How does one generally measure the corrosion potential of steel?

The method of measuring the corrosion potential of steel involves utilizing a voltmeter, which is specifically designed to measure electric potential differences. Corrosion potential is an important indicator of the electrochemical processes occurring at the surface of the metal, which can help assess the likelihood of corrosion occurring. By placing electrodes in contact with the steel and an electrolyte solution, the voltmeter can detect the potential difference, providing insights into the metal's susceptibility to corrosion.

The other options do not serve this purpose. A pressure gauge is used for measuring pressure, a pH meter measures the acidity or alkalinity of a solution, and a thermometer is used to measure temperature. None of these devices can provide information about electrical potential, which is essential for evaluating corrosion risk. Hence, using a voltmeter is the appropriate method for this measurement.