Design of Pressure Vessels to Increase Equipment Reliability

Introduction

Numerous catastrophic accidents occurred in the early twentieth century due to the poor design of pressure vessels intended to hold high-pressure contents. These accidents provided the impetus to create rules and laws to govern the design of pressure vessels. Pressure vessel design is a crucial step to ensure compliance with safety regulations adopted by the local jurisdiction where the vessel will be operated. To increase reliability without failure during operation, pressure vessels must be designed in accordance with a recognized pressure vessel standard and include owner-operator best practices that are typically provided to the contractor responsible for design, manufacture, and commissioning. In countries such as the United States, the ASME Boiler and Pressure Vessel Code (BPVC) is the code adopted by jurisdictions for the design and construction of pressure vessels.

This article describes the procedure to design a pressure vessel in order to meet process requirements and facilitate maintenance and reliability. It will first address what to consider in the sizing of pressure vessels as well as the preliminary operating parameters required to start the process design. These parameters include materials selection, corrosion allowance and the need for cladding or weld overlay, post weld heat treatment (PWHT) requirements (i.e. required by the governing pressure vessel code or for service conditions), maximum design pressure and temperature, design loads, fatigue analysis requirements, the minimum required shell thickness of the vessel components (e.g. shell courses, heads, and nozzles), insulation, and fireproofing. Then, the basis of calculating design parameters will be discussed.

Pressure Vessel Design Codes and Standards

The purpose of a pressure vessel is to safely hold a pressurized fluid, such as oil or gas, even under extreme operating conditions. Extreme operating conditions include high temperature, high pressure, or containment of corrosive fluids. Historically, improper pressure vessel design has resulted in numerous fatal accidents. For example, in 1905, a disastrous vessel explosion occurred in a shoe factory in Brockton, Massachusetts, which resulted in 58 fatalities and 117 injuries, not to mention property damage. One year later, another fatal accident occurred in Lynn, Massachusetts, again leading to death, injuries, and extensive property damage. These and many other incidents highlighted the need to develop a pressure vessel design code. The first such document, "An Act Relating to the Operation and Inspection of Steam Boilers," was established in 1907 in Massachusetts.^[1,2]

In 1915, the American Society of Mechanical Engineers (ASME) developed the first ASME Boiler Code. The first ASME code specifically for pressure vessels, ASME Section VIII, was issued in 1925 with the title “Rules for the Construction of Unfired Pressure Vessels.” In 1934, The American Petroleum Institute (API) collaborated with ASME to establish another code which applied to unfired pressure vessels in the petroleum industry. The two codes were combined in 1952 to become the “Unfired Pressure Vessel Code, Section VIII.”^[1,2]