Material selection for higher sulphur slop oil pump 1

[CPMech]

Trying to determine best materials of construction for a new centrifugal pump in slop oil service. The worst case conditions are:
total sulphur number of 4.0 wt %, acid number of 3.0 (mgKOH/g), a specific gravity of 1, and a temperature of 100 C.

currently we have an older cast iron pump in similar service but significantly lower sulphur content. We have experienced significant corrosion in the carbon steel slop oil storage tank that this pump is piped to.

Any suggestions are appreciated.

 

[taylorg]

Hi CPMech,

The thread below may help you a little although it relates to crude oil with a similar acid no:

thread483-125496

The general concensus was to use metals with +2.5% Moly (best is 317 SS with 3.5% Mo). Not cheap but your only other solutions may entail diluting your slop oil or using corrosion inhibiting chemicals.

 

[Ashereng]

taylorg,

Would it also be possible to coat/line the insides of the tank? If it is corrosion, something like IMPREGLON 410M can be field sprayed/applied on?

 

[CPMech]

Thanks for the feedback. Perhaps I should take both of your suggestions into consideration and use a 317SS impeller in a coated carbon steel pump casing. This would certainly be a more cost effective approach.

 

[taylorg]

Are you also experiencing excessive corrosion in your pipes?

 

[CPMech]

We have not seen extensive corrosion in the pipes. We are attributing this to low residence time. The storage tank has a floating roof and I wonder if water accumulation in the tank due to bad seals is contributing to the corrosion.

 

[JoeTank]

Is your tank corrosion problem mostly on the tank bottom?

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[CPMech]

Yes and no. The tank bottom was significantly corroded but we also had severe corrosion in the vapour space and actually holed through at several locations in the upper course of the shell.