CJP (complete joint penetration) is a joint root condition in a groove weld. Before going to what is CJP, let’s understand what is groove weld.
Groove welds are done to fill the gap between the two pieces of fused metals. They fill the gap formed at the edges of the fused materials. They are different from filler welds that don’t fill the gap formed. Fillet weld forms a triangular cross-section with each leg of the triangle touching the edges touching each metal piece. There are two types of groove weld.
CJP – Complete joint penetration weld is used to fill the gap between the pieces and CJP uses a filler material that is stronger than base metals that are connected.
PJP –Partial joint penetration weld is used to fill the small portion of the gap formed during groove welding. It is used when strong filling materials are not required.
- 1 What is a CJP Weld?
- 2 Which Welding Method Offers Good Penetration
- 3 Welding Positions That Allow More Penetration
- 4 Parameters That Affect Weld Penetration in CJP
- 5 Benefits of CJP Over Fillet Welds
What is a CJP Weld?
CJP weld is a groove weld that penetrates deep into the thickness of the joints of the components. The CJP weld operates on single-sided joints or double-sided joints.
Single-sided vs Double-sided CJP
Single-sided CJP welds need steel backing. Steel backing acts as a supporting agent for the molten weld metal in CJP single-sided welding.
The double-sided CJP weld needs back gouging. Back gouging is required to remove the base metal and weld by arc gouging or grinding at the other side of the weld thereby ensuring the deep fusing and penetration welding on the other side subsequently.
How CJP Works and its Welding Symbols
Complete joint penetration is required only when a full strength of material needs to be developed. CJP groove welds are very strong when compared to the metals to be fused.
CJP groove weld is needed to practice more steel fabrications helping the welder to earn more bids. CJP is needed only when there is a welding requirement in the longitudinal welds on the built-up beam and column section. Mostly, this type of groove weld is used for shear loading which rarely requires the strength of a CJP groove weld.
The longitudinal welding differs in several aspects that too in a conventional plate and wide flange construction. Yet many structures need a weld that meets strength and fatigue performance qualities which are associated with full joint penetration groove welds. The purpose of a full penetration weld is to carry out the full load or strength upon the structural components they join.
To meet the needs of high-stress resistance products, a full joint penetration groove weld will be used. This results in the best weld for the metal products which are used in high-stress applications. A complete joint penetration weld is a thick weld and that weld is chamfered and penetrated with multiple weld passes. CJP also uses a metal sheet of thinness 0.2″ and can be penetrated without a V groove bevel.
CJP uses high power densities of about 1 megawatt per square meter and sometimes more than that depending on the thickness of the base metal. It results in a strong metal product. Full joint penetration weld has symbols that vary according to the joint types used in the groove weld process.
The above figure explains how the welding symbols work on CJP. These weld symbol helps the welder to use appropriate joint weld types to fill the gap between the fusing metals.
A great to easily achieve full penetration easily is with the use of backing. So if you want to make a CJP weld easily you can use one of these top-rated welding backings.
Examples of Full penetration Weld with a Removable Backing:
Examples of Full penetration Weld with a Permanent Backing:
If there is no backing the symbol rectangular symbol with the letter is excluded. In the above example, the weld symbol represents a single bevel v groove full joint penetration weld and there is no depth of penetration called out. So we can assume that full penetration had been done here.
To make the Full joint penetration process easy, CJP uses BUTT joint weld. In this condition, fused metal will have a strong resistant factor the same as the base metal. Thus a metal fuses with the base metal using a butt joint weld will be completely fused. This kind of butt joint can be configured with single and double V configurations.
The above picture illustrates the use of CJP and PJP in Butt joint welds.
The butt welded joint is more powerful and seals the base metal and fused metal to a full extent. It is very appropriate for the steel structural joint which has to be fused continuously and keeps the pipes and fitting in the system in good strength. Buttweld occupies less space in the fused components.
Which Welding Method Offers Good Penetration
Shield Metal Arc welding
Commonly known as stick welding, Shield metal arc welding is a manual welding process. SMAW is the oldest and most frequently used welding process in the steel fabrication and structural pipeline industries. This welding process uses consumable and protected electrodes. The heating-up electrode decomposes and acts as a shielding agent on the weld area. It acts as a cover to protect the area from oxygen and other atmospheric gases. This type of welding provides deep and full penetration due to the electrodes coated with rutile in the weld area. Mostly this kind of welding process is used to avoid the risk of cracking.
Submerged Metal Arc
Submerged metal arc welding is a mechanized process. In this process, a thick layer is formed due to granular flux and the molten metal acts as a complete cover to prevent spatter and sparks. This process provides a deep heat penetration due to the thermal insulator. It is a deep-rooted method and versatile method of welding. This method is preferably suited for longitudinal and circumferential butt weld which gives full penetration through the metal which is required in the manufacture of pipelines and pressure vessels.
Welding Positions That Allow More Penetration
The penetration levels are influenced by factors like the angle between the electrode and workpiece as well as the welding speed. Here are four common welding positions:
Flat position welding is performed from the upper side of a joint. A flat position is also called down and welding. The angle between the electrode tip and the welding surface, the welding motion, and the height of the electrode above the molten puddle has to be maintained rightly to ensure the perfection of the welding process.
For better penetration, you can either decrease the welding speed or increase the angle between the electrode tip and the surface of the plate.
This welding position is used to join two plates, one held vertically and the other kept flat on a surface. The weld axis is approximately horizontal when using a horizontal welding position.
When you use a horizontal welding position to form a groove weld, the face of the weld will lie in an approximately vertical plane.
In the vertical welding position, the weld axis is approximately vertical. The parts to be joined are kept on a vertical plane and the electrode is run vertically between the parts.
In the vertical welding position, the molten metal may flow downwards due to gravity and pile up at the bottom end. The flow can be controlled by pointing the flame upwards in a way that the angle between the plate and the flame is 45 degrees. In addition to limiting the flow of the molten puddle, this strategy facilitates better penetration as well.
In the overhead welding position, the welder stands underside the joint and does the welding.
In this welding position, there is an increased chance for weld metal to sag on the plate. To prevent this from happening, the molten puddle has to be kept small. In case the puddle becomes too large, remove the flame for a second to give time for the weld metal to freeze.
Parameters That Affect Weld Penetration in CJP
It is more important to achieve good penetration for a finished quality. The following variables have an independent effect on the weld material.
The penetration characteristics of various welding processes can be different from one another. For example, SAW, GMAW, and FCAW are associated with high penetration levels while GTAW, GMAW-C, and GMAW are known to have low penetration levels. It should be noted that the penetration levels are strongly influenced by the current and if the current levels were altered, the observations might differ. For instance, the SAW welding process is performed at very high current levels while the short circuit GMAW process involves low current levels. The type of electrodes used can also influence the penetration characteristics of the welding process.
Amperage is defined as the measurement of the amount of electricity flowing through the electrode and the work. The flowing current will be the same throughout the work. Sometimes it may differ as high flow and low flow of electricity depending on the penetration needed to fuse the materials. If there is an increase in the current flow, then there will be a deep penetration and there will be more welding to fuse the material and base metal.
Wire Feed Speed
Wire feed speed applies to the wire-fed process and not to the manual welding process. Wire feed speed is usually measured in inches per minute and basically, it is the rate that the filler wire is added to the weld pool. The wire feed speed is strongly correlated to the amperage and the deposition rate. The wire feed speed can be adjusted conventionally and measured directly regardless of other welding conditions. The welder can adjust the wire feed speed while observing the readouts of amperage.
Voltage is a varying variable for deeper penetration. If the voltage is high, you will get less penetration, and vice versa. The high voltage will spread out of the arc and deposit a wider bead which leads to less density with the drop in penetration.
The voltage will be lower at the work than at the machine. To get an actual measurement of the actual weld voltage, the voltage should be measured at the work which should be as close as possible. The arc voltage has a direct impact on arc length. If the voltage increases so as the length of the arc and vice versa which in turn affects the weld geometry and weld beads. For the manual welding process, the voltage is not monitored as the length of the arc is controlled by the welder.
Travel speed hurts penetration. Travel speed determines the rate at which the electrode is moved to the joint. When the travel speed is high, the amount of time that the arc is over a point on the welding joint will be less and the penetration will decrease.
If you increase the travel speed, then there will be a lesser penetration. The travel speed also affects the weld size and heat input. If you increase the travel speed, then there will decrease in heat input, and also the size of the bead decrease as it has an inverse effect on both variables.
Heat input determines the estimation of thermal energy which is used to weld the steel materials. It also regulates the solidification and cooling rates of the weld metal. The higher the cooling rate will increase the strength of weld metals and decrease the yielding.
Electrode Extension and Diameter
Electrode extension means the length of the electrode beyond the contact tip. It is also known as an electrical stick out which depends on the type and diameter of the electrode. Electrode diameter also affects the productivity of the quality metals. When the diameter of the electrode increases, weld deposition also increases so there will be more weld metal deposited in a short period thereby increasing productivity.
If you take two electrodes of different diameters, the electrode with the smaller diameter will be associated with a better penetration level than that with a larger diameter. The underlying reason is the difference in their current densities. For the same current passing through two electrodes, one having a smaller diameter than the other, the electrode with the smaller diameter will have a higher current density and produce better penetration.
There is a limit to the maximum current density that an electrode can have before it becomes unstable. The current density of an electrode should always be kept well below this limit to ensure the precision of the welding operation.
If different electrodes are used for the same welding process, the penetration characteristics will differ. For instance, an E6010 electrode used in SMAW welding offers better penetration than an E7024 electrode.
Contact Tip to Work Distance
Contact tip to work distance determines the electrode extension and length of the arc. It has an inverse effect on penetration. If you increase the distance then there will be a decrease in the penetration and vice versa.
The position of the torch also affects deep penetration. Backhand welding will give deeper penetration. The backhand welding position is also called pull welding which means the welder handles the weld from left to right. The backhand torch position helps to create an even and consistent arc so that it evenly distributes the weld along with the metals.
The penetration is influenced by the polarity type that you use in the welding process. When it comes to arc welding processes, using DC-(direct current electrode negative) offers lesser penetration than using DC+ . When using DC-, more energy is focused on the electrode and not the base plate. However, when using DC+, more of the arc energy is focused on the base plate.
Travel angle in welding is the angle between the electrode and the weld in a plane that is parallel to the direction of the electrode’s movement. The arc force that will be directed toward the base plate is influenced by the travel angle. Travel angles between 0 and 10 are considered ideal for obtaining good penetration. In these travel angles, the electrode will be nearly perpendicular to the plate.
Shielding Gas Type
Shielding gas is used in the welding process to prevent the molten weld pool from coming in contact with oxygen, hydrogen, and nitrogen in the air. The type of shielding gas used in the process has a significant impact on penetration levels. Deeper penetration can be expected when using shielding gases with high rates of thermal conductivity such as 100% Helium or 100% carbon dioxide. When using a shielding gas of lower thermal conductivity, like Ar/CO2 blend, Ar/O2 blend, or 100% Ar, a shallow penetration profile is produced.
Some other factors which affect deep penetration include techniques like stingers or weaves.
Benefits of CJP Over Fillet Welds
CJP welds are mostly used to weld metal with high-resistance materials. Some of the benefits of CJP welding include:
- It is Corrosion resistant.
- It gives you a strong weld product.
- It gives a complete fusion between the base metal and fused metal.
The precision of CJP welding is influenced by various factors including the skill of the welder, the electrode used, and several other factors. Some welding positions like overhead positions demand more welding skills than others.
The penetration levels, bead size, and strength of the weld joints are influenced by various parameters.