ensures a weld metal with a strength and corrosion resistance at least equal to that of parent metal. 

The alloy will pass a ASTM G48 ferric chloride test at 25C and has superior crevice corrosion resistance compared with 316 stainless steel, nearly as good as that of 22%Cr duplex.  Being a duplex stainless steel, Zeron 21 CLD has very good resistance to chloride stress corrosion cracking (SCC).  In 30,000 mg/L chloride solution, 316 will suffer SCC at 55C and greater, while Zeron 21CLD has been shown to resist SCC at 130C in the same solution. 

In sour oil and gas service, the concern with stainless steels is resistance to sulphide SCC.  Zeron 21 CLD is covered by ISO 15156 part 3 for duplex stainless steels.  Tests to EFC 17 have been conducted in a simulated condensed water and a simulated produced water with 0.1 bar H2S at 90C.  No cracking was seen in either test. 

Worked examples for both a pump and a valve show that typical material savings with lean duplex are ~16% compared with CF8M, without any allowance for reductions in wall thickness due to the higher strength.  Similar or greater savings are possible where Zeron 21 CLD can be used instead of 22%Cr duplex. 

Zeron 21 CLD offers a cost effective alternative to both CF8M and 22%Cr duplex castings in a wide variety of applications.  [rfrancis@rolledalloys.com, 0161 954 4726]

2.2   Managing Corrosion in Upstream Hydrocarbon Production, Bijan Kermani, Keytec 

For the foreseeable future, oil and natural gas remain the principal sources of energy.  Global oil demand will rise by about 1.6% per year, from 75 mb/d in 2000 to 120 mb/d in 2030 with substantial growth in gas.  This constitutes some 60% of energy use.  Hydrocarbon recovering, however, requires advance technology with timely delivery to meet the current and future demands. 

In meeting energy demands, the search for new sources of hydrocarbon has moved to harsher environments in deep high pressure/high temperature wells aiming for increased production in arduous conditions.  These have created greater challenges to the economy of project development and subsequent operations, wherein facilities integrity and accurate prediction of materials performance are becoming paramount.  In addition, the economic constraints have moved the industry towards multi-phase transportation through sub-sea completions and long infield flowlines in which there is a tendency to increased risk of corrosion. 

Materials optimisation and correct corrosion mitigation strategy are overriding elements to ensure safety, security and economy with minimal impact on the environment. 

This presentation outlined the challenges facing the industry sector and described the necessary steps to achieving and managing asset integrity allowing cost optimisation and sustainability. The presentation covered: 

  • Challenges facing upstream hydrocarbon production
  • Key theme areas of corrosion and materials  
    • Past and present success and failures
  • Innovative solutions to materials selection, corrosion mitigation and integrity management
  • Effective utilisation of new technologies.

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4.1   Corrosion of Electronic Components on Phalanx Naval Defence Platforms, Ben Hooker, Devonport Royal Dockyard, Babcock Marine 

An overview of the metallurgical role of the Devonport Materials & Environmental Laboratory at Devonport Royal Dockyard (Babcock Marine) and examples of various engineering failures it has investigated. One of these concerned unidentified blackening of circuit boards and associated electrical components. 

The process of conducting a failure investigation was stepped through, demonstrating the equality necessarily attributed to each piece of evidence, despite many articles subsequently being found irrelevant to the actual failure mechanism. The black substance was identified by SEM EDAX analysis as cuprous sulphide (Cu2S) and was found on gold-plated aluminium, tin-plated copper and bare copper wires. The deposits were locally formed corrosion products from attack by hydrogen sulphide gas. H2S had been drawn into the ventilation system from nearby engine exhausts and extreme humidity accelerated corrosion. Cu2S was able to form on gold-plated components due to poor coating integrity and the presence of a copper coating beneath the gold. Cu2S deposits were found to be removed using a 10% oxalic acid gel. The failure proved an excellent example of how logical and thorough investigation techniques were successfully applied to an unusual problem. [ben.hooker@devonport.co.uk] 

4.2    Corrosion Control on Marine Reinforced Concrete, Brian Wyatt, Corrosion Control

Cathodic Protection is well established for both New Construction and Repair & Protection.  There are well established Standards and an extensive Track Record for Marine Structures.  For New Construction first option should be competent design of a durable concrete and construction defect free concrete placement, compaction & curing, with correct cover.  Cathodic Protection can be the optimum solution for added durability/reliability or for repair/protection when corrosion initiates.

CP of Steel in Concrete is Cost Effective:

        In repairs CP can reduce total project costs to 1/8 of alternates: 

o       No removal of undamaged but contaminated concrete

o       Often avoids temporary support

o       Reduced project programme: traffic management and access costs

        New construction CP costs c. 25% of those for retrofit.

The Proper Design of CP to Steel in Concrete is more complex than for steel in soils or waters:

o       Close Anode/Cathode

o       High IR errors

o       Non uniform and non continuous  Cathode

o       Extensive Anode network often stuck on concrete

The Proper Execution of CP to Steel in Concrete is more complex than for steel in soils or waters due to:

o       All the previous reasons

o       Necessity to integrate with civil construction or repair works

o       Necessity to interface with those who know little, and may care little, for CP

o       Often difficult access

As a result of the foregoing:

        Specifications are sometimes inadequate - Written by the non Specialist or worse

        Designs are sometimes inadequate - Negligible attention to balancing local current demand and provision etc

        Installations are sometimes inadequate - Interfaces between different Engineering or Trade skills

With the appropriate expertise in the selection and specification of the CP systems, in their design, their installation, testing, commissioning and operation there is clear evidence that:

o       CP systems are reliable

o       With appropriate anodes the theoretical life can exceed 100 years

o       With replacement of electronics and external cabling practical life can exceed 25 years

IF the CP industry, Designers, Manufacturers and Specialist Contractors maintain a high quality of delivery to the Client base, Owners, Civil Consultants and Contractors, there is every reason to believe that this application of corrosion control will grow significantly, in both new build and repair. Much will be Marine.  This will benefit economies and provide sustainability and environmental benefits.  IF we fail in quality, the sector will fail.

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