There are 4 samples with different galvanize coating,

Please refer to below original samples photos, specification (from left to right):

Sample #1:  Eletro galvanized tube-1, zinc coating 40g/m2,

Sample #2:  Eletro galvanized tube-2, zinc coating 40g/m2,

Sample #3:  Pre-galvanized tube, zinc coating 200g/m2,

Sample #4:  back-galvanized tubes, zinc coating 250-275g/m2.

*Item #1 and #2 are electro galvanized, #3 and #4 are hot dipped galvanized

*item #3 is pre-galvanized, #4 are back-galvanized tubes.

Sample #1 and #2 are electro galvanized tubes with zinc coating 40g/m2, we can see the rust on the surface obviously after 24hour test, they are full of rust after 72hours test, #2 look better an-rust than #1.

Such electro galvanized tubes can be 20-30% cheaper than hot dipped galvanized tubes, but surely that is not a good choice to use them as greenhouse structure materials, they will rust easily in few months after installation.

Sample #3 and # 4 are both hot dipped galvanized, but #3 zinc coating is 200g/m2, #4 zinc coating is 250g/m2. #4 have better anti-rust performance than #3 due to #4 have higher coating.