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Schematic of canister repository
Issue 168 September/October 2010
Diary events
November 2010
Joint TWI/DVS Conference
Latest developments in
joining plastics in mass
production and fabrication
Tue 2
Dsseldorf
FESI Seminar
Structural integrity of
welded structures
what have we learnt?
Wed 3
Great Abington
Pressure and Process Plant
Technical Group Meeting
Nuclear new build in the
UK
Thu 4
Great Abington
TWI Annual Dinner
Tue 9London
Structural Integrity Technical
Group Meeting
Strain based fracture
assessment
Tue 23
Great Abington
December
18th IoRW Technical Seminar
Developments in railinspection
Wed 1
Great Abington
WJS Seminar
Standards for offshore
power and low carbon
energy
Wed 8
Middlesbrough
Workshops and seminars
are recognised
Continuous ProfessionalDevelopment events
T h e m a g a z i n e o f T W I
w w w . t w i . c o . u k e - m a i l : t w i @ t w i . c o . u k
The safe and effective storage
and disposal of high level waste
(HLW) and spent fuel (SF) arising
from nuclear power generation is a
global issue, posing major technical
challenges. When TWI was asked
by Nagra to advise on suitable
welding technologies for hot cell
encapsulation of HLW and SF,TWI was able to establish a multi-
disciplinary team to investigate the
best choice of welding processes.
Nagra is the Swiss national co-operative
for the disposal of radioactive waste and is
responsible for final disposal of all types of
radioactive waste produced in Switzerland.
TWI was selected for the project due to
significant experience with other long term
dry cask and repository storage projects
for the global nuclear industry such asthe successful development of friction stir
welded copper canisters for SKB and the
hot cell welding procedures for closure
of the canisters to be stored in Yucca
Mountain.
From the outset it was clear that the Nagra
approach to encapsulation would pose
entirely new challenges to the welding
processes. The chosen material for the
canister construction was to be carbonsteel, 190mm thickness with a minimum
lifetime of 1000 years. The timescale for
development also added challenges. With
the weld production not scheduled until
2035, all processes had to be considered.
After brainstorming, literature reviews
and preliminary investigations TWI
engineers reduced the list of potentially
viable welding processes from over thirty
to two: electron beam welding (EBW)
and narrow gap tungsten inert gas (NG-
TIG) welding. These processes were then
researched and investigated extensively
and all details of advantages, disadvantages
and the technology readiness level were
reported. This included in-depth analysis of
potential metallurgical and residual stress
issues arising from each of the potential
techniques. In addition to the welding
process technology, methods of non
destructively testing the welds in a hot
Selection of welding
processes for high level
nuclear waste encapsulation
continued on p. 2
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2
September/October 2010
C on ne ct S ep te mb er /O ct ob er 2 01 0 w w w . t w i . c o . u k e - m a i l : t w i @ t w i . c o . u k
Aker Solutions(Drilling Risers)USAOil and gas engineering
Cytec Industries UK LtdUKCoatings and composites
Fotolec Technologies LtdUKShatterproof coatingsapplication to standardlamps
ILVA SpAItalySteel production of flatproducts and weldedpipe
ITER Organisation -Magnet DivisionFranceDevelopment of magnet
technology for the ITER
programme
Johnson & Starley LtdUKManufacturer of heatingand ventilation products
Swagelining LimitedUKProvision of integratedlining systems
TATA Steel LtdIndia
Design, manufacture andsupply of plant equipmentand cranes
Woodside Energy LtdAustraliaOil and gas exploration,production anddevelopment
Welding Alloys LtdUK
Welding consumables,machines and service
New Membersof TWI
TWI is pleased to welcome the
following as Industrial Members
Aerospace Industry Panel
TWI held its 35th
Aerospace Panel Meeting
on 15 September 2010,
with attendees from the UK,
Japan, USA, Brazil, Germany,
France and Sweden.
There were TWI
presentations on microwave
curing of composites, cold
spray forming for additive
manufacture, developments
in high brightness laser
processing and EB welding
of crack sensitive
materials.
This was supplemented by
excellent presentations from
MTU, GKN Aerospace andBAE Systems.
Two Group
Sponsored
Meetings took
place the previous
day and there were
several meetings
between Industrial
Members and TWIstaff during the
week.
The next
Aerospace
Panel Meeting is
scheduled for
16 March 2011, with two
Group Sponsored Project
Meetings due to take place
on 15 March and a linearfriction welding seminar
planned for 17 March.
Details will follow in
due course and more
information can be obtained
by contacting Richard
Freeman, the Aerospace
Industry Sector Manager [email protected]
cell environment were alsoinvestigated and reported.
The results of TWIs work
were published in a Nagra
report and presented at
a meeting in Wettinngen,
Switzerland. TWIs repor t
was subsequently issued
publicly along with apreviously published material
selection repor t. This work
formed a precursor for a
multi-year study to develop
designs for carbon steel
canisters, which was issued
as an open tender in March
2010.
TWI (with Hitachi
Zosen Corporation as a
subcontractor) successfully
bid for this competitive
tender. Nagra evaluatedthe offers received on
the basis of the financial
offer, qualification and
experience of the bidder,
qualification and experience
of the experts, proposed
project work plan and an
oral presentation made to
Nagra. For more information
about this project and TWIs
services to the nuclearindustry please contact:
or
Cross-section of hot wire, narrow gap gas tunsten arc welding in180mm
P91 steel
Single pass, fully penetrating electron beam weld in 280mm thickness C-Mn
steel
continued from p.1
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September/October 2010
3
The TSB collaborative project
Advanced Design Partitioning and
Test for System in Package electronics
(ADEPT-SiP) has now come to a close.
Partners within the project were:
TWI: lead partner, assembly,
reliability, environmental research
Filtronic Broadband:
RF communications end-user
Zarlink Semiconductor:
medical modules end-user
Zuken: design flow, partitioning,
supply chain management
AWR: RF design flow, ProcessDesign Kits (PDKs)
Leeds University: RF simulation,
models, PDKs
Mentor Graphics: thermal design
QuantumCAD: design rules, layout
Wurth Elektronik: process
architectures, manufacture
The partners formed a complete
supply chain for production of a SiP
module.
The objective of the ADEPT-
SiP project was to develop and
demonstrate a rigorous, right-first-time
design and supply chain management
methodology for novel SiP electronics.
The ADEPT-SiP module architecture
involved a high density interconnect
(HDI) printed circuit board with
integrated passive components.
One face of the HDI substrate wasallocated for RF functions and the
other for digital functions. Active
devices were mounted by wire
bonding or flip chip bonding on both
the upper and lower faces of the
module substrate.
A design kit has been successfully
produced that can select which
passives to integrate according to
cost and other priorities. Models
have been integrated into the designkit, to show RF performance of the
passive components and interconnect.
Resistors, capacitors and inductors
have been successfully printed onto a
HDI substrate and achieved close to
design values. Thermal cycling, humidity
testing and highly accelerated stress
testing has been used to test the
reliability of the embedded passives.
Demonstration medical and RF
modules were produced, showing
promising results for commercial
products.
For further information, please contact
ADEPT at System in Package
collaborative project draws to a
successful close
Active devices
ADEPT-
SiP moduleHDI substrate
Mother board
Encapsulation
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Techn olog y Trans fer
In Part 1 the importance of cleanliness,
particularly the removal of all
sulphur containing compounds, was
mentioned. With respect to defect
free welding of nickel and its alloys this
cannot be over-emphasised.
As well as sulphur, however, there
are several other substances that can
lead to embrittlement of the nickelalloys when they are exposed to high
temperatures. Amongst these are lead,
phosphorus, boron and bismuth.
These may be present in oils, grease,
cutting fluids, paints, marker pen
inks, temperature indicating crayons,
etc; it may not be possible to avoid
using these during fabrication so it
is essential that these are removed
if the component is to be welded,
heat treated or is to enter hightemperature service.
Fuel gases frequently contain sulphur
and it may be necessary to use radiant
gas heaters or electrical elements for
local heating or in heat treatment
furnaces.
Nickel alloys can be welded using
all the conventional arc welding
and power beam processes, the
commonest processes being TIG orMIG with pure argon, argon/hydrogen
or argon/helium mixtures as shield
gases and MMA where basic flux
coatings provide the best properties.
However, if argon/helium mixes are
used it is only when there is more
than 40% helium that any significant
benefits with respect to penetration
and improved fusion will be noticed.
Submerged arc welding is restricted towelding solid solution alloys using basic
fluxes. Matching welding consumables
are available for most of the nickel
alloys. See Job Knowledge 22 for
recommendations for a range of alloys.
Slag from MMA welding and
particularly submerged arc welding
can be difficult to remove from the
nickel alloys and often needs to be
ground between runs to remove it
completely. It is also often necessary
to grind the surface of each run
when welding with the gas shielded
processes to remove oxide scabbing,wire brushing simply polishing these
oxides.
Failure to remove slag or oxide scabs
will result not only in weld metal
inclusions but also reduce corrosion
resistance if left on exposed surfaces.
Total welding times can therefore
be substantially longer than the
equivalent joint in stainless or carbon
steel and welders need to be fullyacquainted with these differences
when converting from welding steels
to nickel alloys.
Comments regarding the
recommended weld preparations
were included in Part 1. Although
the weld preparations are similar
to those used for steel it is worth
considering the use of double V or U
type preparations at thicknesses less
than would be considered with steels.The additional cost of the preparation
is offset by savings in consumable costs
(nickel being an expensive metal) and
welding time.
The majority of nickel alloys are best
welded in the annealed or solution
treated condition, particularly if
the alloys have been cold worked.
As mentioned in Part 1, preheat
is not required except to removecondensation or if the ambient
temperature is below about 5OC
when a moderate preheat of 40-50OC
is recommended.
Interpass temperature should not be
allowed to rise above 250OC although
some alloy suppliers recommend an
interpass as low as 100OC for certain
alloys such as Alloy C276.
Remember the potential hot crack
problems if thermal crayons are
used to measure this temperature!
For most alloys heat input should be
controlled to moderate levels (say
2kJ/mm maximum) to limit grain
growth and HAZ size although for
some Alloys 718, C22, and C276 for
example, a maximum heat input of
1kJ/mm is recommended.
Conversely if too fast a travel speed
is used in an attempt to maintain a
low heat input this can result in a
narrow weld bead sensitive to centre
line cracking. Adequate testing duringwelding procedure development
should be used to optimise the range
of acceptable welding parameters.
The solid solution alloys such as Alloy
200 or 625 do not require post weld
heat treatment to maintain corrosion
resistance but may be subject to
PWHT either to reduce the risk of
stress corrosion cracking if the alloy is
to be used in caustic soda service or
in contact with fluoro-silicates or to
provide dimensional stability.
A typical stress relief treatment would
be 700OC for an hour for Alloy 200;
790OC for four hours for the higher
chromium content alloys such as Alloy
600 or 625.
The nickel-molybdenum alloys are
identified with the prefix B eg B1,
B2, etc. and are used in reducing
environments, such as hydrogen
Job Knowledge108 Welding of nickel alloys
Part 2
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Techn olog y Trans fer
5
chloride gas and sulphuric, acetic
and phosphoric acids. Alloy B2 is
the most frequently encountered
alloy and matching filler metals
are available. Unlike Alloy B1, Alloy
B2 does not form grain boundary
carbide precipitates in the weld
heataffected zone, so it may be used
in most applications in the as-welded
condition.
Alloy 400, a 70Ni-30Cu alloy, has good
corrosion resistance when exposed
to hydrofluoric acid, strong alkalinesolutions and sea water.
A matching filler metal, Alloy 190, is
available but this can become anodic
in salt solutions, leading to galvanic
corrosion and it is recommended
that one of the Ni-Cr alloy fillers such
as Alloy 600 or 625 is used in this
environment.
The age hardened alloy K-500 does
not have a matching filler metal and isgenerally welded using the Alloy 190
filler, the reduction in strength being
taken into account during the design
phase.
Precipitation hardened alloys are
best welded in the solution treated
condition; welding these alloys in the
age hardened condition is likely to
result in HAZ cracking.
The ageing process in the alloysis sufficiently sluggish that the
components can be welded in the
solution treated condition and then
aged at around 750OC without the
mechanical properties being degraded.
A solution treatment of the welded
item followed by ageing will provide
the highest tensile strength.
The sensitivity of the age hardened
alloy to cracking causes problemswhen attempts are made to repair
items, particularly when these have
been in high temperature service and
additional precipitation on the grain
boundaries has occurred.
Little can be done to overcome this
problem apart from a full solution heat
treatment but this is often not possiblewith a fully fabricated component. If
repair is to be attempted, small weld
beads and controlled low heat input
welds are recommended.
If the design permits, a low strength
filler metal, eg Alloy 200 or 600,
may be used to reduce the risk.
Buttering the faces of the repair weld
preparation, sometimes combined
with a peening operation, has been
successful.
Many of the nickel alloy filler metals
have been used for making dissimilar
metal joints with excellent results;
dilution when welding joints between
ferritic, stainless and duplex steels
being less important than when using
a type 309 stainless steel filler.
Nickel also has a coefficient of thermal
expansion between that of ferritic and
austenitic steels and therefore suffersless from thermal fatigue when high
temperature plant is thermally cycled.
Alloy 625 has been a popular choice,
the weld tensile strength matching or
exceeding that of the parent metal.
There are limitations to this approach,
and caution needs to be exercised
when selecting a suitable filler.For example, Alloy 625 has been
extensively used for welding dissimilar
joints in austenitic and duplex steels.
Use of this filler metal has resulted
in the formation of niobium rich
precipitates adjacent to the fusion line
and has been discontinued. Alloy 59 or
C22 filler metals has replaced
Alloy 625 as the filler of choice.
The moral of this is, if there is anyuncertainty, ask an exper t!
This article was written byGene Mathers
Erratum:
In the table included in Job Knowledge
107, the percentage of Fe in Alloy 825should read 28% and not 38%.
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September/October 2010
In-service inspection
In general terms, inspection
may be applied to three
main sectors of industry:
manufacturing, fabrication and
in-service.
The manufacturing and fabrication
sectors have developed inspectionregimes specific to their products.
These products are in many ways
repetitive, predictable and inspection
procedures have been proven to be
effective when applied by competent
inspection personnel.
In-service has not been subject to
the same level of development and
scrutiny.
With ageing assets and capitalinvestment at a premium, it is
necessary to try and develop non-
invasive inspection
techniques to locate
and quantify failure
mechanisms at an
early stage in order to
manage and control the
possible interruption to
production and possibly
safety and revenue.
By identifying the defined
possible failure modes
and mechanisms in a
timely manner, it is then
possible to re-schedule
planned maintenance
shutdown of plant to
accommodate repair and
if necessary replacement
of components.
TWI recognises the
importance of this
sector of industry and
has the necessary
knowledge,
resources and
experience to assist
in the management,
control and development
of relevant and appropriate
inspection processes andprocedures.
These include:
Integrity management
Appropriate research and
development facilities
NDT Validation Centre
Appropriate and relevant
personnel training and
certication, including
Employer Specic Schemes
in accordance with
BS EN 473 and ISO 9712.
Recent developments include:
Specific training and certification in
corrosion monitoring using manual
ultrasonic techniques
Training and CSWIP certification
scheme for personnel inspecting
drillstem components (rotary tool
and drillpipe).
For more information, please contact:
QAJoinITregister now
www.twi.co.uk
Why is preheat used whenarc welding steel and how is itapplied?
Are duplex and superduplexsteels fit for purpose underconditions of cathodic
protection?Are there any standard tests forplastics welds?
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7w w w . t w i . c o . u k e - m a i l : t w i @ t w i . c o . u k C on ne ct S ep te mb er /O ct ob er 2 01 0
September/October 2010
WJS/DVS Conference
on Joining Plastics
International Conference on the
latest developments in joining plastics
in mass production and fabrication
2 November 2010
Handwerkskammer, Dsseldorf,
GermanyThis event, which will be conducted
in English, is organised jointly by the
WJS of The Welding Institute and the
German Welding Society (DVS).
Twenty papers will be presented in
two parallel sessions. Areas covered
will include new developments in laser
welding, infrared welding, ultrasonic
welding and adhesive bonding;
welding of thermoplastic tanks and
pipes; joining of composites; testing
of welded joints; and qualification ofplastics welders.
For further information please contact
[email protected] or visit
www.dvs-ev.de/joiningplastics2010.
Advanced manufacturing and
engineering in the US Midwest and
Indiana. New opportunities for the
UK businesses.
Joint event organised by UK Trade
& Investment East and the State of
Indiana
Thursday 11 November 2010
9:00-14:00 TWI, Granta Park,Great Abington, Cambridge
The United States is the worldslargest manufacturing economy,
employing nearly 12 million Americansand producing manufacturedproducts worth up to $1.6 trillion.The US market represents 18%of theworlds manufactured goods, largely
due to Midwestern manufacturingcompanies that have a strongorientation toward knowledge-
intensive manufacturing.
The state of Indiana and the UK Trade& Investment East would like to ex-
tend an invitation to join UK
specialists and an Indiana businessdelegation and explore new
opportunities in the Midwestadvanced manufacturing andengineering sector.
For the full programme or to bookyour place at this FREE event,please call 01707398382 or [email protected]
Appointment of new TWI Directors
With the signicant growth in TWIsresearch and technology business
during recent years, we have
strengthened the executive team
to lead this key area into the future.
Separate Research and Technology
functions have therefore been
established. Dr Paul Woollin has been
appointed Director, Research to focus
on research strategy and quality to
ensure the maintenance and
enhancement of TWIs technicalreputation and Professor Aamir Khalid
has taken up the post of Director,
Technology to concentrate on
commercial technology development
to drive protable business growth.
News in brief
Over the last sixty years TWI
has been pioneering welding
and associated engineering
technologies.
TWI Services North America was
founded to extend the services
the TWI Group could offer to
engineering companies, from a local
base, within the North American
region.
The new office in Houston primarily
supplies advanced engineering
services to the oil, gas, chemical and
power generation sectors.
The services supplied range
from complex structural integrity
studies to manufacturing and
fabrication support.
If you are based in the North
American region, you can now
find out about the local news
and events via our new website:
www.twinorthamerica.com
Dont forget to add it to yourfavourites.
TWI North America
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For further information on TWI, visit thewebsite at
www.twi.co.uk
8
Connect is thebi-monthly magazine
of TWIEditor:
Penny EdmundsonPhotography:Simon CondieProduction:Penny Edmundson
Copyright TWI Ltd 2010
Articles may be reprintedwith permission from
TWI. Storage in electronic
media is not permitted.
Articles in this publication
are for information only.
TWI does not accept
responsibility for the
consequences of actions
taken by others after
reading this information.
This publication is also
available in alternativeformats. Please [email protected] to
request a copy.
Published byTWI Ltd, Granta Park,
Great Abington,
Cambridge CB21 6AL, UK
Tel: +44 (0)1223 899000
Fax: +44 (0)1223 892588
E-mail: [email protected]
www.twi.co.uk
TWI Technology Centre(North East)
Tel: +44 (0)1642 216 320
Fax: +44 (0)1642 252 218
TWI Technology Centre
(Yorkshire)
Tel: +44 (0)114 269 9046
Fax: +44 (0)114 269 9781
TWI NDT Validation
Centre (Wales)
Tel: +44 (0)1639 873 100
Fax: +44 (0)1639 864 679
TWI AberdeenTel: + 44(0)1224 691222
w w w . t w i . c o . u k e - m a i l : t w i @ t w i . c o . u k
Issue 168 September/October 2010
The first CSWIP Welding Quality
Control Co-ordinator course took
place in Great Abington, UK on
23 August. At the end of this five-
day course, candidates were invited
to a cake cutting ceremony to
celebrate the official launch of this
new programme!
People holding CSWIP welding inspection
certification with several years experience
often asked us about the next logical stepon their career ladder.
In addition, the modern
inspectors roles have
changed in the last few years
and often the title of QC
Engineer is thrust upon them
or they are expected to be
equally proficient in several
disciplines.
The Welding QC Co-ordinator programme is
designed to bridge the
knowledge gap between welding inspection
and quality control.
A highly subscribed second course hasbeen held in Middlesbrough and will be
followed by a furthercourse in Great
Abington starting on 22 November.
Further courses will be available in 2011
This new scheme is proving to be very
popular so dont delay enrolling!
For further information, please
visit www.twitraining.com
call +44(0)1223 899500 or
CSWIP Welding QC Co-ordinator
a popular new scheme