Coupons types

Factors may throw off these rates—these are outlined in ASTM G3I, Standard Practice for Laboratory Immersion Corrosion Testing of Metals. Coupon-type tests cannot be correlated with changing plant conditions that may dramaticahy affect process equipment lifetimes. Other methods must be used if more frequent measurements are desired or correlation with plant conditions are necessary. 

Coupon Type REMOVAL OF COKE % O2 DEPOSITED FROM Feed XH20 ETHYLENE AT 900°C Run Duration, Hours Average Decoking Rate /g coke removed cm2 hr x 101 % burn-off at run end... 

Corrosion coupons. The simplest form of direct measurement of atmospheric corrosion is by coupon exposure. Subsequent to their exposure, the coupons can be subjected to weight loss measurements, pit density and depth measurements, and other types of examination. Flat panels exposed on exposure racks are a common coupon-type device for atmospheric corrosivity measurements. Various other specimen configurations... 

Several measurements can be made after a coupon-type corrosion sensor has been attached to a cathodically protected pipeline. on potentials measured on the coupon are in principle more accurate than those measured on a buried pipe, if a suitable reference electrode is installed in close proximity to the coupon. The potentials recorded with a coupon sensor may still contain a significant IR drop error, but this error is lower than that of surface on potential measurements. Instant-OFF potentials can be measured conveniently by interrupting the coupon bond wire at a test post. Similarly, longer-term depolarization measurements can be performed on the coupon without depolarizing the entire buried structure. Measurement of current flow to or from the coupon and its direction can also be determined, for example, by using a shunt resistor in the bond wire. Importantly, it is also possible to determine corrosion rates from the coupon. Electrical resistance sensors provide an option for in situ corrosion rate measurements as an alternative to weight loss coupons. 

Weight lo.s.s probe.s. Coupons for measuring weight loss are still the primai y type of probe in use. These may be as simple as samples of the process plant materials which have been fitted with electrical connections and readouts to determine intervals for retrieval and weighing, to commercially available coupons of specified material,... 

Electrical re.slstance probe.s. These probes are the next most common type of corrosion probes after coupons. This type of probe measures changes in the electrical resistance as a thin strip of metal gets thinner with ongoing corrosion. As the metal gets thinner, its resistance increases. This technique was developed in the 1950s by Dravinieks and Cataldi and has undergone many improvements since then. 

More recently, attempts have been made to correlate mathematically the chemical composition of natural waters and their aggressivity to iron by direct measurements on corrosion coupons or pipe samples removed from distribution systemsThis work has been of limited success, either producing a mathematical best fit only for the particular data set examined or very general trends. The particular interest to the water supply industry of the corrosivity of natural waters to cast iron has led to the development of a simple corrosion rig for the direct measurement of corrosion ratesThe results obtained using this rig has suggested an aggressivity classification of waters by source type i.e. 

We performed SPEM studies on hard disc coupons covered with lubricant films of different types and thicknesses [70]. No evidence of dewetting was observed with films of submonolayer average thickness (17 A for Zdol and 14 A for Zdol-TX). Dewetting was observed, however, when the film thickness was above one monolayer. The stracture of these films during dewetting differs depending on the type of lubricant. 

Another device that finds frequent use is the stirred cell shown in Fig. 20-54. This device uses a membrane coupon at the bottom of the reservoir with a magnetic stir bar. Stirred cells use low fluid volumes and can be used in screening and R D studies to evaluate membrane types and membrane properties. The velocity profiles have been well defined (Schlichting, Boundary Layer Theory, 6th ed., McGraw-Hill, New York, 1968, pp. 93-99). 

This type of testing generally involves inoculation of a coupon (chosen to simulate cleanroom surfaces, e.g., stainless steel, polycarbonate, etc.) with the challenging organism. 

The weight, thickness, and hardness of each coupon was measured before and after designated periods of exposure to determine the type and rate of physical and mechanical change. The hardness was measured with a Type D Durometer Instrument in accordance with ASTM D2240, and visual observations were made to identify changes in color or form. In addition, scanning electron micrographs of specific coupons were used to further identify the type and rate of surface attack. 

Portable deposit/corrosion monitors are typically housed in an enclosure of perhaps 30 in. H x 20 in. W x 15 in. D. Components include inlet flow controller, strainer, adjustable electric heater, (outer) see-through glass housing, (inner) heated specimen tube or block, hot/cold temperature readout, corrosion rack, plus thermal overload, low-flow cut-off, and other safety devices. The specimen tubes or blocks are available in different metals (as are the corrosion coupons) and can usually be replaced in a matter of minutes. Unlike test heat exchangers, the cooling water in this type of monitor flows on the shell side of the specimen tube. 

Coupons of Type 304 stainless steel were prepared by mechanical abrasion and rinsed with methanol. Each sample was analyzed by XPS prior to treatment to ensure that no detectable casually-introduced chlorine was present. Two separate series of laboratory experiments were done one series (a) followed the effects of short-term contact between chlorocarbon and the alloy surface, a second series (b) investigated the effects of prolonged vapor and liquid contact with the alloy in a glass refluxer. In series (a) the clean alloy surface was swabbed using trichloroethane-soaked tissue and immediately inserted into the vacuum chamber of an XPS spectrometer for analysis. After analysis, the same coupon was exposed to the atmosphere for periods of 72 and 336 hours... 

Bond A long-term debt-type of security generally issued by corporations or governments to generate cash. The coupon rate is the interest rate paid to the bondholder. The maturity date is when the face value of the bond will be paid to the bondholder. 

This section will focus on explaining the electrochemical bases for two generic types of testing accelerated coupon testing and electrochemical testing. 

Figure 38 Comparison of data from SL-EPR, acid ferric sulfate, and oxalic acid etch test for seven separate heats of Type 304 and 304L stainless steel. Note that for low levels of sensitization, the SL-EPR can quantitatively distinguish among degrees of sensitization. At higher levels, the coupon exposure tests are more discriminating. (From Ref. 32.)...

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Metal coupons were inserted at various positions in the horizontal tubular reactor. The coupons had two types of surfaces an Incoloy 800 surface and an aluminized Incoloy 800 surface. To prepare these coupons, flat pieces of Incoloy 800 were aluminized (or alonized) by the Alon Processing, Inc. of Tarentum, PA. In this process, gaseous aluminum was contacted with the Incoloy 800, and aluminum diffused into the surface. The alonized samples as received from Alon Processing were cut in small coupons so as to expose an Incoloy 800 surface which was cleaned and polished before use. 

The metal coupons in the horizontal reactor were exposed at reactor temperature to either acetylene, ethylene, propylene, or butadiene for 120 minutes. The coupons were removed from the furnace, and pictures of the coke were taken using a JSM-U3 scanning electron microscope. Most pictures were taken using a magnification of 10,000. The type of metal in the coke was determined using EDAX Model 707, that was attached to the electron scanning microscope. 

Figures 4 and 5 indicate that the types of coke formed on Incoloy 800 as ethylene and propylene, respectively, were contacted with an Incoloy 800 surface at various temperatures and at slightly different conversion levels. In these experiments, the Incoloy 800 coupons were positioned at different positions in the horizontal tubular reactor. The residence time of gases in the reactor was about 7, 10, 15, and 25 sec by the time the gases reached the coupon. The temperature of each location was about 460°, 560°, 600°, and 565°C, respectively. The cokes...

Figure 9. Examples with more than one type of coke. (Top left) Butadiene—560°C (2nd position), incoloy coupon (top right) ethylene— 500°C (3rd position), incoloy coupon (middle left) acetylene—800°C (alonized tube) (middle right) acetylene—780°C (4th position), alonized coupon (bottom left) butadiene—460°C (1st position), alonized coupon (bottom right) ethane pyrolysis—800°C, SS 304 tube.

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