How long to passivate 316L pipe? 1

[FrankIndy]

Troops,

This request comes from the field. I'm the Program Director for a mid west (U.S.) firm. We're validating the new SS tanks, piping and control system for a client.

The client will be producing a nutritional ingredient for baby formula. Very high profile.

Presently we have an estimate to passivate our SS pipe at around 3 days. This seems very excessive and also will destroy our Sumdo valves (sp) throughout the system. This alone will be a 2-3 month process and an excessive expense.

What is a more realistic time frame for passivating our 316L pipe. The make up of the pipe is: 136L primary and 304 secondary.

Any thoughts on this?

 

[unclesyd]

Give a little more details on how you are going to passivate and what chemicals you will be using.

Is this pickling/cleaning and passivating or just passivating?

 

[mcguire]

The "passivation" is to correct which correct what condition? How have the welds been treated? What was the material's base sulfur level?
The critical pitting temperature of 316L welds is typically 15C lower than that of the base metal if the material has the roughly 0.010% sulfur desired for weldability. This measure of corrosion resistance, the CPT, probably best measures the inertness of the system to the nutritional ingredient. This resistance can be brought back to the level of the parent metal by electropolishing. I have not seen research data published on the effectiveness of other treatments, such as passivation. EdStainless has done a lot of tubing and pipe pickling and he may have the answer.
Isn't this the kind of application where electropolishing is typically used?

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[EdStainless]

My hunch is that the system is built with mechanically polished tubing. This is typical for food/bev/dairy applications. Not the best finish for cleanbility, but not too bad.
The process that I often see is for the system to first be flushed with a cleaner. TSP or some similar alkaline cleaner is used, often with some added surfactants.
The passisvation then does two things. First you are removing any stray iron in the surface of the material from handling. Second you do make sure that there is a good passive layer formed. My favorite passivation is CitriSurf. It is good, quick and easy to dispose of.

I'll make a few more comments, since I have the floor. I presume that the product does not containe ANY chlorides. If so you may be in for some issues.
Does the system have CIP? What chemicals will be used for this? Some of these are very agressive.

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Corrosion never sleeps, but it can be managed.

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