There is a kind of ventilator looks like a goose's neck, so called gooseneck ventilator, it is usually used on oil tank or exposed deck.
Standards for such marine ventilators here are CB/T 4220-2013 and its previous version CB/T 296-1999， they are equal to other standards from other countries.
According to the shapes of the pipes, there are circular type, oblate and rectangular type, while according to the shape/craft of neck, there are welding angle type and direct bending type, 3 multiply by 2, total 6 models. with nominal diameter range from 100~300mm(rectangular types upto 500mm)
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