Problem Solving

Failures, by their very nature usually happen when no one is expecting them. So when we get called to help, key bits of information needed to diagnose a problem are often lacking. Because not having all the information needed is a fairly common occurrence for us, we've become pretty adept at the "art" of scrounging for information from a multitude of sources. In the following cases, we were using not just our knowledge and testing skills in the lab but also the "art" of "knowledge management" to get to correct diagnoses, or root causes of problems, and from there to solutions that would prevent future failures.

Pool Handrail Mystery

Our first case involves a recent project where a client asked us to examine a tubular stainless steel handrail from an exercise pool. Our client reported that it had been returned by a customer because of a discoloration on the surface. Now, usually, when we get discolored stainless steel, the problem is rust spots, so that's what we were expecting, but when we opened the package and took a look at what he'd sent us, we found that the rail didn't have any rust spots at all it just wasn't shiny anymore. In fact, it had a rather attractive matte silver color (above). A closer look at the surface with a stereo microscope revealed small crystals projecting from the surface.

Puzzled, we scraped a few crystals off and took a look at them in our scanning electron microscope, where we determined their composition via energy-dispersive x-ray spectrometry (SEM-EDS). The analysis revealed that the surface deposits consisted mostly of copper and silver. Calcium also was present, along with small amounts of silicon, aluminum, and chlorine, but the bulk of the material was copper and silver. Now, it's not too unusual to find copper deposits associated with piping systems usually that's an indicator a copper component somewhere in the system is either eroding or corroding; thus, if the plumbing system on the pool used copper pipe, then the presence of a little copper might be expected. But silver?where in the dickens could that be coming from?

Turning to what has become an increasingly useful tool, we did a search on the Internet and soon learned that in the pool and spa industry, water treatment gizmos called pool ionization devices are utilized that intentionally inject small amounts of silver and copper ions into the water. The metal ions kill bacteria, viruses, algae, and fungi, which clump together and are then removed by the pool filter.

Basically, the systems consist of a couple of copper-silver alloy electrodes, through which a precise low voltage DC current passes, controlled by a micro-processor control. Less than a part per million (ppm) of metal ions are released, and although chlorine is still used in the treatment system, the use of a pool ionization system can cut the chlorine requirement by as much as 80 percent.

A quick check by our client revealed that his customer did indeed have an ionization system installed on his pool. Presumably, there was a problem with either the equipment or the installation itself that was responsible for this rather unusual "discoloration" problem.

Microbial-Induced Corrosion

Our next case revisits a problem we discussed in our summer 1999 newsletter where we discussed the microbial-induced corrosion of stainless steels by sulfate-reducing bacteria (SRB). Basically, the "food" for these bacteria consists of sulfate (or sulfite), which, through a complex process, convert to sulfide. The result of their "feeding" process is an increase in the acidity of the local environment, to the extent that the stainless steel is subject to aggressive, localized attack.

Recently we saw another example of this type of corrosion in a wastewater treatment facility, where a 0.14-inch thick Type 304 stainless steel pipe sprung a leak after less than a year in service. The corrosion occurred at the bottom of the pipe during a seasonal shutdown, under stagnant conditions. A cross section through the leak revealed an elongated cluster of pits that began under some deposits on the inside surface (photos right and below).

In the past, when we've encountered microbial-induced corrosion, we've usually relied on the appearance of the damage and an analysis of the deposits to deduce the probable mechanism of attack. That's because there hasn't been a convenient method of analyzing for the presence of sulfate-reducing bacteria themselves. The only way to test for them has been to remove samples from the corroded area, attempt to grow the bacteria in a laboratory incubator using culture media, and then after several weeks of painstaking nurturing, attempt to identify the culprits.

So recently, we were excited to learn there is now a commercial test kit available that can rapidly detect the presence of SRB organisms using a nifty procedure called immunoassay. (Home pregnancy test kits utilize immunoassay techniques, as does one of the test procedures used in the medical field to detect the HIV virus.)

The immunoassay test utilizes purified antibody molecules, which react with an enzyme produced by the SRB bacteria, forming a reactive layer that turns blue when exposed to a chromogen. The concentration of SRB is indicated by the shade of blue.

In the case of the corroded pipe, the immunoassay test quickly confirmed our suspicions, namely, that the corroded area was teeming with SRB happily enjoying a free lunch at the client's expense.

Plugged Filters

In this project, our client sent us a stainless steel filter element from a plastics processing machine. The filters were plugging for no apparent reason, causing a pressure buildup, which in turn was slowing production.

First thing to do? Take a look inside a filter to see what was there. Sectioning and dissecting the filter element and examining the contents, we found the filter was clogged with particles, which ranged in diameter from 10 to 100 microns (see photo below). The next task, of course, was to identify the composition of the particles, which we did using a combination of scanning electron microscopy, energy dispersive spectroscopy, and Fourier Transfer Infrared Spectroscopy (FTIR).

The analysis revealed the particles were calcium phosphate. So, end of story? Hardly. Calcium phosphate wasn't being used anywhere in the system! So where was the calcium phosphate coming from?

Doing a bit more detective work on what additives were present, we learned that an organophosphate additive was being used and that a calcium salt of an organic acid was also likely present. With this information, we were able to deduce that at the high temperatures in the machine, the additives were breaking down and reacting with one another to form calcium phosphate, thereby clogging the filter.

Nickel-Plated Fasteners

In this project, our client was concerned because the nickel-plated fasteners he specified in his equipment were turning black when his customer, a hospital, cleaned the equipment with a disinfectant solution. The client wanted to know the cause and, more importantly, the cure.

We examined both a used, blackened fastener and an unused fastener. The first thing we learned was that our client had more than just a cosmetic discoloration problem he also had a coating cracking problem! That is, not only was the nickel coating black, it was riddled with extensive microcracks and as such, was defective, in addition to being unsightly.

Examining the coating further, we learned that it was very thin, only about 10 microns thick, that it contained 3 percent phosphorus, and that it had been deposited by an electroless nickel process.

From our client, we learned that several types of disinfectants, including alkaline and acidic phenols and peroxides had been used. After a few laboratory tests, we concluded that the coating had been blackened by the acidic components in the disinfectants.

So much for the causewhat about the cure? The first problem to focus on was the cracks in the coating; after that, we could concentrate on the cosmetic aspects of the discoloration.

Because hospitals place a high priority on disinfecting, they weren't about to alter the cleaning solutions they were currently using. So any recommendations would have to approach the problem from the standpoint of obtaining a coating that would work in the existing disinfecting solutions.

Standard nickel-coating specifications call for coating thickness of 40 microns or more for severe service applications, so as a start, the coating needed to be much thicker than the current 10 microns. (Severe service? ...Why is a hospital considered severe service, you ask? Because they clean the equipment with a combination of acidic and alkaline disinfectants, that's why.)

Next, the coating should be specified with a higher phosphorus content, 10 percent or more, because high phosphorus coatings have internal compressive stresses rather then tensile stresses, which reduce the cracking potential.

Although these changes would solve the cracking problem in the coating, we also had to consider the discoloration, relative to the disinfectants the hospital was using. Unfortunately, the discoloration was due to a complex chemical reaction, dependant upon not only the specific chemicals being used but also on the specifics of the coating itself. In situations like this, it's generally easier to simply test a sample of the material in the service environment, rather than try to predict in advance how it will behave.

Our suggestion to the client was to order some fasteners with the revised coating specification and see if they performed acceptably in trial tests; if not, then it would probably be necessary to switch to a different type of coating altogether, such as a noble metal or fluorocarbon.

Plugged Irrigation Equipment

In this project our client's facility was supplying used process water to a municipality, where it was used to irrigate fields. The municipality had complained that the irrigation equipment was becoming clogged with metallic deposits, and, aware that the client had recently sandblasted a large steel clarifier, they suspected the residue from the sandblasting was the cause.

We were asked to analyze the deposits and determine their source. For our analysis, all we received was a sample of brown rusty flakes that had been removed from the irrigation equipment.

Discussing the project with the client, we learned that the purpose of the sandblasting project had been to remove a coal tar epoxy coating and that the sandblasting had been done using a copper slag material as the grit.

Examining the material with an optical microscope and analyzing it further in the scanning electron microscope and energy dispersive spectrometer, we found it was black iron oxide, along with some graphite (carbon) and a host of minor/trace elements. We also noticed that many of the flakes had either a yellow or red paint coating on them.

One thing we didn't find was any copper slag, so right off the bat we were skeptical of the sandblasting theory. Then, looking at the red and yellow paint in more detail via Fourier transform infrared spectrometry, we learned that although it was epoxy based, it wasn't a coal tar epoxy, thereby showing the flakes hadn't come from the clarifier.

So if the flakes weren't from the clarifier or sandblasting operation, what were they from? The composition and appearance of the flakes was consistent with corrosion products from cast iron; further, the larger flakes had a slight curvature to them, all of which suggests they may have been derived from the inside of a large diameter, cast iron pipe. Unfortunately, we didn't get the opportunity to evaluate the flakes further and determine their specific source, because from our client's perspective, we'd already solved his problem by showing that his sandblasting operation was not responsible for the pluggage.

West Side Big Pipe

Recently, we had the opportunity, through our electrical testing division, American Product Safety, to perform field evaluations on several pieces of interesting equipment for use on the tunnel and shafts for the West Side Big Pipe project.

Part of the City of Portland's 20-year, $1-billion Combined Sewer Overflow projects, the $125-million West Side Tunnel project involves the construction of a 14-foot diameter, 4-mile long tunnel, 120 feet underground. Beginning at SW Clay and Naito Parkway near Riverplace, the tunnel will run beneath Front Avenue and Waterfront Park, then cross under the Willamette River, and terminate at a pump station being built on Swan Island.

The purpose of all this work going on under our feet is to capture the combined stormwater and sewer overflow (CSO) that currently ends up in the Willamette River during heavy rainstorms when the current system exceeds its capacity. From Swan Island, the CSO will be pumped to the Columbia Boulevard Wastewater Treatment Plant.

So far, we've done field evaluations on two 150-foot tower cranes, two 5-ton overhead cranes, two vacuum lifters, a rock processing machine, a 15-KV panel, and 14,000 feet of electrical wire... WHEW!

ODOT Contract Award

MEI-Charlton has been recently awarded a three-year contract with the Bridge Engineering Section of the Oregon Department of Transportation (ODOT) to provide professional services in the evaluation of state highway bridges. Under this contract, we will provide services to ODOT on a project-by-project basis, in the areas of failure analysis, materials evaluation, nondestructive testing, and performance testing via strain gage/data acquisition.