How can we find the center of 90 degree elboe?

if long type of 90EL the center is 1.5 X Diameter

and if short one the center is same of Diameter

if 45EL the center is Diameter / 1.6

If your elbow is a short radius it is 1 times your nominal pipe diameter. If it is a long radius it is 11/2 times your nominal pipe diameter.show me the exact pattern of long radius.

(90/2tan*Dia*1.5*25.4)(45/2tan*Dia*1.5*25.4)u will obtain Ur answer in (mm)

For 90 degree elbow(Dia*38.1) this formula used for only 90 degree elbow.For 45 degree elbow(45/2of tan*Dia*1.5*25.4) this answer obtained in (mm).

For LR ELBOW

1.5 x D

For SR Elbob

1 x D

where, D = Nominal Bore (MM)

IF the elbow is short is 1.5XDXtan 90/2

D = Nominal pipe Diameter 

At the center you will have a least possible reading taken by multiple thickness measurement.

the best way to find is to take multiple readings