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[mykid]

Hi Need some advise from the expert:

1. Anyone has the experience in corrosion inhibitor injection to firewater ring main made of galvanised CS. 

What is the dosage and frequency? 

 

2. The current firewater ring main pressure is maintained by jockey pump, as the pipes are leaking and not in a good conditions, the priority is to ensure the seachest is clear or micro and macro organism. It is proposed to use Cu-Al (MGPS ) in place of chlorination for the sea chest. For the firewater pump, since it's not normally running, it is then recommended to dose corrosion inhibitor during fire testing to keep the pipework intact.

 

3. Is PSV mandatory for firewater pump? I understood from NFPA 20 that only diesel driven firewater pump is required to have a PSV to protect the pump. What about electric motor driven firewater pump in engine room, they are typically not supplied with any PSV, and if the shutoff head is within the 150# rating, i don't see the requirement of the PSV too. Can anyone share more about the requirement of PSV?

 

4. For shock dosage of sea chest/caisson with hypochlorite, can someone share more about the shock dosage ? if 5ppm is too excessive to cause corrosion ?

 

Thanks a lot for sharing ur experience..

[sanchit_11]

1. Injection of corrosion inhibitor (CI) in fire water ring main will not serve any purpose, because continuous flow of water does not occur in fire water ring main and CI injected will remain accumulated near injection point. Normally high corrosion resistant CU-Ni pipes or GRE pipes are used for fire water ring main.

 

2. Normally all fire water pumps are provided with upstream pressure control valve which dump any excess water back to sea. Thus, injection of CI during fire water pump testing will also not serve any purpose as during fire water pump test operation this PCV will keep dumping back to sea.

 

3. Fire water pumps are centrifugal pumps and PSV's are provided to prevent increase in pressure downstream of pump. So it does not matter whether pump is diesel driven or electric driven PSV is be provided if downstream piping and pump do not have adequate mechanical strength. If pump and downstream piping is designed to handle max shut off pressure than PSV is not required.

 

4. Normal hypochlorite injection rate and shock dosage rate to pump caisson are 3ppm & 6 ppm, respectively.

 

Hope this answer your queries.