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All You Need To Know About Pressure Vessel Nozzles

A pressure vessel nozzle is an opening in the pressure vessel that allows fluid to enter or exit the vessel. In general, the nozzle projects from the surface of the pressure vessel and ends with a means of joining (flanged or welded) piping or equipment. These nozzle connections are essential to carry out the usual process or operation of the pressure vessel. The following are the primary purposes of a pressure vessel nozzle opening:


  1. To allow the content to flow into or out of the vessel to assist in the subsequent processing of the fluid.
  2. To allow instrument components to be inserted.
  3. To provide inspection or access to internal parts (manholes).

An opening is formed to connect the nozzle to the vessel, resulting in the pressure-retaining wall being penetrated. As a result, it weakens the boundary, causing a breach in the pressure vessel wall. Nozzle openings can be constructed in the pressure vessel’s shell or head. This article will look at the types of pressure vessel nozzles used in process plants, their maximum loads and a few nozzle design considerations.

Pressure Vessel nozzle Parts

A pressure vessel nozzle is made up of three parts.

  • A flange connection (used to connect a flange to a pipe).
  • Neck section of the nozzle and
  • Reinforcement (in case of requirement)

Pressure Vessel Nozzle Types

Pressure vessel nozzles are broadly divided into two categories.

  • Radial Nozzle 
  • Non-Radial Nozzle
    • Hill Side Nozzle
    • Tangential Nozzles
    • Angular Nozzles

They are classified into groups based on the position of the nozzles.

  • Shell Nozzles 
  • Head Nozzles 

Again, two types of nozzles are commonly known, depending on the welding and location of the nozzles.

  • Set-in Nozzle: The nozzle is located inside the vessel’s surface. The diameter of the pressure vessel opening in the shell/head corresponds to the outside diameter of the neck.
  • Set on Nozzle: The nozzle is placed on the vessel. The ID (inside diameter) of the nozzle neck corresponds to the diameter of the pressure vessel opening in the shell or head.

Two types of nozzles are utilized depending on the pressure vessel nozzles’ reinforcement requirements.

  • Nozzles with added reinforcement: An additional reinforcing plate is inserted to withstand external nozzle loading. Non-cyclic loads are preferred.
  • Self-reinforced nozzles: Because the nozzle thickness is sufficient to sustain external nozzle loads, an additional RF pad is not required. It is commonly used for fatigue or cyclic loading. They are classified into two types:
    • Nozzles with straight hub
    • Nozzles with variable hub

Nozzles in a pressure vessel can also be positioned perpendicular or angular to the shell axis. It can intersect or be offset from the vessel axis. 

Allowable Nozzle Loads

Manufacturers specify the maximum nozzle loads for pressure vessels. Typically, engineers have their specifications for determining minimum nozzle loads about attached pipe size and flange rating.

Design of Pressure Vessel Nozzles

Various codes and standards are available for the design of pressure vessel nozzles. However, the most widely used and internationally recognized standard is ASME BPVC Section VIII by the American Society of Mechanical Engineers (ASME).

Other pressure vessel codes and standards that are occasionally used are:

  • Europe: EN-13445
  • United Kingdom: British Standards BS PD 5500
  • France: CODAP
  • China: GB-150
  • Germany: A. D. Merkblatt Code

The nozzle design consists of three parts:

  • Deciding the nozzle size or nozzle opening
  • Choosing and designing nozzle thickness
  • Calculating reinforcing requirements depending on pressure and external loads.

The process team generally determines the size of the nozzle opening based on the volume of fluid input and output in the pressure vessel. Once the nozzle opening size is selected, the nozzle thickness is computed based on the contained/flowing medium’s design pressure. The calculated thickness is often converted into standard nozzle thickness by ASME B 36.10 or ASME B 36.19 standards. 


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