The answer to the first part of your question can be found here:
Answer to the second part:
If all the conditions required are present, it will still take come period of time for the sulfide stress cracking to occur. This depends on the following factors:
- Stress Level – higher the stress, lower the time to failure
- Hardness of the steel – higher the hardness, lower the time to failure.
- Hydrogen sulfide concentration – higher the concentration, lower the time to failure.
- pH of the fluid – lower the pH, lower the time to failure.
- Temperature -at ambient conditions, lower the time to failure, above 150 ºF the chances of failure decreases.