Multiple service piping problems

[StoneCold]

We have a severe corrosion problem with our multiple use piping. Whe have numerous batch reactors, each batch reactor has a utility manifold which allows steam, condensate, cooling water and refrigerated methanol in and out of the jackets of the reactors. Obviously what fluid is being used depends on the temperature required but we switch back and forth on a regular basis.

The piping manifoldes are made up of 1-1/2" sch 40 A106 grade B pipe. The pipes will rust through after about two years of service. The corrosion is much worse in these multiple use pipes than anywhere else in the utility system. We add corrosion inhibitors to our steam and to our cooling water but it does not seem to be having any affect. We recently changed water chemical companies to Nalco in hopes that their experience would help us out but we don't seem to be getting any better.

The main cooling water system is 3" copper piping that transitions to carbon steel at the branches. We do not see severe corrosion near the transitions so I don't think that we are having a galvonic corrosion problem but I could be very wrong.

The steam and condensate piping is all carbon steel.(A106 grade B).

The reactors are a mix of stainless and glass lined carbon steel. The jackets of the carbon steel reactors are not faring very well either. Large amounts of iron scale can be seen when you drain out a jacket.

What would you suggest?

 

[metengr]

Based on your information, the use of dissimilar materials is probably the root cause of the corrosion problem. The carbon steel is behaving like an anode (corroding), while the 3" copper pipe behaves as the cathode. Also, from your description, it would appear that the ratio of anode/cathode surface area is small, which is not desirable.

Are the carbon steel manifolds joined to copper piping using bolted flanges? If so, you might attempt to use Teflon or some other nonmetallic material to prevent direct contact of the carbon steel manifold piping with the copper pipe. This way you have no direct contact to establish an anode and cathode between materials.

 

[StoneCold]

metengr
Unfortunately the copper is joined to the carbon steel using sweat x threaded fittings. Would grounding the copper pipe at the transitions help at all? What about putting zinc rods in strainer baskets at the transitions?
I need to do something as the corrosion is killing us, but I hate to tear out all the copper.

Thanks
StoneCold

 

[metengr]

Mg or Zn anodes that are threaded directly into the carbon steel pipe manifolds and exposed to the process fluids would be my second choice. Unfortunately, you will need to monitor these anodes because over time they will corrode and once they are gone, you are back to your corrosion problem.

 

[PVRV]

Please provide more details' specifically:

1. Corrosion features; you mentioned rust any other
specifics??

2. Batch reactors; how often is the stream online.

3. Any sampling in progress by Nalco ? what is checked if
any?

4. Why is refrigerated methanol being used?

At any rate:

I would sample the stream you may find intersting results with water & regrigerated methanol


Cheers