Hydrogen probes

Install and monitor corrosion and hydrogen probes in key areas,... 

Hydrogen probes are mainly used in refineries to detect the onset of conditions when HjS cracking of carbon-steel equipment could become a real risk. As a qualitative monitoring technique, it has a long and proven service of worth. 

Fincher, D. R., Nestle, A. C. and Marr, J. J., Coupon Corrosion Rates Versus Hydrogen Probe Activity , Materials Performance, 15, 1, 34-40 (1976)... 

Vennett, R. M., Corrosion Monitoring in Oil Field Operations Using a Vacuum Hydrogen Probe , Materials Performance, 16, 8, 31-41 (1977)... 

Thomason, W. H., Corrosion Monitoring with Hydrogen Probes In The Oilfield , Materials Performance, 23, 5. 24-29, May (1984)... 

Figure 12.3 Rigid and flexible molecular interaction field maps with the hydrogen probe in the active-site cavity for CYP2C9 and UCT2B7 enzymes. It is worth noting that, with flexible side chains, the overall cavity volume changes considerably. This demonstrates the important role played by MIF-flexibility calculations in enzyme-substrate recognition.

Figure 28 illustrates a soil hydrogen permeation cell mounted in a general-purpose probe used for screening soil corrosivity. Other examples of specific hydrogen probes are illustrated in Fig. 29. 

The intrusive hydrogen probe (IHP-200) shown in Fig. 29 can be placed in access fittings in industrial plants (pressure vessels, pipelines) and withstands pressures up to 200 bar. It is typically used to monitor the efficiency of measures taken to diminish the risks of hydrogen damage (use of inhibitors, H2S scavengers, etc.). 

Figure 12.1 shows the molecular interaction fields produced by the hydrogen probe interacting with the amino acid sidechains inside the active site cavities of the cytochromes. Such MIFs are important in evaluating the available volume in the active site cavities, and the shape of these cavities. 

With the enzyme sidechains in fixed positions, the active site volumes computed by the GRID hydrogen probe ranged from 1500 for CYP3A4 to 640 for CYP1A2. With flexible sidechains, the accessible cavity volumes increased from 5% to 10%, probably due to the release of steric hindrance and consequent reduction in steric interaction between the chemical probe and the lateral chains. The explanation put forward is that the cytochromes may use sidechain flexibility to allocate more space when necessary, making sub-pockets or small charmels accessible without changing the structure of the protein backbone. 

Figure 12.1. First column molecular interaction fields, produced by the hydrogen probe, showing the volume and shape of the active site cavities, for CYPs 1A2 2C9 2C19 2D6 and 3A4 respectively. Second column with flexible sidechains, the overall cavity volumes increase due to sub-pockets or small...

The vibrational modes of hydrogen-doped nanocrystalline palladium have been studied by INS [23]. Two sizes of palladium particles were used 17 run with 2.9 at. % hydrogen and Pd black 4 nm with 4.0 at. % hydrogen. The hydrogen probed the vibrations of palladium atoms at... 

The techniques used for monitoring corrosion in a process plant are (i) visual inspection (ii) weight loss coupons (iii) electrical resistance probes (iv) measurement of corrosion potential (v) linear polarization measurement (vi) hydrogen probes (vii) thickness measurement and crack detection (viii) visual inspection (ix) sentinel holes. 

Other methods include i) ordinary potential measurement with a reference electrode and a voltmeter with high internal resistance, ii) hydrogen probes that measure the rates of hydrogen development and absorption of hydrogen in steel, and iii) analysis of the process fluid, for example with respect to ferrous ions, which indicate that dissolution of steel has taken place. 

Fleischmann, M. and Hiddleston, J.N. (1968) A palladium-hydrogen probe electrode for use as a microreference electrode. Journal of Scientific Instruments, 1, 667. 

Monitoring Internal Corrosion in Oil and Gas Production Operations with Hydrogen Probes," NACE Publication 1C184, NACE, Houston, TX, 1984. 

The hydrogen ions (or protons) dissolve and pass through the iron lattice structure of the vessel wall. When some of them emerge at the outside of the vessel wall, they are trapped inside the hydrogen probe chamber. There, the ionic hydrogen is converted into molecular hydrogen. 

Instruments such as hydrogen probe, corrosometer, corrater, pirameter, galvanic probe, and oxygen meter... 

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