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Study on H2S-corrosion Resistance of ZG25CrNiMo after Modified Inclusions by LPC Rare-Earths

Author: WangJi
Tutor: ZhaoPing
School: West China University
Course: Materials Science
Keywords: Blowout preventer ZG25CrNiMo LPC Rare Earth Hydrogen Sulfide Corrosion
CLC: TG174
Type: Master's thesis
Year: 2011
Downloads: 51
Quote: 0
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Abstract


Blowout preventer （BOP） is a key component of controlling device for drilling which is used to control the wellhead pressure and make near-balanced or underbalanced drilling. It can improve drilling speed and the quality. Thus the oil and gas reservoirs could be discovered and protected to the maximum limit. Once the BOP lose efficacy, it will lead to blowout fatal accidents. So the BOP is the most important equipment of entire drilling system. The energy consumption and production costs is greatly reduced as a result of BOP casting instead of forging. The content of hydrogen sulfide in China is relatively high in the oil and gas fields and oil and gas fields equipments are easy to be corroded by hydrogen sulfide, which puts forward some requirements of corrosion resistance of the ZG25CrNiMo. LPC is a novel kind of rare earth, which is the by-product of abstracting neodymium and cerium from rich cerium rare earth. A small range of applications seriously limits the development of Chinese rare earth industry. A great number of studies indicates that rare earth can improve the shape, size, distribution and quantity of inclusions in steel, thereby the corrosion resistance of the materials can be improved. In this work, the modification of inclusions and H2S-corrosion resistance in wet environment of the ZG25CrNiMo was studied. The main contents are as follows:（1） Design the 25CrNiMo of cast steel which have diverse consist of LPC Rare earths, quantitative analysis the inclusion’s quantity and size through optical metallographic microscope.And cooperation with scanning electron microscope and energy spectrum to analysis of the constituents of the microregion about the inclusion of the type of MnS,oxide and Portland . Then prove that LPC rare earths have the capability to change the related inclusion;（2） In this experiment, average corrosion rates of the 25CrNiMo cast steel samples, containing different amount of LPC rare earth were measured by the weight loss method under H2S environment. The result shows that the testing samples added LPC rare earth have reached the anti-corrosion grade. The corrosion resistance of 1# sample of without rare earths was worst. The average corrosion of four rare earth samples of different content were 0.381 g/（m2·h）,0.281 g/（m2·h）,0.251 g/（m2·h） and 0.257 g/（m2·h）.Description of the modified samples, corrosion resistance were improved to a certain extent, but the more amount of rare earths was not better;（3） By polarization curves of electrochemical experiments, according to the size of the slope of the curve and the level of corrosion potential also proved the corrosion rate of 0.3%LPC rare-earth is the slowest and the corrosion-resistance of it is also the best, while the corrosion rate of sample without rare earth is the fastest and its corrosion-resistance is the worst;（4） We have used SEM, EDS to observe and analyze corrosion product membrane, which shows that the surface membrane of samples has changed from similar to honeycomb, membrane grains are small and osteoporosis with a great deal of porosity, and local surface has bubbling and peeling into relatively flat, concentration, laminated structure, so the LPC joined is conducive to improvement of corrosion-resistance;（5） We have cooperated to use XRD method to study the phase composition of the corrosion product membrane before and after adding rare earth samples, which shows that FeCO3 polymer, which can slow down the corrosion effect, is only formed in the samples with rare earth joining in, and LPC rare earth can promote the transition from instableγ-FeOOH to stable and protectiveα-FeOOH, thereby improved their corrosion-resistance capability.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Corrosion control and protection
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