Category Archives: Metals

Recommendations for reducing worker injuries for steel and metal manufacturers

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From Scott Brooksby’s article, “Secondary Processes Don’t Translate to Secondary Risks“, published in FF Journal, a metal fabricating and forming trade magazine, which includes recommendations for reducing worker injuries for steel and metal manufacturers:

Global demand for steel continues to increase, with mills and production facilities focused on production processes and ramping up output. With the urgency to increase production, however, risk of serious workplace injuries often is under-recognized in secondary processes—most notably, quality control testing operations.

Through our experience, we’ve identified simple and affordable steps mill management can take to reduce the incidence of major injuries and associated liabilities that occur at an inordinate rate in quality control testing processes of metals manufacturing.

A recent example took place at a steel mill that processes around 30,000 samples per year, operating a customized, decades-old conveyor system.

On the main production line at this mill, tail samples are cut from steel plate.  The samples, slabs about 1 1⁄2-in.-thick, 8-ft.-long and weighing more than a ton, are sidled to a conveyor system leading to the sample-burning room. There, the sample tail is cut into smaller pieces to be shipped to a lab for testing. Electronic and manual controls are in place to prevent slabs from posing a danger to workers. When the system operates as it should, samples are restrained by a series of gates, arriving at a final gate that secures the slab as a laser torch cuts the tail sample into pieces, each weighing about 500 lbs.

One day, the final metal gate remained shut as the penultimate gate opened, freeing the sample slab to collide with the sample still in the clutch of the final gate. The sample tail flipped into the air, striking a temporary employee before destroying the machinery’s electronic control system.

A co-worker prevented further injury and damage by deactivating the equipment with a retrofitted electronic emergency override. Claims against the mill were resolved at significant financial expense.

What lessons can heavy industry draw from this incident to prevent similar events from occurring?

Immediately examine equipment involved in secondary processes—such as QC test sampling—and put requisite safeguards into place. It’s common for management to concentrate on production line safety and operations. All the more reason to exhibit prudence by reviewing conditions in areas such as sample burning, and take steps such as safety engineering studies to identify issues and develop options to retrofit or augment existing safety devices.

For example, conveyor equipment in sample-burning lines often is customized, and can lack safety elements incorporated in standardized, production line equipment. In this case, an engineering study on the sample conveyor may have identified a safety retrofit as simple as horizontal spacers spanning across the conveyor to prevent a sample tail from careening off the conveyor.

Document safety or process improvements. Virtually every steel, metal or component manufacturing facility has old equipment in use. In most cases, it has been upgraded or retrofitted for operation with the safety of the worker and the workplace as priority concerns. We recognize that documentation on its own won’t prevent injury.

At the same time, we’ve seen how dramatically lack of production environment safety retrofit documentations can impact the size of settlements and verdicts in manufacturing workplace personal injury cases.  Safety retrofits have value in and of themselves. But strictly from a standpoint of managing financial risk, it’s crucial to document safety retrofits, retain these documents indefinitely and maintain them in strict compliance with formal document destruction policies.

Review workforce management and training practices in “first assignment” areas such as test-sample burning. As with the  case of our real-world example, secondary processes often are areas where less-experienced or temporary workers are first put to work in steel production facilities. Facility management is wise to recognize this as a potential risk, put in place precautions, staff these areas appropriately and sufficiently train inexperienced workers who may not be conscious of dangers inherent in quality control sampling.

Product Liability Issues Arising From Rail Car Wheel Cracking and Fatigue

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Rail car wheel cracking and fatigue can lead to significant product liability exposure and potential negligence claims.  Unless specifically exempted by another statute or federal regulation, Oregon’s product liability statutes, starting at ORS 30.900, govern product liability actions in Oregon, including products such as railroad car wheels.  This article will explore three important studies regarding rail wheel cracking and fatigue issues and will end by discussing critical product liability issues associated with rail wheels.  In rail wheel cases, the phenomena commonly known as rolling contact fatigue (“RCF”) can lead to cracking and even the uncontrolled discharge of portions or rail car wheels.  In extreme circumstances, the wheel itself may be subject to vertical cracking and disintegration.

Rail Car Wheel Cracking:  Three Scientific Studies

There is a vast body peer-reviewed scientific literature that examines the relationship between various manufacturing processes, uses and stresses on railway wheels, and metal fatigue and cracking.  This article explores three such scientific studies that focus on the susceptibility of railway wheels to wear and RCF damage.  As explained in further detail below, studies have found that rail wheel damage is influenced by the properties of the wheel material, including steel composition and hardening techniques.

Below there are links to each study discussed.  If, however, you cannot access the links and would like to review the studies, please contact Olson Brooksby.

The Molyneux-Berry, Davis, and Bevan Study

This study examined railway wheels on fleets from the UK and concluded that the materials that make up the wheels themselves influence the amount of wear and RCF damage that the wheels are subjected to.  Factors that contribute to wheel damage are the composition of the steel, the process by which wheels are manufactured, and loading during operation.

This study can be found here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3914578/

The Liu, Stratman, Mahadevan Study

This study developed a 3D “multiaxial fatigue life prediction model” to calculate the life of a rail car wheel and to assist with predictions regarding the timeline of its fatigue.

This study can be found here: http://yongming.faculty.asu.edu/paper/fatiwheels-ijf.pdf

The Peixoto and Ferreira Study

In this study, fatigue crack growth rate behavior tests were performed according to ASTM E647 (2008).  The purpose of this study was to contribute to the development of accurate models that predict fatigue problems in rail car wheels in order to assist with maintenance and safety standards.

This study can be found here: http://www.deepdyve.com/lp/emerald-publishing/fatigue-crack-propagation-behavior-in-railway-steels-6SBquFt7Pn

Defenses to Rail Wheel Product Liability Claims

A common issue in rail wheel cases is the age of the wheel at issue and the amount of use it has received.  When an older wheel is involved, defense counsel for the manufacturer should look first for a defense based on statute of ultimate repose.  ORS 30.905 provides for a ten year statute of repose.  If the plaintiff does not file a claim for personal injury or property damage within ten years from the date the product was first purchased for use or consumption, the claim is barred.  Oregon has a strong statute of ultimate repose.  There are no “useful safe life” or other exceptions or rebuttable presumptions codified in the statute that provides for an absolute ten years.

Absent an ability to obtain a complete dismissal under the statute of ultimate repose, the three studies discussed above illustrate the variety of causation factors and scientific models concerning rail car fatigue issues.  Manufacturing materials and processes, steel fabrication techniques and materials for both wheels and rails, the nature of the loads, gradients, and cycles are all among the factors that provide fertile ground for defending rail wheel claims.

Titanium Aluminide and Its Use in Aviation Manufacturing

Companies are starting to manufacture turbine blades from titanium aluminide. This makes the blades more lightweight, resulting in less energy output.  A titanium aluminide blade weighs about half as much as a traditional blade made of nickel superalloy.

Three principal compounds are formed by titanium aluminides: TiAl, TiAl2 and TiAl3. Dixon Chandley, Use of Gamma Titanium Aluminide for Automotive Engine Valves, 18 (1) Metallurgical Sci. & Tech. 8 (2000).   “Gamma titanium aluminide-based alloys (y-TiAl) have become an important contender for high-temperature structural applications in the aircraft industry to replace current nickel-based superalloys as the material of choice for low-pressure turbine blades.”  L. Patriarca, Fatigue Crack Growth of a Gamma Titanium Aluminide Alloy, 9th Youth Symposium on Experimental Solid Mechanics, 2010, 36.  y-TiAl compounds have the highest melting point and therefore are most “useful for engineering purposes.”  Chandley, 18 (1) Metallurgical Sci. & Tech. at 8.

Ti-Al was not really used in manufacturing and production until the 2000s.  One reason is that it was brittle and therefore “difficult to form and to process”.  Daniel Hautmann, Titanium Aluminide–A Class All By Itself, 1 MTU Aero Engines Rept. 27 (2013).  Through decades of research work, it was found that brittleness could be tackled “by adjusting the material composition, and manufacturing processes and the design were tailored to suit the material properties.”  Id. at 28.

Ti-Al is now revolutionizing the field of aviation and more and more companies are working to incorporate it into their blade manufacturing technology.  For instance, the Boeing 787 Dreamliner uses GE engines that include “titanium aluminide (Ti-Al) blades in the last two stages of the seven-stage low-pressure turbine.”  Stephen F. Clark, 787 Propulsion System, 3 Aero Quarterly 10 (2012).

 

Turbine Engine Hot Section Manufacturing: Complex Metallurgy and Dangerous Work Environments

Turbine engine hot section manufacturing is a complex industry that involves risk of serious injury and an adherence to safety rules and best practices.

There is a common maxim that two technologies liberated the modern world: the automatic washing machine and the jet engine.  When RAF Lieutenant Frank Whittle received an English patent on the basic design for the modern jet engine in 1930 (the first flight was not until 1941), he probably could not have imagined the changes that would occur, in materials, complexity, and performance capability.

Today’s commercial jet engines have as many as 25,000 parts.  They are up to eleven feet in diameter and twelve feet long.  The engines can weigh more than 10,000 pounds and produce 100,000 pounds of thrust.  Even the engine on a fully tested and approved design may take two years to assemble.  A super-jumbo jet can carry 500-800 passengers, depending on configuration, and have a take-off weight of 1.2 million pounds.

Section I will provide a basic overview of the production and metallurgical complexities associated with the manufacture of some hot section components.  Section II will address a unique aspect of jet hot section manufacturing.  Specifically, the complex and exacting standards required to avoid catastrophic in-flight aviation accidents also require the most disciplined adherence to best practices for safety to avoid catastrophic occupational injury, particularly burns, in high temperature work environments.  Section III will briefly discuss the catastrophic burn injuries that result from failure to follow exacting safety precautions.

Section I:  The Hot Section

At the front of the engine, a fan drives air into the engine’s first compartment, the compressor, a space approximately 20 times smaller than the first stage of the compressor.   As the air leaves the high-pressure compressor and enters the combustor, it mixes with fuel and is burned.  As the gas is combusted and expands, some gas passes through the exhaust and some is rerouted to the engine’s turbine (a set of fans that rotate compressor blades).  The turbine extracts energy from the ultra-hot gases to power the compressor shaft and generate power.

Because the turbine is subject to such incredible heat, labyrinthine airways in the turbine blades allow cool air to pass through them to cool the turbine.  With the cooling mechanism of the airstream, the turbine can function in gas streams where the temperature is higher than the melting point of the alloy from which the turbine is made.

Titanium, purified to aviation specifications in the 1950s, is used for the most critical components of the “hot section” such as the combustion chamber and turbine.  The hardness of titanium is difficult to work with, but it is resistant to extreme heat.  It is often alloyed with other metals such as nickel and aluminum for high strength/weight ratios.

Hot Section Component Manufacturing

The intake fan.  The fan must be strong so it does not fracture if large birds or debris are sucked in.  It is made of a titanium alloy.  Each fan blade consists of two skins produced by shaping molten titanium in a hot press.  Each blade skin is welded to a mate, with a hollow cavity in the center being filled with titanium honeycomb.

The compressor disc. This is a solid core, resembling a notched wheel, to which the compressor blades are attached.  It must be free of even minute imperfections, since these could cause creeping or develop into fractures under the tremendous stress of engine operation.  Historically machined, compressor discs are now manufactured through a process called powder metallurgy, which consists of pouring molten metal onto a rapidly rotating turntable that breaks the molten metal into millions of microscopic droplets that are flung back up almost immediately, due to the table’s spinning.  As they leave the turntable, the droplets’ temperature plummets by 2120 degrees Fahrenheit (1000 degrees Celsius) in half a second, causing them to solidify and form a very fine metal powder, which solidifies too quickly to absorb impurities.  The powder is packed into a forming case and vibrated in a vacuum to remove air.  The case is then sealed and heated, under 25,000 pounds of pressure per square, inch into a disc.

Compressor blades.  These blades are still formed by traditional methods of casting.  Alloy is poured into a ceramic mold, heated in a furnace, and cooled.  The mold is broken and blades are machined to final shape, often to exacting tolerances on the order of 7 microns.

Combustion chambers.  Combustion chambers blend air and fuel in small spaces for long periods of time at incredible temperatures.  Titanium is alloyed (to increase ductility) and then heated to liquid before being poured into several complex segment molds.  The segments are welded together after cooling and removal.

The turbine disc and blades.  The turbine disc is formed by the same powder metallurgy used to create the compressor disc.  However, turbine blades are subjected to even greater stress due to the intense heat of the combustor.  Copies of the blades are formed by pouring wax into metal molds.  Once set, the wax shape is removed and immersed in a ceramic slurry bath, forming a ceramic coating.  Each cluster of shapes is heated to harden the ceramic and melt the wax.  Molten metal is then poured into the hollow left by the melted wax.

The metal grains of the blades are then aligned parallel to the blade by directional solidifying, which is important due to the blade stresses.  If the grains are aligned correctly, the blade is much less likely to fracture.  The solidifying process takes place in computer-controlled ovens to precise specifications.  Parallel lines of tiny holes are formed to supplement internal cooling passageways, either by a small laser beam or by spark erosion, where sparks are carefully allowed to eat holes in the blade.

Turbine blades are subject to temperatures of around 2,500 degrees Fahrenheit (1,370 Celsius.  At such temperatures, creep, corrosion, and fatigue failures are all possible.  Thermal barrier coatings, such as aluminide coatings developed during the 1970s, facilitated cooling.  Ceramic coatings developed during the 1980s improved blade capability by about 200 degrees F. and nearly doubled blade life.

Modern turbine blades often use nickel-based superalloys that incorporate chromium, cobalt, and rhenium.  Some superalloys incorporate crystal technology.  Nimonic is another super low-creep superalloy used in turbine blades.  Titanium aluminide, a chemical compound with excellent mechanical properties at elevated temperatures, may replace Ni based superalloys in turbine blades.  GE uses titanium aluminide on low pressure turbine blades on the GEnx engine powering Boeing 787s.  The blades are cast by Precision Castparts Corp.

Exhaust system.  The inner duct and afterburners are molded from titanium, while the outer duct and nacelle are formed from Kevlar, with all components welded into a subassembly.

Section II.  Defects in Both Hot Section Components and Safety Procedures Can Result in Catastrophic Injuries

An imperfection in the hot section, which results, for example, in a blade fracture during flight, or excessive creep, may result in an uncontrolled engine failure, among other catastrophic inflight mishaps, putting lives at risk.  In an interesting corollary, unique to very few manufacturing settings, adherence to the safest manufacturing processes will minimize both product defects and worker injuries, primarily serious burns.

Few Things Drive Higher Verdicts, Workers Compensation Costs, or Settlements, Than Burns

In those industries where “serious large burns” can arbitrarily be defined as full-thickness burns over 20% or more of the total body surface area (TBSA), the location of the burns and the relative availability of certain types of grafts can be outcome determinative and correlate directly with litigation risk, settlements, and verdicts. Most problematic are 4th degree burns to the hands or face, which can never, ever, be fully repaired with current surgical technology or therapeutic treatments.

Skin Graft Classification

There are two common types of skin grafts.  A split-thickness graft (STSG), or mesh graft, includes the epidermis and part of the dermis.  A mesher makes apertures in the graft, allowing it to expand approximately 9 times its original size.

Alternatively, a full thickness skin graft, or sheet graft, which involves pitching and cutting away skin from the donor section, is more risky in terms of rejection.  Yet counter-intuitively, this method leaves a scar only on the donor section, heals more quickly, and is less painful than split-thickness grafting.  This type of grafting, sheet grafting, must be used for hands and faces/heads where graft contraction must be minimized, and it is therefore extremely difficult to achieve in large TBSA burns.

Remedies

Although workers compensation laws will generally bar litigation by workers against their employers, in cases where the exclusive remedy provision of workers compensation does not apply, it is not uncommon in the United States to see burn verdicts or settlements in the millions or even tens of millions of dollars.  Mandatory PPE and best safety practices for dealing with ultra-high temperature work environments can minimize injuries, although the practical reality is that elimination of such injuries remains an aspirational goal.