What are the similarities and differences between lap joint flange and FF plate welding flange？

Loose sleeve flange and FF plate welding flange are two common flange connection types. They are similar in some respects, but there are also some important differences. The following are their similarities and differences:

Similarities:

Connection method:

Both loose sleeve flanges and plate flat welding flanges with FF faces are used to connect pipes, valves and equipment to transfer fluids or gases in different industrial applications.

Flat weld connection:

Both are flat weld flange types that require welding to secure them to the pipe.

Flange pressure grade:

Both loose sleeve flange and FF plate welding flange can be used in different flange pressure grades. The specific pressure grade depends on the design and manufacturing standards, which usually covers a range of pressure grades.

Difference:

Flange surface shape:

Loose sleeve flange: The flange surface of a loose sleeve flange is usually flat, but there is a slightly raised hill in the center of the flange, which is often called a “sleeve” or “thrust”.
FF panel type flat welding flange: The flange surface of the FF type flat welding flange is completely flat without a central raised sleeve. The flange surface has a flat appearance with no concavities or convexities.

Gasket type:

Loose-Tube flange: A sleeve-type sealing gasket or metal gasket is usually required to accommodate the bulge in the center of the flange.
FF panel type flat welding flange: Flat sealing gaskets are usually used because the flange surface is flat, and no additional sleeve is required.

Use：

Loose sleeve flange: Typically used in high-pressure, high-temperature, or high-precision applications because it provides additional sealing protection and can accommodate more demanding environmental conditions.
FF panel type flat welding flange: Generally used in general industrial applications that do not require extremely high sealing performance.

In short, there are obvious differences in appearance and characteristics between loose sleeve flanges and plate flat welding flanges with FF faces, mainly in the shape of the flange face and the type of sealing gasket. You should select the appropriate flange type based on your specific application needs.