Monday, September 6, 2010

[MW:6878] MW:6877] Chloride Content

Prafulla,

Both 316 and 316L would work at the said 25 ppm chloride content level, provided the operating temperature does not exceed typically 20 deg C. Given a choice 316/316L (dual certified) grade should be the ideal material, otherwise, 316L shall  be used for piping. Welding consumable shall be of 316L grade  for all cases.

Following is an extract from :-Materials Selection for Refineries and Associated Facilities(A NACE publication)- by R A WHITE, Ex Materials and Corrosion Group Manager, Materials Quality Services Department,Bechtel Corporation

For materials selection, cooling water is normally categorized as either freshwater or salt water.Austenitic SS's are  used in freshwater. For freshwater application, to avoid pitting, type 304 (UNS S30400) SS is normally limited to services in which the chloride ion concentration is at a maximum of 100 ppm, and type 316 SS is limited to services in which the chloride ion is a maximum of 500 ppm.( The designer may have to apply his/her conservatism to this number depending on plant design and operating conditions). 

The relative pitting and crevice corrosion resistance of SS alloys can be approximated by the following equation:-PRE = %Cr + 3.3%M0 + 16%N.

Theoretically, pitting will not occur (regardless of the chloride ion concentration) if the temperature in degrees Celsius is limited to 5°C plus 7 times the molybdenum content. Thus, for a 2% molybdenum alloy (e.g.,  316 SS), the limit would be typically : 19deg C

When austenitic SS's are required, low carbon or stabilized grades should be  used to avoid intergranular corrosion.

For salt water application:- theoretically, austenitic SS's can be used in salt water if the velocity exceeds 3 ft/s (0.9 m/s). But in stagnated water different scenario may arise.Experience has shown that stagnant conditions will always occur in a salt water system resulting in rapid pitting (average penetration rates are on the order of 70 mpy ). Typically for salt water application, the  new super SS's that are high in molybdenum and resistant to seawater attack  and duplex stainless steels are being used more frequently in cases in which seawater attacks from both side

I hope this clarifies your query.

Thanks.

Pradip Goswami,P.Eng.
Welding & Metallurgical Engineer/Specialist
Ontario Power Generation Inc.
Email-pgoswami@sympatico.ca,
 


From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Praphulla Phirke
Sent: Sunday, September 05, 2010 12:46 PM
To: materials-welding@googlegroups.com; 'Kisan Gamane'
Subject: RE: [MW:6877] Chloride Content

Hi Kisan

Thanks for your help but I want to select either SS 316 or SS 316 L… So can you guide me up to what limit SS 316 is OK and beyond which its not?

 

Thanks & Regards

Praphulla

praphulla.dp@gmail.com

 

From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Kisan Gamane
Sent: Sunday, September 05, 2010 5:41 PM
To: materials-welding@googlegroups.com
Subject: Re: [MW:6873] Chloride Content

 

Dear Praphulla

I think material u can used 316 or 316 L. But a cooling water which will enter inside the plumblene ie. to be cloride contain up to 25 ppm.

On Sat, Sep 4, 2010 at 11:32 PM, Praphulla Phirke <praphulla.dp@gmail.com> wrote:

Dear All, Can someone guide me where I can get the details to select the materials according to chloride content in water?

 

Recent in our project customer has asked us to choose the material as per the chloride content..whether to go for SS 316 or 316L.

 What is the limit for SS 316  & 316 L considering the chloride content in the cooling water?

 

 

Thanks & Regards

Praphulla

praphulla.dp@gmail.com

 

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Kisan Gamane

 

सर्वे भवन्तु सुखिनः, सर्वे सन्तु  निरामयः
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