Reading an Intermittent Fillet Weld Symbol on a Base Frame
A fabricator is making a base frame from 100 × 100 × 8 mm mild steel angle and 10 mm mild steel plate. On the drawing, the joint between the angle and the plate carries a fillet weld symbol on the solid reference line. To the left of the triangle is '6'; to the right is '80–160'; the tail contains 'WPS-12'; and a flag is shown at the junction of the arrow and the reference line. The note under the drawing says all dimensions in millimetres and the joint length is 1,200 mm. The shop foreman reads the symbol as a continuous 6 mm fillet along the full joint and plans to weld it in the shop before galvanizing. The welder has already tacked the frame and asks you to confirm the weld details before starting.
1. Explain what the symbol requires: weld type and size, arrow-side or other-side, length and pitch, the flag, and the tail. State how many 80 mm weld lengths are needed along the 1,200 mm joint, showing your assumption.
Read the worked answer
The symbol is a fillet weld. '6' to the left of the triangle is the leg length, 6 mm. The triangle on the solid reference line means the weld is on the arrow side of the joint. '80–160' is an intermittent weld: 80 mm weld length with a 160 mm pitch, meaning the distance between corresponding points on adjacent welds is 160 mm. The flag means the weld is a field or site weld, not a shop weld. 'WPS-12' in the tail identifies the welding procedure specification that governs process, consumables and parameters.
Along the 1,200 mm joint, if the first weld starts at the end, welds run 0–80, 160–240, …, 1,120–1,200 mm. That gives 8 welds (8 × 80 = 640 mm of weld metal) and 7 gaps of 80 mm. If the drawing required an end clearance, the number could be 7, so the drawing and WPS must be checked; the assumption should be recorded.
2. The foreman wants to weld continuously in the shop to save time. Assess this deviation and state what must be done before it can be accepted.
Read the worked answer
Continuous welding in the shop is not what the drawing requires. It changes an intermittent 6 mm fillet into a continuous 6 mm fillet: heat input and shrinkage increase along the 1,200 mm joint, distortion risk rises, and the saving in weld metal is lost. The flag also says the joint is to be welded on site. If the frame is galvanized before the site weld, the zinc coating must be removed locally and restored afterwards; welding over galvanized steel can cause porosity and zinc fume exposure.
A deviation can only be accepted through a documented concession or design change approved by the responsible engineer, with a revised drawing and WPS. The welder should not act on the foreman's verbal instruction. If continuous welding is approved, use a balanced or backstep sequence and record the change. If the field-weld flag is to be removed, the drawing must be revised.
3. What documents should the welder check before striking the arc, and why is the tail important?
Read the worked answer
Before striking an arc the welder should check the drawing revision and joint details, WPS-12 and its supporting procedure qualification record, the welder's qualification for the process and position, the electrode certificate and condition, the current and polarity requirements, and any preheat requirement. The tail matters because it is the formal link between the weld symbol and the qualified procedure. Without reading WPS-12 the welder does not know the electrode type, size, current range, travel speed or whether preheat is needed. A 6 mm fillet is not simply any 6 mm weld; the procedure controls how it is made.