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[MW:12885] RE: 12866] Preheat maintenance for the Welds b/w P15E & P5A materials

By Materials & Welding
Hello Srinivasu,
 
Post Weld “Bake-Out or Hydrogen Bake Out is  critical  especially for heavy sections or where flux-type processes are used for welding P-91 steel. This involves maintaining the preheat/interpass window for an extended period of time subsequent to interruption or completion of the weld in order to facilitate hydrogen diffusion from the weldment.
 
The default welding and PWHT cycle for P-91 steel is as shown as below. For a weld between P-91 and P22 alloy, involving with P-91 consumable or P22(9018-B3) welding consumable unless the default welding and PWHT cycle is followed the welds would always be prone to HIC. With P-91 consumables the chances would be more.
 
Hence in cases of interruptions or delayed PWHT some form of post weld bake out or hydrogen bake out would always be advisable. The extent of bake-out time may be varied as a function of  joint thickness, welding consumable used  and welding  process followed. The nominal industry standards are  as  stated  below:-
  • 30-60 minutes min @ 315 Deg C(600 deg F) up to a thickness of 3/4 inch
  • 60-120 minutes @ 315 Deg C(600 deg F)  up to 3/4 inch  to 2 inch
  • typically 4 hrs @ 315 Deg C(600 deg F) for  thickness beyond  2 inch
If the the weld process is GTAW or GMAW , then bake out may be minimized or eliminated, subject to the welding conditions and construction code requirements.
 
Thanks.
 
 
Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist & Consultant
Ontario,Canada.
Email-pgoswami@sympatico.ca,
 

From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of srinivasu
Sent: Friday, November 04, 2011 8:40 AM
To: materials-welding@googlegroups.com
Subject: [MW:12866] Preheat maintanace for the Welds b/w P15E & P5A materials

Dear Experts,
Is it required Hydrogen Baking / Post heating for the welds between grade P91 & grade P22?
 
Please clarify me.
What is the purpose of Hydrogen Baking for Grade 91 materials?
 
 
With Regards
 
 
Srinivasu V
Welding Engineer

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