preheating of austenitic ss

[khatri ankit]

Dear Experts,

i want to know the technical reason that "why preheat is not required
in Austenitic SS"

what will the effects of that?

plz clarify me the reason.

Thanks and regards,

Ankit Khatri

[prem nautiyal]

Hi   Due to following three main reasons Austenitic Stainless Steel(ASS) are not preheated:   1. ASS have a very low Thermal conductivity, thus will retain heat for more time and will lead to more distortion   2. ASS have a very high thermal coefficient of expansion. If preheated will result in more distortion   3. Preheating will result in a wider HAZ and deteriorate the properties.   Regards   Prem S Nautiyal --- On Fri, 7/8/11, khatri ankit <nids01...@gmail.com> wrote:

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[Pieper QSI]

Dear Sir,

Because of the austenitic microstructure there is no risk for hardened
structures which can cause cold cracks. Therefore it's not necessary.
Preheating can also cause problems in case it is applied by way of gas
burner. Poorly adjusted burners can cause carbon pick-up which due to
welding may result in Chromium Carbides and structure therefore will be
sensitive to Intergranular Corrosion. Normally you use preheating of
Austenitic Stainless Steel (up to max. 75 °C) only for large wall thickness
and / or to remove moisture present on the surface before welding.

Met vriendelijke groeten / Best Regards

Herman Pieper

Pieper Quality Support & Inspection
Phone: +31 (0)521 380083
Fax: +31 (0)84 7539225
Cell: +31 (0)6 51691215
www.pieper-qsi.nl

-----Oorspronkelijk bericht-----
Van: material...@googlegroups.com
[mailto:material...@googlegroups.com] Namens khatri ankit
Verzonden: vrijdag 8 juli 2011 10:28
Aan: Materials & Welding
Onderwerp: [MW:11627] preheating of austenitic ss

Dear Experts,

Thanks and regards,

Ankit Khatri

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[Shashank Vagal]

Prem, thanks, In ASS preheating is done only in the early morning hours to drive away moisture or during damp weather. It has nothing to do with general preheating purpose for better weld making so to say. --- On Fri, 8/7/11, prem nautiyal <prem_na...@yahoo.com> wrote:

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[Tarek Yehia]

Dear Khatri,

In addition to the reasons mentioned below u have to take care of Sensitization phenomenon as following:

One of the common problems found when welding the austenitic grades is referred to as carbide precipitation, or sensitization. When heated to the welding temperatures, a portion of the base metal reaches temperatures in the 8OO0-1600”F range, and within this temperature range, the chromium and carbon present in the metal combine to form chromium carbides. The most severe temperature for this formation is about 1250°F, and this temperature is passed through twice on each welding operation cycle, once on heating to weld and again on cooling to room temperature. 

These chromium carbides typically are found along the grain boundaries of the structure. The result of their formation is the reduction of the chromium content within the grain itself adjacent to the grain boundary, called chromium depletion, resulting in reducing the chromium content below that required for resisting corrosion. The final result of this chromium depletion of the grain is a reduced corrosion resistance of the grain itself due to its reduced chromium content. In certain corrosion environments, the edges of the grains corrode at a high rate, and is called intergranular corrosion attack, or IGA.

and to prevent sensitization of austenitic SS during welding can being by several methods:

1-Reheating the complete structure by 1950-2000 F. but  may distortion will happen.. followed by rapedly quenching in water to avoid reformation of chromium carbides.

2-Addition of stabilizers to the base and filler metals such as titanium or niobium in ammounts equal to 8 or 10 times the carbon content.

3-Reduction of the carbon content in the base and filler metals, such as low carbon austenitic SS.

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--

Best regards,
 
Tarek Yehia
QA/QC Inspection Engineer 

AWS-CWI (Cert.# 11042201)
BEMCO Steel Industries, Jeddah, Saudi Arabia
E-mail: t.yeh...@gmail.com
            

Cell. #+966546154198

          +966567726160

[mohd shah]

Dear Expert, The vendor are fabricating Glycol Reflux Condenser. They want to change coil material SA790 UNS31803 to SS 316. Is there any problem if they change the material? If yes why? Thanks and Best Regards, Syam.

[pgoswami]

Hi Syam,

 

What's your project requirement?? What're the design and the operating conditions and the process fluids involved.

 

Typically if the process fluid involves, CO2, H2S then 316L could be an option also for such condensers, subject to the fact it is acceptable by the project design specications. However if the service environment involves chlorides then Duplex SA 790 UNS31803 would certainly be a better material.

 

Advice would be to get the acceptance from the client.

 

Below is the generic warning from API spec for such units.

 

Thanks.

 

Pradip Goswami,P.Eng.IWE

Welding & Metallurgical Specialist & Consultant

Ontario,Canada.

Email-pgoswami@sympatico.ca,

pgos...@quickclic.net

 

API SPECIFICATION 12GDU- Specification for Glycol-Type Gas Dehydration Units

Pressure retaining components exposed to corrosive gases such as carbon dioxide and hydrogen sulfide shall meet the requirements as specified by the purchaser