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Research Papers: Internal Combustion Engines

Mineral-Metal, Multiphase Coatings to Protect Combustion Chamber Components Against Hot-Gas Corrosion and Thermal Loading

[+] Author and Article Information
Vadim Verlotski, Rudolf H. Stanglmaier, Günter Moormann, Ralph Geraets

 Märkishes Werk, GmbH, Haus Heide 21, D-58553 Halver, Germany

J. Eng. Gas Turbines Power 133(10), 102802 (May 04, 2011) (5 pages) doi:10.1115/1.4003165 History: Received October 25, 2010; Revised November 25, 2010; Published May 04, 2011; Online May 04, 2011

Many marine and stationary engines operate on fuels that contain corrosive elements, with the result that some highly loaded combustion chamber components must be replaced frequently. Märkisches Werk, GmbH (MWH) has pioneered the development of mineral-metal, multiphase coatings to protect valves and other highly loaded engine components against hot-gas corrosion. Mineral-metal, multiphase coatings are a unique and innovative approach to improving hot-gas corrosion resistance in a cost-effective manner. In general, these coatings combine the beneficial chemical and thermal attributes of ceramic coatings with the mechanical properties and substrate adhesion characteristics of a metal. Extensive laboratory and field trials have proven that MWH CrystalCoat protects heavy fuel oil (HFO) engine exhaust valves against hot-gas corrosion. It is projected that the newest coating formulation (CrystalCoat HT) will protect four-stroke HFO exhaust valves against hot-gas corrosion over their entire service life.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Typical steady-state temperature distribution of a large-bore, four-stroke, HFO exhaust valve spindle

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Figure 2

Illustration of the effects of hot gas corrosion on the face of a Nimonic exhaust valve

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Figure 3

Microscopic view of the MWH CrystalCoat HT coating structure (five phases, applied through plasma spraying)

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Figure 4

Typical test sample for the MWH laboratory corrosion test (left) and microscopic view of corroded cross section (right)

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Figure 5

Measured corrosion rates of Nimonic 80A, CrystalCoat, and CrystalCoat HT in laboratory testing. Hot-corrosion tests performed at 700°C and 900°C.

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Figure 6

Illustration of the CrystalCoat four-stroke exhaust valve spindles. The CrystalCoat thicknesses applied are indicated on the figure. Valve material was Nimonic 80A.

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Figure 7

Close-up view of the valve seat region of the CrystalCoat four-stroke exhaust valve spindles. Note that the valve seat itself is not coated.

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Figure 8

Cross section and microscopic views of a four-stroke CrystalCoat exhaust valve after 4630 h of operation. Remaining CrystalCoat thicknesses at the various locations are indicated on the figure.

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Figure 9

Cross section and microscopic views of a four-stroke CrystalCoat exhaust valve after 7323 h of operation. Remaining CrystalCoat thicknesses at the various locations are indicated on the figure.

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Figure 10

Example of catastrophic failure caused by a crack originated at the underhead radius of an uncoated Nimonic 80A valve. The crack most likely started at the sharp notches formed by the intergranular hot-gas corrosion.

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Figure 11

Maximum measured corrosion rate of CrystalCoat on the four-stoke HFO field trial and projected corrosion rate of CrystalCoat HT on the same application (red line indicates corrosion rate below which a 1000 μm layer will last 36,000 h)

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