MS Reducer

Here are some ways:

• T-joint
• Concentric reducer piece
• Eccentric reducer piece.
• Interposing orifice plate
• Etc.

The piping standard appropriate to the line size, class, temperature, pressure and nature of the contents will determine the correct way to go.

Consider the need to join them in the first place and whether it is better to replace the one size with the other size size: if 1500mm is the correct size for the flow, for example, why go to 2000mm and vice-versa <rhetorical question - NNTR>?

Cut with gas cutter at end of 2000mm pipe 6" length from end x 8 nos all around . bang them all around till you get the 1500mm dia. Weld the cut lengths . The 2000 mm now will look like a reduced 1500 mm dia. Weld it on the 1500 mm pipe. If you cannot understand this tell it to your fabricator.

All answers received are valid and usable. Only the user needs to determine the purpose and medium that is being used. If flow needs to be laminar , example for instrument attachment, I would recommend that you follow the industry standard attachments in the market like the concentric reducer ( all vertical pipes) and eccentric reducers ( for horizontal pipes, installed depending on the flow medium). This would definitely give you laminar flow ( lower Reynauld's Number).

Welding the reduction is definitely a quick way for fast solutions, but there is a problem of incomplete weld penetration and rough internal surfaces that would give room for future leakages and affect flow characteristics.

http://www.teekaycouplings.com/products/p26reducerflange.html

As Satish mentioned. You can contact them for 2000 mm x 1500mm Reducer