Pickling of A333 Grade 6

[PMarinshaw]

I'm considering this alloy for low pressure (2-100 psig) marine vessel piping system (-40F design, ~+40-60F operating) which will need to be flushed with sea water about once a year and then pickled & coated with rust inhibitor. Does anyone have any recommendations or concerns regarding the pickling process with this alloy and a recommended rust inhibitor.

 

[unclesyd]

What is normally circulating in the line?

 

[PMarinshaw]

Crude oil. Once drilling is over, the pipe will be cleaned by pickling and put into dry lay-up for an extended period until drilling starts again. This will be repeated over many times.

 

[gr2vessels]

I'm assuming relative long section of piping, not few meters of pipe.
I don't believe that pickling (washing the carbon steel pipe with acid) is appropriate cleaning for your pipe after flushing it with sea water, not to mention the environmental problems with the acid effluent (please, don't tell me if you dump any of it in the ocean!). How do you intend to clean the pipe after the acid wash, using another chemical to neutralize the acid? What do you do with that cocktail?
I would suggest to use a neutralizing inhibitor in the flushing sea water, no pickling. You still have to collect the effluent and treate it according to the law. Can you do a cleaning pig run, that will help the drying process, ie. stop the progress of corrosion.
I got no idea how do you intend to coat internally a longer section of pipe, but if you can, that will help. I suggest a 'Shell' type of corrosion inhibitor, but the market is flooded with many other inhibitors, you select one based on the supplier advice and guarantee for suitability to your pipe.
Cheers,
gr2vessels

 

[blacksmith37]

And,,,,if stored in a marine atmosphere, you may have more corrosion in storage than in service. Rolling the pipe and spraying with inhibitor +oil while in storage helped (every couple months).