Technical Presentations at the July 2008 Meeting
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.
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.
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.
alloy will pass a ASTM G48 ferric chloride test at 25°C 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 55°C and
greater, while Zeron 21CLD has been shown to resist SCC at 130°C in the
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 90°C. No cracking was seen in either test.
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.
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.
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
optimisation and correct corrosion mitigation strategy are overriding
elements to ensure safety, security and economy with minimal impact on the
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:
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
Protection is well established for both New Construction and Repair &
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.
of Steel in Concrete is Cost Effective:
repairs CP can reduce total project costs to 1/8 of alternates:
removal of undamaged but contaminated concrete
avoids temporary support
project programme: traffic management and access costs
construction CP costs c. 25% of those for retrofit.
Proper Design of CP to Steel in Concrete is more complex than for steel in
soils or waters:
uniform and non continuous Cathode
Anode network often “stuck on” concrete
Proper Execution of CP to Steel in Concrete is more complex than for steel
in soils or waters due to:
the previous reasons
to integrate with civil construction or repair works
to interface with those who know little, and may care little, for CP
a result of the foregoing:
are sometimes inadequate - Written by the non Specialist or worse
are sometimes inadequate - Negligible attention to balancing local current
demand and provision etc
are sometimes inadequate - Interfaces between different Engineering or
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:
systems are reliable
appropriate anodes the theoretical life can exceed 100 years
replacement of electronics and external cabling practical life can exceed
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.