Hydrogen measurements corrosion testing

The nozzle of original design was fabricated from a niobium alloy coated with niobium silicide and could not operate above 1320°C. This was replaced by a thin shell of rhenium protected on the inside by a thin layer of iridium. The iridium was deposited first on a disposable mandrel, from iridium acetylacetonate (pentadionate) (see Ch. 6). The rhenium was then deposited over the iridium by hydrogen reduction of the chloride. The mandrel was then chemically removed. Iridium has a high melting point (2410°C) and provides good corrosion protection for the rhenium. The nozzle was tested at 2000°C and survived 400 cycles in a high oxidizer to fuel ratio with no measurable corrosion.O l... 

Owing to their simplicity, measurements with the hydrogen sensors are easily automated. Figure 30 shows a setup in which eight hydrogen contact cells are used in an investigation with a steel pipe filled with a corrosive test medium underpressure. Temperature, pressure, and hydro-... 

Corrosive sulfnr componnds can be detected by their effect on copper and the form in which the general copper strip corrosion test (ASTM D1838) for petrolenm prodncts is applied to liqnefied petrolenm gas. Hydrogen sulfide can be detected by its action on moist lead acetate paper, and a procedure is also used as a measure of sulfur compounds. The method follows the principle of the standard Doctor test. 

The results of such measurements are known as current density-potential curves. They represent cumulative curves given by the superimposition of the current density-potential curves of the individual reactions. For simple electrodes with defined electrode processes, these are the overpotential curves. For metals exposed to electrolytic attack, superimposition of several overpotential curves gives the actual current density-potential curves that are of significance in corrosion testing and research. Figure 20.9 shows the superimposition of the overpotential curves of a hydrogen electrode... 

Hay, M. G., "CorrelatiQn of Laboratory Hydrogen Induced Cracking Test Environments with Field Sour Gas Environments Using Hydrogen Permeation Measurements, Corrosion/ 92, Paper 13, NACE, Houston, TX. 

Several tests are not related to any particular part of the corrosion process, but involve only a specific test specimen that responds to corrosion by complete failure. These tests are used in the measurement of certain forms of corrosion involving factors such as stress. Examples are corrosion fatigue, stress corrosion cracking, and hydrogen embrittlement In designing such corrosion tests, the variety of test specimens parallels the number of apphcations. 

Corrosion detection plays an important role in any corrosion control program. Most of the methods employ nondestructive test methods and include hydrogen evaluation, radiography, dynamic pressure, corrosion probes, strain gauges and eddy current measurements. Of these, the methods employed in cooling tower practice are hydrogen evaluation and corrosion probes. 

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