Sometimes our assignments have a storyline that makes the project seem more like an episode of Columbo than a laboratory test.  This was one such case. The story starts in upstate Michigan where two individuals stole an airplane and began an unauthorized flight from Michigan to Texas.

 The flight was uneventful until the airplane engine failed and the flyers had to make an emergency landing in Missouri.  Abandoning the airplane, they went to a local airplane rental business and rented a Piper Lance to complete their trip to Texas.  Unfortunately for them, this airplane was even less reliable than the first one, and it ultimately took their lives.

 The Piper had been owned by an individual in Portland several years earlier.  After having the airplane rebuilt and refurbished to new standards, he had sold it to the rental business in Missouri.  Since then, the airplane had been flown about 500 hours over a period of several years but had received only limited maintenance.

 During its most recent inspection, a cracked motor mount had been found.  However, the company that had been servicing the airplane was unable to fix it at their facility because a series of relentless rainstorms had flooded their shop.  So instead, the Piper was moved to a nearby airport where the engine was removed to fix the broken mount.

 Unfortunately, this work was done by a mechanic who knew little about this model of Piper.  To fix the motor mount, he had removed the engine and disassembled the exhaust system.  However, he didn’t have the proper manuals to show how it should be reassembled, and when he put things back together, he left out several critical brackets.

 The airplane was then returned to its home base, where our fugitive flyers from Michigan became the first ones to use it for an extended trip.

 They flew successfully to Texas, but the next day on their return trip, they had gone only a  few miles when the engine caught fire.  Although they had previously survived the engine failure in the first airplane, this time they weren’t so lucky.  They lost control of the Piper and crashed, and both of them were killed.

 As you might expect, lawsuits by the surviving family members soon followed.  But the company that had rented the airplane to the deceased parties had no assets and neither did the mechanic who had done the recent repair work.  So the families filed suit against the shop that had worked on the airplane years ago back in Oregon.

 By the time we got involved in the project, other investigators had already determined that the in-flight fire was caused by a problem with the exhaust system.  We were retained by the attorney representing the shop in Oregon and asked to examine the exhaust system to determine the cause of the failure and resulting fire.

 The cause of the fire turned out to be quite obvious.  When the mechanic in Missouri reassembled the exhaust system, several critical brackets and clamps had been left off.  During the flight from Missouri to Texas, the exhaust pipes had vibrated excessively because of the lack of support, resulting in the rapid formation of fatigue cracks; this led to a separation of the pipes on the return trip, which allowed the hot exhaust gasses to flow directly onto the fuel pump and fuel lines.  The 1500ºF exhaust gasses quickly ignited a fire, which was then fed directly from the burned fuel line.

 Our testimony in court cleared our client of any wrongdoing.

 Elsewhere in this edition of the newsletter, we have noted that Mark Habel has passed his Level III examination for radiographic testing.  As those of you familiar with nondestructive testing know, Level III certification is the highest level attainable and is achieved only after meeting strict education, experience and training requirements, and passing a rigorous, two-part, 8-hour national examination. 

As many of you know, we have been involved in a broad range of nondestructive testing for many years; but it has been nearly 30 years since we owned a radiographic source.  So why are we excited about Mark achieving Level III certification in radiographic testing?

 Well, because even though we don’t own a source or do the actual radiographic shooting, we are actively engaged in radiographic testing and evaluation.  To us, radiographic testing is but one of many tools, nondestructive and otherwise, that we have available to solve engineering problems.   Recently, we have had several interesting engineering problems in which the solutions have focused on radiographic testing.  For example, last year we completed a detailed evaluation of a recovery boiler for stress assisted corrosion.

 Stress assisted corrosion is a phenomena that has only come to light in the last dozen years or so, but it has become recognized throughout the recovery boiler industry as a serious problem.  Basically, stress assisted corrosion, or SAC as it is called, is a long-term, corrosion-driven mechanism in which fissures develop on the inside of the tubes at locations of external  welded constraint.  SAC propagates slowly through the tube wall as broad, blunt-tipped fissures until it eventually penetrates the wall, resulting in a leak.  Because the bottom of a recovery boiler contains a molten bed of smelt at 1500ºF, the results can be catastrophic.

 Our work on the SAC project entailed the coordination of all inspection activities.  This included not only determining where to look for the SAC but establishing exactly how the radiographic inspection should be done.  Utilizing a radiographic subcontractor, we specified the shooting technique, directed the radiographers to the designated sites, coordinated the shooting activities with the other activities in the boiler, and then read the radiographs after they had been developed.

 To estimate the depth of the SAC found in the radiographs, we developed a grading procedure in which we measured the radiographic film density in both the SAC groove and the adjacent tube wall, then compared this ratio to the corresponding ratios obtained by shooting tube standards with machined notches of known depths.  In the course of the evaluation, we read, graded, and cataloged nearly 2,000 radiographs!
 Another example of our work with radiographic evaluation  involves a project to replace large castings that support the miter gates of a navigation lock on the Columbia River.  In this project, our assignment was to develop the acceptance criteria for radiographic evaluation of the castings.

 The project was interesting because of its mix of unknowns.  For example, the casting should be loaded only in compression, that is, unless the seal blocks along the edges of the gates become worn, in which case, side thrust would also be introduced.  This, of course, would alter the significance of defects in the casting.  An additional concern was the presence of cracks in the bottom girder of the gate where it was bolted to the existing castings.  The presence of these cracks suggested that the service stresses were probably higher than anticipated.  After considering these factors, we specified a fairly stringent acceptance level for the casting.

 We then prepared an inspection plan designating the appropriate radiographic shooting technique.  Additionally, we specified ultrasonic, visual, and magnetic particle testing for certain critical areas of the casting after determining that because of its geometry, certain areas could not be effectively inspected radiographically.

 All in all, radiography is a valuable inspection technique, not only because of its ability to rapidly inspect an entire cross section, but because it provides a permanent record of the inspection results.  So, while we may not own a radiographic source or do the actual hands-on radiography, that doesn’t stop us from using the method as an extremely useful tool. As such, Mark’s newly acquired certification lends an additional level of qualification to our capabilities.

 As we mentioned in our summer newsletter, MEI-C, in cooperation with General Chemical in Anacortes, Washington and Saturday Academy, sponsored David Blindheim, a junior at Lincoln High School, in the Apprenticeships for Science and Engineering program.  The program offers outstanding students from Oregon and Washington the opportunity to spend the summer working at various academic and industrial centers.

 David’s project for the summer, which was done at MEI-C under the guidance of his mentor Dr. Andrew Held and chemist Ahmad Mehrabzadeh, was a study of crystal formation in catalyst beds.  The subject developed from an observation by General Chemical of a puzzling phenomenon.

 During an inspection of a catalyst bed, a mat of very fine crystalline material was found downstream from the bed, in an area where the hot sulfur dioxide gas had cooled.  These crystals had presumably formed by condensing out of the gas, like frost forms on a cold window.  But the presence of the crystals was puzzling because no one had reported seeing such a thing before.

 Further investigation revealed no references in the literature of such a thing happening and no good scientific reason for it to occur.  Since the efficiency of the catalyst can be affected if the catalyst bed material changes in structure or form, the subject was of special interest to General Chemical.  Also, from a purely scientific point of view, investigating any new phenomenon usually leads to a better general understanding of how materials behave.

 The first step was to analyze the mystery crystals.  Electron microscopy showed a mixture of amorphous material and very small, long, slender crystals.  (see photograph right)  The composition of the crystals was determined through a combination of Fourier transform infrared (FTIR) spectroscopy and X-ray Energy Dispersive Spectroscopy (EDS).

 The analyses indicated the major constituent of the crystals was silicon dioxide, but they also contained a substantial amount of other elements in a complex mixture.  And while the overall elemental ratio was about the same as for the catalyst, we found that the elemental ratios for the individual crystals were not quite the same but varied from crystal to crystal.  This  was particularly interesting because it contradicted the generally accepted view of single crystals as having very specific fixed ratios of elements.  So we still had a mystery.

 We then had an X-ray diffraction englysis done; the result confirmed the presence of a crystalline structure, but it was unlike any known mineral in the X-ray library.  This was the low point of the investigation.  To make additional progress we had to try something else, but what?

 Like many scientific investigations, an earlier observation turned out to be the key to solving the puzzle.  Noticing that the crystals were partly water soluble, we immersed them in a solution of water and weak acid to see what would happen.  Interestingly, all the elements except the silicon went into solution, yet amazingly, the crystals retained their shape perfectly! (see photograph left)  This had to be the key!

 We next turned our attention to a literature search and carefully examined the available information about the different forms of silicon.  We learned that the spectra and behavior of our unknown crystals were much like a form of silicon known as “stuffed” tridymite.

 So, what is “stuffed” tridymite?  Well, tridymite is one of just several forms of silica (silica is simply silicon dioxide, or SiO2).  And, “stuffed” tridymite is tridymite in which the crystalline lattice is packed or stuffed with other elements.

 We finally had a likely identification of the mystery crystals:  They were a form of stuffed tridymite with a polycrystalline mass of cesium, potassium, sodium pyrosulfates, and vanadates doing the stuffing.

 The identification, however, led to a new mystery:  How did silica evaporate and then recrystallize at the temperatures in the reactor (about 1,000ºF) when it is well known that silica doesn’t even melt, let alone evaporate, at that temperature?  If silica did this sort of thing normally, pottery kilns (which are made of silica refractory brick) would produce fumes and fluffy crystalline deposits even at fairly low temperatures.  But of course they don’t, so how did we explain this mystery?

 In a future newsletter we will tell how we approached this second mystery.

Allen Sharp, administrative assistant, and Veleria A. Rascoe were married on 28 November 1998 in Raleigh, North Carolina.  After a 3-day honeymoon in Gatlinburg, Tennessee, Allen and Valeria spent the next 3 days driving back to Portland.  Congratulations, Allen and Veleria!