Pre - galvanized pipe: pre-galvanized pipe is made of hot dipped galvanized steel strip directly ,
Usage: Used for low pressure liquid delivery, such as water, gas, and oil,fence,conduit,green house etc.
Standard: GB/T3091 - 2001 ,BS1387 - 1985 , DIN EN10025 ,EN10219 , JIS G3444:2004 , ASTM A53
Steel Grade: GB/T3091 - 2001:Q195 , Q235 
BS1387 - 1985 , DIN EN10025 EN10219 :S235JR
JIS G3444:2004:STK400 
ASTM A53: GR. A , GR. B

Pre galvanized steel pipe:

Hot dipped galvanized pipe : hot dipped galvanized pipe owns thicker zinc coating than pre-galvanized pipe ,black pipes will be dipped into zinc pool for galvanized. 
Standard: GB/T3091 - 2001 ,BS1387 - 1985 , DIN EN10025 ,EN10219 , JIS G3444:2004 , ASTM A53
Steel Grade: GB/T3091 - 2001:  Q195,Q235 , Q345
BS1387 - 1985 , DIN EN10025 ,EN10219 :S235JR ,S275JR,S355JR, S355J2H
JIS G3444:2004:STK400 ,STK500
ASTM A53: GR. A , GR. B, GR. C , GR. D

 Hot dip galvanized steel pipe:

1.Black square&rectanhgular steel pipe:ERW steel tube

2.Pre-galvanized square&rectangular steel pipe: Pre-galvanized square/rectangular tube is made of hot dipped galvanized steel strip directly.

3.Hot dipped galvanizedsquare&rectangular steel pipe : Hot dipped galvanized square/rectangular tube owns thicker zinc coating than pre-galvanized square/rectangular tube. Black tubes will be dipped into zinc pool for galvanizing.

4.Electro galvanized square&rectangular steel pipe : The technology of electro galvanized square/rectangular tube is similar to hot dipped galvanized tube, but the thickness of zinc coating is less than hot dipped galvanized tube.

5.Painted square&rectangular steel pipe:Painted square/rectangular to remove the rust and clean the oil first and then paint the required color paint. 

Standard:GB/T6728:2002,ASTMA500,JIS G3466,EN10210,EN10219 

Steel Grade:

GB/T6728:2002 : Q195 , Q235 , Q345 

ASTM A500:GR. A , GR. B, GR. C , GR. D

JIS G3466 : SS440,SS540

EN10210, EN10219: S235JR ,S275JR,S355JR, S355J2H