Coolant system experiencing heavy internal and external corrosion 1

[myname_earl]

Currently, we are evaluating a historic system in the plant due to changes in degradation rates and evidence we're seeing.

Knowledge as of today:
1. Our coolant is 74% Water, 20% Methanol, and 6% Ethylene Glycol.
2. The system is made of A53 Gr. B and A106 Gr. B carbon steel piping.
3. Maintenance has been noticing metallic scaling/flaking being picked up in strainers and exchangers when opened. (When I saw it, it was a magnetic "goop" with solids in it.)
4. Piping and Equipment are insulated, but not painted... Known CUI targets with yearly evaluation as the pipe sweats profusely.


The latest find was a dripping leak on a pipe shoe that was welded to the pipe (also has a tie point weld in that same HAZ). This has evidence of CUI but certainly looks like there is an aggressive internal-to-external mechanism in play as well.

My question is what could be causing internal damage as aggressive as CUI in this service? SCC from the Methanol? Glycol becoming acidic? I don't have samples collected yet, but will once we replace the spool.
Fixes for my potential problem(s)?

Mechanical Integrity Specialist (Year 1)

 

[TugboatEng]

My guess would be that it's the water causing the corrosion. You need to treat the water with corrosion inhibitors.

You will also need to pickle any corroded piping. Film forming corrosion inhibitors can't protect metal under corrosion deposits.

 

[Hajiwaji]

As far as I know, corrosion and scale inhibitors dosing are required for closed loop cooling water system. Galvanized A53 Gr.B is commonly used too. For CUI, external coating is important and it is one of the mitigation of CUI in API 571.

 

[myname_earl]

We're having the system tested now to verify we're on spec. Any new fabrication is coated or painted, we're just running into 60+ year old equipment and pipe that gives us trouble. unfortunately, the leak is under a welded pipe shoe on the main return header so isolation isn't possible and temporary repairs are extremely limited.

Mechanical Integrity Specialist (Year 1)

 

[TugboatEng]

Corrosion does it's damage in much less than. 60+ years. Do investigate any changes that may have occurred to accelerate corrosion of you're suddenly having problems now. I will restate: water is corrosive to steel. If you have water in your system it must be treated with a corrosion inhibitor.

 

[myname_earl]

Thats where my investigation is alluding to. We changed from brine or propylene glycol to a methanol/ ethylene glycol mixture. That was ~20 years ago which still seems way too long.