Topic 8: Welding terms and symbols

IntroductionThis topic enables you to understand and apply welding symbols and welding terms.

All trades use their own unique terminology where words and/or symbols take on specific meanings that apply specifically to that trade. The use of standard language eliminates misunderstandings and allows people in the fabrication and allied engineering industries to communicate effectively with each other.

Without such communication mistakes will be made due to a lack of understanding and incorrect interpretation.

To improve communications, the Standards Association of Australia (SAA) issue a glossary of specialised words for use with all welding operations.

This terminology can be confidently used anywhere in the country and across all engineering fields to minimise mistakes arising from incorrect interpretation. These common terms help workplace communications by providing a standardised trade language.

Welding terms and symbols can be found in two standards:AS 2812-2005 Welding, brazing and cutting of metals — Glossary of termsAS 1101.3—2005 Graphical symbols for general engineering — Welding and non-destructive examination.

The terms and definitions used in this topic are commonly used in welding and fabrication industries and are extracted from the above Standards.

Types of welds Butt welds: are where weld metal is mostly confined to the thickness of the parts being joined. Parts may be in the same plane as each other or meet at an intersection.

Butt welds are used to join sheet, plate, pipe and other hot rolled sections.

This type of joint has the advantage of strength without changing the profile of the structure.

Butt weld joints can be designed for full penetration in order to achieve maximum joint strength.

Figure: Butt weld

Fillet welds: are triangular in shape and most of the weld metal is external to the parent metal. A fillet weld can be found in joint various configurations including:

Figure: Tee fillet weldFigure: Corner fillet weld

Fillet welds, in particular the tee fillet joint, account for the majority of welds made in fabrication and construction industries.

They suit most weld joints used in structural steel construction.

They require less edge preparation, are cost effective and are quickly and easily assembled.

Figure: Lap fillet weld

Figure: Parts of a weld

Weld toe: the junction of the parent metal and the weld face or weld face to weld face in a multiple run weld.

Figure: Weld face

Parent metal: the metal being welded together or surfaced.

Weld face: the visible surface of a completed weld.

Root: the innermost part of a weld directly opposite the weld face.

Root penetration: the amount by which the weld metal penetrates past the edge preparation.

Figure: Root

Figure: Root penetration

Weld reinforcement: the amount the weld face extends beyond the parent metal in a flat butt weld or beyond a line joining the toes of a fillet weld.

Leg length: the distance from the original root of a fillet weld preparation to the toe of the weld.

Figure: Leg length of a weld

Heat affected zone (HAZ): the area adjacent to the metal melted by the heat of welding which has become metallurgically changed.

Figure: Heat affected zones of a weld

Throat thickness: the distance from the root of a weld to the face of the weld.

Fusion Zone: area of parent metal that has been fused in the welding process.

Parts of a weld preparation

Fillet welds require very little preparation apart from squaring and cleaning both edges and fusion faces.

Edge preparation terminology is generally limited to the preparations for butt welds as indicated in the diagram below.

A welding procedure, when used, will provide guidelines as to the minimum and maximum included angle, root gap and root face.

Figure: Parts of a single V butt preparation

Weld sizes

Fillet weldsThe size of a fillet weld is determined by the finished weld’s leg length.

To comply with normal design requirements, the weld must also have a throat thickness equal to 70% or 0.7 of the required leg length.

For example, a metre fillet weld of 10 mm leg length should have a throat thickness of 7 mm.

Figure: Leg length and throat thickness

If weld size is specified by leg length then the concave fillet welds throat thickness, as illustrated above, will be less than 70% of the required leg length.

In this instance the finished weld will be under size and under strength.

However, concave weld shapes are better suited for transmitting stress in loaded structures because of its gradual change of direction. If this type of profile is permitted on a job then the throat thickness has to match design specifications and the leg length will need to be greater.

The convex fillet weld, as shown above is more likely to be produced using the GMAW or MMAW process using hydrogen controlled electrodes.

The extra weld metal outside the mitre line does not contribute to the strength of the weld; however a small amount of reinforcement is acceptable.

Excessive reinforcement can cause problems with stress concentration along the weld toes.

However, for concave and convex bead shapes the size of the weld can change. In the examples shown below, the leg lengths are the same, but due to the shape of the weld face, their throat thicknesses are different.

Butt welds

On full penetration butt welds, the depth of weld should at least be equal to the thickness of the metal being joined.

On partial penetration welds the depth of the weld may be stated on the weld procedure specification.

Reinforcement height does not form part of a butt welds size.

Reinforcement should not extend more than 2 mm beyond either side of the edge preparation for a 10 mm plate thickness.

Figure: Full and partial penetration butt welds

Weld positions

The type of weld is indicated by a letter:

•G—signifies a grooved or butt weld

•F—signifies a fillet weld.

The position of weld is indicated by a numeral:

•1—signifies a flat or downhand weld

•2—signifies a horizontal weld

•3—signifies a vertical weld

•4—signifies an overhead weld

•5—signifies fixed position pipe axis horizontal

•6—signifies fixed position pipe axis 45o to the horizontal.

Examples of weld types and positions include:

Figure: 1F or flat fillet weld

Figure: 1G or flat butt weld

Figure: 2F or horizontal fillet weld

Figure: 2G or horizontal butt;

Figure: 3F or vertical fillet weld

Figure: 3G or vertical butt weld

Figure: 4G or overhead butt weld

Figure: 4F or overhead fillet weld

Figure: 5G or vertical butt, pipe in horizontal axis

Figure: 6G or vertical butt, pipe in 45o axis

Welding symbols

Engineering drawings must convey all information needed to fabricate metal products. Since space is limited on drawings, a system of symbols has been devised to provide weld joint information.

For example, welding symbols provide details relating to the side of the joint to be prepared and welded, as well as the type of joint preparation and weld size can be clearly indicated by the use of welding symbols.

In general, a welding symbol is the combination of an arrow and reference line. The type of weld is depicted as a stylised drawing and is located on the reference line.

Further information such as location, shape, edge preparation, size and length of the weld can also be added.

A basic welding symbol consists of an arrow line, horizontal reference line and a symbol depicting the type of weld and its location.

Figure: A basic welding symbol

Use of symbols on engineering and fabrication drawings

The following diagrams indicate how symbols are used on engineering and fabrication drawings.

•Weld symbol positioned under the reference line

The triangular weld symbol positioned under the reference line indicates a fillet weld is required on the side of the joint the arrow is pointing towards.

The diagram above shows how the completed joint would look after welding.

Figure: Weld symbol positioned under the reference line and completed weld

•Weld symbol positioned above the reference line

This example below shows the weld symbol is located above the reference line. This indicates a fillet weld is required on the other side of the joint the arrow is pointing towards.

The diagram on the right shows how the completed joint would look after welding.

Figure: Weld symbol positioned above the reference line and completed weld

•Weld symbol positioned above and below the reference line

In this example the weld symbol is positioned above and below the reference line.

This indicates a fillet weld is required on both sides of the joint.

The diagram on the right shows how the completed joint would look after welding.

Figure: Weld symbol positioned above and below reference line and completed weld

•Weld size symbol

The numeral six (6) shown next to the fillet weld symbol indicates a 6 mm leg length fillet weld is required on the arrow side of the joint.

This method of advising weld leg length size may be necessary if other welds on a fabricated structure are to be a different size.

Figure: Welding size symbol

Site weld symbol

The flag located at the junction of the arrow line and reference line is the field weld symbol and indicates the weld is to be completed.

A tail at the end of the reference line is used when important information needs to be added to the welding symbol. Information may include:

• the welding process to be used

• weld procedure specification data.

Figure: Site weld symbol

Figure: Tail symbol with important information for welding process

Weld all round symbolsThe circle located at the junction of the arrow line and the reference line is the weld-all-round symbol.

It indicates the weld is to be made all around the vertical member as shown in the diagram below.

The diagrams on the right show how the completed joint would look after welding.

Figure: Weld all round symbols completed weld

Butt weld symbolThe inverted vee shape positioned under the reference line indicates a single vee butt weld is required on the side of the joint the arrow is pointing towards.

This configuration informs the operator the butt weld is to be done in the 1G position (flat butt weld).

Supplementary symbols used in association with this butt weld symbol may include the type of weld face finish required, or back-gouging and welding of the root run.

Figure: Butt weld symbol

Common butt weld symbols

The following table summarises the weld symbols used on various types of preparation.

Table: Common butt weld symbols

Welding symbol summary

The following diagram summarise the various symbols used in engineering and fabrication drawings.

Figure: Summary of welding symbols