Re: CUI Part 2

Coming from the chemical processing industry, I have seen some effects of SCC. One of the best ways to ward this off is to use a closed cell insulation - such as foamglas. We have found this material to perform very well even at high temperatures 600 degree plus. The hi-temp foam glass is expensive but in some situations is worth the cost. The impervious nature of foamglas makes it ideal. You do got to make sure to seal all the joints very well with cloride free mastic. Another approach is to apply a coating on the S/S such as: silicone type epoxy amine paint.

• Original Message ----- From: SARE, RALPH H. <SARERH@YANPET.SABIC.com> To: <PipingDesign@yahoogroups.com> Sent: Monday, June 25, 2001 4:51 AM Subject: [PipingDesign] CUI Part 2

> The following was taken from ASTM STP 880 by Pollock and Barnhart.
>
>
> Very serious corrosion problems can occur to plant equipment and piping
> components that are thermally insulated if the insulation becomes wet.
> On carbon steels, the corrosion is usually of genral or pitting type. On
> stainless steels, the corrosiion is almost always SCC.. The isnualtion
> usually hides the corrosidng metal and the problem can go undetedcted for
> years u ntil metal failure occurs.
>
> To complicate the problem, the degree of corrosion when insulation gets
wet
> is dependendt on the type of insulation. Inspection for the problem is
also
> difficult Determning the the metal has corroded under the insualtion is
not
> widely available.
>
> The STP also touches on the subject related to SCC and the effect of
service
> temp. Here are some.
>
> Service TEmp is important in CUI for 2 reasons
> 1. higher temp allows water to be present againts the steel for less time
> 2. higher temp make the water more corrosive, and paints and caulking fail
> sooner.
> generally, equipment that operates below freezing is protected againts
> corrosion. Howveer, attachment to the equipment which are not as cold are
> vulnerable in the transiiton out of the vapor barririer into warm humid
air.
> Cororsion associated with equipment below freezing temp is corrosion
outside
> of, not under insulation
>
> Corrosion under warm inuslation is equally difficult to manage due to dry
> out of entering water. Summary of the study showed that:
> 1. temp range of 60 and 80C appears to account for the gretaest amount of
> damage.
> 2. on very warm equipment even with small weatherporffoing defects,
> coorosion tends to be at the oint of entry of water.
> 3. annual corrosion rate amy exceed 1.5 mm per year.
>
> Guys, the problem is real and will cost a lot of dollars to detect and
> repair. The report further stated that there are seven contributing
factors
> to CUI. Top on the list is, now hear this, "equipment design".
>
>
>
>
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Received on Tue Jun 26 12:51:00 2001