Precautions for Installation and Use of Vessel Flanges

Pressure vessels are the most widely used equipment in the petrochemical industry and serve as one of the main production facilities. Due to process requirements, as well as installation and maintenance of internal components, pressure vessels are often equipped with vessel flanges (common examples include shell-and-tube heat exchangers, reaction kettles, towers, filters, etc.). According to the connection structure of the flange ring, pressure vessel flanges are classified into:integral flanges, lap-joint flanges, and loose flanges.
When flanges are installed on pressure vessels, the flange connection sealing structure generally consists of flanges, gaskets, and fasteners. This is the most basic flange connection structure, commonly used in piping or vessel connections. In this structure, two flanges of the same size are connected via gaskets and fasteners, with only sealing gaskets between them and no other components. The two flanges are subjected to identical temperature and pressure loads. Such flanges can be designed and calculated directly using formulas specified in relevant standards.
The most commonly used pressure vessel flanges in China are in accordance with JB/T 4701—4703, which include three types:Type A flat-welding flange, Type B flat-welding flange, and long weld-neck flange.Among them, Type A and Type B flat-welding flanges belong to loose flanges.
Flanges together with their gaskets and fasteners are collectively referred to as flange joints. Flange joints are widely used in engineering design and are critical components where problems often occur during design and service. The design of flange joints is an important part of pressure vessel design.
In addition, for shell-and-tube heat exchangers, the sealing structure of the channel flange connection differs from that of vessel or piping flanges. This structure consists of channel flange, channel gasket, tubesheet, channel-side gasket, and shell flange. The two flanges are separated by the tubesheet. When the gaskets, temperature loads, and pressure loads on the two sides are inconsistent, loads such as bolt force and gasket reaction cannot be simply calculated using standard formulas.

Types of Vessel Flanges

1. Flat-Welding Flanges

1. Type B flanges are equipped with a short cylinder, providing better rigidity than Type A, making them suitable for higher pressure and larger diameter applications.
2. Weld groove types:
   • Type A: V-groove
   • Type B: U-grooveType B allows easier full penetration welding, resulting in higher strength and rigidity.

2. Weld-Neck Flanges

With a long neck and welded neck connection, they feature excellent rigidity and are used for higher pressure conditions.