African Fusion March 2015

AFRICAN MARCH 2015

Journal of the Southern African Institute of Welding

Contents

March 2015 FEATURES 4 SA’s Young Welder, 2015

Published four times a year and mailed out together with Mechanical Technology by:

Jaco vanDeventer, a product of Steinmüller’s appren- ticeship scheme, has won this year’s Young Welder of the Year competition, which was held at the SAIW during February. 5 Changing of the guard Following the resignation of Jim Guild, this article looks at his accomplishments since his tenure began back in 2000. 6 Introduction to thermal spray coatings During January, the SAIW and the Thermal Spray As- sociation of Southern Africa (TSASA) hosted thermal spray specialist, Heidi Lovelock to present a one-day seminar at Emperor’s Palace. African Fusion sum- marises the opening session. 18 Small bore pipe socket weld inspection using phased-array UT This paper from the 67 th IIW Conference is about the use of phased array ultrasonic testing (UT) for small- bore pipe socket welds on nuclear power plants. 24 Microstructural study of trial weld joints for steam turbine rotors Also from last year’s IIWConference, this paper details procedure development for welding turbine rotors for steam power plant using creep resistant rotor steels and the hot-wire GTAW welding process. 28 Wind Tower fabrication: the DCD way African Fusion visits DCD Wind Towers in the Coega industrial development zone (IDZ) and talks to pro- duction manager, Leonard Jauka. 32 Robot welding, catalytic converters and PE African Fusion visits Yaskawa PE and takes a tour of a local state-of-the art catalytic converter manufactur- ing facility. 35 Welding of super duplex stainless steels This article outlines voestalpine Böhler Welding’s super-duplex stainless steel (SDSS) solutions and consumables for the oil and gas industry. 36 Weco’s HSL solution: the smarter choice African Fusion attends the launch of Smarter Weld- ing Africa’s Weco brand and talks to Smarter’s CEO, Fernando Amaral and Weco director Giorgio Toniolo. REGULARS 3 Jim’s comment 12 SAIW News 16 Front cover story: Total solutions for tank fabrication 36 Welding and cutting forum 40 Component refurbishment using the PTA process

Crown Publications cc Crown House Cnr Theunis and Sovereign Streets Bedford Gardens 2007 PO Box 140

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Bedfordview 2008 Tel: (011) 622 4770 Fax: (011) 615 6108

Editor: Peter Middleton E-mail: mechanical@crown.co.za Advertising: Norman Welthagen E-mail: normanw@crown.co.za Publisher: Karen Grant Director: Jenny Warwick Cover design: Air Liquide Production & layout: Gail Smith Circulation: Karen Pearson Subscriptions: Wendy Charles Printed by: Tandym Print

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For thewelding of large storage tanks, a partnership between local automation specialist Mazolutions, Lincoln Electric and Chinese-based All Time is dramatically improving the quality and productivity of storage tank construction for the oil and gas sector. African Fusion talks toAndrewMasuret, MD of Mazolutions, about the technology.

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www.crown.co.za

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Young Welder of the Year 2015 Creating Employment: Skilling our Youth

Jaco van Deventer has been crowned Young Welder of the Year for 2015 after a very closely fought competition. He will represent South Africa in the WorldSkills competition in Sao Paolo, Brazil in August. SAIW General Manager Sean Blake says that the central aim of the Young Welder of the Year competition is to promote welding as a career to the youth of South Africa and that the 2015 competition played its part with flying colours.

Well done Jaco van Deventer, Young Welder of the Year 2015

Young Welder 2015 Sponsors

SAIW: Jim's comment

SAIW and SAIW Certification

SAIW President M Maroga - SAIW President Council members JR Williamson - Personal member T Rice - Personal member DJ Olivier - Personal member W Rankin - Personal member P Viljoen - PEMA A Koursaris - Personal member F Buys - TÜV

M ostofyouwillknow by now that I have retired and will be leaving this post at the end March. I started inDecember 2000 and, on reflection, I

G Joubert - SAISI J Pieterse - Afrox J Zinyana - Personal member L Breckenridge - CEA A Paterson - University of the Witwatersrand W Scurr - SASSDA J Botha - SAISI Technology and Training Board P Venter - Chairperson, ArcelorMittal SAIW Certification Governing Board G Joubert - Chairperson, ArcelorMittal A Koursaris - SAIW F Buys - SAQCC IPE J Guild - SAIW D Olivier - SAQCC CP R Williamson - Consultant/Service Industry P Viljoen - Fabricator’s Board W Rankin - Velosi J Zinyana - New Age Welding Solutions P Bruwer - Sasol Synfuels

Jim Guild Finally to Sean Blake who takes over from me in April. There is still much to be done but you are now at the helm of an organisation which is recognised as a leader in its field and that has the provisions for significant future growth. You have the experience and thewisdom to take the SAIW to unprecedented heights and I look forward to your and your teams’ future successes. Congratulations and good luck! A thank you from Crown African Fusion was JimGuild’s idea. When he first joined at the Institute in 2000, SAIW and Crown cooperated to produce Welding Handbooks. Following increasing success of theWelding feature inMechanical Tech- nology, Guild suggested expanding the feature into a welding journal, partially sponsoredby SAIW. The first issuewas produced in June 2006. For consistently overseeing the quality and content of the maga- zine, for the support given to Crown, African Fusion readers and to the broader welding industry, thank you JimGuild. We believe youdeserve a long and happy retirement. Karen Grant, Jenny Warwick and Peter Middleton must say that I have enjoyed this job immensely. I have enjoyed the challenges, the achievements and, most of all, working with the very special people that have been connected in oneway or another to this Institute and to me through my job as its executive director. When I began 14 years ago the SAIWwas a very small organisation with no international recognition of its courses and reliant almost exclusively on sponsorship for its viability. Today the picture is some- what different. Our courses are recognised internationally, we have more than doubled our training population and, while we still have an excellent relationshipwith our sponsors, our level of self-generated income has improved greatly with the financial reserves now at an appropriate level for significant future development. For details of themore importantmilestones of the last 14 years you can read the “Changing of the Guard” article inside but, in summary, I am particularly pleased with the respect we have gained in Africa and globally as a welding training organisation; the Young Welder of the Year competition, which saw a record entry this year is helping to show the youth of South Africa that welding is an excellent career; the growth of our activities in the regions; the improvements in our training facilities and our premises and the establishment of the SAIW foundation, whichwill become an industry vehicle for social upliftment and development. Regarding this journal and our communications in general there have been significant improvements over the years. African Fusion has helped give the industry at large an opportunity to keep up to speed with technical and global welding news and issues, while our news- letter, Fusion , has played its role in disseminating SAIW and industry information to our members and the welding industry in general. I want to thank all those who have helpedme in this job – the vari- ous SAIWcouncils and presidents, the great SAIW team, our members, our industry contacts and all our dedicated suppliers – I couldn’t have done the job without you.

M Moraga - Eskom S Moodly - SAPREF B Beetge - Sentinel Inspection

SAIW and SAIW Certification representatives

Qualificationandcertifica- tionmanager H Potgieter Tel: (011) 298-2149 potgieterh@saiw.co.za Technical services and training manager S Blake

Executive director JC Guild Tel: (011) 298-2101 Fax: (011) 836-6014 guildj@saiw.co.za Executive secretary D Kreouzi Tel: (011) 298-2102 Fax: (011) 836-6014 kreouzid@saiw.co.za General manager, operations S Blake Tel: (011) 298-2103 Fax: (011) 836-4132 blakes@saiw.co.za

Tel: (011) 298-2103 Fax: (011) 836-4132 blakes@saiw.co.za

Finance and administra- tion manager M Warmback Tel: (011) 298-2125 Fax: (011) 836-4132 warmbackm@saiw.co.za

SAIW regional representatives

Western Cape representative L Berry

KZN representative A Meyer Tel: 083 787-5624 meyera@saiw.co.za

Tel: (021) 555-2535 Fax: (021) 555-2517 berryl@saiw.co.za

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SAIW: Young Welder of the Year 2015

SA’s Young Welder, 2015 Jaco van Deventer, a product of Steinmüller’s apprenticeship scheme, has won this year’s Young Welder of the Year competition, which was held at the SAIW during February.

W ith 20 participants, the Young Welder of the Year (YWOY) 2015 was the largest in the history of the competition. It was, there- fore, an evenmore special victory for the ultimatewinner, Jaco vanDeventer, who will now represent South Africa at the WorldSkills competition to be held in Sao Paolo, Brazil in August 2015. “I am very excited to have won this historic event,” says Deventer. “It’s an honour to get the chance to represent the South African welding industry at theWorldSkills competitionandabonus for my welding career to have won this prestigious event.” Apprenticedat Steinmüller – amulti- service provider to the power generation andpetrochemical industries –Deventer faced tough competition this year, and only beat overall runner-up Romario Arendse from West Coast College by 1.25 points. The win boiled down to the stainless steel section of the competi- tion, which required the young welders toweldaboxwithout rotating ormoving it inanyway. Deventer scoredan impres- sive 9.3/10 for this project, pushing him to the front of the competition. “Jaco demonstrated a high-skill level fromday one,” says Nell. Deventer says he loves welding. “I’ve always been good with my hands

and I like working on practical projects. But more and more I enjoy the science of welding, which is so interesting across somanymaterials andapplica- tions,” he says. YWOY convener, SAIW’s Etienne Nell, says that the

The 2015 Young Welder of the Year, Jaco van Deventer, with SAIW President Morris Moroga.

tive within this focus area. We need to get asmany young SouthAfricans skilled in the various disciplines that welding offers in order to reduce our reliance on importing these skills. “When we have such a high rate of unemployment and an industry like welding that can almost always offer a job to someone with the right skills, it seems a real shame that we continue to have to import welders from other countries. This Institute, through the YWOY and many other initiatives, re- mains dedicated to reversing this trend,” says Guild. SAIW GM Operations Sean Blake concurs, saying that despite the major shock to the economy in 2008 and the lingering economic challenges we continue to face in 2015, welding still remains a very viable career. “Because it is so widely used in industry, welding is still – in terms of employment and a career – one of the best hedges against a struggling economy,” says Blake. SAIW President Morris Moroga adds that the YWOY competition plays a crucial role in finding the young stars of the future in welding. “The stories are numerous of those who have done well in the competition going on to stellar careers in welding and it is important that the SAIW, the competition spon- sors and the welding industry generally continue to support this initiative for the sake of the development of our youth,” concludes Moroga. The 2015 competition was spon- sored by: Abicor Binzel, Afrox, AFSA, Air Products South Africa, ArcelorMittal, Columbus Stainless, ESAB, Hulamin, Laser Cut Varios, Macsteel VRN, Sangari, Sassda, ThuthukaWeldingProducts and Welding Alloys South Africa.

quality of thewelding this yearmatched the quantity. “Each year we see an im- provement in the standards of the young welders and 2015 was no exception,” Nell says. “I was particularly impressed with the winners of the various cat- egories and, of course, Jaco’s work was outstanding.Wehavehighhopes for him to do well in Sao Paolo, where he will be up against the best young welders in the world.” SAIW executive director Jim Guild says that the Institute will definitely continue with the YWOY. “We have to continue encouraging the youth of South Africa to see welding for what it is – an exciting and potentially lucra- tive career. Welding is ubiquitous. It is involved in up to 98% of manufacturing processes and it offers opportunities for peoplewhomay have a Grade 10 educa- tion to people who have a PhD. “From an SAIW perspective the youthwill continue to be amajor part of our focus and the YWOY a central initia-

With 20 participants, the Young Welder of the Year (YWOY) 2015 was the largest in the history of the competition.

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SAIW: Jim Guild’s achievements

JimGuild has resigned as executive director of the SAIW, with SeanBlake being appointed as successor fromApril. Changing of the guard

J im Guild, executive director of the SAIW since December 2000, is retiring and will be leaving his post at the end of this month. Current SAIW GM operations, Sean Blake, has been appointed SAIWexecutive director as of April 2015. Guild says that his tenure at the Institute can be described as “steady progress”. The fact, however, is that it is more apt to describe his achieve- ments as massive. When he started at the end of 2000, the SAIW was a very small organisationwith no international recognition for its courses; it was strug- gling financially and was reliant on sponsorship for its viability. Today it is the leading welding training organisa- tion on the continent. Its courses are recognised internationally; it has more than doubled its training population and SAIW has earned the respect of the global welding community. Financially it still enjoys good relationships with sponsors but it has greatly improved its level of self-generated income and has an appropriate level of reserves, which it can use for future development and growth. “I put our successes down to excep- tional team work,” says Guild. “From the beginning of my tenure the old stalwarts, such as Ted Barwise, rallied around me to help get things going the way we wanted. Their input was abso- lutely invaluable. Since then, each and every person at the Institute has played his and her part to ensure that we met our goals and achieved what we did,” he says. These achievements include: 2001: SAIW became a regional des- ignated centre (RDC) of the African Regional Cooperative Agreement for Research, Development and Training Related to Nuclear Science and Tech- nology (AFRA). The Institute acted as AFRA’s Anglophone centre for NDT in Africa. Since then, the SAIW has trained around 500 African fellowship students sponsored by the International Atomic Energy Agency (IAEA). The SAIWhas also conductednumerous expertmissions to assist other African countries to estab-

lish NDT training and service facilities and has hosted several scientific visits from NDT personnel throughout Africa. The IAEA periodically sends three ex- perts from around the globe to assess the SAIW standards. 2003: SAIW became an Authorised Na- tional Body (ANB) of the International Institute of Welding (IIW), which enabled it to offer all IIW training courses and to issue qualification diplomas. 2005: The YoungWelder of the Year com- petition was established. This biennial event has become the premier welding competition in South Africa attracting youngwelders fromall over the country. The winner represents South Africa at the WorldSkills competition. The Young Welder competition plays an increasing- ly important role in promoting welding as a career to the youth of South Africa. 2005: SAIW Certification was estab- lished as an independent body within the SAIW in order to enhance the cred- ibility and recognition of SAIWqualifica- tion and certification activities and to foster good growth opportunities. 2006: Permanent representation in Cape Town and Durbanwas established and, in 2013, a fully-fledged training fa- cility in Cape Town was added. A similar facility in Durban is imminent. 2006 and 2012 : SAIW hosted IIW Re- gional Congresses attended by speakers and experts from all over the world. 2008: SAIW was accredited by the IIW as an Authorised National Body for CompanyCertification (ANBCC) enabling it to certify fabricators to the ISO 3834 standard. To date, more than 100 com- panies and sites have been certified by the SAIW. 2011-2013: A cutting-edgemetallurgical andmechanical test laboratorywasbuilt and equipped, along with a state-of- the-art multi-purpose auditorium, and the interior of the SAIW building was completely refurbished. 2014: SAIWFoundationwas established, which will become an industry vehicle for social upliftment and development. Other accomplishments over the period include: • SAIWbecame an associatemember

of the International Committee for Non-Destructive Testing (ICNDT) and established the African Fed- eration for Non-destructive Testing (AFNDT), which is nowrecognisedas a regional body by the ICNDT. The Institute supported the estab- lishment of training schools at WITS and UP, which offer International Welding Engineer and International Welding Technologist programmes. The SAIW sponsors professorial chairs and research and develop- ment programmes in these centres of welding expertise. Since 2009, the SAIW has been ac- credited for its personnel certifica- tion activities by SANAS, which is South Africa’s member of the Inter- national Accreditation Forum (IAF). “One of our very important accomplish- ments,” says Guild, “was the improve- ment in our communications. The Fusion newsletter has played a major role in disseminating SAIW and indus- try information to our members and the welding market in general, while the SAIW journal, African Fusion , has helped in giving the industry at large an opportunity to keep up to speed with technical and global welding news and issues. I thank all those involved in the production of these important publications.” “I want to thank all those who have helped me in a job that I have really enjoyed – the various SAIWcouncils and presidents, the great SAIW team, our members, our industry contacts and all our dedicated suppliers. I couldn’t have done the job without you. “Finally, to Sean. There is still much to be done but you are now at the helm of an organisation that is recognised as a leader in its field and that has the po- tential for significant future growth. You have the experience and the wisdom to take the SAIW to unprecedented heights and I look forward to your and your teams’ future successes. Good luck!” Sean Blake (left) will become SAIW executive director in April. Jim Guild has retired after 14 years at the helm. • •

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SAIW: Thermal spray coatings seminar

Introduction to thermal spray coatings Heidi Lovelock

On January 21, 2015, SAIW and the Thermal Spray Association of Southern Africa (TSASA) hosted South African-born thermal spray specialist, Heidi Lovelock, who is now with TWI in the UK, to present aone-day seminar at Emperor’s Palace. African Fusion summarises the opening session.

Heidi Lovelock, surface engineering specialist with TWI in the UK, at the TSASA-hosted thermal spray coatings seminar at Emperor’s Palace .

“People often don’t realise just how important surface engineering is to modern life. While the technology is largely invisible, it is also indispensable,” Lovelock begins. The general role of surface engineering is to optimise the surface of a component to better suit its environment. While one can optimise mechanical properties such as strength and toughness of a product by selecting an appropriate base material, surface engineering allows one to separately optimise the surface for better wear, corrosion, high temperature oxidation or thermal degradation resistance. And the material property requirements for the bulk materials of a product often contradict the requirements at the sur- face,” she points out. Also, from a cost, design flexibility and fabrication point of view, corrosion and wear resistant materials are often very difficult to fabricate or they cost too much. Citing some examples, she says that in the transport industry, coating technologies are used in catalytic con-

verter cartridges, jet engines and aircraft landing gear. In the energy field, the technology is indispensable for coating solar cells, for the cathodic protection of offshore wind turbines and, for conven- tional fossil fuel power plants, coatings are usedon the blades of steamturbines and for erosion protection of critical boiler tubes. “In the healthcare industry, people are living longer, so knee and hip im- plants are needed. The success of these depends on thermally sprayed ceramic and titanium alloy coatings that ensure the implant is biocompatible andable to bind to bone,” Lovelock reveals. Surface modification treatments and coatings include a multitude of processes such as carburising, nitriding and anodising surface layers, for im- proving the hardness of gear teeth, for example. Hard chrome andother plating processes, such as copper, nickel, zinc, cadmiumand tin coatings, are inexpen- sive but, in the case of hard chrome, in particular, are under pressure due to environmental considerations. Other

coatings, many of which can be very sophisticated. Thermal spray coating characteristics “Thermal spray coatings adhere via a mechanical bond as opposed to a met- allurgical one. Sometimes people react to this fact with nervousness, think- ing the surface layer can’t have much bond strength. But it most certainly can. Tensile bond strengths of greater than 80 MPa are achievable but the true strength is difficult to determine accurately due to the limitations of the glues used in testing,” Lovelock reveals. “The bonding mechanisms at the coating/substrate interface and be- tween the coating ‘splats’ is still subject to some speculation, though, but while both mechanical interlocking and dif- fusion bonding may occur, mechanical bonding predominates.” In principle, all thermal spray pro- cesses involve the use of a coating con- sumable, usually in wire or powdered form. An energy source is used to heat the consumable tomelt or soften it, after which the particles are propelled toward the surface being coated. Representing thermal spray coating processes in two dimensions, Lovelock displays a pro- cess map with particle temperature on the y-axis and particle velocity on the x-axis. There are four broad processes: the flame spray processes on the left at medium temperatures and low par- ticle velocities; the plasma processes that give very high temperatures but relatively low particle velocities; the high velocity oxy-fuel (HVOF) processes, which can produce particle velocities of

modern process- es include thin film processes such as chemical and physical va- pour deposition (CVD and PVD), which offer layer thicknesses from a fewnanometres to 50 µm; as well as a wide range of paints, epox- ies, synthetic lay- ers and powder

Courtesy of TWI Limited.

The thermal spray process map shows the combination of particle velocity and particle temperature inherent in the different thermal spray processes.

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SAIW: Thermal spray coatings seminar

Overview of thermal spray coating technologies Flame spray processes Powder flame spray is a subsonic flame-based process. Powder is blown or drawn into an annular combustion chamber where an aspirating gas and a fuel gas are mixed and combusted, creating a high velocity (subsonic) ex- haust stream. A second outer annular gas nozzle feeds a streamof compressed air around the combustion flame, which accelerates the spray particles towards the substrate and focuses the flame. The powder can be fed through a small hopper on the gun, or via larger freestanding powder feeders. There are also several fuel gas options, depending on the application and temperatures required. “It is a low velocity, low tem- perature process and, because the par- ticles are projected through air, a surface layer with relatively high proportions of oxides, porosity and unmelted particles is produced,” says Lovelock. Wire flame spraying is a similar process, except that the coating mate- rial is fed into the flame spray gun as solid wire. The flame melts the wire, which is then atomised and accelerated towards the substrate by the annular compressed air flow. Also a subsonic process, Lovelock says that the wire feed rate and flame settings have to be balanced toproduce continuousmelting of thewire anda continuous spray of fine particulate. Showing amicrograph of an aluminium coated sample she points out the black lines of oxide stringers and says, “If you consider how easily aluminiumoxidises, this is not too bad”. The flame spray processes have low capital and running costs. They can be done on-site and by hand, if appropriate safety precautions are adopted, and they offer adequate surface properties for low-stress build-up applications and sacrificial coatings. “They are suitable for non-demanding applications such as repairing wear or corrosion damage on non critical parts that are not intended for demanding engineering applica- tions. A variety of iron- and nickel-based powders are available for repair and salvage,” she adds. Avariationof theseprocesses are the spray and fuse processes, also known as spray-brazing, which involve remelt- ing the fused layer – with a flame, in a furnace in by induction heating – after it has been deposited. “The fusingmelts and seals the surface and can produce

up to 300 to 800 m/s; and the modern cold spray process, which, at tempera- tures below300 °C, accelerates particles towards a substrate at up to 1 000 m/s. Each process type has its own niche in the market. “From left to right, we can see these processes as first, second, third and fourth generation thermal spray developments. The higher the particle velocity, the better the layer quality and bond strengths. And the lower the temperature can be kept, the less the chance of oxidisation occurring while a particle is travelling to the surface. The combination of high velocity and low temperature characteristics make cold spray processes very attractive for sensitive and expensive coatings,” she adds. In terms of the coatings themselves, since substrate temperature can be maintained below 200 °C with good thermal management, there is no heat- affected zone (HAZ) or dilution between the substrate and coating. Due to the mechanical bondand the layerednature of the coating structure, the material properties of the coating are not the same as bulk cast/wrought coating ma- terial properties would be. And while a vast range of coating properties can be achieved, it is generally not a good idea to subject coatings to high point or line impact loading. “Components can be coated with metals, alloys, carbides/cermets, oxides, polymers, blends and graded coatings. Deposition rates of between 1.0 and 20 kg/hr can be achieved and, with the addition of the cold spray process, the thickness range is almost unlimited – from 20  m to > 30 mm. “The greatest limitation is that it is a line of sight process. If you have a thin narrowborewith limitedaccess, it is very difficult to coat the inside of it,” Lovelock informs. She also advises caution in some aqueous corrosive environments, because “thermal spray coatings are not generally recommended for corrosion barrier protection in the as-sprayed condition, because they do not seal. While penetration could take years, the coating itself cannot be guaranteed to last forever, even if it has been success- fully subjected to laboratory corrosion tests and appears to be fully dense. This does not apply to sacrificial corrosion protection coatings, however, because this protection does not depend on a sealed barrier,” she explains.

Void Oxide inclusion Unmelted particle Substrate

Features of thermal spray coatings: “The bonding mechanisms at the interface and between the coating ‘splats’ is still subject to some speculation, but while both mechanical interlocking and diffusion bonding may occur, mechanical bonding predominates,” says Lovelock. Image ©ASM International.

ametallurgical bondwith the substrate. The process is commonly used to coat glass formingplungers andglassmoulds with a NiCrBSiFe alloy, a ‘self-fluxing’ alloy with low melting point. This coat- ing is known to produce a favourable surface interaction with molten glass (silica) which at 700 °C is very abrasive,” says Lovelock. Arc wire spray The key difference between these pro- cesses and flame-based process is that an electric arc is used to generate the requiredheat. Themost commonly used variation is twinwire arc spraying, where a dc electric arc is struck between two continuously fedwires. Thewire speeds are set to balance the melt-off rate of the wires and to keep the arc stable. On melting, droplets are propelled by compressed air or an inert gas jet onto the surface being coated. Arc spraying is a very high produc- tivity thermal spraying process with de- position rates for steel at 10 to 14 kg/hr and up to 5.0 to 8.0 kg/hr for aluminium. “With flame spray, it is possible to spray unmelted powders onto a surface, but with twin wire arc spray, the coating material has to be melted before it is sprayed,” Lovelock notes. The process is simple to operate; canbe usedmanually or automated and a wide range of met- als, alloys andmetal matrix composites (MMCs) can be deposited, including a limited rangeof carbide-basedmaterials that are available in cored-wire form. Generally speaking, the coating quality is better than flame sprayed coatings, with less porosity, fewer ox- ides and higher bond strengths. The

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AFRICAN FUSION

Afrox shielding gases protect advanced materials in sensitive places

Shielding Gases

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AFRICAN FUSION

SAIW: Thermal spray coatings seminar

key disadvantage, however, is that the consumable must be available as wire. Typical uses include: aluminium or zinc coatings for corrosion mitigation; salvage, build-up and repair of pitting damage, casting defects and/or wear damage; the reclamation of steel and cast iron parts, typically using NiCr, NiCrAl alloys; the repair of aluminium and magnesium alloy parts, “although cold spray is fast becoming the preferred process here”; and aluminium-based coatings for anti-skid wear resistance. The twin wire arc spray process is commonly used for onshore wind tow- ers, where a zinc layer is sprayed onto the area around the flange connections andaccessdoors for cathodicprotection. Arc sprayed aluminium is widely used to protect offshore steel structures, such as offshore wind turbine foundations, fromseawater corrosion. This is the only coating option that is truly effective in the highly corrosive splash zone, where the water line meets the air. Plasma spray coating As the heat source, the plasma spray coating process relies on a highly con- trolled plasma arc, struck between a tungsten cathode and a copper anode within the plasma gun. An inert or reduc- ing gasmix is fed into the space between the anode and cathode, where it is ionised and dissociated in the arc, trans- forming the gas into a plasma stream of charged particles. The plasma passes through a nozzle as a high velocity jet and recombines into the gas phase along the way, releasing heat energy that raises the gas temperature to up to > 10 000 °C. A powder consumable is injected into this hot gas/plasma stream, where it is melted or softened and pro- pelled onto the substrate. Ideal for materials with very high melting points, such as oxides, interme- tallics, and refractory metals, Lovelock says, “through a combination of high temperature, high energy, a relatively inert spraying medium and fairly high particle velocities, the process produces high quality coatings”. The gasmixtures used strongly influ- ence energy content and temperature. A mixture of two gases, selected from Ar, He, H 2 and N 2 are typically used, with N 2 and H 2 mixes offering higher enthalpy of melting (heat of fusion) for higher temperaturematerials and Ar and/or He being more suitable for materials that melt or vaporise easily.

“A wide variety of powders are avail- able with the finer powders (5-25  m) offering smoother and denser coatings. There is a need to balance economics of the process, i.e. high deposition rate vs. the ability to melt or soften the powder sufficiently. If the feed rate is too high, unmelted particles and/or a low depo- sition efficiency will result,” she warns, adding that numerous process variables, such as spray distance andangle, surface speeds, heat input, cross-over speedand the plasma arc parameters need to be understood and optimised for success- ful results. Plasma spraying can also be done in various low pressure or soft vacuum atmospheres (LPPS/VPS), for reactive metals such as titanium alloys – and underwater spraying is also possible, though seldom used. In terms of porosity, oxides and bond strength, plasma spray offers bet- ter results than the conventional flame and arc spray processes and “the coating bond strength can be nearly as good as HVOF coatings. For carbides, however, bonding is not as goodasHVOF. Carbides are not aswell retained in thematrix and tungsten and chrome carbides begin to decompose because of the higher temperatures,” Lovelock adds. As well as the high capital cost, the only other disadvantage is that the consumables must be in free-flowing powder form. Uses include: • Aluminium and Al alloys: for build- up and repair of Al/Mg parts (al- though cold spray is now becoming preferred). Copper alloys: In the printing indus- try, for example, copper and CuAl is used and for build-up of copper print rolls. CuNi alloys are applied to resist fretting and cavitation and CuNiIn alloys are used on turbine blade roots. Molybdenum: Mo-NiCrSiB coatings offers a high bond strength, good sliding wear and scuffing resistance and a low friction coefficient, mak- ing these coatings ideal for piston rings in large diesel engines. Titanium, tantalum, tungsten al- loys, which can be used for corro- sion resistance in chemical plants if properly sealed. These alloys are best deposited using VPS/LPPS, however, andcold spray is becoming the preferred process for depositing Ta and Ti alloys. Ti and Ti-6Al-4V is widely used for medical implants. • • •

Other applications include: the ap- plication of CoNiCrAlY coatings for re- sistance to high-temperature oxidation. These are used as bond undercoats for thermal barrier coatings (TBCs) – which are later applied using ZrO 2 stabilised with MgO, Y 2 O 3 , CaO, CeO 2 , and others – and the nickel-aluminium/nickel- chrome (NiAl, NiCrAl, NiCrAlMoFe, NiCr) alloys, for salvage and repair applica- tions and as bond coats under oxide- based layers. Pure alumina (Al 2 O 3 ) has high di- electric strength, is a good electrical insulator and is very hard and abrasion resistant. Adding TiO 2 to Al 2 O 3 makes the surface less electrically insulating and decreases resistance to chemical attack, but adds toughness and makes finish grinding easier. Pure TiO 2 resists static build-up, is abrasion resistant and chemically inert inmany environments. Its sliding wear resistancemakes it ideal for textile guides/rollers, pump plungers and mechanical seals in the chemical industry. “Plasma sprayed chromium oxide (Cr 2 O 3 ) coatings are applied to resist corrosion, sliding wear, abrasion, and low-angle erosion at up to about 600 °C. Thermal conductivity is quite high com- pared to other oxides and it is used for pump impellers and housings and, in the printing industry, because the coating is laser-engravable, it is used for Anilox rolls that areprecisely textured to control ink transfer.” HVOF The HVOF process evolved from Union Carbide’s Detonation flame spraying (D-gun) process, which was a propri- etary technology of Union Carbide from the 1960s, and was the only supersonic flame spraying system available until the early 80s when HVOF was developed as a commercially available alternative.

Courtesy of Kennametal Stellite.

An HVOF WC-Co-Cr coating being applied to a hydraulic cylinder.

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SAIW: Thermal spray coatings seminar

With a nozzle design based on jet engine technology, HVOF dif- fers from conventional flame spraying in that combustion is internal and the gas flow rates and delivery pressures are much higher. HVOF torches generate a supersonic flame with characteristic shock dia- monds. “Very high particle velocities are achieved, but at the relatively low temperatures of a combustion process. This combination makes it the ideal process for modern wear resistant carbide coatings,” says Lovelock. The HVOF process produces exceptionally high quality cermet coatings (e.g., WC-Co), but it is also used to produce coatings ofmetals, alloys and (less often) oxide ceramics. Although similar in principle, significant details, such as powder feed position, gas flow rates and oxygen to fuel ratios, are apparent between systems from different manufacturers. The fuel can be propylene, propane, ethylene, acety- lene, hydrogen, natural gas, MAPP, kerosene, and others, depending on the system design. Combustion parameters are the most important variable in HVOF spraying: the ratio of oxygen to fuel; volume flows of oxygen and fuel; and combustion pressure. Powder size and shape are also important and eachHVOF gun is optimised for a specific powder size range. Pow- der feed rate, standoff distance and traverse speeds also need to be taken into consideration. HVOF coatings, because of the high velocities and moderate temperatures, result in less oxidation, less thermal decomposition and high impact energy. This makes them ideal for depositing ther- mally sensitivematerials such as carbides, without degrading particle properties. HVOF is ideal for depositing dense, highly adherent wear resistant coatings with very low levels of oxide, porosity and unmelted particles. Bond strengths are among the highest available, particular for the tungsten carbide-cobalt (WC- Co) and tungsten carbide-cobalt chrome (WC-CoCr) coatings, whichare fast becominga replacement for hardchrome coatings. HVOF-depositedcarbide coatings have replaced hard chrome on the landing gear cylinders of the A380 and the Boeing Dreamliner, which have to sustain very high stresses when landing. On the downside, it is a process suited only to automation – HVOF guns are often manipulated by a robot – and while some internal diameter guns are available, internal bores are usually problematic. It is also not well suited to onsite or in-situ work. Cold Spray coatings Cold spray, or gas dynamic cold spray (GDCS), is a modern coating deposition method based on accelerating solid particles in a super- sonic gas jet at velocities up to 1 000 m/s. The particle temperatures remain below the melting point (typically below 800 °C) while being projected to the substrate and, on impact, are subjected to extreme local deformation with high transient temperatures at the interface. There are twobroad variants of the process, lowpressure andhigh- pressure cold spray. “In low pressure systems, the powder is injected downstream of the nozzle throat, so the feeder itself does no have to be pressurised. These systems areavailableas portable systems for the surface repair of aluminiumandmagnesiumor copper components,” says Lovelock. “High pressure cold spray systems inject the powder upstream of nozzle throat, which requires that the powder feeder be classified as a pressure vessel,” she adds. While the full potential of this relatively new thermal spray process is still being developed and explored, the process is already used for high value repairs of aeronautical components made of aluminium and magnesium alloys; the coating of dense oxygen-free copper for electrical conductors, additive manufacturing, titanium coating of medical implants and the application of zinc and zinc-magnesium alloys onto laser engravable print rolls.

Courtesy of Kennametal Stellite.

The as ground finish of an HVOF applied WC 10% Co 4% Cr coating.

Courtesy of TWI Limited. Courtesy of TWI Limited.

The cross section of an HVOF-applied WC-Co-Cr coating. The coating offers resistance to sliding, abrasive and low angle erosive wear at temperatures of up to 540 °C and chromium in the matrix gives better corrosion resistance compared to WC-Co coatings.

The cross section of an HVOF-applied Alloy 625 coating, a barrier coating for corrosion resistance. Conclusions “While there aremany thermal spray processes, it is impor- tant to select the right coating for thewear conditions, wear mechanism, corrosiveenvironment, operating temperature and loading requirements of the component. Tight control of process parameters is crucial, and standards and cus- tomer specifications are becoming increasingly stringent as the global thermal spray industry is required to service ever more critical applications,” Lovelock concludes.

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SAIW bulletin board

TSASA seminar and thermal spray exhibition

• Engage with research and develop- ment organisations in South Africa. Promote andprovide education and training of all stakeholders. To develop a thermal spray compa- ny certification programme – “simi- lar to ISO 3834 for welding industry” – that enforces standardisation of approvals/standards for use in local and/or international markets. And to develop integrated technical advisory programmes for applica- tions within every industry sector. TSASA stakeholders include thermal spray contractors, OEMs, companies servicing the thermal spray industries, welding and other supply companies, engineering jobbing shops, gas and fume extraction suppliers, and robotic and automation specialists, “and we have a spread of these people here today” Blake says. “This makes me feel very positive about the future of TSASA and the thermal spray industry in South Africa,” he concludes before introducing Heidi Lovelock. Sponsors for the event included: Yas- kawa Motoman; MacKays Metal Spray- ing; Weartech; Praxair; Thermaspray; and P&S Engineering. • • •

AdamWintle, acting chairperson of the TSASA, Brandon Smith, Weartech Natal and Steve Maynard from Johannesburg photographed at the Weartech exhibition stand.

A t Emperors Palace on Jan 21, 2015, the Thermal Spray Association of South Africa (TSASA), a sub-committee within the SAIW, hosted a thermal spray seminar presented by Heidi Lovelock of TWI in the UK, along with a small exhibition. Says Sean Blake, SAIW GM, “TSASA, as part of the SAIW, is developing af- filiations with the International Thermal Spray Society from the US and the In- ternational Thermal Spray Association,

as well as GTS in Germany, which also operates in conjunction with the Ger- man Welding Society (DVS), our sister organisation.” Objectives of TSASA include: • To develop an organisation that will ensure that the southern African thermal spray offering and usage is on par with that of the rest of the world. Toensure that themembersof theor- ganisation receive tangible benefits. •

Students from Cameroon and Sudan at the SAIW T he Southern African Institute of Welding (SAIW) is currently hosting a group of non-destructive testing (NDT) students as part of the triangular regional development programme sponsored by the International Atomic Energy Agency (IAEA),

the relevant country and the SAIW. Four students fromHYDRAC inCameroon and five students from the Sudanese Atomic Energy Corporation (SAEC) in Sudan participated in this training and qualification programme. According to Harold Jansen, SAIW NDT manager, the programme aims at having the participants qualify in the four basic NDT methods: magnetic testing (MT), penetrant testing (PT), ultrasonic testing (UT) and radiographic testing (RT). “Not only will they receive training and examination up to and including Level 2 qualification, but they will also be exposed to the process of how the lecturing is handled as well as the handling of invigilation and examinations. The training programme started in January 2015 and is expected to last until the last week in May 2015. The objective of the regional development programme is to help es- tablish approved training bodies (ATB) and approved examination centres (ExC) within various African countries. The SAIW facilitates this programme in countries that are proficient in English with other languages, such as French and Portuguese, being facilitated via regional development centres catering for these languages in cooperation with the African Federation of NDT (AFNDT). Once the qualification programme has been completed, the nine stu- dents will return to their respective countries in order to gain the industrial experience required as part of their NDT certification process. Certification is based on the SAQCC NDT scheme, which is a third party personnel cer- tification scheme compliant with ISO 9712, the internationally recognised standard for qualification and certification of NDT personnel. We wish these students a long and successful career in NDT.

The Southern African Institute of Welding is currently hosting a group of NDT students as part of the triangular regional development programme.

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SAIW bulletin board

ISO TC44 meeting hosted by SAIW in Cape Town D uring January 2015, at the Lagoon Beach Ho-

tel in Cape Town, the SAIW hosted the ISO TC 44 SC8 sub-committee meeting, which deals with equipment for gas welding, cutting and allied processes. “This was the first time this committee has met in South Africa and an honour for South Africa to host the experts in this field,” says SAIW GM, Sean Blake. Thecommitteemembers include: Kurt Ziegler fromthe German Metrology Institute who chairs the committee; Stephan Wellendorf from DIN, the German Institute for Standardisation; Uwe

Some of the committee members for ISO TC 44 SC8, which deals with ISO standards for equipment for gas welding, cutting and allied processes.

well as Peter Cross, TheroMalumane and Thembi Hlongwane from SABS. The main items dealt with included the revision of ISO standards for flash- back arrestors; the terminology for gas welding equipment; rubber hosing for gas welding equipment; Acetylene manifold systems for welding, cutting and allied systems; Pressure regulators with gauges and flow metering devices;

Blowpipes for gas welding, heating and cutting; Quick action couplings with shut-off valves; Pressure regulators for manifold systems and gas tightness; and materials used for gas equipment. “This event affirmed SAIW’s and the South African welding Industry’s com- mitment to the development and imple- mentation of international standards,” concludes Blake.

Schulze from BAM, the Federal Institute for Materials Research and Testing; Cesar Joubert from Air Liquide, France; Francois Chaussat; Marco Giannelli from Harris, Italy; Marco Arzenton fromAir Liq- uideWelding in Italy andDavidWarhurst from the United Kingdom. Overseas visitors were joined by Ro- berto Dionisio fromAfrox, Philip Doubell from Eskom, Sean Blake from SAIW as

SKS torch solutions.

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Wire Select 2.0

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Water Joint Lite

Power Clutch water-cooled

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SAIW bulletin board

ISO 3834: demand continues to grow N ew Age Welding Solutions, a dy- namic young company that pro-

wherever possible,” Zinyana concludes. “More than 75 companies and more than 35 sites have been certified since the inception of the scheme in 2008, and the demand continues to grow,” says Herman Potgieter, SAIW Qualifica- tion and Certification manager. “There is no doubt that the ‘push-pull’ effect in the South African welder fabrication market has been an important reason for the success of the Scheme. Life is made so much easier for the larger end users when they see that a potential supplier is certified as they can have confidence in the quality of the product supplied. End users are reluctant to work with

vides professional welding and me- chanical services solutions to the South African Engineering industry, has been certified to ISO 3834 Part 2 – compre- hensive quality requirements – via the SAIW Welding Fabricator Certification Scheme. “This is an important moment for us,” says Joseph Zinyana founder and GM of New Age. “ISO 3834 is the basic quality benchmark in our industry and ISO 3834 certification officially confirms for all our current and future customers that we provide a world class service,” Zinyana says. He adds that ISO 3834 certification is not only an affirmation for the ‘outside world’ that New Age is a thoroughly professional organisation, but it is also an internal affirmation. “It is important for every company to get an objective statement about its quality. No matter how big or small one’s company is, one can fall into bad habits without realising it. So independent verification is vital and that’s one of the reasons we are so delighted that we ‘passed the test’ with ISO 3834,” he says. Sean Blake, SAIW GM Operations, says that the certification process with New Age went smoothly. “It is pleasing that somanymore professional welding companies like NewAge are applying for certification. There was a time when the industry felt that ISO 3834 certification was for the biggest companies only. Of course this is not true and now the num- ber of companies, both big and small, applying for certification continues to grow in South Africa. This is an excel- lent thing as compliance with ISO 3834 ensures that our fabricators areworking to the best possible standards,” he says. Zinyana complimented the SAIW team which he says was “thoroughly professional” at all times. ISO 3834, supplements the already certified ISO 9001-2008 quality management system in New Age. Both systems ensure that New Age delivers a quality product to all its clients. Other companies which have re- cently attained ISO 3834 certifica- tion through the guidance of New Age Welding Engineering services include: Petrochemical Piping Services and D&M Engineering.” New Age shall endeavour to assist general welding companies to achieve this ISO 3834 certification

non ISO 3834-certified companies and this has pushed fabricators to get certi- fied,” he says. New Age’s Joseph Zinyana and SAIW’s Herman Potgieter.

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