Burner rig

Oxidation tests on Nimonic 90A, in which sodium chloride was introduced into the atmosphere, showed that this constituent produces a significant deterioration in the protective nature of the normally adherent film. Although under certain service conditions the presence of sodium chloride is likely, this is not always so, and thus the general applicability of the results of laboratory tests in sodium sulphate and mixtures involving sodium chloride may be questioned. Test procedures for hot-salt corrosion have been reviewed by Saunders and Nicholls who concluded that burner rig testing is the most appropriate procedure provided contaminant flux rates similar to those found in an operating turbine are used in the rig. 

However, under more realistic test conditions Hancock and Islam showed that in burner rig tests with contaminant flux rates greater than about 0-1 mgcm h" the corrosion rate of nickel- and cobalt-base superalloys was largely independent of alloy composition in the temperature range 7(X)-850 C. However, in burner rig tests at 6(X) C, simulating diesel engine combustion, Saunders et reported that Nimonic 80A (20% Cr) had superior resistance to Stellite 6 (Co-28%Cr) and EN 52 (Fe-8%Cr-3%Si). 

Several others have also explored turbine engine and other aerospace applications of phosphor thermometry. For instance, Alaruri et al. exposed samples of Y2O3 Eu to the combustion flows in a burner rig. ° The gas velocities in the rig ranged from 245 to 407 m/sec at roughly atmospheric pressure. Data were taken over the range from 400° C to 1000°C with the overall accuracy of the measurements estimated to be 3%. They noted that the phosphor s fluorescence... 

For hot corrosion testing burner rigs can be applied [26]. The agent is injected into the flame of the burner and the sample is held or agitated at a distance, which allows deposition of the corrosive agent from the gas phase at a constant rate. 

A much better constancy of conditions is achieved in burner-rig methods [75-78]. However, even here a quantification is difficult as the usually highly porous scales containing sulfate, silicate and silica are liable to spalling. Furthermore, the attack is often in the form of pitting, and so there is a change in exposed surface and the attack is nonuniform. The statistical nature of pit distribution is probably not due to a distribution of secondary phases but the result of the action of surface tension effects, because two immiscible liquids (sulfate and silicate) with differing surface stresses are present [74],... 

AT S00 C Ultimate Tensile Strength Retention after 100-hr burner rig 60% 100% 100% ... 

FIGURE 10. Typical room-temperature stiess-strain curves for the N22 CMC system with Sylramic and Hi-Nicalon Type-S fibers, and for the N24-B CMC system with Sylramic-iBN fibers before and after combustion gas exposure ofthe systems in a low-pressure burner rig at -800°C for -100 hours. The fibers in the N22 systems each had carbon on their surfaces before BN interphase deposition. 

FIGURE 13. Cross sections of a CVD SiC/glass former coated SiC/RBSN monofilament composite after 10 h burner rig testing in air at 1600°C showing stability of carbon core and coating. 

Oxidative stability of surface coated SiC/RBSN monofilament composites in burner rig testing prompted interest in utilization of this composite for uncooled components for small engine applications. Turbine vanes were machined from blanks of 1-D and 2-D SiC/RBSN composites, and surface coated with a layer of CVD SiC and glass former. Both uncoated and coated vanes were engine tested in at 1315°C for 10 h. The uncoated vanes showed severe damage, but the surface coated vanes survived engine tests with minimal damage [28]. 

NASA GRC facilities to study hot corrosion include Mach 0.3 burner rigs and a high-pressure burner rig, a high-temperature mass spectrometer (one of the two in the country) to study chemistry of salt deposition, and a multitude of laboratory rigs, including microbalances, to study hot corrosion under controlled atmospheres. 

Another oxidation/sulfidation test to assess the performance of gas turbine alloys is the burner rig test A schematic of the burner rig is shown in Fig. 6. Here a jet fuel is burned in a combustion chamber with an air-fuel ratio of 30 1. The flame jrasses down a tube at the end of which are the samples to be evaluated, mounted in a rotating platen. The samples are in the form of pins. The jet fuel normally contains a certain amount of sulfur. There are provisions to add additional sulfur in the form of volatile sulfur compounds. In addition, seawater can be added into the gas stream to simulate a marine environment. The setmples are typicaDy exposed to the flame temperature for 58 min and cooling air for 2 min in a 1-h cycle. The test is typiccJly conducted for about 500 h. 

In a standard burner rig test, mass change data are not usually acquired during testing. The metal loss and depth of maximum attack can be obtained after completion of the test by mounting transverse sections cut from the... 

In addition to burner rig tests, additional laboratory tests such as the Dean test and modified Dean tests have been developed to study the hot-corrosion resistance of gas turbine alloys [36]. These differ from the burner lig in the way salt is carried to the specimens at a specific temperature. 

FIG. 1—Diagram of burner rig used to test alloys for high-temperature hot corrosion. 

Simulation Burner Rigs—In the gas turbine industry, burner rigs have been developed to rank materials. The designs may... 

FIG. 2—Weight change data and degradation microstructures for alloys tested In a burner rig and a laboratory cyclic hot corrosion test. The microstructures after 70 h In the burner rig (left) are similar to those of the laboratory test after 12 h exposure (right). 

FIG. 3—Diagram of ducted burner rig used in iow-temperature hot corrosion tests. 

Aprigliano, L. F., Burner Rig Simulation of Low Temperature Hot Corrosion, Proceedings of the 1978 Tri-Service Conference on Corrosion, October 1978. 

In burner rig tests at 913 and 982 °C with JP-5 fuel (plus 200 ppm NaCl), Kaufman (1969) found that Ni-50.9A1 at.% suffered hot corrosion attack with the formation of a porous scale of NiO and AI2O3. Whereas NiAl was apparently considered relatively resistant, Al was removed from the alloy... 

Romeo and McKee (1975), using crucible tests and thermobalance exposures, found that the resistance of NiAl to hot corrosion was excellent, whereas y-Ni and Ni3Al were susceptible to attack, with Ni3Al being the worst. McCarron et al. (1976), found that NiAl was more resistant to hot corrosion than Ni3Al in hot corrosion tests in a burner rig using 1 % S fuel (plus 125 ppm Na, as sea salt) with a specimen temperature of 871 °C. NiAl containing ca. 8-9 at.% Cr was the most resistant alloy -minimal corrosion penetration was apparent after 800 h. A porous corrosion product was almost always formed, and internal sulfides were present. The beneficial effect of Cr was attributed to the stabilization of NiAl. 

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