The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Passivation of ss pipes for gelatine production

I am new in this company and this industry. My previous employment was in the pharmaceutical and healthcare industries were we use to passivate all our stainless steel with both citric and nitric solutions. In the gelatine industry we have a lot of problems with contaimation in our s/s lines. we we dismantle them there are signs of pitting, even on wetted 316L diaghrapm fittings for our instrumentation. I am told this happens a lot and the pipe work is changed. Could passivation of this pipe work help with the corrosion problem? the gelatine is at about 140 °C with a ph of around 5 -5.5. Any help or suggestionss would be greatly appreciated.

Bernie Steele
Produce gelatine from cow hide - Beaudesert, Queensland, Australia
2004

---

2004

It is simply that the material you use does not have adequate inherent corrosion resistance for the service conditions you impose.

For some years I have been a regular reader of, and occasional contributor to, this forum. It has become very clear to me that a regrettably large number of people choose material that has insufficient corrosion resistance for their application and then spend vast amounts of time and money trying to modify the surface characteristics to make it adequate, or spend vast amounts of time and money repeatedly cleaning up the damaged surface.

Corrosion resistances of the many grades of stainless in many environments are well documented, and it's not difficult to select a material suitable for a given application.

It may be that you are stuck in the thinking of 30 years ago, when 316 or 316L was the latest wonder stainless. It was then, but among the stainlesses routinely available today, it's a pretty ordinary material.

You should at least be considering the duplex stainlesses such as 2205 or 2507, and the super-austenitics.

Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.

---

If the steel is passivated after manufacture it will definitely give you better corrosion resistance. If you have any chlorides in the gelatine at all you will not survive with 316L at these temperatures, etc. If you passivate it you will get the best resistance you can. If this does not do it you need to go to a better alloy.

Lee Kremer
Stellar Solutions, Inc.

McHenry, Illinois

2004