316 weld failures in ocean cooling water piping due to MIC (microbial induced corrosion) 3

[jxc0yjp]

I have a question about 316 welding.A condenser ball cleaning system was installed at our facility in April 2019, the large bore circulating water piping (96”) was replaced with 2205 and doing well so far but the small bore (2”-14”) was specified by our engineers to be 316L. The welds of the 316 piping are corroding through at an alarming rate due to MIC (microbial induced corrosion). In 2 weeks after installation we saw our first hole, looks like the welds are turning into charcoal. The small bore piping is now all going to be replaced. My question is the leaks will have to be repaired in the mean while, what welding wire compatible with 316L would give the best corrosion resistance to MIC.

 

[EdStainless]

You won't be able to re-weld these. They are too porous to get clean and dry.
Now if you are cutting the welds out you might be able to re-weld the pipe, but I bet that the seam welds in the pipe will look about the same.
If you need to weld then use something overalloyed. I would go ahead and use C276 (or C22, or 686, or 59) weld filler. It is overkill but 317L is not enough of an improvement to really help you.
First, 316L will not stand up to seawater.
Second, 2205 will last longer, but if this is raw water with microbes in it you will eventually loose that also.

You understand that you need clean dry surfaces, and good dry (low dew point) Ar for both weld and back-shield gas. IF the welds have any discoloration other than a very light straw tint they are no good. This applies to both sides of the weld.

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P.E. Metallurgy, Plymouth Tube

 

[Dhurjati Sen]

Dear jxc0yjp,

It seems you are not doing any water treatment. As EdStainless has mentioned, you would loose any exotic material much quicker than their expected life-span. That would really be a loss of capital, resources and a lot of downtime.

The solution is to clean up the system, passivate and start dosing biocides.

Regards.

DHURJATI SEN
Kolkata, India

 

[jxc0yjp]

Thank you for the responses. It is disappointing to hear 2205 is also likely to have problems in the future. Originally the system was specified to be all 2507 then was re-specified to save costs. We do have sodium hypochlorite injection but do to issues it doesn't run constantly.

 

[weldstan]

You will need to replace the 316L, which was wrongly specified for the service. There may well be other sites in the base piping as well where through wall corrosion will occur. It would appear that your flow rate is very low or that the piping was exposed to stagnant seawater during initial installation. I have a number of such instances that led to through wall corrosion of 316L in both seawater and lake water containing approximately 1000 ppm chloride.

 

[EdStainless]

Dhurjati,
Many operations departments don't get it. They chose 2205 in place of 2507 to save money, but the real price is that if hypo injection stops your operation must stop. If you don't then you have consciously chosen to destroy the piping.
I'll wager that 316 was put in because they were in too much of a hurry because someone didn't bother ordering the pipe early enough.

So break the news to them that this system must be superduplex or superaustenitic, no options.
And the hypo system needs to be two completely separate independent systems in order to assure its operation.

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P.E. Metallurgy, Plymouth Tube

 

[Dhurjati Sen]

Dear EdStainless,

First of all, a star from my side for your 2nd post.

Even the hypochlorite injection has long been outdated. We are in the age of dosing bromine continuously and shock dosing biocides (phosphate based) in order to have a stable system.

They need to hire a water treatment agency but before that they need to line up the contract with quarterly evaluation methods using corrosion coupons and strict penalty clauses if the agency fails to meet the specified corrosion rate.

Of course, this forum can only provide directions, the hard work has to be done by the owner.

Regards.

DHURJATI SEN
Kolkata, India

 

[jxc0yjp]

The small bore 316L piping 2”- 14” operates intermittently and is stagnant depending on the section of pipe from 50% of time to only being in-service a few minutes a day depending on the section of pipe. The large bore 96” 2205 is under constant flow 200,000 GPM per pipe (2 loops) and is only stagnant when the system is shut down and drained.

 

[weldstan]

That's the reason the 316L was doomed from the start to a very early demise.

 

[EdStainless]

Agree DS, there are better systems than hypo, but I'll take what I can get for biocyde.
In continuous service with good biocyde 2205 will last a while, as in years.
But intermittent service is much more severe.

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P.E. Metallurgy, Plymouth Tube

 

[MJCronin]

Any chance that plastics or FRP piping would be a solution ???

I worked on a couple of DOE labs where groundwater was collected and HDPE and FRP was the preferred long term fix.

MJCronin
Sr. Process Engineer

 

[Dhurjati Sen]

Dear MJCronin,

The problem is both corrosion and deposition. FRP etc. would rule out corrosion, but the small bore piping would be highly clogged resulting in low flow.

A regular corrosion management system using chemicals is a necessity.

Regards.

DHURJATI SEN
Kolkata, India