Definition Of Buttering From Asme Section Ix 6z6016

Definition of buttering from ASME Section IX, QW/QB-492 Definitions:

Buttering: the addition of material, by welding, on one or both faces of a t, prior to the preparation of the t for final welding, for the purpose of providing a suitable transition weld deposit for the subsequent completion of the t.

Simply it is weld build up of (one or both) base metal(s) before beginning to weld the t itself. This can be done in order to make up for poor t preparation as indicated previously, but also is done to minimize the effect of PWHT on a sensitive material or eliminate subsequent PWHT. For the latter cases a couple of examples may be in order: 1. If you wanted to weld P91 pipe to a stainless steel pipe, ASME Code would require a PWHT of the P91 at nominally 1400F (760C). This temperature would, however, “sensitize” the stainless steel (cause carbide precipitation along the grain boundaries). One way to eliminate this problem is to butter (or overlay) the P91 with ERNiCr-3 (or similar weld material). The thickness of the butter must be sufficient to avoid the weld heat affected zone from extending into the 91 during completion of the weld. You would then PWHT the buttered P91. The t would be completed by welding the stainless steel pipe to the ERNiCr-3 butter with ERNiCr-3 material and no subsequent PWHT would be required. 2. A steam turbine manufacturer I am familiar with used to butter 2 ¼ Cr – 1Mo casing materials with carbon steel at some nozzle connection sites where it was undesirable to have stubs. The casing was heat treated prior to final machining. In the field carbon steel nozzles/pipes were welded to the carbon steel butter with no subsequent PWHT. ASME Section IX, QW-283, discusses and governs welding procedure qualification when buttering is to be performed. While not complex there are some significant details that need to be paid attention to. I would suggest that peruse this section of the Code and if enquire further if you have subsequent questions.

Buttering for welding SA-335 Gr P91 to SS 316 by Hollan Petersen » Mon Jun 10, 2013 10:02 am By the design and material selection of a boiler under the scope of ASME VIII, it happens that I need to weld pipes SA-335 Gr P91 to weld neck flanges SS 316. Since I have been consulted that such a welding requires buttering, could any one explain me what buttering is and why it is

considered as necessary for such a welding. Moreover, may I have some instructions for the qualification of the welding procedure. Hollan Petersen Posts: 13 ed: Tue May 21, 2013 1:43 pm Top

Re: Buttering for welding SA-335 Gr P91 to SS 316 by wg » Mon Jun 10, 2013 10:18 am In accordance with ASME IX, buttering is the addition of material, by welding, on one or both faces of a t, prior to the preparation of the t for final welding, for the purpose of providing a suitable transition weld deposit for the subsequent completion of the t. As far as this specific welding is concerned, the reason that you need to do buttering is to avoid PWHT after the completion of the welding. According to ASME VIII, table UCS-56 the welding of SA-335 Gr P91 (P-no 5B, Group-no 2) needs PWHT in a temperature higher than 700 deg C. But if you do PWHT in such temperatures there is the possibility the austenitic SS to be made vulnerable to cracking http://www.weldinguide.com/viewtopic.php?f=5&t=29 or to lose its corrosion resistance http://en.wikipedia.org/wiki/Intergranular_corrosion For that reason you shall overlay (buttering) the SA-335 Gr P91 with a nickel based consumable like AWS 5.14, ErNiCr-3 (or similar), then you shall PWHT the buttered pipe and finally you shall complete the welding by ing the SS flange to the buttered pipe using the same welding consumable as the one that used for the buttering. Since after completion of the welding the HAZ shall not be extended to the SA-335 Gr P91, the actual thickness of the buttering (after completion of bevel preparation) must be sufficient to permit HAZ to be included in the buttered area. As for the PQR requirements, you could have a look to the ASME IX, QW-283 that gives the scope and the requirements for the buttering. wg Site Posts: 44 ed: Wed May 15, 2013 2:53 pm