Dimensions and Standards
When we are talking about a tee of size NPS 3, the tee is an equal tee. When we are talking about a tee of size NPS 3 × 2, the tee is a reducing tee. The formal presentation should include three sizes, e.g., 3 × 3 × 2, with the first two numbers being the two sizes of the main and the last number indicating the pipe size of the branch. This expression comes from the case of a tee with three sizes. However, this type of tee with three different sizes is now rarely used and has usually been replaced by a combination of an equal tee and a concentric or eccentric reducer
Equal tees can be supplied in all conventional sizes. However, reducer tees are different because many sizes are not produced, or cannot be produced. For example, an NPS 6 × 4 Reducing Tee is a standard conventional type of tee for manufacturers, but a Reducing Tee in the size NPS 16 × 2 is not practical or economical for manufacturers. In this case, a bypass fitting such as a stub table would be used.
In addition to equal and reducing tees, there are also equal and reducing tees. However, equal and reducing tees are rarely used in the petrochemical industry. They may be used when space is limited, such as in the marine industry.