Dear dhlpt45, I have to admit that for your second question I have no answer but concerning the first, third and fourth one I put forth these answers: 1-H2S is a well known corrosive substance in water which by lending its atomic Hydrogen to the metal develops Hydrogen belittlement. 2-H2S effect is pronounced at lower pHs while bisulfide effect is dominant at higher pHs (presence of NH3). In Nace standard MR0103-2003 there is paragraph related to your question which reads and I quot "Susceptibility is primarily associated with two environmental parameters: pH and H2S content of the water. Typically, the hydrogen flux in steels has been found to be lowest in near-neutral pH solutions, with increasing flux at both lower and higher pH values. Corrosion at low pH values is caused by H2S, whereas corrosion at high pH values is caused by high concentrations of the bisulfide ion. In many refinery sour water environments, dissolved ammonia is present, which increases the pH thereby increasing the solubility of H2S that results in a high bisulfide ion concentration." and you have to bear in mind that bisulfide is not less aggressive than H2S. 3-To determine the conc. of NH3 in the solution what you need is its K(eq. constant) and the pH by which you can easily find the conc. of NH3. Hope it helps