This document analyzes thin and thick walled pressure vessels made of different materials. It discusses the thick wall theory and thin wall theory for calculating stresses in pressure vessels. For thick walled vessels, Lame's equations and maximum stress theories are applied. Stress variations through the thickness are considered. Barlow's equation is used to analyze high pressure pipes. Numerical analysis is conducted in C++ software to efficiently solve stresses in thin and thick cylinders made of ductile and brittle materials. The modeling methodology and numerical approach are discussed in detail.