Hi Sandeep,
Service application of Grade 91 steel is for very demanding applications, which involve extremely high design pressure and temperature.Anything wrong associated with fabrication could cause serious harm both to plant and equipments as well as to human beings.
From the description provided below the intended design or application would be the main steam line for a super critical power plant, which would be designed for extremely high pressure and temperature. In as welded condition P-91 alloys would invariably have a hardness of 350BHN or more. Upon PWHT hardness could be reduced to any value between 240-280 HB.Many utilities restrict this hardness values to 275 HB Max .
From the PWHT scenario by induction coils if the temperature difference between OD and ID is more than 80 deg C, then the I.D (wetted surface) would not be properly post weld heat treated and evenly tempered at all. The resultant hardness could be anyone's guess ?? Such a heat treatment condition would definitely not be acceptable to any client
AWS-D-10.10, the universally accepted standard for local PWHT in piping accepts induction heating as one of the methods for local PWHT. As per this code the frequencies coils to be used are typically 60,480 and 9600 HZ. Higher the frequency quicker would be the heating, but the heat would stay more on the skin (OD) and would cause hot spots.Thus a moderate frequency for coils and a slower heating and cooling rate from 600 deg C upwards would be desirable, along with the insulations inside the pipe to minimize heat losses.The heat treating contractor has to demonstrate that soaking temperature of 740- 760 Deg (usually recommended for P-91steel in electric utilities) is achieved both in the O.D and I.D.
As a due diligence , if the PWHT mockup could be sectioned in the lab and hardness gets recorded it would provide far more confidence on the PWHT method with induction heating.
You may find the attached article and the link below as a good resource. In the hyperlink below look at page 50, which shows the significant cross sectional variance of hardness in grade -91 alloys.Also author of the paper(Jonathan.Parker) is a well known authority on P-91 fabrication and life management and is known to us.
I hope the attached information would be of good use to you.
Thanks.
Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist & Consultant
- www.vgb.org/en/event_mqa_pres.html?dfid=23397
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Harish Kannepalli
Sent: Saturday, March 24, 2012 12:04 PM
To: materials-welding@googlegroups.com
Subject: [Norton AntiSpam]Re: [MW:13986] PWHT OF P91 BY INDUCTION HEATING
Dear sandeep,
-- Please try putting coil inside the pipe also. As per code more than 60°C difference is not allowed.
--
2012/3/24 sandeep monody <smv.monody@gmail.com>
Dear experts,In my site we conducted a demonstration of PWHT on SA335 P91 material (OD-450mm X 70mm Thk) as our clients requirement and details as given below.Heating/cooilng rate;-60 deg C,Holding temparature:-760deg C and holding time:-180minutes,Heating band width:-210mm and insulation band width 630mm,Heating method :-Induction heatingDuring pwht we observed a temparature difference on outside and inside of pipe more than 80 deg C.Now problem is that client is not accepting this method and asking for uniform temparature in outside and inside of pipe.How can i control temparature at both sides?Is it possible a uniform temp on both side with induction heating?Please give ur valueble advice in this matter.Sandeep.QC Engr--
To post to this group, send email to materials-welding@googlegroups.com
To unsubscribe from this group, send email to materials-welding+unsubscribe@googlegroups.com
For more options, visit this group's bolg at http://materials-welding.blogspot.com/
The views expressed/exchnaged in this group are members personel views and meant for educational purposes only, Users must take their own decisions w.r.t. applicable code/standard/contract documents.
regards,
Harish.
To post to this group, send email to materials-welding@googlegroups.com
To unsubscribe from this group, send email to materials-welding+unsubscribe@googlegroups.com
For more options, visit this group's bolg at http://materials-welding.blogspot.com/
The views expressed/exchnaged in this group are members personel views and meant for educational purposes only, Users must take their own decisions w.r.t. applicable code/standard/contract documents.
Comments