Tickets answers pressure vessels

Tickets with the answers to all important questions on the subject of "installation and safe operation of vessels working under pressure". As for engineering technicians, workers, students.
ticket №1
1. vessels with which the parameters of the work, subject to rules.
2. For what purpose vessels are provided with nipples?
3. What are the requirements for the welder when welding on vessels?
4. What kind of vessels are subject to hydraulic test?