Oil & chemical factories are composed with few hundreds of pressure vessels and few hundreds or thousands km of pipes in one plant.

What is Pressure Vessel?

It shall be defined as vessel accommodating fluid (liquid or air) having pressure and include boiler.

Pressure vessel in terms of narrow sense shall be defined as the designed and manufactured vessel in order to endure the pressure for the purpose of preserving liquid or air, responding or separating in oil & chemical industry
 The treating with the solid or flame being combusted in operating is defined as fired pressure vessel and the not treating is defined as unfired pressure vessel.