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MolyReview 1 /2018Innovative bridge uses stainless steel 2Tank containers shrink the world 4Safer seas with stainless steel 8MoRe© unique implants 10Lighter and safer offshore platforms 13IMOA news 16

Publisher:International Molybdenum Association454-458 Chiswick High Road London W4 5TT, United Kingdomwww.imoa.infoinfo@imoa.info+44 20 8747 6120

Editor in Chief:Nicole Kinsman

Managing Editor:Curtis Kovach

Contributing Writers:Catherine Houska (CH), Alan Hughes (AH),Curtis Kovach (CK), John Shields (JS), Nancy Baddoo (NB)

Layout and Design:circa drei, Martina Helzel

The International Molybdenum Association (IMOA) hasmade every effort to ensure that the information presented is technically correct. However, IMOA does notrepresent or warrant the accuracy of the informationcontained in MolyReview or its suitability for any generalor specific use. The reader is advised that the materialcontained herein is for information purposes only; itshould not be used or relied upon for any specific orgeneral application without first obtaining competentadvice. IMOA, its members, staff and consultantsspecifically disclaim any and all liability or responsibilityof any kind for loss, damage, or injury resulting fromthe use of the information contained in this publication.

Cover photo: The West 7th Street Bridge in Ft. Worth, Texas USA uses angled 2205 duplex stainless hanger bars in itsstructurally innovative precast concrete network archdesign. © Liam Frederick Photography

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On-site placement of a bridge arch. © Liam Frederick Photography

Innovative bridge uses stainless steelIconic bridges that combine cutting edge technology and aesthetic beauty are increasingly used tocreate visual focal points in city centers, but very few are constructed on modest budgets and ahead ofschedule.

When a 100-year old Ft. Worth vehicularbridge was beyond rehabilitation, the engineers at the Texas Department of Transportation (TxDOT) designed avery special replacement – the world’sfirst precast concrete network archbridge. The 12 nearly 50 meter long and7 meter high arches, each weighing 284 tonnes, are believed to be theworld’s largest precast concrete archestransported to a bridge location. Thestructural molybdenum-containing stainless steel hanger bars within themare also believed to be a first.

The 299-meter-long, multi-award winning, four-lane West 7th Street bridgewas completed in 2013. This vehicularbridge also provides a walkable gatewaybetween the downtown area and museums designed by some of theworld’s most famous modern architects.It offers spectacular views of the river,downtown and the museum district.Lights within its graceful arches highlightthe gleaming angled stainless steel bars. The sidewalk’s position, right nextto the arches, encourages pedestrian

interaction with them, so this sculpturalbridge appears frequently on socialmedia. The bridge was opened a monthahead of schedule, and its US $25.9-million cost was under budget and wellbelow the typical cost per square meterfor a high-profile bridge.

The key feature of a network arch bridgeis its angled hangers. These hanger barsconnect the ‘tie’, which holds the archends at the bottom of the arch together,to the top of the arch. The combination of the tie and hanger system creates a truss-like behavior where the hangerstransmit loads from the deck through the tie and into the arch. In contrast to a traditional vertical hanger system, the angled bars reduce bending in the arch when vehicles and people pass overthe bridge. This system is structurallyhighly efficient. Most network arches usesteel box arches, whereas the West 7th

Street Bridge uses precast, prestressedconcrete arches.

In total, nearly 100 tonnes of stainlesssteel were used for the very visible

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While the angled 2205 duplex stainless bars stabilize the bridge, their location beside the sidewalk makes them a lovely place to pose for photos. © TxDOT

Light gleaming off the 2205 duplex stainless steel hanger bars adds the sculptural look of this beautiful bridge. © Liam Frederick Photography

inclined hanger system at the center ofthe 12 arches. These large, 44.5 milli -meter diameter bars are made of 2205duplex stainless steel, containing 3%molybdenum, and are up to 8.2 meters inlength. The link plate, pin and hanger tubecomponents were manufactured from2205 duplex stainless steel plate, and thecast clevises were CF8M stainless steel (cast Type 316). This molybdenum-containing stainless steel alloy com-bination was selected for its corrosion resistance and structural performanceduring TxDOT mock-up testing.

Traditional bridge replacement can taketwo to three years, causing significanttraffic and business disruption, but thisinnovative design used arches which werecast off-site and required the bridgeto be closed for less than five months. Theconstruction and its unique challenges

were documented in the award-winningUS public television documentary, the ‘Arc of Innovation’.

Charles Walker, P.E., Senior Associate,Walter P. Moore and Associates (formerlyof the TxDOT) played a key role in thestructural design of the stainless steel elements of this special bridge. Whenasked about stainless steel selection, hesaid that, “the combination of stainlesssteel and concrete in compression takesus towards infinite durability of the network arch elements because stainlesssteel does not require the coatings and maintenance that would have beennecessary for carbon steel hangers.”“Infinite durability” is a big phrase for any bridge engineer to use, but with theproven longevity of molybdenum-containing stainless steel, he may beright. (CH)

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Tank containers use stainless steel for a variety of applications besides the main tank, includingwalkways, hatches and valves. © IMOA/Nicole Kinsman

The first International Organization forStandardization (ISO) tank containerswere manufactured in the late 1960s, withthe ISOTANK name being registered by Andrews of Aintree Ltd, Liverpool, UKin 1969. These were also the first tanks to gain design approvals for internationaltransport by Lloyds Register and the UK Department of Transport.

Today, tank containers are used to trans-port a wide range of cargoes includinggases, powders, liquids and other hazardous and non-hazardous loads, as

It is no exaggeration to say that the tank container has revolutionized freight transport. From its humbleorigins, the ISO tank container industry now numbers more than half a million units across the globe. Tankproduction is growing at nearly twice the rate of the world economy and they are almost always made of molybdenum-containing stainless steel. Such is their popularity that these containers now represent asignificant end-use application for molybdenum.

Tank containers shrink the world

well as a wide range of perishable andnon-perishable food and food-gradeproducts including orange juice, wine andeven liquid chocolate. They can be cooledor heated using thermal jackets, either to protect perishable goods or to turn viscous commodities like heavy fuel oilinto a more liquid state for unloading.

The majority of tank containers are constructed from stainless steel and aremanufactured by a handful of globalcompanies. One such company is WelfitOddy, based in South Africa. In 2016, they

manufactured 6,300 containers, some14% of the global total. Approximately80% of the stainless steel used to manufacture the containers is Type 316 –containing 2% molybdenum – althoughother grades including 304 and lean duplex 2001 are also used. Stainlesssteel accounts for more than 60% of theweight of the container – 2.5 tonnes of the total empty weight of 4 tonnes. Atleast one manufacturer has started toproduce the tank barrel from higher-strength 2205 duplex stainless steel tomake lighter packages with even bettercorrosion resistance.

A typical container has a capacity of25,000 liters and a maximum grossweight of 34 tonnes. The tank is usuallysurrounded by a protective insulatinglayer of polyurethane and aluminium andis secured inside a rectangular steelframe made to ISO specifications, nearly20 feet (6 meters) long, nearly 8 feet (2.5meters) wide, and approximately 8 feet(2.5 meters) high. The ISO accreditation is important as it guarantees that thetank unit will seamlessly connect with an entire transport infrastructure by road, railand sea, just as regular ISO containersdo.

Global product flows

It is this intermodal capability which has proved such a catalyst for the growthof the container industry, as the goods remain in the same container throughouttheir journey, whatever the mode oftransport.

Roger Gloor is Technical Manager for Bertschi AG, a global logistics serviceprovider. Sharing his insights ›

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The tank containers can be stacked just as regular 20-foot ISO containers. © Bertschi

The product stays in the same intermodal container from storage at the original production facility all the way to storage at the receiving facility. The exampleshows a tank which is moved from the factory in China via road truck, freight train, container ship, another freight train and road truck to the destination facilityin Portugal.

of tank container transport and its growing impact on cargo movements, hesaid: “What we have seen in the pastdecade is a globalization of product flow.Products are increasingly sourced notjust regionally or on the same continent,but globally, and containerization makes this easier, allowing us to ship cargo‘door to door’, using the most appropriatemethod. This means we can plan better,reduce lead times, and fix costs muchmore competitively.”

Container transport is as flexible as theinfrastructure allows, and because of this,it is usually also the most sustainable,saving energy and resources.

Moly makes the grade

So why use molybdenum-containingType 316 stainless steel? “Type 316 hasseveral advantages,” said Roger. “It is easy to clean, provides excellent ›

ChinaShanghai

ChangshanTown

Netherlands

Rotterdam

Portugal

Portalegre

The fabrication of a tank container includesautomated welding. © IMOA/Nicole Kinsman

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resistance against chemical corrosionand has good tensile strength. Becauseof its global availability, it’s also easy to source and repair anywhere inthe world, and given its durability, it is competitively priced. Chemicals are increasingly complex and present newcorrosion challenges, but providing thatthe tanks are thoroughly cleaned andloaded correctly, there is no reason whycontainers shouldn’t give many years of reliable service.”

Once the product has been delivered,the tank is cleaned according to the nature of its contents and is ready to beused again. There are many differentcleaning processes depending on thecargo, and each process has a differentapplication time, ranging from a few minutes to several days. These processesare an important factor in ensuring thequality and safety of transportation, andare regularly checked in accordance with international regulations.

The ease of cleaning stainless steel and its durability over repeated cycles isalso an important logistical consideration.Historically, many commodities weretransported in bulk by sea or in drums,which can be difficult to clean and areoften disposed of after a single journey.In comparison, tank containers are rarelyunused for any stage of a journey –

including when they are initially deliveredto their logistics customers. New containers built in South Africa typicallyleave laden with the country’s largest export – wine – in an elegantly efficientmatching of one-way supply and demand.

A growing global industry

Products are transported to and fromevery continent, with the flexibility of

intermodal container transport helping to make previously unviable journeyspossible. New rail routes have recentlybeen opened up between China and Europe, taking advantage of the shorterdistances and transit times over landcompared to the sea route. Convoys oftank containers complete the 8,000 kilometer rail journey in just 18 days.

The efficiency – and ultimately, sustain-ability – of tank containers are fuelling aboom in this sector which shows no sign of abating. In 2016 another 44,450tanks were manufactured around theworld, using more than 110,000 tonnes ofstainless steel and nearly 1,800 tonnes of molybdenum, making tank containersa significant end-use application formolybdenum.

At the end of 2016, there were some508,000 containers in existence aroundthe world, an increase of 8.5% over theprevious year. This popularity is due in part to the durability of the containersand their resistance to corrosion. Despitea variety of corrosive cargo, endlessmovement and vigorous cleaning, thecontainers are used over and over again,thanks to molybdenum-containing stainless steel. (AH)

Installation of thermal insulation, covering the entire stainless steel tank. © IMOA/Nicole Kinsman

Tank containers are loaded on a freight train. © Bertschi

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Chemical tankers are specialized ships carrying liquid cargoes that may be environmentally hazardous,flammable or highly reactive. They are designed and operated under special rules, and increasingly havebuilt-in molybdenum-containing stainless steel tanks. Sailing around the world, they transport liquid goodssafely over long distances. They represent a significant market for duplex stainless steels and molybdenum.

Safer seas with stainless steel

The term ‘tanker’ often brings to mind animage of the great supertankers plyingthe seas, carrying bulk and refined oil.These behemoths can have capacitiesexceeding 400,000 deadweight tonnes(dwt). Chemical tankers are smaller, typically 5,000–40,000 dwt, but are noless important to the world economy. Because chemical cargoes can be extremely corrosive, many of these shipsare built with molybdenum-containingstainless steel tanks for longevity, safety,and flexibility. Duplex stainless steels, in particular, are more and more specifiedfor the demanding conditions that thevessels must withstand.

Rules and classification of chemical tankers

All ships are subject to numerous stringent regulations regarding safe navigation, air pollution, and the discharge of liquids and solids. Ships that travel in international waters are subject to the International Maritime Organization (IMO) regulation known as the ‘International Code for the Construction and Equipment of ShipsCarrying Dangerous Chemicals in Bulk’,or IBC Code. This code establishes design standards based on the hazardspresented by ships’ cargoes.

Because chemical cargoes present many kinds of safety and pollution risks,construction and operation requirementsfor chemical tankers are much morestringent than those for oil tankers andcommodity carriers. Tank design and fabrication are complex. The IBC Codeincludes provisions for cargo pumpingand monitoring; tank coating, cleaningand venting; vapor detection and fire protection. It also promulgates specific

requirements for tank heating, cross-compatibility, corrosion control, and cargodensity. Chemical tankers are arguablythe most technically sophisticated of alllarge cargo ships.

Chemical tankers can be categorized according to size, products carried, and markets served. Parcel tankersare relatively large vessels with multiple separate tanks carrying high-gradechemicals, often in stainless steel tanks;product tankers are also large, but theycarry less difficult cargoes, frequently in coated-steel tanks; and specializedtankers are small to medium size, carrya limited number of chemicals in a dedicated trade and use either coated-steel or stainless steel tanks, dependingon their cargoes.

The ship

Chemical tankers may be distinguishedby an array of pipes that run above theship’s deck. Liquid chemicals are pumped

via these pipes and their associatedvalves to load and unload the varioustanks. For example, the large chemicaltanker, the Odfjell SE Bow Star, built in 2004 at Poland’s Szczecin New Shipyard, has thirty-four square and rectangular 2205 duplex stainless steelcargo tanks below deck and six cylindrical tanks mounted on the deck.The vessel is 183 meters long with abeam of about 32 meters and a capacityof 39,832 dwt. The construction of thetanks required 3,000 tonnes of duplexstainless steel (some 90 tonnes ofmolybdenum) and they provide 52,106cubic meters of storage volume.

The cargo tank

Design and construction – Inboardtanks contain hatches, ladders, heatingsystems, piping and drains. Tank wallsare typically 20–25 millimeters thick andare corrugated to increase tank stiffness.This enhances the ship’s structural rigidity and saves weight compared to

The schematic shows the location of the different stainless steel tanks on theOdfjell SE Bow Star. © Odfjell

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straight-walled tanks. The corrugationsare about 1 meter wide and 1 meter deep. Tank fabricators must employ precision welding techniques to ensureweld integrity, and careful post-fabricationcleaning to ensure the quality and corrosion resistance of the stainless-steel

surface. A typical size vessel requiresabout 1,500 tonnes of stainless steel.

Materials – Early chemical tankers usedType 304L stainless steel, but today a grade with 2.0–3.5% molybdenum isstandard. Type 316 austenitic stainlesssteel and its variants are sometimesspecified, but the duplex stainless steelgrade 2205 is now the most widely usedtank material.

This grade is popular because it isstronger and more corrosion-resistantthan Type 316 stainless steel. The alloy’s higher strength requires less steel and therefore reduces the ship’sweight. Its superior corrosion resistance,due in large part to the addition of 3% molybdenum, allows it to carry awider variety of aggressive liquids. The coefficient of thermal expansion of 2205 is closer to that of carbon steelthan Type 304 or 316, making it morethermally compatible with surroundingcarbon steel structures.

Cleaning – Tank cleaning is an essentialpart of chemical tanker operation,

directly affecting both product quality andoperating cost. Many owners consider it the most important operating cost because it is the one over which they havethe most control. Stringent design codesand operating regulations tend to equalizecapital and most operating costs for all operators across a given tanker size,so efficient cleaning practices can providea competitive edge.

The tank material and its coating, if present, control the particular cleaningpractice. Stainless steels do not absorbliquids like epoxy coatings on carbonsteel tanks, and they are not porous likezinc silicate coatings. Because they arecorrosion resistant, they are compatiblewith a great variety of cleaning methodsand products, thereby offering owners a significant operating-cost advantage.

Chemical tanker ship market

The average life of a chemical tanker is23 years. A 2012 study of 138 majorchemical tanker operators showed some1,800 ships to be operating at that time,of which about 400 had stainless steel

Interior of a stainless steel tank on a chemicaltank ship. © Stolt Tankers

The chemical tanker Bow Sagami is docking for loading or unloading. © Odfjell

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People in the refractory metals field typically associate Mo-Re alloys with applications such as infra-red halogenlamp filaments, heating elements forchemical vapor deposition furnaces, thermocouple sheathing, heat shields,and space-vehicle thrusters, all of whichoperate at extremely high temperatures.Recently however, the traditional “Mo-50 Re” alloy, actually a 52.5%molybdenum - 47.5% rhenium alloy, hasfound new applications at body

a tubular mesh. This mesh, or stent, is used to expand an occluded artery torestore its blood flow. To place a stent, a surgeon makes a small incision in an artery located in the arm or groin, insertsa catheter containing one or more stents into the artery, maneuvers it to the affected vessel, and expands thestent using a balloon. Traditionally, stentshave been made from small-diameterstainless steel, titanium, cobalt-base, ornickel-titanium (Nitinol) alloy seamless

temperature that exploit its mechanicaland biological properties. MiRus, a medical device manufacturer in Atlanta,Georgia, is at the forefront of this excitingwork.

The cardiovascular connection: a Mo-Re stent

Most cardiovascular stents are madefrom a solid tube by micro-machining orlaser cutting intricate patterns to create

Molybdenum-based alloys containing rhenium have been used primarily for high-temperature applications.However, the traditional “Mo-50 Re” alloy has now been clinically evaluated for a cardiovascular stentand is certified for this application. Furthermore, an ASTM standard covering its use in implants has beenpublished recently. The alloy’s high strength, excellent toughness, ductility and biocompatibility makeMoRe® an excellent alternative to traditional implant materials.

MoRe® unique implants

tanks. These numbers suggest a demandof 75–80 ships per year, 15–20 of whichwould contain stainless steel tanks. However, more recent statistics publishedby IHS Markit showed that 144 stainlesssteel-tanked ships were either under construction or on order in 2016–2017.

The market for new chemical tankers has historically grown at 1.3–1.7 timesthe rate of the global GDP. Increasing demand for chemicals and their world-wide production and trade favor a continued expansion of chemical tankerfleets, especially those using stainlesssteel tanks. Furthermore, ships are becoming larger and more complex. Shipreplacement, market growth, and a continuing shift in alloy choice for tankscombine to produce a substantial marketof tens of thousands of tonnes of duplexstainless steel every year. These factorsimply that the demand for molybdenum inchemical tank ships will remain strong for the foreseeable future. (CK)

The topside of a chemical tank ship is busy with a myriad of pipes and valves. © Nordic Tankers

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tubing. Outside diameters are typicallyless than 2 millimeters for use in small arteries and 2–5 millimeters for large arteries.

Stent-placement is monitored using real-time radiography, allowing the surgeon to see the stent on a screen and direct it to the required location. Since radiation absorption is proportional to amaterial’s density, Mo-Re, with a densityof 13.5 grams per cubic centimeter, is superior to traditional materials withdensities ranging from 4.5 (titanium) to8.8 grams per cubic centimeter (cobalt-chromium). With Mo-Re stents absorbingmuch more radiation than traditional alloys, these stents are much easier tosee during implantation. Surgeons cantherefore manipulate and place themmore safely and precisely than traditionalstents.

In the last decade, a Mo-Re stent designwas successfully developed by Icon Interventional, a predecessor of MiRus,and is now available for clinical use inEurope. The high strength of the alloy

has allowed production of a stent with a0.06 millimeter wall, the thinnest onrecord. This success led MiRus to conferwith a number of orthopedic specialistsabout other potential applications for thealloy. The ensuing discussions identifieda number of unique opportunities to develop new surgical implants for spinaland craniomaxillofacial (head, face, and jaw) applications. Device designers,design engineers, and orthopedic surgeons are now focusing on applica-tions in these areas.

Mo-Re material properties

Mechanical properties – Cold workingincreases the strength of Mo-Re alloy, as it does for metals generally. However,when cold worked, much of the deformation in Mo-Re is accommodatedby an unusual process called twinning- induced plasticity (TWIP). TWIP simultaneously imparts high strength and high ductility, and MoRe® implantsbenefit from this unique phenomenon.The newly issued ASTM standard,F3273-17 Standard Specification forWrought Molybdenum-47.5 RheniumAlloy for Surgical Implants (UNSR03700), defines several differentstrength levels of Mo-Re alloy based onthe amount of cold working done. The strongest has minimum yield and ultimate tensile strengths in excess of1300 MPa with double-digit percentageductility. Higher strength allows designersto create smaller and lighter implants that disturb less of the bone structureinto which they are placed. They alsoprotrude less, blending better with thebone’s natural shape.

Surgical implants are often subjected to cyclic loading. Therefore, a large proportion of implant breakage occurs as a result of fatigue failure, so fatigue resistance is an important property for implant alloys. Fatigue tests comparing

Mo-Re, Co-Cr, and Ti-6Al-4V bent spinerods showed a great advantage for Mo-Re alloy even though its rod’s cross-sectional area was only 53% of the otherrods’. Improved fatigue strength offersbetter implant reliability, lower probabilityof implant failure, and less product liability exposure.

Magnetic properties – Magnetic resonance imaging (MRI) procedurespresent special challenges to implant designers. The extremely high magnetic

Fatigue runout load (N) of bent spine rods @ 2.5Mcycles. Source: MiRus

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MoRe4.0 mm

CoCr5.5 mm

Ti5.5 mm

The Nuloy® coronary stent using Mo-Re alloy. © MiRus

Reduced MRI artifact for MoRe® mesh implant compared to titanium. © MiRus

MoRe mesh Titanium grade-4 mesh

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Bone growth after 13 weeks showing continuous bone maturation at the implant-hard tissue interface.© MiRus

MoRe Titanium

New bone growth

and provide greater aesthetic appeal.This is especially important when skincoverage is minimal, as in the skull. Implants with smaller cross-sectionalarea also reduce the amount of disturbedbone, leading to more robust structures.

Small and medium-sized trauma platesused for cranial, midface, mandible,wrist, finger, pelvic, and ankle fracturesmay have anatomically designed shapes,but surgeons often must contour theseimplants to fit a specific patient’s bonestructure. For example, spine rods arebent to establish correct alignment for

fields present in MRI equipment exertenormous stresses on magnetic materials.Implant alloys must be nonmagnetic to eliminate torque, displacement, orheating during MRI procedures. MoRe iscompletely nonmagnetic, so it presentsno problems in this regard. Another potential problem is artifact, or ‘starburst’patterns in MRI images, a function of the implant’s magnetic susceptibility.Artifact can interfere with diagnostic interpretation. Unalloyed titanium implantsexhibit the least MRI artifact of the traditional metallic-implant alloys. Due toits lower magnetic susceptibility, Mo-Rereduces MRI artifact below that of pure titanium, a major clinical advantage.

Density and elastic modulus – Thehigher density of Mo-Re alloy is not soimportant for small and medium-sizedsurgical implants because the additionalimplant weight is minimal. However, ahigh modulus of elasticity is normally undesirable for orthopedic applicationsbecause the stiff implant reduces theload on the bone, a phenomenon calledstress shielding. It can result in a reduction in bone growth because thebody has less load to support. The effectbecomes more important as implant sizeincreases, so designers must work tokeep implant dimensions at a minimum.This means high-modulus alloys mustalso have high strength to allow thinnercross-sections, a plus for Mo-Re.

Design freedom

The high strength and high ductility ofMo-Re alloy implants allow designers tosignificantly reduce implant dimensionscompared to current materials, enablingthinner implants that are less prominent

A lowprofile MoRe® craniomaxillofacial (CMF) plate (right) demonstrates its size advantage over a titanium alloy plate (left). © MiRus

patients with scoliosis. The high ductilityof Mo-Re alloy permits this deformationwithout forming superficial cracks, a problem that may occur during intraoperative contouring of other high-strength orthopedic alloys. Eliminatingcracks maximizes implant fatigue life.

Bone friendly

Mo-Re alloy implants do not present the biocompatibility problems or allergicreactions sometimes seen in implantscontaining nickel, cobalt or chromium. A number of biocompatibility tests have been performed comparing Mo-Re and Ti-6Al-4V alloy; summary results are included in ASTM F3273-17. Osteoconduction (the process of bonegrowth on the implant surface) is anotherimportant property because it is observed mainly on highly biocompatibleimplant materials. In a bone implantationstudy where test pins were implanted in animal femurs, osteoconduction wassimilar for both MoRe and Ti-6Al-4V pinsafter 4, 13, and 26 weeks’ implantation.

This new application of Mo-Re alloys inimplants is an exciting field that is only inits infancy. It has the potential to providebetter solutions to the problems seen byorthopedists every day. (JS)

IMOA gratefully acknowledges the assistanceof Mr. John Disegi, Principal, Advanced Bio-material Consulting, in ensuring the technicalaccuracy of this article. Mr. Noah Roth, COO,MiRus Spine & Orthopedics is acknowledgedfor the development of the MoRe material for biomedical applications and directing theresearch work presented in this article.

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Offshore platforms produce and processoil and gas from a well in the seabed.They are basically chemical plants placedin the middle of the ocean. They oftencontain all the equipment necessary tomake them self-sufficient, includingpower generation, water desalination andcrew accommodations. All of this issqueezed into the smallest amount ofspace possible. Platforms should also beas light as possible, to minimize the size of support and anchor structures.The pumping and processing of oil andgas requires many miles of pipes in addition to the processing equipment itself. The pipes are typically flanged together, using hundreds of thousands of bolts. Traditionally, these bolts havebeen made of hot dip galvanized (HDG)steel.

Material selection for oil platforms

The Norwegian oil company Statoil iscurrently developing the Johan Sverdrupoil field on the Norwegian ContinentalShelf. It is one of the region’s largest oilfield discoveries in recent times and willbecome by far the North Sea’s largestproducing oil field when both phases areoperational from 2022 on. The oil fieldhas a life expectancy of 50 years. Thislong expected life and the need to keepthe platforms as compact and light aspossible, drive the material selection forthe project’s structures, equipment andpiping.

The company’s experience with other oilfields in the North Sea showed that traditional bolting, in particular, sufferedfrom corrosion problems and the lifetime

Offshore oil and gas platforms see some of the most demanding environmental conditions for constructionmaterials anywhere. Exposed to extreme weather, wind and waves, these structures must operate safely fordecades. The most challenging sites are located in or near the Arctic oceans, where frequent storms intensify the extremely corrosive exposure to seawater. Molybdenum-containing alloys, especially duplexand super duplex stainless steels, last longer than almost all other materials in these difficult situations. One small but critical example is super duplex bolts.

of these HDG steel fasteners turned outto be limited. The protective zinc coatingtypically lasts about 8 to 10 years, afterwhich the steel fasteners themselvesbegin to corrode. The total lifetime of thistype of fastener, when exposed to marineenvironment, is therefore only about 15 years, but properly working fastenersare crucial for safe, reliable, and environmentally secure operation of thecomplex piping systems.

Because of this, and because the expected useful life of older platformshas been extended thanks to improve-ments in technology and oil recovery,thousands and thousands of fastenershave to be replaced, as they come totheir end of life.

Lighter and safer offshore platforms

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Hot dip galvanized bolts suffer from corrosionwhen exposed to the severe marine environmenton a platform. © Statoil

The Johan Sverdrup riser platform jacket being installed. © Jan Arne Wold/Statoil

The Johan Svertrub oil platform is scheduledto start production in 2019. © Statoil

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several different forms of corrosion. Thelatter can be largely attributed to the3.5% molybdenum typically contained inthese grades. As a result, super duplexstainless steels are found in seawater environments, fluids with high chloridecontents, and acidic chemical processes.They are increasingly used in oil andgas, desalination, power generation, marine industries and other corrosive applications.

Duplex and super duplex stainless steelshave twice the yield strength of solutionannealed austenitic stainless steels such as Type 304 or 316 and are strongerthan the work hardened versions ofthese grades, which are typically usedin offshore applications. They also havegood ductility and toughness down to temperatures as low as -80 °C, an important consideration in the Arctic orfar North.

Beyond the oil field and into the future

Super duplex fasteners have recentlyalso found application in energy projectsbeyond oil and gas, in the emerging field of offshore wind turbines. At the Greater Gabbard Wind Farm, located in the North Sea, 23 kilometers off the coast of England, 140 offshore wind turbines have UNS S32760 super duplex fasteners. The Humber GatewayWind Farm, also located in the NorthSea, uses over 50,000 of these bolts tofasten turbine components. These operations encounter many of the sameproblems facing offshore oil: a corrosive marine environment and the need for

This is a huge undertaking, extremely expensive and disruptive for the operationof the platform. To avoid similar work in the future, Statoil is replacing the HDGbolts on the older platforms with superduplex stainless steel bolts.

For the Johan Sverdrup project, with its50-year life expectancy, duplex stainlesssteels were specified from the beginning.Lean duplex stainless steel is used for a variety of structural elements suchas cable trays, pipe supports and othersecondary structures which are not exposed to high temperatures. Its bene-fits include longevity, low maintenanceand weight reduction. Weight manage-ment is the most cost-critical issue whenbuilding platforms. Higher weight on thetopside of the platform requires the use of crane ships with higher lifting capacity,which increases the cost significantly.Conversely, a lighter topside also allowsfor a smaller, lighter, and therefore lower-cost support structure underneath.

Standard 2205 duplex stainless steel is used for piping that carries condensate,oil and gas; super duplex alloys, mean-while, have been selected for pipes carrying seawater as well as for caissonsand umbilical tubing. The duplex stainless-steel piping in this enormousproject spans diameters from 50 to 500millimeters. The super duplex fastenerswhich connect the flanged joints rangefrom 12 to 36 millimeters in diameter.

Super duplex stainless steel

Super duplex alloys provide high strength and very good resistance to

Super duplex bolts and nuts of different sizes. © Bumax

Super duplex bolts are also used on offshore windturbines. © West Special Fasteners

high-strength alloys to reduce weight, maximize efficiency, and guard againstenvironmental disasters.

Offshore technology is evolving to supplythe world’s energy needs with greater efficiency, safety, and environmental protection. At the same time, the differenttypes of duplex stainless steels have become an ever more important factor in the design decision. They have excellent resistance to multiple kinds ofcorrosion, high strength, and good ductility and toughness. They thereforelast throughout the life of a project withminimal maintenance and enable lighter,more cost-efficient designs, more than recouping their higher initial cost. Inthese technologies, molybdenum showsits merit by helping to create the uniqueproperties that makes these sophisticatedmaterials so desirable. (NB, JS)

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IMOA news

Boston, one of the oldest cities in theUnited States, provided the venue for IMOA’s 29th Annual General Meetingin September 2017, kindly hosted by H.C. Starck. Outgoing President CarlosLetelier welcomed more than 120 delegates to the Massachusetts capitalfor the two day meeting. Here a numberof experts gave unique insights into arange of subjects, alongside the formalbusiness of the AGM.

Francois Dary from H.C. Starck gave apresentation on the rationale for the use of molybdenum metal in a range ofhistoric and emerging applications.Richard Oppelt from Accenture talkedabout the outlook for the U.S. steel industry, including an assessment of theprospects for global steel to 2035 whichmodeled the potential impacts of disruptors. Jim Lennon from Red DoorResearch returned to the AGM to

give his predictions on the medium-termprospects in the molybdenum market,while Markus Moll from SMR entertainedus with his very animated review of theend uses of molybdenum and an outlookfor the molybdenum market in the longerterm.

Graham Gedge from Arup presented anindustry view of the value of the technicalsupport provided by organizations like IMOA, while Hardy Mohrbacher fromNiobelcon gave an overview of the technology and market prospects forpress-hardening steel when combinedwith hot stamping. Volker Friedrich fromGBP International presented a uniqueview of the risks and opportunities if theeconomies of Asia become dominant in the future, and Aziz Asphahani fromQuestek gave delegates an update onhow computational material engineeringdisciplines are being utilized in the design of molybdenum-containing steelsand alloys.

AGM 2017 Finally, Nicole Kinsman presented highlights of IMOA’s market developmentprogram in the last twelve months andSandra Carey updated delegates withIMOA’s proactive and reactive work in response to global HSE and regulatorychallenges. New for this year was apanel discussion held on the second day,moderated by Markus Moll, with five industry experts giving their views ondrivers and disruptors in the molybdenummarket, providing a fascinating conclusionto the proceedings.

IMOA hosted a dinner in the JFK Library,an impressive venue dedicated to thememory of the thirty-fifth U.S. President,now managed by the U.S. NationalArchives and Records Administration.Our hosts H.C. Starck very kindly reciprocated on the next evening, with adinner at the Seaport Hotel and WorldTrade Center.

London plays host to two internationalmetals conferences this Spring, both ofwhich are supported by IMOA. ArgusMetals Week (formerly NiCoMo) returnsto London on 27 February (until 2 March

Metals conferences in London 2018), promising more molybdenum-dedicated sessions. IMOA members re-ceive a discount of 10% on the standarddelegate rate. Those wishing to take advantage of this offer should bookthrough www.tinyurl.com/amw2018 usingthe discount code IMOA10.

Later that month, CRU hosts ‘Metals in the Future’ in London on 19-20 March,exploring the long-term impact of green technology on metals supply anddemand. IMOA members receive 15% off the standard delegate rate usingIMOA15 at www.tinyurl.com/crumetals18.

Outgoing President Carlos Letelier ofMolymet and Benjamin Zhao of THH Molyprocessing raise a glass toanother successful AGM.