INSIDE THE WTIA: WTIA HOTLINE
Can you provide some detail on the calculation of range on the heat input in the WPS (Welding Procedure Specification)? The heat input range shown on the Welding Procedure Specification is calculated from the welding amperage, welding voltage and welding travel speed range, all of which are developed during the welding procedure qualification. Heat Input (welding energy) is based on the following formula: Q = E x I x 60 V x 1000 Q = welding energy input, kJ/mm E = arc voltage I = welding current V = welding speed, mm/min During the procedure qualification process, the specific welding current, arc voltage and travel speed are measured for each run. But not all welders weld in exactly the same way and variations in joint geometry require the welder to adjust the amperage, voltage and travel speed to optimise the welding conditions for that particular joint. Australian and New Zealand standards typically allow a variation of +/- 10% for amperage, +/-7% for voltage and up to +/- 15% for travel speed. However, in some cases the weld integrity is governed by the heat input. A methodology is required to determine the associated maximum and minimum heat inputs. The minimum recorded voltage and amperage, divided by the maximum travel speed will provide the lowest heat input and vice-versa for the highest heat input. Care must be taken to ensure the resultant heat input range on the Welding Procedure Specification does not fall outside any pre-prescribed ranges.
For instance, when welding stainless steel, it is not uncommon to have a maximum allowable heat input that must not be exceeded, regardless of what range is calculated by this method. It is also important to ensure the +/- 10% amperage and +/- 7% voltage range does not create welding conditions outside the range specified by the welding consumable supply nor, with GMAW in particular, cause the mode of metal transfer to change. For example, GMAW dip transfer welding only works within a relatively small current and voltage range so any allowance in current or voltage must be kept within this operating window. References • AS/NZS1554.1:2014 - Welding of steel structures • WTIA Technical Note 1 - The Weldability of Steels
Can you provide details on the requirements for ‘smoothing’ of weld bead during Submerged Arc Welding (SAW) and its effect on the mechanical properties? Smoothing in this context refers to how well the weld bead blends into the parent metal. It is a function of weld reinforcement height and the angle between the weld bead and parent metal measured at the weld
49
toe. This parameter is important for structures subject to fatigue loading and also for painting, epoxy coating or galvanising in some instances. The Submerged Arc Welding (SAW) process is capable of giving a ‘smooth’ finish in the as-welded condition if correct welding parameters are adhered to, particularly the optimising of welding current, voltage and travel speed during the capping runs. Purchasers that need specific performance requirements may specify a maximum weld reinforcement as well as the angle between the weld reinforcement and parent metal. Where a suitably smooth finish cannot be achieved in the as-welded condition, post weld grinding or milling will need to be carried out. These operations will not affect the mechanical properties of the joint as measured by tensile, bend or fracture toughness tests but they will improve fatigue performance. References • AS/NZS 1554.5:2014 - Welding of steel structures subject to high levels of fatigue loading • AWS D1.1:2015 – Structural Welding Code - Steel
About the WTIA Hotline Corporate Members have access to the WTIA Hotline, which is manned by WTIA Technology Manager, Sasanka Sinha. Sasanka is also happy to provide initial help on technical matters to non-members. To reach the WTIA Hotline, please phone 1800 620 820.