Corrosion rate on CS from undrained hydrotest water 2

[JasonLouie]

Does anyone know of a ballpark figure for a corrosion rate on CS if the hydrotest water is left stagnant for a few months?

I believe potable water was used without corrosion inhibitor, oxygen scavenger, or biocide. The heat exchanger was fabricated overseas, and when it was received and opened up about 1 gallon of water came out. I have tried doing an internet search but the only problem I found was MIC in stainless steel systems. In carbon steel systems, would the corrosion only amount to a few mils?

Thanks. I appreciate any help anyone can provide.

 

[gr2vessels]

Jason,
A high corrosion rate for carbon steel in corrosive environment is perhaps 0.2 mm/year. If you allow say 0.1 mm/year corrosion rate, you could expect from that test water a localised damage / metal loss of 0.05 mm.
This is equivalent of a thin layer of oxide...
However, depending on the quality of internal surface, if the mill scale has not been removed, you could expect some advanced corrosion in crevices located at the bottom of your vessel. Can you enter the vessel? I imagine the vessel was designed to a PV code, hence inspection openings should exist, for your viewing convenience. You could also do some low energy cleaning (even carefull grinding) of the affected internal surface and then do a UT thickness test, to evaluate the metal loss.
Overall, I don't expect your vessel to be severely damaged, but I would back charge the cleaning costs to your supplier for that shonky job.
I also assume that your purchasing specification allowed for the final inspection prior to delivery and the ITP was signed off by your inspector at the end of drying operation post hydrotest, in accordance with your specification. Is that correct?
cheers,
gr2vessels

 

[strider6]

Corrosion rate of carbon Steel in freshwater is mostly a function of oxygen concentration and temperature.
As a reference from the NACE Corrosion Engineers Reference Book p156, the Corrosion of Steel in aerated water is approx 10 mpy (0.25 mm/y) @ 25 °C with 6 ppm of O2 (air saturation) and pH 7. It could change if your system is closed or open but i think that 0.25 mm/y could be a good figure if you want to calculate approx the Corrosion of your equipment.

hope this help

S.

http://www.corrosionist.com

 

[JasonLouie]

Thank you gr2vessels and strider6 for your replies. From your responses, it looks like not a lot of corrosion is expected. I have recommended going into the exchanger and doing UT and pit depth measurements.

Thank you again for taking the time to respond!

 

[laner5]

It has been well documented that hydrotesting using nontreated water, and allowing some water to remain after testing can lead to MIC. MIC can significantly increase rates of attack for carbon steels, among other metals. Check out the following article for informatin on MIC.

http://ammtiac.alionscience.com/pdf/AMPQ9_1.pdf

 

[ash9144]

Also you may want to dry the exchanger before putting in service, depending on service. Even trace moisture could lead to process or corrosion problems.

 

[robsalv]

On the face of it, I'd expect some rust blooming or possibly some pitting, but no gross corrosion. Even if MIC were to occur, I doubt it'd have had enough time to severely impact on the pressure containing envelope.

The fact that you're expressing doubt means you should get into the item and conduct a visual.

My guess is that you'll allay your concerns very rapidly.



My assumption is that this hX is a garden variety shell and tube, floating head, removable bundle type hX. The water was on the shell side yes? In that case, full dismantling will be required for access and hopefully this will be a redundant comment; don't reuse the gaskets!


Cheers

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"Life! No one get's out of it alive."
"The trick is to grow up without growing old..."

 

[stanweld]

We normallly see hydrotest water in HRSG boiler components; corrosion has been minimal. I have seen a great number of carbon steel valves purchased on one project that had some undrained hydrotest water standing for a number of months and up to 1/16" corrosion pitting was observed. Crevise corrosion at valve seats was also observed, which required repair (megabucks) to provide leak tightness.

 

[gr2vessels]

It is scary to see the break down of elementary fabrication requirements in the "pressure" industry.
Under no circumstances should a pressure equipment (valve, pump, vessel, exchanger) be delivered without evidence of inspector's signature on the ITP sheet for drying after hydrotest, full and complete preparation for shipment, including corrosion inhibitor sprays, desiccant bags, openings cover and N2 blanketting if required. All the above should be part of any decent purchase order. If the supplier is in breech of purchasing terms, then he is liable for the damages, including full replacement.
On the other hand, if you buy cheap, you get cheap. Why would anyone expect un-rusted equipment if they are not prepared to pay for drying?
I assume if anyone would care for his investment, would specify all the required protection on the purchasing documentation.
gr2vessels

 

[robsalv]

Excellent point GR2VESSEL. It reminded me that shipment preparation requirements are a standard part of our purchase specs.

It should be a standard practice for a quality workshop too.

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"Life! No one get's out of it alive."
"The trick is to grow up without growing old..."