Hi
# Wilfred kojo
Heating the base metal to a specific desired temperature, called the preheat temperature, prior to welding & interpass temperature applies after the first pass is made.
Preheat temperature affects the properties of only the first weld pass; interpass temperature affects the properties of all subsequent passes.
Here the discussion about ONLY "Preheat temperature" for the first weld pass... forgot about interpass temperature.
Client question is simple, Preheat 30 Deg C in PQR and 110 Deg C in WPS ? i.e. increase in 80 Deg C, can u explain the basis for this and why it is not accepted by his client?
In my opinion,
whatever you recorded during qualification is qualified as min preheat temperature and Increase in Preheat temperature more than 56°C is supplementary essential variable requirements for PQR ( I mean properties of the first weld pass only, not sub sequent passes)
Hi Prasad
During qualification did your PQR taken care the minimum preheat requirement based on material category and thickness as per table 3.3 of AWS D1.1 ?
Because prequalified Minimum Preheat temperature is 65 Deg C for your PQR thickness (30mm) but u indicate preheat temperature as 30 Deg C, Why ?
Why don't get interpretation from aws which will be very useful for all members. Why this code is different in somany aspects on essential variable from ASME, for example, position is essential for PQR, Product form etc.--On Thu, 10 May 2018 5:29 pm 'wilfred kojo' via Materials & Welding, <materials-welding@googlegroups.com> wrote:--Hi,It is true that inter pass temperature is measured after the pass (just before the commencement of subsequent pass) but why should it be controlled?It's not measured because of previous pass but subsequent pass because it serves as preheat for subsequent pass which also control the cooling rate and mechanical properties.On Thursday, 10 May 2018 10:36:16 WAT, 'wilfred kojo' via Materials & Welding <materials-welding@googlegroups.com> wrote:Hello Experts,I think something is wrong here, we are interpreting code without understanding the background and the intent of clause requirements.What is the difference between preheat temperature and inter pass temperature?The preheat temperature is for first pass for the commencement of welding.The inter pass temperature is the preheat temperature of the subsequent weld that why once PQR is qualified, the minimum preheat temperature also become the minimum inter pass temperature. In the same way maximum inter pass temperature also become the maximum preheat temperature qualified.If the inter pass temperature of 110 deg. did not affect the mechanical properties of subsequent weld negatively why will the preheat of 110 deg.Note minimum preheat temperature is essential variable while the maximum inter pass/preheat temperature is supplementary essential (only applicable when impact property is essential).The maximum inter pass temperature is applicable because at higher inter pass or preheat temperature cooling rate will be low which lead to grain growth (the same reason why heat input is also supplementary essential variable). The higher the grain size the lower the impact property.On Thursday, 10 May 2018 05:41:03 WAT, Ramesh <rameshkannandevaraj@gmail.com> wrote:Hi
Practically your PQR was not preheated. It's room temperature and it was recorded as 30 Deg C. but your WPS indicates preheat 110 Deg C !!! how is this acceptable when code does not allow to increase more than 56 Deg C from your PQR,
i.e. 30+56 is maximum allowed in WPS. So u have to restrict up to 86 Deg C NOT 110 Deg C
in case of interpass , your PQR recorded 173 Deg C, so 173+56 is maximum allowed in WPS i.e. 229 Deg C
In your case , preheat temperature is mentioned wrong i.e. 110 Deg C instead of 86 Deg C which is not acceptable. IP temperature mentioned / restricted 220 Deg C which is OK.
Thanks and Regards
Rameshkannan Devaraj
M.Tech in Welding Engineering
"What you have learned is a mere handful; What you haven't learned is the size of the world – Avvaiyar"
--On Thu, May 10, 2018 at 9:13 AM 'Rajnish Dixit' via Materials & Welding <materials-welding@googlegroups.com> wrote:Hi,Please check respective WPS and refer the recorded maximum inter pass temperature. The condition is applicable if there will be increment of more than 56 deg Celsius in recorded/qualified inter pass temperature.--Thanks,
Warm Regards,
Rajnish Dixit
Lead - QA-QC/QMS/Welding/NDT/Inspection
+91 972 4200 357
On Wed, May 9, 2018 at 18:11, harish katesia<harish.katesia@gmail.com> wrote:hello,The subject under discussion is Max. preheat..It is 173 °c( Preheat/Interpass Temperature7) An increase of more than 100°F [56°C] in the maximum preheat or interpass temperature qualified )Max. preheat = Interpass temperature...So anything between 30°c to 173°c is ok.--On Tue 8 May, 2018, 7:27 PM 'james gerald' via Materials & Welding, <materials-welding@googlegroups.com> wrote:--Moreover though maximum Interpass temperature controls the Austenitic Grain size and thus the Charpy values and Preheat controls the Temperature between 800-500 degC , but under ideal conditions using ASME Materials.But below also have a effectChemical comp, method of maufacture, product form, Hardness, strength, Heat Treatment, microstructure, uniformity, homogenity, Grain size etc.. which are mostly controlled in the ASME Materials since its low temperature properties are controlled whereas material used in AWS D 1.1 have a effect.Thanks & Regards
J.Gerald Jayakumar
0091-9344954677
On Tuesday, May 8, 2018, 1:10:17 PM GMT+4, Kannayeram Gnanapandithan <kgpandithan@gmail.com> wrote:In ASME, % carbon is restricted to max 0.35%, where as in AWS it is more and properties will be deteriorated if use higher Pre Heat than qualified. That is why it is restricted.--THANKS & BEST REGARDS,KG.PANDITHAN, BE, IWE, AWS-CWI, CSWIP 3.1,CONSULTANT-WELDING & QUALITYMobile no: +919940739349On Tue, May 8, 2018 at 1:03 PM, George Dilintas <dilintas@gmail.com> wrote:in ASME IX also the increase is only for the interpass temperature and the decrease for the preheat.The increase of interpass is a supplementary essential variablethe decrease of preheat is an essential one--2018-05-02 6:54 GMT+03:00 N VENKATESWARA PRASAD <weldengr.velosi@gmail.com>:Dear Experts,--We have received a comment on Increase in Preheat temperature greater than 56°C is essential variable as per AWS D.1 from our client.
My interpretation is the increase in 56°C is applicable only for inter pass temperature. The details are as given below.
PQR Test coupon thickness : 30 mm
PQR Preheat temperature : 30°C
PQR Inter pass temperature : 173°C
Job Thickness : > 38 mm to 65 mm ( As per Table 3.3)
Preheat temperature : 110°C
Inter pass temperature : 220°C
MDMT : -40 °C
As per AWS D 1.1 Table 4.6 Point no. 7 an increase more than 56°C in max preheat or interpass temperature is essential variable for CVN testing applications.
Based on the above clause, the client is insisting that the Qualified Range for thickness in WPS shall be restricted to 38 mm as the preheat is increased from 30°C to 110°C which is not acceptable .
Please provide me if you any interpretation on it from AWS.
RegardsPrasad
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