Oregon Maritime Museum — Sternwheeler Portland

Just before Christmas last year, we had an interesting call from a consulting engineer regarding some possible cracks in a steam boiler. We frequently assist clients with boiler-related problems in a variety of industrial settings, so when the call came in, we were expecting another visit to a factory or industrial plant somewhere. But no, this time the boiler was for something a bit more out of the ordinary, a steam-powered tugboat—none other than the stern wheel tugboat "Portland," which is tied up at the Portland Seawall on the west bank of the Willamette River. Moored between the Burnside and Morrison Bridges, the Portland serves as the home of the Oregon Maritime Museum and is a familiar sight along the waterfront to residents and visitors alike.

After a brief discussion, the client asked if we could come down and take a look at some unusual markings which had recently been discovered in the metal of the boiler header and were suspected of being cracks. What?... a trip out of the office on an otherwise slow pre-holiday workday to take a look at the inside of an actual operational, honest-to-goodness, steam-powered, sternwheel tugboat? Absolutely!

For our readers who may not be familiar with the Portland's history, a little background is perhaps in order. The Portland was built at Northwest Marine Iron Works in 1946 and was launched in 1947 as a working tugboat for service in Portland Harbor. While in regular service, she was owned by the Port of Portland and primarily worked the harbor, with occasional trips to Vancouver and elsewhere nearby. In 1981, she was retired from service, and, for the next several years, she sat idle, deteriorating as a relic of the past. Then, in 1989, a group of volunteers began the slow process of restoring her. After two years of work, the volunteers got a much needed financial boost when the Meyer Trust gave $300,000 toward the restoration. Then, the Port of Portland gave the vessel to the Maritime Museum, where today, she is one of the last running steam tugs on the West Coast.

Well, that is, she would be running... if it weren't for those unusual marks in the header of her boiler. So, what were they? That part was easy for us—they were cracks, definitely service-related, probably many years old, and based on their appearance, likely the result of caustic embrittlement, an environmentally assisted cracking mechanism that occurs under the influence of tensile stresses and an aggressive chemical environment, in this case, accumulated alkaline (caustic) boiler water minerals.

Ok, so they were cracks--what could be done about them? That part was also pretty easy. Fix them, in this case, by cutting off the cracked portion of the header and welding in new steel plate material. For our part, after first establishing the marks were indeed cracks, and after establishing they needed to be repaired, we assisted with the repair process by removing a sample of material from the header and analyzing it at our laboratory to establish its chemical composition. Once that information was available, the repair contractor was able to select an appropriate replacement material and determine the correct welding procedure to install the new material in the boiler.

And the best part of the assignment from our perspective? Well, since we were on site anyway, we just had to take a tour of the vessel, from the engine room, with its twin, 900-HP steam engines, to the Pilot House, 32 feet above the water and without an electronic gizmo anywhere in site—talk about a trip to the past!

For those of you interested in classic, state-of-the-art things (last-century, that is), the vessel is open for public tours on Fridays, Saturdays, and Sundays. In addition to seeing firsthand the engine room and pilot house, you can view a collection of models on display and look back at history through early photographs of sternwheelers and other vessels that traveled the Columbia and Willamette in a bygone era. The museum is a private nonprofit corporation funded by admission fees, membership dues, and private contributions. You can visit their website at www.oregonmaritimemuseum.org.

Currently our client is working out the final repair details with the US Coast Guard, who has jurisdiction. Then, once the funds are in hand, the museum will be able to proceed with the repairs, and they will indeed, once again, have one of the few remaining running steam-powered tugs on the west coast.

LAYERS

In our Spring 2000 newsletter, we discussed passivation, which, simply put, is the changing of the chemically active surface of a metal to a much less reactive state. Passivity is important in the real world because passive metals corrode at very low rates in environments that would normally cause them to corrode very rapidly.

Beauty is Only Skin Deep

As you may recall, stainless steels passivate by rapidly forming a very thin, chromium-rich oxide layer that acts as a barrier to further corrosion. So, just how thin is "thin"? Well again, simply put, it's really, really thin, or to put it in slightly more technical terms, it's only about 10 to 100 atoms thick. And it's this invisible and self-healing skin that keeps the material looking pretty and not visibly corroding. Ironically, the formation of this protective film is in reality a corrosion process; but when formed in an appropriate manner, its presence halts further corrosion of the base material, resulting in that "stainless" appearance the materials are named after.

Now, at 100 atoms thick or so, the protective film is invisible, at least to the naked eye. But what happens as it starts to get thicker? As you might expect, it loses its "invisibility" and starts to take on different colors.

One means of achieving a thicker film layer is temperature. That is, heating a piece of stainless steel to progressively higher temperatures will cause it to develop a progressively thicker oxide layer. These so-called "temper colors" progress from a faint straw yellow, to light brown, then to purple, then blue, then gray, and finally black, at which point it's about as "non-invisible" as it gets... in other words, it's opaque.

Interestingly, what gives the film on stainless steel the various colors is exactly the same phenomenon that gives a thin film of gas or oil on water its characteristic rainbow-colored hues. That is, it's due to waves of light interacting with each other to produce constructive reinforcement or destructive cancellation of the waves. Without getting too bogged down in detail here, it's the result of light reflecting from the top surface of the film interacting with light reflecting from the bottom surface of the film when the thickness of the film is on the order of the wavelength of the light.

Back to our discussion of layer thickness, one finds the oxide on steel continues to thicken as the temperature and time at temperature increase until, for steel that is hot rolled, the thickness approaches around 0.050 to 0.100 inch, many orders of magnitude thicker than the passive film we started out discussing.

Visualizing just how thick an oxide layer is can be somewhat confusing because of the lack of an everyday reference. But just as the newspaper seems to think that everyone can somehow relate the size of a 747 wingspan to the size of a football field, even though most of us only watch football on television, or that we can somehow relate the size of a middle-east battlefield to the size of Delaware or some other obscure east coast state that most of us west coasters have never been to, we too will try our hand at the "size comparison" sweepstakes.

So for our size comparison example, consider the following chart: Each row in the chart represents 1/10 the thickness in the previous row. Columns show the sizes of some features. So, for example, your finger is about a centimeter thick, and a dime is about 0.1 cm thick. Compare this with an iron atom, which has a diameter of only 10E^-8 cm, and remember, the passive film which protects stainless steel is only 10 to 100 atoms thick!

Oh, and just in case you prefer the newspaper's football field analogy, the passive film would be between about one-tenth and one-hundredth of one-billionth of a football field thick!

APS Update

So, your daughter just came home sporting a tattoo of her new boyfriend's name prominently displayed on her cheek…. or, perhaps elsewhere. Fret not, medical technology has the answer! Think lasers… no, not like the one that Goldfinger was going to use on 007 in the movie... besides, we're not talking about an answer to the boyfriend, we're talking about the tattoo, once she tires of it.

How so? Well, in the 1990's medical lasers joined the ranks of surgery and dermabrasion (sanding the surface of the skin) as a means of removing unwanted tattoos. Basically, the process consists of firing repeated, short pulses of laser light onto the tattoo, which breaks the pigments into minute particles, allowing the body to flush them from its system.

So how does all this affect us? That's simple… it's just one of a myriad of electrically powered devices that our electrical testing division, American Product Safety, has recently evaluated for field labeling. In fact, we've recently evaluated over two dozen interesting medical devices. Let's see, there was the blood analyzer, the six-axis x-ray chair, and then there was that strange looking borescope… although, we didn't quite learn what it was used for because when we asked, the client just laughed and said, "you don't want to know!"

APS manager, Sandy Mikalow's projects have had him traveling throughout Oregon, Washington, and California in recent months, and last summer, he spent eight days in Japan evaluating a product before it was shipped to its new home in Oregon.

Oh yes, Sandy even spent a day in prison recently… no, not as an involuntary "guest" of the state, but as a paid consultant evaluating some machinery that was to be used in the prison workshop. Strange, Sandy says he came away from that job with a whole new appreciation of what it means to come home in the evening after a day at the "office"!

And one last thing, the next time your daughter talks about getting a new tattoo, try to steer her toward a dark color like black or blue, rather than lime green—the dark colors are a whole lot easier to "zap" with a laser than are the yellows and greens.

MEI-People

Sandy Mikalow, APS Manager, and his wife, Wyla, recently completed the formal adoption of their two grandchildren, Amanda, seven, and Seth, three. Congratulations, Sandy and Wyla, and of course, Amanda and Seth too!

Visit Our Booth at: 13th Annual Northwest Plant Engineering & Maintenance Show and Northwest Material Handling Show and Conference Oregon Convention Center June 11 & 12, 2003 For complimentary tickets, contact Holly Howard at hmh@meic.com or 503-228-9663