304SS Pressure Equipment Susceptability to SCC from External Chlorides 4

[spayette]

What is the likelihood of type 304 stainless steel pressure equipment (pressure vessels, piping, fin fan header boxes, etc.) developing cracks from chlorides depositing on the external surface? The operating temperature may vary from equipment item to equipment item. One source of the chlorides would be plumes from cooling towers. A second source, depending upon equipment location, would be mist generated from a nearby body of ocean water.

 

[EdStainless]

If the equipment is thermal cycled so that the surface will see wet/dry conditions, and the peek surface temp reaches 120F, then the chances for external CSCC are high.

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Still trying to help you stop corrosion.
formerly Trent Tube, now Plymouth Tube
eblessman@plymouth.com
or edstainless@earthlink.net

 

[spayette]

EdStainless,

Thanks very much for taking the time to reply. I appreciate your response.

 

[strider6]

The possibility to have external SCC is a function of different parameters, Temperature, Ambient Exposure, Insulation of the Item ...
I agree with the suggestion of Ed.
When we have an item made in SS with op temp in the range 50-150 °C we use a coating to protect the materials and avoid CSCC.
If you have an insulated item it's a little bit complex 'cause chlorides can concentrate. I suggest you to have a look at the NACE standard
NACE standard RP 0198-98, “The Control of Corrosion Under Thermal Insulation and Fireproofing Materials—A Systems Approach,”

hope this help

S.

http://www.corrosionist.com

 

[spayette]

Strider6,

Thanks for providing input as well. I just read NACE RP0198 and it provided the information that we were seeking.

 

[unclesyd]

From the practical standpoint look at this fairly large site.
On our site approximately 85% of the processing equipment is SS. As our process is mostly exothermic, operates at 120C, most of our SS process equipment and storage tanks are uninsulated. We have had very little problems with external SCC on said equipment. What few problems we've had have been on equipment where water can be trapped and evaporated. Our only SS storage tanks that are insulated are for a product that freezes at 45C.

Aside from being in close proximity to a salt water bay we have a guest facility on site that uses HCl.

http://www.mapquest.com/maps/map.ad...9999999&longitude=-87.253207000000003&dtype=h

 

[spayette]

Unclesyd,

Thanks for your input. Your experience has been similar to mine.

 

[TVP]

unclesyd,

Is the 85% subsegment all Type 304 stainless steel, or are there a number of different alloys that comprise this segment?

 

[unclesyd]

TVP,

The greater part of the SS equipment exposed to the elements is 304L with a small percentage being 316 SS. The 316 SS is mostly insulated.
The 304L is mainly due to HNO3 production and where it is involved in the process. The only other SS we have used exposed to the weather was 2RE10 for a storage tank.
The areas where HNO3 is involved was originally all insulated with Foam Glass due to high chloride level in the calcium silicate insulation at the time. The Foam Glass was a problem from several perspectives, weather covering deterioration and our small acidic leaks reacted with the H2S blowing agent and created a SS dissolving solution. All our SS process storage tanks, above 100C, are now on grillage, integral nozzle pads, and full weld on the wind girders.

All but five of our distillation columns are insulated. The MOC is 304L and 316 SS about equal basis.

 

[metengr]

From the practical standpoint look at this fairly large site..

Nothing beats looking at the practical side of things..

 

[strider6]

There is a good report of the ARMY on Materials Selections in Corrosive Environments. A CSI, Corrosive Severity Index, is defined for various locations around the word for different materials like Steel, copper, zinc...
I think it's a useful source of informations for ambient corrosion severity.

Materials Selection Guide for Army Installations Exposed to Severely Corrosive Environments

http://stinet.dtic.mil/cgi-bin/GetTRDoc?AD=A401129&Location=U2&doc=GetTRDoc.pdf

hope this help

S.

http://www.corrosionist.com