HEAT EXCHANGER CONSTRUCTION

[Vishwas Keskar Welding Manager WELDING]

Dear Experts 

One of HEX involves  following MOCs -

HEX tubes - SA 789 TYP 32205 

Tubesheet -SA 266 CL 2 CS - Tube sheet IS cladded with TYP S32205  overlay.

Shell side - CS -SA 516 GR 70 - 75mm thk 

Channel side - CS- SA 516 GR 70 - 75 mm thk 

PWHT is required for  Tube sheet to Shell welding and Tube sheet to Channel welding. These are butt welds with CS Weld metal .

PWHT is not required for  Tube sheet to HEX Tube  welding due to DSS tube to DSS cladding.

Pl advice for the  care that shall be taken during PWHT  of Tube sheet to Shell welding and Tube sheet to Channel welding.

Thanks and regards

Vishwas - IWE

International Welding Engineer

[Raghuram Bathula]

Does the tube sheet have a lip? Please share a sketch at the weld location? practically it is difficult to avoid heat exposure to duplex clad? you need to change clad material, check with your process metallurgist

[Prabhu kumar Loganathan]

Hi,
In general, DSS weld overlay is not recommended in CS due to cracking and other weldability issues. Moreover, Tube sheet forging with heavy weld overlay requires stress relieving too. 
However, stress relieving is not recommended for DSS, Hence in my opinion DSS weld overlay on TS to be replaced with Alloy 625 weld overlay wherein all these these issues related to weldability & PWHT will be solved.
Regards,
Prabhu.

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[Vishwas Keskar Welding Manager WELDING]

Sir ji 

I too concerned  about DSS cladding including   DSS HEX tubes .

Is it ?

Vishwas 

[james gerald]

Nice to see you back Prabhu.

If service restrictions are only due to chloride concentration then we try the SASS like 904L, 254 SMO & 654 SMO/

Your views

Thanks & Regards

J.Gerald Jayakumar

https://groups.google.com/d/msgid/materials-welding/1665030135.S.10013.29756.f5-224-128.1665063217.15589%40webmail.rediffmail.com

.

[Prabhu kumar Loganathan]

Hello Gerald,

Yes, below specified Super ASS is an alternate to DSS due to high Cl environment, however market availability is very less which leads to long delivery time and hence suggested to go for Inconel 825 or 625, again Alloy 825 weld deposition is having cracking issues >5mm thick which is not recommended.

Regards,
L. Prabhu kumar

https://groups.google.com/d/msgid/materials-welding/1665030135.S.10013.29756.f...@webmail.rediffmail.com

.

 

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[james gerald]

Thanks Prabhu.

Is SCC in chloride environment  a problem with SASS & 625.

Moreover SASS are available mostly in European market.

Thanks & Regards

J.Gerald Jayakumar

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[Vishwas Keskar Welding Manager WELDING]

Pl. note that all the HEX Tubes are also of DSS TYP S32205 .

  So  the concerned is for these DSS tubes also.

[james gerald]

sorry for being out of track.

I believe the welding between Tube sheet and Shell/Channel via a LIP provided in the TS forging where you can excercise a control.

Ensure DSS is not exposed to temperature greater than 400 degC to avoid 475 embrittlement (alpha prime intermetallic)

Thanks & Regards

J.Gerald Jayakumar

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[Prabhu kumar Loganathan]

Hi Vishwas,

Yes, Tube also to be changed to Alloy 825 and TS to be overlay with Alloy 625 (ENiCrMo-3) with PWHT.

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[james gerald]

Just some info on 475degC embrittlement.

Thanks & Regards

J.Gerald Jayakumar

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[Vishwas Keskar Welding Manager WELDING]

Thanks  a lot !!

What is recommended distance of Lip  that is required  for  avoiding the exposure of heat ?

[james gerald]

Normally I have seen LIP provided for Nozzle to shell welding to obtain 100% RT. But one of our vendor sometime back has proposed and so you discuss with your Design Engineer.

In AWS Handbook, vol.1,chapter 3 Heat Flow in welding have distance vs Peak Temperature calculation (Snap shot provided below) based on the same calculate for Tp of 400degC in DSS.

Thanks & Regards

J.Gerald Jayakumar

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[Vishwas Keskar Welding Manager WELDING]

Thanks 

Pl help to inform the  name of the book /literature from where the below  snap  is taken

Thanks and regards

Vishwas 

[james gerald]

API 571 Damage Mechanisms

Thanks & Regards

J.Gerald Jayakumar

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[Vishwas Keskar Welding Manager WELDING]

Can anybody help for Lip Length that is to be  planned in the tube sheet so that during PWHT of Tube sheet to Channel and Tube sheet to Shell , the DSS TYP 32205 weld over lay and  DSS TYP 32205 Tubes  will not get exposed to temperature of  400 Deg C or more .?

Thanks 

Vishwas - IWE 

International Welding Engineer

[anthony chundal]

Hi,

You have provide lip of 40mm,

Make sure you pull the tubes back while heat treatment, 

Kind Regards

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[Vishwas Keskar Welding Manager WELDING]

One of thought is Nitrogen Purging  in the HEX tubes during PWHT of Shell  to Tube sheet , Tube sheet  to  Channel joints 

Can any one throw light on Nitrogen purging system and its effectiveness ?How it is done / system in market ?

This will keep DSS HEX tubes cool (< 300 Deg C) and serve the purpose 

Thanks and regards

Vishwas - IWE

International Welding Engineer 

[Kannayeram Gnanapandithan]

better argon. nitrogen will react with material beyond 450 degcel

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