In the Unlikely Event of a Failure
By Ron Graham
Director, Processing Engineering
Oremet-Wah Chang is very
careful to make suitable recommendations for our materials based on intended
service, be they Zircadyne®, various grades of titanium, niobium, or
niobium-titanium alloys. We recognize that failures can be very costly, not
only in terms of replacement of the failed component, but also for lost
opportunity costs.
This article is intended to provide rudimentary guidance to
field engineers, maintenance personnel, and fabricators regarding collecting
information pertinent to a failure investigation.
It is a fact of life, however, that failures can occur.
Failures can happen during the design or fabrication of the component, as a
result of improper material processing, or during service. Common design errors
include improper design for erosion-corrosion in elbows or tees. Another
example is inadequate support for tubing in heat exchangers. This can cause
fretting and excessive mechanical wear.
Typically we find most competent fabricators have perfected
their fabrication techniques so that fabricability issues are minimized.
Occasionally, we are asked to examine failed parts that may have cracked during
forming operations, gotten contaminated during welding, or were heat treated
improperly.
Failures can also occur because of material problems.
Control of size and distribution of second phase particles and inclusions is
important. Large, aligned regions of iron-rich particles or carbides can cause
failures during forming. A poor surface with large scratches can lead to
cracking during forming. Grain size control during ingot breakdown and forging
is important to provide optimum fabricability and mechanical properties.
In-service failures can occur as a result of upset
conditions or design errors. For example, Freon® refrigerant was
used in the process to cool a unit operation. A
refrigerant leak combined with process chemicals caused excessive, rapid
corrosion of Zircadyne. The investigation determined that the refrigerant (CFCl2)
broke down into the constituent chemicals, fluorine and chlorine. The fluorine
combined with moisture to make HF acid, which is highly corrosive to Zircadyne.
Upon request by our customers, we provide failure analysis
as part of our technical services. We have analyzed many failures that occur
during fabrication and welding and during the service lifetime of the
component. The more information that we can glean from the individual(s)
requesting the failure analysis, the better we can pinpoint the root cause and
provide recommendations to prevent recurrence.
The first action, of course, is to properly secure equipment
and the process to prevent injuries or further damage to equipment. Once the
process or operation has been stabilized, it is recommended that a group of individuals
be gathered to investigate the evidence before it is disturbed. Many times,
important clues can be destroyed because adequate care was not exercised in
obtaining samples.
Photographic documentation is
important.
The purpose of the investigating group is to document
operating conditions and any off-normal conditions that may have occurred.
Before any samples are obtained, careful photographic documentation of the
failed region and how it relates to the remainder of the component, can be
extremely helpful. Remember the old cliche: "A picture is worth a thousand
words."
Many
times, important clues can be destroyed because adequate care was not exercised in
obtaining samples.
Samples of the failed region can yield invaluable
information if they are obtained and handled with care. Modem metallographic
techniques can provide powerful tools to gain insight into a failure. In many
cases, these techniques rely on highly magnified images of the failed surfaces.
Often times as an investigation proceeds, we rely on increasingly more complex
analytical methods to unravel clues about a failure. Preservation of the sample
is important in order to maximize the opportunity to utilize our full "bag
of tricks."
Examples of analyses that Oremet-Wah Chang can perform
include optical and scanning electron microscopy, microanalysis using X-ray
fluorescence, Auger electron microscopy, texture analysis, mechanical property
testing, including hardness, room and elevated temperature tensile strengths,
bend radius, flare testing, impact toughness, and bulk chemistry, including
interstitials like carbon, oxygen, hydrogen and nitrogen. We also have the
ability to simulate material performance in many corrosive media under static
and stressed conditions.
One of the worst things that can happen is inadequate
handling procedures in obtaining the sample, examination of the sample, or
packaging and shipping the sample. Typically, we are looking for things like
minute traces of chemicals or high magnification images of a fracture surface
to determine the failure mode. This requires the sample to remain in as an
undisturbed state as possible following the failure.
Care must be exercised in obtaining the sample. Samples can
be destroyed by overheating (as in torch cutting, plasma cutting, abrasive
cutting) or by allowing adjacent fracture surfaces to fret or rub together
during sectioning. The ideal method for obtaining a sample would be to unbolt
the component (if possible) or to provide adequate support so that a slow speed
saw can be used to cut out the component. Lubricants, which are typically used
in sawing, can mask or destroy residual chemicals or elements on the failed surface.
If the component has failed in the middle of a large area, more aggressive
cutting/sectioning techniques may be warranted, but care should be taken to
stay well away from the failed region.
One of the worst practices is to idly "piece
together" two or more mating surfaces of a failed sample to "see how
it fits together." Our materials are relatively soft. Microscopic features
on the failed surfaces can be observed to determine the specific failure mode, but
these features are easily destroyed by rubbing the surfaces together.
Packaging of components for shipping to us is equally
important. Wrapping them directly into a plastic bag or placing pieces directly
in a plastic bottle or container can introduce unwanted hydrocarbon
contaminants. Fingerprints on the failed surfaces can introduce unwanted
contamination. One method to prevent unwanted surface contamination is to wrap
failed components in a layer of aluminum foil. The component can then be
further wrapped in bubble wrap or soft cotton wadding to prevent physical
damage during shipping.
Through wall, transgranular crack.
Remember those photographs that you took during the original
stages of the failure investigation? Be sure and send them along with the
samples. Also, drawings of the failed component and of the assembly that incorporates
the component can be very helpful. In corrosion failures, samples of the
corrosive media can provide important clues. It is important to document
process conditions, including upset conditions, at the time of the failure. The
upset condition may have started a chain of events that leads to eventual
failure.
Documentation of fabrication failures should include
information such as forming or heat-treating temperatures, welding procedures,
surface conditions/roughness of the part and the tooling, type of forming
operation, and lubricants used to aid machining or forming. Additionally,
drawings/dimensions of the finished component and material identification (our
heat number and SFC or lot number, if available) can be equally important in
assisting us to understand the history of the failed component.
If all of this seems like a lot of work, it is! I can't
overemphasize the importance of gathering information at the front end of the
investigation. Otherwise we may ask questions of you regarding the event, and
these questions may go unanswered as memories fade with time. This can impede
or even throw a fatal roadblock into the subsequent investigation.
Generally, proper determination of the root cause of a
failure and corrective action to prevent that cause are sufficient to prevent
reoccurrence of the original failure. The important evidence and clues used to
determine root cause are obtained through careful, systematic investigation.
Shortcuts in this process can cloud or mask knowledge
that can be used to save money, time and effort later on.
For more information on analysis, contact OWC's Corrosion:
Laboratory at 541-917-6777.
Mr. Ron Graham has a B.S. and M.S.
Metallurgical Engineering. He joined Oremet-Wah Chang in 1985 as' a process
development engineer. Prior to that, Mr. Graham worked 12 Years for the
Department of Energy on breeder reactor fuel manufacturing and development. He
currently is Director, Process Engineering, of OWC.
New Technical Services Group
Oremet-Wah Chang is pleased to introduce its new Technical
Services group. OWC recently created the group in response to customer requests
for more in-depth technical support. Technical Services personnel still hold
other responsibilities within the company but also meet on a regular basis to discuss
customer support issues.
This issue of Outlook contains articles by several
team members. Mr. Ron Graham contributed a paper on Failure Analysis (opposite
column); Mr. Rick Sutherlin wrote this issue's Question and Answer feature,
focused on weld contamination (page 10); and frequent contributor, Mr. Jack
Tosdale kicks off Outlook's first Corrosion Lab Chronicles column
(page 7), covering tests the lab is performing on zirconium oxide.
The whole Technical Services crew officially makes its debut
at Oremet-Wah Chang's Reactive Metals in Corrosive Applications Conference this
fall, presenting a Poster Session and answering attendees' technical questions.
Following is a roster of the immediate Technical Services
group (OWC can draw on many additional resources) with brief descriptions of
members' backgrounds and areas of expertise.
Ron Graham
--Mr. Ron Graham, Director of
Process Engineering, leads the Technical Services Group. He has 26 years'
experience as a metallurgist, 14 in Process Development Engineering with OWC.
His expertise covers a broad range of topics, including process engineering,
microstructural analysis, alloy and product development among other
capabilities. Mr. Graham can be reached by phone at 541-926-4211 ext: 6385 or
by fax at 541-967-6990.
John Belfanti
--Mr. John Belfanti, a Process
Engineer, has 2 years' experience working with Oremet-Wah Chang's zirconium,
niobium, and nickel-titanium product lines. Mr. Belfanti, a metallurgist, can
offer customers help with production processes and capabilities. He can be reached
by phone at 541-926-4211 ext: 6261 or by fax at 541-917-6764.
Craig Euken
--Mr. Craig Euken, a Process Development Metallurgist, has
26 years' experience working with zirconium and other metals. Mr. Euken's areas
of expertise include process development, failure analysis, microstructural
analysis, and alloy and product development. For technical support, contact him
by phone at 541-926-4211 ext: 6256 or by fax at 541-967-6990.
Jim Hall
--Mr. Jim Hall, currently Director of Titanium Technology,
has 32 years' experience in materials science, including in-depth experience in
CPI product development. A metallurgist, Mr. Hall's areas of expertise include
titanium metallurgy, manufacturing, properties, microstructure control, and
fabrication. In addition, he has studied alloy and structure effects on
corrosion behavior of titanium and its alloys. Mr. Hall can be reached by phone
at 541-926-4211 ext: 7312 or by fax at 541-812-7222.
Rob Henson
---Mr. Rob Henson, Manager of Business
Development for the Chemical and Mineral Process Industries, has 22 years'
experience working with zirconium, titanium, niobium, and other metals. Mr.
Henson's background includes a 12-year stint in OWC's Corrosion Lab. His areas
of expertise include applications engineering, corrosion analysis, and failure
analysis. He can be reached by phone at 541-967-6920 or by fax at 541-967-6979.
Derrill Holmes
--Mr. Derrill Holmes, a Corrosion
Specialist, has 20 years' experience working in OWC's Corrosion Lab. Mr.
Holmes, who has nearly completed an advanced degree in Materials Engineering,
is expert in materials selection, corrosion analysis, alloy development, and
failure analysis. He can be reached by phone at 541-917-6752 or by fax at
541-967-6987.
Rick Sutherlin
--Mr. Rick Sutherlin, Manager of Product
Engineering, has over 20 years' experience in CPI-related projects. Mr.
Sutherlin, a Metallurgical Engineer, has expertise in applications engineering,
failure analysis, corrosion testing and research, fabrication, and welding. He
can be reached at 541-967-6924 or by fax at 541-967-6990.
Michael Toney
--Mr. Michael Toney, a Process Engineer, has 3 years'
experience working with OWC's zirconium and titanium product lines, including
tube and pipe, bar, and rod. Mr. Toney, who has a degree in Metallurgical
Engineering, assists customers with production capability questions. For technical
support, contact him by phone at 541-926-4211 ext: 6767 or by fax at
541-917-6765.
Jack Tosdale
----Mr. Jack Tosdale, Senior Corrosion Engineer, has 20
years' experience as a metallurgist with Oremet-Wah Chang. Mr. Tosdale's
strengths include material failure analysis, corrosion engineering, process
analysis and manufacturing statistics, and process development. For technical
support, contact him by phone at 541-917-6777 or by fax at 541-967-6987.
Services Available
…we are diverse in our
abilities.
By Chris Hanson, Analyst,
Analytical Laboratory
Our ICP Mass Spectrometer detects most elements to the
parts-per-trillion level.
For more than 40 years, the laboratory personnel of
Oremet-Wah Chang have been producing high quality analytical test results.
Using a diverse array of equipment and methods, the lab has consistently met
and exceeded customer expectations in a variety of industries. By far the
largest customer base is in metals manufacturing. But a significant portion
also lies in the electronics industry, the nuclear business, health product
manufacturing and many other areas. If you need inorganic analyses done but you
think Oremet-Wah Chang deals only with the metals industry, think again. We
have our specialties, but we are diverse in our abilities.
Oremet-Wah Chang's analytical laboratory is equipped to
handle most any inorganic analysis. We have extensive expertise on interstitial
gas analysis, environmental analysis and a wide variety of other techniques,
from gamma ray spectroscopy to particle size analysis. However, we place
special emphasis on the analysis of metals in metals.
We currently utilize instrumentation dedicated almost solely
to metals analysis. These instruments include:
•
Four Inductively Coupled Plasma Atomic Emission Spectrometers
• Four Direct Current Plasma Atomic Emission Spectrometers
• Arc/Spark 3 meter Spectrograph
• Graphite Furnace Atomic Absorption
• Two Inductively Coupled Plasma Mass
Spectrometers
• Flame Atomic Absorption
• Hydride Analyzer
• Spark Ablation-Atomic Emission Spectrograph
This group of instruments allows us to analyze for 83 of the
elements on the periodic table, from trace concentrations to alloy
concentrations. In fact, we can detect attograms (1 x 10-18) of
certain elements. We have the ability to analyze liquids, conductive solids by
spark ablation-AES or spark ablation-ICP-AES and run difficult-to-dissolve
samples as solids by arc/spark 3 meter spectrograph. In the case of finely
divided oxides where the samples are difficult to dissolve or reagent
contamination is a concern, we can inject them directly into an ICP-AES for
ultra-low-level trace analysis. Many other methods and sample types are
available. However, if none of our current methods works for your samples, our
chemists will develop a method that will meet your needs.
A technician works on a LECO hydrogen analyzer in one of our
gas labs
Another specialty of the laboratory is analysis for the
interstitial gases of oxygen, nitrogen, hydrogen, carbon and sulfur. Most of
the gas analyses are done on metal samples, but we are capable of analyzing
other compounds as well. Among the instruments utilized for gas analysis are:
The number of instruments we have, coupled with the
knowledge and experience of our gas lab staff, make turn-around time for gas
analyses especially low.
...the lab has consistently met and exceeded customer
expectations in
a variety of industries.
Two additional specialties of the analytical laboratory at
Oremet-Wah Chang are customer service and experience. Our laboratory staff of
36 full-time employees averages over 20 years of experience at Oremet-Wah
Chang. They are among the most capable and adaptable chemists and technicians
you are likely to find in any analytical lab. One example of that is our
chemists' abilities to develop dissolution techniques and analytical methods
unique to each customer that ensure no analyte is lost and that you receive the
best available service. In order to offer such service, the laboratory is
staffed seven days a week, often 20 hours per day, thereby shortening
turnaround time for many analyses. We have also achieved certification in a
number of areas. We are currently accredited by ISO 9002, NPDES, NADCAP and a
wide base of customers. Our quality control program ensures the highest quality
results and consistency, and we continually strive for service excellence.
If you need quality analysis, consider the analytical
laboratory of Oremet-Wah Chang. We have a wide array of instrumentation for
most any inorganic analysis, years of experience and customer service second to
none. To consult with an expert regarding your needs or to obtain current
pricing, please contact us at 541-967-6913.
•
Two LECO TC-436 oxygen and nitrogen analyzers
• Two LECO RH-404 hydrogen analyzers
• LECO CS-444 carbon/sulfur analyzer
• LECO IR-12 dual range carbon analyzer
• LECO gasometric carbon analyzer for
high carbon analysis
• Kjeldahl nitrogen distillation
apparatus
--Mr. Brian Van Doren, a Process Development Engineer, has
14 years experience with OWC. A metallurgist, Mr. Van Doren has worked with
titanium, nickel-titanium, niobium, tantalum, and zirconium alloys. His areas
of expertise include failure analysis, microstructural analysis, and alloy and
product development. For technical support, contact Mr. Van Doren by phone at
541-926-4211 ext: 6154 or by fax at 541-917-6764.
The Technical Services group is also listed (with e-mail
addresses) in a directory on Oremet-Wah Chang's web site at
www.corrosionresistant.com. If you are unable to contact a group member or
would like further information on OWC's products and services, including
literature, call us at 541-926-4211. We at Oremet-Wah Chang welcome the
opportunity to help industry meet its toughest materials challenges!
Corrosion Lab Chronicles: Zirconium Oxide
By Jack Tosdale, OWC Senior Corrosion Engineer
Ever wonder about that oxide film on
zirconium we keep talking about--the film that provides the superior corrosion
resistance of zirconium? Well, look at Figures 1 and 2 for a close-up of that
film. These samples were first pickled then oxidized at 565°C for 4 hours to
put the characteristic shiny black film on the surface. This type of film has
been measured at about 0.0002 inch (0.2 mils) thick. After the heat treatment
step, the samples were immersed in an electrochemical test cell, where a
steadily increasing voltage was applied to determine the voltage level where
pitting first starts. The solution was HCI with some
ferric chloride present. The transition to the pitting condition was not abrupt
and large enough, so we missed it and let the voltage increase far beyond the
pitting potential. Of course, pits were produced, and we finally saw the gas
bubbles coming from the pits. We terminated the test and looked at the pits
under the microscope.
The picture in Figure 1 (20x) shows some broken oxide pieces
laying in the pit. The picture is quite telltale, but it does not show the
scale through the thickness and does not show its strength. We surmised that
the rapid evolution of gas during the test caused the oxide film to fracture at
the pit's edge. So, we repeated the test using a much slower voltage rate of
rise. Figure 2 (24x) shows the intact scale with the enlarged void beneath it.
The pit diameter is almost twice that of the visible opening and is shown by
the ring where the oxide film has sagged a little into the void. In Figure 3
(40x), taken at 30° angle from perpendicular, it appears that there
are two separate layers of oxide.
How these pits form may help explain the layered effect.
Pits form at some anomaly in or on the Zr oxide surface. This anomaly can be a
broken film, an intermetallic particle (Zr-Fe or Zr-Cr, for example), a
non-metallic particle (hydride, sulfide, phosphide, etc.), or some other
discontinuity in the oxide film. In this test, the impressed voltage was high
enough to exceed the pitting potential of the Zr oxide and electrochemically
attack the anomaly in this oxidizing chloride environment. In a corrosion cell
in a plant environment, the electrochemical potential could be supplied by the
reduction reaction of ferric to ferrous irons, or a galvanic cell, for example.
In the past, Te-Lin Yau has reported that a pickled surface
resists corrosion pitting much better than an as-milled surface. The pickling
process removes many sites on or in the Zr surface that could be the initiation
sites for pitting. Also, a proper heat treatment can help minimize non-metallic
and intermetallic particle sizes, by distributing the atoms throughout the Zr
matrix instead of as discrete particles either within the grains or at the
grain boundaries.
The Zr oxide film formed in this study is much thicker than
that formed in air or a corrosive chemical media at ambient conditions.
However, this study shows the oxide is quite stable and strong and should
resist abrasive or erosive attack along with electrochemical corrosive attack.
Perhaps, there are elements that can be included in the oxide film to improve
its resistance to corrosion, including the pitting corrosion seen in this test.
We intend to pursue this further.
For more information, contact Jack Tosdale, OWC's Senior
Corrosion Engineer, at 541-917-6777.
Ammonium Nitrate Producers Study Group
Royster Clark Nitrogen will host the 1999 Ammonium Nitrate
Producers Study Group (ANPSG) Meeting at the Marriott Mountain Resort in Vail,
Colorado, October 11-14. Oremet-Wah Chang and a group of suppliers to the
chemical process industries will be on hand to co-host a golf scramble (October
11), a luncheon (October 12), and evening receptions (October 11, 12, and 13).
Most importantly, the exhibitor group will offer solutions to challenges facing
plant operators and engineers. For more information about the meeting, contact
Royster Clark's Bill Stampe at 815-747-3101, ext: 241. For further information
on the exhibitor and hospitality programs, contact Oremet-Wah Chang's Kirk
Richardson at 541-967-6955 or Sheryl Renzoni at 541-926-4211 ext: 6280. (Note:
space is limited, so sign up soon!)
We look forward to seeing you in the Rockies this fall.
The Marriott Mountain Resort in Vail,
Colorado.
Titanium '99
The International Titanium Association (ITA) is hosting its
15th Annual Applications Conference and Exhibition October 12-15 at the Four
Seasons Resort and Club in Las Colinas, Texas. Allegheny Ludlum, Allvac, and
Oremet-Wah Chang personnel will be available to answer questions about the
sister companies' wide range of metal products.
Titanium '99 session and workshop topics include "World
Titanium Industry Trends," "Advantages of Using Titanium in Consumer
Products," "Titanium Use in the Medical and Dental Industry,"
"Titanium in Aerospace," "Titanium in the Oil and Gas
Industry," "Titanium in Architecture," and much more. In
addition, the conference will feature a two-day special event, "The
Fundamentals of Titanium: 101" on Friday, October 15 and Saturday, October
16.
For further details about Titanium '99, including
registration forms, agendas, and information on workshops, tours and events,
contact the International Titanium Association at 303-443-7515.
NY Chem Show
The 48th CPI Exposition ('99 Chem Show) will be held at the
Javits Convention Center in New York, New York, November 16-18. Allegheny
Ludlum, Allvac, and Oremet-Wah Chang will join forces as the Total Corrosion
Solutions team in booth #2663. Technical staff will be available to
answer questions on the group's stainless steels, High Tech Alloys®,
nickel alloys, titanium, and zirconium products. Come by our unique display
(featuring a vintage stainless steel car) and learn about our full line of
corrosion resistant products. Chem Show hours are Tuesday (November 15), 10
a.m. - 5 p.m.; Wednesday (November 16), 10 a.m. -5 p.m.; and Thursday (November
17), 10 a.m. - 4 p.m.
In addition, the Total Corrosion Solutions team
will offer a free seminar on corrosion resistant alloys at the Grand Hyatt,
Monday, November 15. Space is limited and restricted to current and potential
customers of Allegheny Teledyne, Inc. For more information, contact Kirk
Richardson at 541-967-6955. For more information on the Chem Show, contact
International Exposition at 203-221-9232.
Corrosion/Materials Education
If you couldn't make it to the 1999
Reactive Metals in Corrosive Applications Conference, here are a few samples of
the 36 presentations that you missed. Conference books will be available for a
fee in early 2000. Call Sheryl Renzoni to reserve a copy or check our web site
at www.corrosionresistant.com in December for further details. For those who
want their information live, we offer one-day seminars on corrosion and
materials selection at locations around the world. Call OWC's Kirk Richardson
at 541-967-6955 for more information.
Abstract 1: Pitting Corrosion of Zirconium 702 in Hot,
Dilute Sulfuric Acid Contaminated with Copper
The following abstract was submitted by
David B. Orrell, Staff Corrosion Engineer, Celanese, Corpus Christi, TX.
Severe pitting corrosion to zirconium
702 (UNS No. R60702) reboiler tubes was experienced in hot dilute sulfuric
acid. An Alloy C-276 (UNS No. N10276) reactor is healed using steam reboilers
tubed with zirconium 702. Alloy C-276 is the preferred material of construction
used to handle hot, dilute sulfuric acid in this processing step. However,
zirconium 702 was employed in the tubing of the steam reboilers because of past
problems with reduced life to the Alloy C-276 tubing caused by pitting
corrosion. The zirconium 702 tubes had operated with no corrosion for several
years in this service.
In early 1997 corrosion problems
developed in another part of the process unit exhibited by rapid unexpected
corrosion to austenitic stainless steel piping and pumps by organic acids. In
an effort to arrest this corrosion, two charges of cupric acetate solution were
added to the reactor. The cupric acetate, known to inhibit corrosion by organic
acids in austenitic stainless steel, was used in an effort to mitigate the
corrosion downstream of the reactor. The corrosion to austenitic stainless
steel was found to be due to ingress of chlorides into the system due to
cooling water leaks ill shell and tube heat exchangers. These were repaired and
normal operations commenced. No additional cupric acetate was used.
In mid 1998, severe pitting corrosion
to the zirconium 702 reboiler tubes was discovered. The failure investigation
confirmed that the pitting corrosion was attributed to the copper ions placed
in the reactor to inhibit corrosion elsewhere in the system. The copper ions,
in conjunction with the ingress of high levels of chlorides, combined to cause
rapid severe pitting of the zirconium 702 reboiler tubes. The residual copper
in the system was chemically removed before the reboilers were placed back in
service.
Abstract 2: Nondestructive Evaluation of Hydrogen Absorption
Embrittlement of Tantalum and Life Management in Chemical Plant
The.following abstract was submitted by
Seiichirou Tomoura and Masao Nakahara, Asahi Chemical Industry Co. Ltd.,
Kawasaki, Kanagawa, Japan.
Tantalum (Ta) shows excellent corrosion
resistance and is a rather expensive material. Therefore, Ta has been used for
critical components in chemical plants under highly corrosive environments.
However, one of the typical degradation phenomenon of Ta is the hydrogen
absorption embrittlement. Only a few studies have been done on nondestructive
evaluation (NDE) of hydrogen absorption embrittlement and its life management
of Ta components with respect to hydrogen embrittlement.
A case study of failure analysis on Ta
sheath tubes used in environments containing sulfuric acid will be presented.
The NDE method for estimation of hydrogen concentration and the mechanical
properties changes of Ta with hydrogen were performed. Furthermore, for the
sake of life extension of the components of interest, hydrogen desorption
treatment was examined for the recovery of the mechanical properties. Based
upon NDE of hydrogen concentration of % and hydrogen desorption heat treatment
on service exposed material, life estimation and a management procedure for such
components in chemical plants is proposed.
Q&A:
This issue's Question and Answer column
was submitted by Mr. Rick Sutherlin, a member of Oremet- Wah Chang k new
Technical Services Team and Manager of Product Engineering, Mr. Sutherlin has
been involved in CPI-related applications engineering, failure analysis,
corrosion testing and research, fabrication and welding for over 20 years. He
is a member of the ASME Boiler and Pressure Vessel Code Committee Subgroup on
Non-ferrous Alloys and is a member of two American Welding Society committees
on reactive metals. Mr. Sutherlin has taught welding seminars on reactive
metals for 15 years. His Q&A deals with weld contamination.
Weld Contamination
QUESTION:
Of what significance is the final weld
discoloration on a reactive metal weld?
Microphotograph showing a crack at the
toe of a contaminated weld
ANSWER:
This is one of the most common questions that come up during
discussions on reactive metal welding. Another way of stating the question is
"How do you know (nondestructively) if a discolored weld is
contaminated?" A discolored weld condition or even lack of weld color may
or may not be significant to determine whether the weld is acceptable. Weld
discoloration is "one way" to determine whether contamination is
present in a weld. If weld discoloration is free from each pass during the
welding process and it passes all other weld quality testing criteria, then the
weld should be fully ductile and acceptable. The significance of the weld
coloration is "when was the color formed?" If the weld coloration was
formed during the time the weld was molten or at an elevated temperature, an
extremely contaminated weld would result. If the discoloration occurs at
temperatures less than 425°C during weld cooling, then this is probably only a
thin oxide coating and not detrimental to the weld itself. Even if the final
weld shows a metallic silver color, it does not guarantee that the weld is
ductile. Interpass welds may have been contaminated, but the final weld may
show a bright silver color.
Some have suggested that a hardness test be performed to
determine whether a weld is contaminated. All areas of any weld will vary
slightly in hardness due to a variety of reasons whether or not discoloration
is present. A surface hardness test will only give a rough indication of the
potential contamination at the weld surface, but not necessarily. If a hardness
test is used, this may be "one" criterion for weld acceptance.
To help ensure that a high quality weld is produced, it is
important that proper procedures are established and strictly adhered to.
Proper preparation and weld shielding should include the following:
1. Welding in an
area that is clean, free of air drafts and away from any dust, paint or
dirt-producing operations,
2. The weld joint
must be kept clean and free from burrs. The final weld preparation must be
clean and dry. The equipment (files, grinding stones, brushes, etc.) should be
dedicated strictly to the alloy being welded.
3. The joint being welded must be
inert-gas-shielded to protect it from the atmosphere, while cooling, to less
than 425°C. Welding torches, trailing shields and a backing bar are employed to
protect the cooling weld from the atmosphere.
4. A weld procedure must be established
and followed meticulously.
Establishing proper welding procedures and adhering to those
procedures are critical to produce a high quality weld. On interpass welds, some
light discoloration may take place. This slight discoloration should be removed
prior to making another pass. Reactive metals such as zirconium and titanium
will dissolve their own oxides at temperatures greater than 650°C. If the
surface oxide is not removed, the oxygen will be dissolved back into the weld
during subsequent passes and cause the weld to be less ductile. This cleaning
should consist of brushing with a clean, dedicated stainless steel brush and
wiping the area down using an approved solvent with a lint-free rag. Do not use
contaminated (with grease, dirt, etc.) or colored rags that may transfer color
agents to the weld preparation. If for some reason a loss or reduction of inert
gas shielding occurs during a weld pass, this would be indicated by a dark blue
or gray color. If this occurs, the discolored weld area would be contaminated:
The weld and adjacent area should be ground out and repaired.
Examples of titanium (left two) and
zirconium welds (right two) with and without discoloration. Discoloration
should not be the only criterion used for weld acceptance.
Some customers will require that all welds be straw or
silver and that the final weld pass not be brushed. The final weld color is
used as one criterion to determine if the weld itself is acceptable. One of the
better methods to determine weld acceptability is to qualify the weld procedure
using a bend test, then adhering strictly to that procedure throughout the
production process.
Since weld coloration is one indicator in determining
whether the weld is contaminated, it is recommended that all welds and weld
passes show little or no (preferred) weld coloration. However, weld
discoloration should not be the only factor in determining weld acceptability,
but other factors, such as strict adherence to procedures, cleanliness, good
shielding, to name a few, will help ensure that a ductile weld is produced. For
more information on reactive metal welding or if you are interested in
attending an upcoming reactive metals welding seminar, contact Oremet-Wah Chang
at 541-926-4211 ext: 6225. B
Failure analysis and other services offered by OWC
Did you know that Oremet-Wah Chang offers corrosion
consulting services? The company began corrosion testing in the 1950s and has
generated volumes of useful data. OWC currently consults to a variety of
customers in chemical and mineral processing as well as other industries. Here
are some of the services the Corrosion Group offers:
The corrosion laboratory is able to
test and analyze a variety of materials, including Ti, Zr. and other metals.
• Materials selection and evaluation of
customers' test results and specimens.
• Corrosion testing according to the methods established by ASTM, NACE, EPA and
other groups and agencies.
• Corrosion testing according to
methods established by Oremet-Wah Chang customers.
• Material failure analysis.
For more information on these services or to discuss
research services not covered in the above list, contact Mr. Jack Tosdale,
Senior Corrosion Engineer. 541-917-6777 or reach him by fax at 541-967-6987.
News in Review
by Heidi Lopez
Anglo American plc is investing
$320 million in Australia's Anaconda Nickel to fund the Murrin Murrin
Nickel Cobalt Project, turning Anaconda a major mining house and easing capital
concerns. Anglo American, one of the world's largest mining companies, bought
77 million new shares at $3.15 per share to hold a 23% stake in Anaconda. This
move gives Anglo American a strategic nickel source in Australia. Other
shareholders include Glencore AG, a Swiss metals trader, with 16% and Sherritt
International Corp, a Canadian mining company, with 9%. Australia Financial Review 8/2
Pratt & Whitney held the last
bolt ceremony for its newest engine, the PW6000. Airbus Industrie and TWA
were present to mark the new generation of engines. PRNewswire via COMTEX 7/21
Pratt & Whitney will also be
celebrating its 75th anniversary in 2000 with aggressive new programs including
offering the PW6000 for Boeing's 747, 767 and 777 and Airbus' A330 to
increase range and add capacity. The PW6000 is ideal for 100-passenger aircraft
while the PW8000 meets the need for a larger 150- to 180-passenger craft. "Soaring Through Time:
2000 and Beyond" www.pratt-whitney.corn 8/13
Koch Industries is capitalizing
on synergies created by the growing need for ultra pure chemicals. The company
is working with Hewlett-Packard to supply chemicals for computer chips
and buy back used acids such as sulfuric acid. These used acids are still about
95% pure and can be resold for low-tech uses. The Journal Record 7/27
Dow Chemical and Union Carbide have
announced their merger in a tax free stock to stock transaction. The combined
company will be a global leader in chemical technology and facilities. "Press Conference
Summary" www.dow.corn 8/4
AlliedSignal Plastics in Morristown,
NJ, and Bayer Corporation with headquarters in Germany, announced
an agreement in accord with their globalization programs that will provide
Bayer, Pittsburgh, with polyamide 6 resin and AlliedSignal Polymer, Germany,
with caprolactam, a polyamide used in AlliedSignal Plastics’ Capron®,
Nypel®, Infinity® and Petra® resins
as well as Bayer's Durethan® and Triax® resins for
engineering plastics applications. PRNewswire 8/16 Additional resources: www.bayer.corn and
www.alliedsignal.com.
LaRoche Industries was awarded a
$10.5 million contract by the Tennessee Valley Authority (TVA) for a new
ammonia storage and supply plant. The plant will be located at TVA's Paradise
Fossil Plant Units 1 and 2 near Drakesboro, Kentucky. Ammonia is a key reagent
in TVA's process to remove nitrogen oxide emissions from the power production
process. LaRoche is pleased to provide a comprehensive system that is also
environmentally conscious. Business
Wire via COMTEX 8/17
Toyo Engineering (TEC)
received an order from Bangladesh Chemical Industries Corporation to
renovate an ammonia and urea plant built by TEC in 1970. The project, located
outside Dhaka, is for 6 billion yen and is to be completed by the summer of
2001. Proposed changes include increased production capacity, better
environmental controls and higher energy efficiency. Nikkei English News via NewsEdge Corporation
8/16-23
Solvay Interox is leading a 3
cent/lb hydrogen peroxide price hike in the US following the announcement from
European producers of a DM50-100/tonne hike effective July 1, 1999. European
demand was flat due to poor performance in the pulp and paper sector while US
markets were relatively stronger after several plant closures over the past two
years. European Chemical News 8/16-23
