Cost effective corrosion protection of structural steelwork should present little difficulty for common applications and environments. piping system instead of flange to save space and weight had offered either Hot Dip Galvanized is the good idea. Flanges always creates problem for corrosion because the nuts bolts are very prone to corrosion due to sharp configuration. The hot dip galvanized painting is proven technology.

The key to success lies in recognising the corrosively of the environment to which the structure will be exposed and in defining clear and appropriate coating specifications. Where steel is in a dry heated interior environment the risk of corrosion is insignificant and no protective coating is necessary. Conversely, a steel structure exposed to an aggressive environment needs to be protected with a high performance treatment and may need to be designed with maintenance in mind if extended life is required.

The optimum protection treatment, which combines appropriate surface preparation, suitable coating materials, required durability and minimum cost, is achievable using modern surface treatment technology. Painting provides a barrier film between the steel and the environment. A paint system involves the use of several layers of coating, and sometimes, different formulations of paint, depending on the type of environment in which the structure will be exposed.

THE ADVANTAGES OF HOT DIP GALVANIZING

1. Lower first cost.

2. Lower maintenance / lower long term cost. Long life

3. Surface preparation.

4. Long life

5. Adhesion

6. Environmentally friendly.

7. Speed of coating application.

8. Uniform protection

9. Sacrificial protection for damaged areas

10. Toughness

11. Reliability

12. Faster erection time

13. Ease of Inspection

14. Over coating with paint, (duplex protection).

THE DISADVANTAGES OF HOT DIP GALVANIZING

1. Hot dip galvanizing can only be done in a galvanizing plant. Site application is not possible.

https://www.scribd.com/document/60347298/Painting-Over-Hot-Dip-Galvanized-Steel

Hi Prem,

Thanks for your answer. I think hot dip galvanizing is more common for bolting of the valves and flanges in piping system. But it can be done on other carbon steel materials such as clamps and coupling between valve and actuator which are made of either carbon steel or low alloy steel.

Both paint and hot dip galvanized in that case are applied at manufacturers or manufacturer subcontractor. It is also difficult to say if HDG is stronger that paint because it depends what type of painting we are talking about. Thermal Spray Aluminum as an example is stronger than HDG.

Dear Karan

You are saying current hot dip galvanizing are common for flanges/nut bolts .But whenever required to reopen Not bolts the thread are covered with paint hard to operate but not impossible.

Regards,

Prem Baboo

Dear Prem,

I am not sure if I understand your comment correctly.

But that is very common to apply HDG on flange and valve bolting. I have seen applying paint on the bolting but rarely. I am talking about oil and gas industry. We normally prefer to ask valve suppliers to use some sort of plastic plugs inside the bolt holes to mask and prevent paint on the threaded holes and nut bearing area if the valve is coated.

Regards,

Karan