Consider the following statements regarding the ends of the pressure vessels flanged by pre-tensioned bolts:
1. Pre-tensioning helps to seal the pressure vessel.
2. Pre-tensioning reduces the maximum tensile stress in the bolts.
3. Pre-tensioning countermands the fatigue life of the bolts.
4. Pre-tensioning helps to reduce the deleterious effect of pressure pulsations in the pressure vessel.
Which of the above statements are correct?
(a) 1, 2 and 3 only (b) 1, 3 and 4 only
(c) 2 and 4 only (d) 1, 2, 3 and 4