Material for a coil (serpentine) to heat caustic soda.
Material for a coil (serpentine) to heat caustic soda.
(OP)
Hi.
It is the first time I am writing a question.
I live in South Brazil and I am currently working on a petrochemical Plant as a Maintenance Engineer.
We are having serious problems with a storage tank for caustic soda. In the winter times, temperatures usually drop below zero. So, in the bottom the tank there is a coil with steam at 220ºC and 4,5 kgf/cm² to heat up the caustic soda. We had tried few materials for the coil, but always end up having SCC.
Anyone have any suggestion, because in brazil, we are the only state that have such problem with incrustation of caustic soda.
Thanks
It is the first time I am writing a question.
I live in South Brazil and I am currently working on a petrochemical Plant as a Maintenance Engineer.
We are having serious problems with a storage tank for caustic soda. In the winter times, temperatures usually drop below zero. So, in the bottom the tank there is a coil with steam at 220ºC and 4,5 kgf/cm² to heat up the caustic soda. We had tried few materials for the coil, but always end up having SCC.
Anyone have any suggestion, because in brazil, we are the only state that have such problem with incrustation of caustic soda.
Thanks





RE: Material for a coil (serpentine) to heat caustic soda.
You said you have tried several materials, the specific materials you have tried might get you better suggestions.
What concentration of caustic are you storing? If you are having a freezing issue I'm suspecting it's close to 50 wt%
Dow chemical puts out a caustic soda handbook which you can find with Google. For heating of caustic tanks, they suggest a bayonet heater with suggesting materials being a high nickel alloy.
RE: Material for a coil (serpentine) to heat caustic soda.
You are right, the concentration is 50%. The materials we had used are all stainless steel. The original project is from final 70's, and the demand of caustic soda increased in the last few years.
I will give a look in the material you suggested.
thanks
RE: Material for a coil (serpentine) to heat caustic soda.
RE: Material for a coil (serpentine) to heat caustic soda.
You need a high nickel alloy or perhaps a super-duplex stainless steel might work.
You also need lower temperature/pressure steam. You want to warm the stuff, not to locally boil it!
RE: Material for a coil (serpentine) to heat caustic soda.
We took 250 psig steam, reduced it to about 15 psig through a regulator and then further reduced it through a control valve. The design steam pressure used to size the heater was 5 psig, the 50% caustic was to be maintained at 90F.
RE: Material for a coil (serpentine) to heat caustic soda.
A coil with high nickel alloy will probally solve our problem.
RE: Material for a coil (serpentine) to heat caustic soda.
Even with inconel construction, one of our senior engineers was concerned with corrosion, that's why we dropped the steam pressure down to 5 psig along with the saturation temperature.
RE: Material for a coil (serpentine) to heat caustic soda.
It is the best material to mitigate the effects of caustic SCC.
However, it is very expensive and you may not be able to find it in a tubular shape.
Inconel is the next best choice, if you can find it in the shape you desire.