PWHT Exemptions D2 to A1

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    AS4458, Table 14.1, Note 18 give a usefull exemption for materials below 12mm & below 127OD, in my exsperence this is often used in conjuction with dissimilar parent metal joints P22 to A106,

    Q1………Item (c) refers to carbon content being equal to or less than .15%

    Is item (c) refering to parent material C. content or consumable C. content or the diluted combind weld metal C. content?

    It seems to me that in the case of A106Gr.B to P22 that this particular exemption doesnt apply and PWHT is mandatory for all thicknesses and diameters…………………..?

    Q2………Also reference is made in Note 18 "for welds in pipes and tubes" therefore are joints incorperating forgings (valves) included in the exemption…………………….?



    I have come across this exemption before. Power station boiler tubes & piping – can’t remember exact thicknesses, but around 60mm OD x 5 – 6mm thick; Material 2.25%Cr, 1Mo.

    P22 material has a maximum allowable carbon content of 0.15% IIRC.

    A1 – Item C refers to parent metal composition. PWHT for carbon steel is not required below thicknesses of 32mm.

    A2 – Yes, correct. Go off the thickness of the thinner material.


    My point is the combination of the two dissimiar materials one of A106 Gr.B having 0.25% C forms the basis of the joint, there for does that joint still conform to the requriments of the exemption, i dont beleive so.

    a) equal to or less than 12mm

    b) equal to or less than 127 OD

    c) less than 0.15 C content

    Its all a matter of interpretation but im definitly in favour of majority rules, so lets hear some more opinions.

    I might be setting myself up for dissapointment but here goes.



    If the carbon steel is less than 12mm, it automatically does not require heat treatment.
    Carbon steel only requires heat treatment at 32mm and above.


    cassgazz, I totally agree with you …

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