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HomeHomeDiscussionsDiscussionsMaterial Select...Material Select...PWHT RequirmentPWHT Requirment
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4/25/2010 10:00 PM
 
Dear EXperts I have a query regarding PWHT requirement. PWHT requirment of pipe (Based on thickness) 19mm plate : 38 mm Why there is a different in PWHT requirement based on thickness for pipe and plate ? Regards
 
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4/25/2010 10:00 PM
 
Inspector 1978 Your question if it is related to power plant requirements in variations in code limits for PWHT - yes different codes allow variations in limits for PWHT from thickness and also materials grades from P 1 to P 3. ASA B 31.1 Power Piping code gives exemptions based on hardenability criteria for materials (See Table 132 in B 31.1 2001 edition) ASA B 31.3 code for Process Piping requires PWHT for P1 to P 3 grade materials if thickness > 0.75". B 31.3 also specifies the minimum T.S criteria for PWHT . See Table 333.1.1- B 31.3 code. As additional criteria for P 3 material this code specifies a limit of 225 BHN for PWHT. Pressure vessel code exemptions from PWHT are also based (in part) on the hardenability of the materials. P Nos. (established by ASME Section IX for the general purpose of weldability) are used, although in this case they are not necessarily good criteria. A review of the strengths of the materials in Section IX reveals that P No. 1 materials may have minimum specification tensile strengths within the range of 45 to 95 ksi. Carbon equivalence is a better and more reliable measure of the hardenability of materials than the P Nos. Preheat is also a consideration when determining the resultant hardness of weldments. As the temperature of the material prior to welding increases, the cooling rate (and therefore the hardness) will decrease. The Code exemptions for thicker materials usually require a minimum preheat. Generally variation in limits from Piping vs Pressure Vessel Plate PWHT is based on lower hardenability, particular material grade, Tensile Strength, Pre heat operations before welding and choice of heat input from welding processes (variations from TIG/SMAW/Submerged Arc etc). Hope this helps C.V.Srinivasan Nishi Engineers Pvt Ltd India April 27, 2010 E-mail: nishi@vsnl.com >Dear EXperts > >I have a query regarding PWHT requirement. > >PWHT requirment of pipe (Based on thickness) 19mm > plate : 38 mm > >Why there is a different in PWHT requirement based on >thickness for pipe and plate ? > >Regards
 
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4/26/2010 10:00 PM
 
[updated:LAST EDITED ON Apr-27-10 AT 02:32 AM (CDT)]The difference in PWHT requirements for pressure piping and pressure vessels depends upon the acceptable hardenability. For the case of pressure vessels, resulting hardenability of materials after welding is acceptable up to 38 mm and in pressure piping code ASME B31.3, it is advisable to post weld heat treat any weld above 20 mm so that the resulting residual stress and hardness should come within the acceptable range. Regards, Ashfaq Anwer http://forums.thepetrostreet.com >Dear EXperts > >I have a query regarding PWHT requirement. > >PWHT requirment of pipe (Based on thickness) 19mm > plate : 38 mm > >Why there is a different in PWHT requirement based on >thickness for pipe and plate ? > >Regards
 
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4/28/2010 10:00 PM
 
Thank very much Mr Srinivasan and Mr Ashfaq for your replies Regards
 
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