Fireside Corrosion on Heat Exchanger Surfaces and Its Effect on the Performance of Gas-Fired Instantaneous Water Heaters

The heat exchanger in a gas instantaneous water heater is a thermal device used for heat transfer from the high-temperature flue gas to the low-temperature water. The fireside corrosion, due to the reaction of acidic condensate formed on the heat exchanger surfaces and its metallic material, is one of the major hazards for gas instantaneous water heaters. This paper focuses on identifying and quantifying the fireside corrosion on the surface of heat exchangers in gas-fired instantaneous water heaters. Durability tests lasting for 2000 cycles were undertaken for five gas-fired instantaneous water heaters, which were different in terms of the heat input and coating of heat exchangers. The corrosion deposits on the surface of the heat exchangers were surveyed by several methods. The results show that the corrosion deposit grew as the test duration increased. The fins of the heat exchanger with a lead coating had been corroded and copper was exposed. Cu4(OH)6SO4 was the main corrosion product of heat exchangers without a lead coating, whereas PbSO4 was the main corrosion product of heat exchangers with a lead coating. The experiments demonstrate that the corrosion rate decreased with the increase of the heat input. The experiments also show that the thermal efficiency of gas instantaneous water heaters decreased by 2.4% to 6% at the end of the test duration.

INVESTIGATION RESULTS PERTAINING TO DETERMINATION OF REVERSE FLOW PRESSURE ON TREATED FLAT SURFACE

The executed investigations have shown that it is possible to prepare sheet-like material for laser cutting economically viable and with small amount of power expenditure while using reverse jet cleaning for surface treatment. As compared to conventional jet cleaning technologies efficiency of the reverse jet cleaning is attributed to significant pressure increase (by 25–50 %) when the jet is interacting with the treated surface. The paper proposes a mathematical model on the basis of approximate energy method (upper-bound method) and the model is used for calculation of fracture pressure due to action of the reverse jet on the treated surface which consists of a corrosion deposit layer. A variational problem was solved within a framework of the developed model and the problem solution has made it possible to obtain a theoretical dependence for calculation of minimum fracture pressure value pmin in the point reverse jet impact with a barrier oretical dependence and it has taken into account yielding point of the deformed material ss, density of fractured material med material r, jet velocity uстр and parameter of reverse flowing – jet reduction ratio l. Comparison theoretical data and experimental ones (experimental data have been obtained while using a differential pressure transducer ЭДП-30 and a spring dynamometer with measuring limits 25 and 80 MPa, respectively) has shown difference by 4–15 %. Determined insignificant difference between a theory and an experiment demonstrates that the obtained theoretical dependence is considered as a quite correct one and it can be used in engineering practice for prediction of power and kinematics parameters which are necessary for selection of the required pump equipment designed for realization of reverse-jet cleaning process.

Crystal structure of an unusual corrosion deposit, bis(ethylammonium) tetrachloroiron(II)

An Fe-containing deposit isolated from a commercial plant was identified by indexing its powder diffraction pattern, using the NIST Crystal Data Identification File to locate an isostructural Mn compound, and carrying out a successful Rietveld refinement. The principal phase in the deposit was confirmed to be bis(ethylammonium) tetrachloroiron(II). This compound crystallizes in the orthorhombic space group Pbca, with a=7.3291(6), b=7.2603(6), c=21.7544(8) Å, V=1157.59(14) Å, and Z=4. The structure consists of single perovskitelike layers of corner-sharing FeCl6 octahedra parallel to the ab plane, separated by bilayers of ethylammonium cations. The octahedra are tilted 4.4° with respect to the c-axis, and the layers are ruffled. The compound was apparently formed by reaction of the ethylamine corrosion inhibitor with Fe from the steel process vessel and chloride in the process stream.

Combining CDIF and PDF information in problem solving: Crystal structure of a corrosion deposit, hexaaquairon(II) trifluoromethanesulfonate

The title compound was identified as the major phase in a corrosion deposit by indexing its powder pattern, and locating an isostructural vanadium(II) compound in the NIST Crystal Data Identification File. The identity of the compound was confirmed by a Rietveld refinement. Hexaaquairon(II) trifluoromethanesulfonate crystallizes in the monoclinic space group C2/m, with a=18.6415(14), b=6.9291(5), c=6.5938(5) Å, β=104.742(6)°, V=823.68(10) Å3, and Z=2. The structure consists of alternating layers of octahedral hexaaquairon(II) cations and triflate anions. The cations and anions are linked into layers parallel to the bc plane by hydrogen bonds. Each water molecule donates two protons to sulfonate oxygens, and each sulfonate oxygen acts as an acceptor of two protons. A reference powder diffraction pattern is reported.

Corrosion products associated with attached bacteria at an oil field water injection plant

Attached populations of corrosion enhancing sulfate-reducing bacteria (SRB) and organic acid-producing bacteria (APB) were measured on steel plugs at an oil field water injection plant near Wainwright, Alberta. The sample plugs were colonized to ca. 106 SRB/cm2. Counts for APB ranged from 102 to 10/cm2. Scanning electron microscopic examination of the sample plugs revealed an uneven distribution of surface corrosion deposits. A thin iron sulfide layer covered most of the exposed areas. Thicker sulfur-enriched deposits occurred randomly. The bulk of the thicker deposits were smooth, whereas peripheral regions exhibited a porous texture. The elemental composition of the different regions was the same; however, bacterial cells were concentrated in the porous areas and were not found in the thinner deposits. In transmission electron microscopic thin sections cut perpendicularly through corrosion deposits, bacterial cells were found mineralized in successive stages by iron sulfides. The corrosion deposit matrix also generated strong Cl peaks in energy dispersive X-ray spectra. This entrainment of bacterial cells within a corrosion deposit matrix is consistent with the concept of bacterial enhancement of corrosion by removal of reducing power from iron sulfides galvanically coupled to the steel surface. Key words: microbial corrosion, iron sulfide, cathodic hydrogen, electron microscopy.