What is Consumable insert in welding, its symbol?


What is Consumable insert in Welding & its definition?

Consumable inserts are metal strips in special sizes and dimensions that are used for root pass welding with one side access. Consumables inserts are beneficial for high quality welds that are required with minimum repairs, or rejects, and where welding conditions may be less than optimum, such as a confined space for welding or the necessity for maximum assurance against weld cracks, etc. Consumable inserts are most often used in pipe joints, and frequently used in pressure vessel and structural applications. They are available as strips for flat plate.

Open root weld joint fitup using consumable insert

Consumables inserts are made of similar metallurgy as the welding wire of base metal. Dissimilar inserts are not used as they will produce dissimilar weld metallurgy due to weld dilution.

consumable insert weld symbol

The welding symbol for consumable inserts are specified by placing the consumable insert symbol on the side of the reference line and opposite to the groove weld symbol as shown in the below figure.

The weld geometry with insert application is shown below with a groove weld example. The insert are placed in the groove weld, either pipe or plate joint thus allowing a open root similar to with backing appearance.

The AWS consumable insert class may be placed on the tail of the welding symbol. The classes for welding consumables are classified into 5 classes.

Welding consumables inserts are classified as per ASME Section IIC, SFA 5.30 into 5 classes:

  1. Class 1: Inverted T-Shaped Cross-Section
  2. Class 2: J Shape Cross-Section
  3. Class 3: Solid Ring Inserts
  4. Class 4: Y Shape Cross-Section
  5. Class 5: Rectangular-Shaped Cross Section (Contoured Edges)

The diameter and dimensions of class 1, class 2, class 3, class 4 and class 5 consumables inserts are given in the below table.

consumable insert for gtaw

Consumables inserts or fusible inserts for TIG welding are classified as per AWS A5.30 in 5 classes and 4 shapes A, J, K and Y. The same consumables inserts are used with other welding processes such as stick welding or MIG-MAG welding. consumable inserts or backing rings are used to control penetration and the inside contour with TIG welding.

consumable insert vs backing ring

Both consumables inserts and backing ring provide surface for weld bead before depositing. The backing rings usually are not part of the welds and they can be temporary (removable backing) or permanent type while the welding consumables inserts are fused with the weld and they become part of the weld itself. The backing ring can be either same metallurgy or copper backing or ceramic backing while the consumables inserts are always same metallurgy as the welding filler and base metal.

Backing rings are mostly made of metals and provide backing to the weld beads to be deposited. Backing rings are Backing in the form of a ring, generally used in the welding of pipe.

use of consumable insert

Consumable inserts are used for various purposes. They help for ease in weld joint fitup. By using inserts, a uniform weld root is achieved which results in high quality weld joints without any rejections in radiography or visual inspection. This becomes very important to use inserts in critical welds used in nuclear projects or military projects that uses costly materials and each repair can increase their overall cost. Thus with inserts, it help in quite lot of saving.

Welding inserts helps the welders to weld with a uniform root gap and even weld joint profiles. The weld roots produce very good fusion with the weld ID especially when welding small or large diameters pipe where only side access is available. Consumables inserts gives higher welding speed compare to weld without inserts as welder can weld faster without any worry of root such back or burn through. This also help to save the welding filler wire.

How to choose consumable insert for welding?

The selection of the shape of an insert (designated “class”), is largely determined by the preference of the engineer and operator for a given application. The Class 1 shape has been preferred for many highly critical weld joints especially in nuclear piping and in high temperature, high pressure piping installation.
The Class 2 shape is suitable where the pipe alignment is less critical. The Class 3 shape requires
compositions normally found in rod or wire forms for welding filler metals, and thus requires flattering and forming into solid rings to the required shapes and sizes.

The Class 4 shape is suitable mainly for V-groove weld preparations. The Class 5 shape, like that of Class 3, is flattened from rod or wire comparable to bare welding filler metal compositions, but is not formed into solid rings, allowing the operator to size the ring to that of the pipe diameters.

Reference: AWS A 5.30.

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