Weld Faults 120102h

Categories of incorrect weld profile?

1. Convex reinforcement 2. Insufficient throat or leg 3. Overlap 4. Undercut

What are dimensional defect after welding types?

1. Distortion or warpage. 2. Incorrect weld profile.

What is fracture toughness?

A material resistance to crack growth or extension.

What is a defective property?

Any departure from specific mechanical and chemical property giving for fabrication is considered a defect.

What is laminar, for internal defect?

Are generally not acceptable even in less critical operations. these internal discontinuities can be in the form of: 1. Lack of fusion 2.Incomplete penetration 3. Cracking

What is the general rule for tapered transition?

As a general rule, if you use a tapered transition ratio of 3:1, you will probably have a good welding design that falls within the acceptance criteria of many codes and standards. To achieve this ratio: 1. determine the difference in thickness between the two materials, 2. multiply that dimension by 3 and 3. use the result to measure the distance you need to taper back on the thicker material.

What are the effects of excessive concavity (insufficient throat or leg)?

As a result of insufficient throat or leg, the following problems may occur. Weld size does not meet specifications. Strength is low. Notch effect occurs (in more severe cases). Undercut can occur.

What are the effects for overlap?

As a result of overlap, the following problems may occur. Weld size does not meet specifications. Strength is low. Notch effect occurs (in more severe cases). Poor weld metal appearance results.

Name some physical weld imperfections?

Cracks Porosity Slag inclusion Lack of fusion Undercut Lack of penetration Dimensional defects

Sheared surface on preparation methods:

Depending on the condition of the shear blades and lubricants used, various undesirable foreign materials may become embedded on the joint edges. These lead to porosity, slag entrapment and lack of fusion. Make sure the shear and blades are reasonably clean and in good operating condition.

Characteristics of an acceptable weld?

Meet acceptable criteria code, code specification or a standards Good appearance Ripple definition Blend smoothly in parent metal at the toe Show slight reinforcement Weld should be flat to slight convex across the face Crater should be filled

Explain moisture that causes porosity.

Moisture pick up in flux-coated electrodes or flux-cored wire can cause porosity. The same situation pertains to externally applied flux in welding process such as submerged arc welding.

What is the notching effect?

Occurs whenever a notch is placed or formed within the cross-section of a material, creating a point of weakness.

Notch effect can also happen as the result of?

Poor joint design Poor weld profile Structural discontinuities in the weld zone Any weld fault that causes a similar weakness is said to have a notching effect on the weld.

Weld faults classification?

Poor or incorrect material preparation Poor or incorrect fit-up Incorrect weld size and profile Distortion or warping (warpage)

What are the factors to keep in mind when considering the cause of a weld fault?

Properties of the base plate Chemical composition Surface condition (mill scale, grease, paint or oil) Mechanical properties and dimension

What is porosity?

Refers to gaseous voids trapped within the weld metal. Porosity may manifest itself in a variety of patterns, sizes, shapes and quantities. Porosity may be present in any position in the deposited weld metal.

What is advise you do with regards of parental materials to avoid porosity?

Select a filler metal that matches the chemistry of the material to be welded. In cases such as high sulphur-bearing steels, porosity is commonly encountered. Other elements, such as zinc found on galvanized steels, may also create excessive porosity in the weld. Materials with dense oxides, such as aluminum, should be carefully cleaned to avoid porosity. Laminations in plate may also be a source of porosity in the welding operation.

What are the effects of slag inclusion?

Slag inclusions left in the weld have much the same effect as porosity; they can cause a notch effect. They reduce the overall strength of the weld because there can be no fusion where slag is present.

What section accordance to CSA 5.3.1 says about gas and metal arc welding?

Slight oxidation such of traces of rust, thin mill scale or oxides resulting from thermal cutting or gouging may remain, provided that does not interfere with the process, nor adversely influence weld properties.

What are dimensional defects?

Some dimensional defects are irregularities in the weld zone that occur prior to welding. Other dimensional defects occur after the welding has been done.

What section accordance to CSA 5.3.1 says about how much of the surface should be free from loose or thick scale, slag, loose rust, paint, grease, moisture and other foreign materials?

Surface shall be free within 50 mm (2") of any material that will prevent welding to the acceptance criteria of this standard.

What section accordance to CSA 5.3.1 says about material preparation?

Surfaces and edges to be welded shall be smooth, uniform and free from fins, cracks, and other defects that would adversely affect the quality or strength of the weld.

How to prevent undercut?

Remove all impurities from the weld zone. Maintain correct electrode angle. Use correct current settings and polarity for the electrode. Use proper welding technique. Remove internal undercut between passes by grinding or melting out with successive passes. External undercut should be filled in with another pass and blended in by grinding if necessary.

What are the effect of undercut?

notch effect, lack of strength, structural discontinuities such as porosity, slag inclusions and lack of fusion and poor weld appearance.

What are the causes of undercut?

poor joint preparation, incorrect travel speed, improper electrode angles, incorrect electrode selection, improper welding techniques, wrong electrode diameter, improper current settings, impurities such as oil, paint, rust and mill scale and poor joint accessibility.

What are the causes of careless or poor material preparation and fit-up causes?

-Difficulty in maintaining dimensions when fitting and welding the assembly, -High stresses that can lead to distortion or cracking, -Structural discontinuities including incomplete or excessive penetration, lack of fusion and slag inclusions -Defective properties within the weld zone if the joint edges are not properly cleaned before welding.

What are the causes of slag inclusion?

-High viscosity of weld metal (resistance to metal flow), -Rapid solidification, -Too low a temperature (inadequate preheat or rapid cooling of weldment), -Current setting too low, -Improper manipulation of the electrode, -Undercut from previous passes and -Foreign material trapped in laminations in the joint edges of the parent metal.

Name two chemical properties deficiency?

-Incorrect weld metal composition causes too much dilution between the weld metal. -Base metal, resulting in loss of corrosion resistance at the weld.

What are the causes of porosity?

-Moisture in the electrode or parent metal or both, chemistry and structure of the parent material, -Surface impurities and contaminants, faulty electrodes, fluxes, insufficient gas shielding, trapped slag and -Incorrect welding techniques.

What section accordance to CSA 5.3.4 says about notches allowance?

-Notches, not more than 5 mm (3/16 ") deep, on otherwise satisfactory surfaces shall be removed by machining or grinding. -Occasional notches, exceeding 5 mm (3/16 ") and less than 10 mm (3/8 ") deep, in oxygen-cut edges of plate up to 100 mm (4 ") thick, not to be welded, may, with the Contractor's Engineer's approval, be repaired by welding. -For material 100 mm (4 ") thick or over, the depth of the notch shall not exceed 15 mm (9/16 ").

Name some examples of undercut can happen?

-Root bead undercut in single-welded groove welds, -Undercut of the sidewall of a welding groove at the edge of a layer or bead and -External undercut at the point where the weld metal meets the base metal (toe), resulting in a reduction in base metal thickness and creating a notch effect.

What are the three general classifications for weld fault?

Dimensional defects (prior to and after welding) Structural discontinuities in the weld or the surface Defective properties (mechanical or chemical)

What are dimensional defects prior to welding?

Dimensional defects that occur prior to welding are a direct result of poor workmanship or mistakes in operations leading up to the assembly and welding of the components. There are three general types of faults that occur before welding: 1. incorrect joint preparation and fit-up, 2. irregularities in the surface of the joint preparation. 3. surface discontinuities

Types of surface discontinuities?

Discontinuities on the surfaces to be welded may also lead to weld faults and defects. The method of preparation usually determines the type of weld fault that may be experienced. These faults include: -Sheared surfaces, -Flame-cut surfaces and -Gouged surfaces

What are the effects of convexity?

Distortion Point of high stress Poor weld profile that causes notch effect

What are the causes of distortion or warpage?

Distortion may have a number of contributing causes such as: 1. lack of control over heat input 2. inadequate control of weld pass sequencing 3. inaccurate preparation of the joint 4. inadequate control of fit-up 5. incorrect joint design

What are the causes of excessive concavity (insufficient throat or leg)?

Excessive heat input for the second pass in groove welds can cause the root pass to suck back. This gives a concave finish due to surface tension breakdown. It is more common with gas tungsten arc welding. Other causes include: travel speed too fast, insufficient number of passes or layers, incorrect welding technique and excessive groove angle.

What is a weld crater?

Fill weld ends and apply a wash coat of metal to the ends if necessary. Build-up of ends should not be heavy enough to create a notching effect. With intermittent fillet welding, always fill craters and never stop on a corner; instead carry the fillet weld around the corner.

How do you determine the weld profile?

Fillet weld deficiencies due to insufficient or excessive size and poor profile may be detected with visual examination or with a suitable fillet weld gauge. Gauges are available for checking bevel angles and reinforcement in a groove weld.

What is tensile strength?

How much a material can resist a pulling force. When the tensile strength is exceeded, the material tear or pulls apart.

What is stress flow on lap joints?

If stress flow lines are applied to fillet welds on lap joints, excess convexity or excess concavity leads to a severe notching effect. The weld profile lends itself to a less severe notching effect because of its shape and the smooth blending into the plate.

How are the stress flow lines on an object that is not uniform dimensions and with defects are?

If the object is bend or deflected, the stress flow lines are also deflected. However, if there is a void in the plate or in a weld within the object, the stress flow lines must go around the fault. They do not go through the fault because the void cannot carry any load.

Example of tapered transition?

If you were joining 25.4 mm (1") material to 12.7 mm (1/2") material, the difference in thickness is 12.7 mm (1/2"). You then multiply 12.7 mm (1/2") by 3, which equals 38.1 mm (1 1/2"). You would then taper the thicker material back over a length of 38.1 mm (1 1/2"). 1/2" (12.7 mm) x 3 = 1 1/2" (38.1 mm)

Gouged surfaces on preparation methods:

Improper carbon arc gouging operations can leave deposits of carbon, copper and / or oxidized metals in the joint area. This can lead to structural discontinuities such as porosity, lack of fusion and slag entrapment. The melting of these deposits into the weld can significantly alter the mechanical and chemical properties of the deposited metal. Remove any slag or oxides to prevent them from getting trapped in the weld

What are the precautions to avoid convexity and excessive reinforcement?

Increase travel speed Use appropriately sized electrodes and filler metals Use recommended welding technique Preheat if required Use the proper current settings for electrode.

What is weld fault?

Is a broad term that describes a variety of welding - related issues that may compromise the quality of a weld and it fitness for service. They could range from metallurgical characteristics to physical imperfections faults.

What is Convex reinforcement?

Is a bulging profile of a fillet weld. It tends to produce a notch effect in the multi-pass weld.

What is a wagon track?

Is a condition that occurs when an undercut is done on the root pass and in the attempt to correct it, sufficient care is not done cleaning the slag. This lines appear in the x-ray as slag line trapped between the root bead and fill pass in the internal undercut.

What are stray arc or stray arc flashes?

Is a serious weld fault, that creates a quench, hard brittle condition (often called metallurgical notch) in steels, specially alloys. The effected area are prone to cracking, and repair of such damage can be difficult and costly. In circumstances where welds are subjected to sour gases service, the weld must be cut out and re-done.

Nick Break Test is?

Is a type of destructive testing that is used to evaluate the quality of a weld. To perform a nick break test, a specimen is prepared out of the weld metal. Stress concentrators are then machined into the specimen.

What happens if a weld has insufficient throat or leg?

Is a weld with excessive concavity may occur in the root pass of a groove weld, but it is more often associated with fillet welds. A concave fillet profile is dependent on service conditions. An excessive concave weld profile gives deceptive appearance as its actual size.

What is excessive weld reinforcement?

Is associated with groove welds. It is undesirable since it tends to increase shrinkage stresses and to create a notch effect.

What is excessive concavity on welding?

Is caused by shrinkage of the weld pool in the through-thickness direction of the weld. Melting of the root pass by the second pass can also produce root concavity. ... Excessively high welding speeds make the formation of root concavity more likely.

What is excessive convexity on welding?

Is defined in AWS A3. 0:2010, Standard Welding Terms and Definitions, as "the maximum distance from the face of a convex fillet weld perpendicular to a line joining the weld toes.

What is rapid changes in contour?

Is like tapered transition therefore the same ratio of 3:1 is applied however the notch is on both side of the weldment structure. Rapid changes in the contour can also be found on the welded structure. Sometimes this is unavoidable because of the shape of the weldment, but in some cases, this is faulty design.

What is ductility?

Is the ability of a material to bend or permanently deform without breaking.

What is a weld profile?

Is the complete weld appearance.

What is yield strength?

Is the point at which a material begins to deform permanently. The amount of force required to cause a material to take a permanent upset or deformation.

What is incorrect joint preparation surface irregularities fault?

Is when a joint preparation may have irregularities that may also cause problems prior to welding. Care must be taken to ensure the weld area is cleaned properly before any welding operation begins.

What is Tapered transition?

Is when heavier sections are machined to match the lighter pipe wall and the excess thickness tapered both internally and externally to form a transition zone.

What is overlap in welding?

Is when molten metal flows over the surface of the base material and then cools without fusing with the base material. A typical cause of overlap is the supply of too much weld metal due to low welding speed. or Is a condition in which an excess of weld metal exist at the toe of a weld beyond the limits of fusion. This condition can produce a notch effect that can result in stress concentrations under load In the case of a fillet weld, the overlap may actually reduce the weld's effective size.

What is under cut?

It describes the melting away of the parent material during the welding process. If undercutting is not corrected, it may be detrimental to the component.

What is a surface discontinuities?

It is a surface discontinuity that forms a severe mechanical notch parallel to the weld axis.

What happens if you use an electrode that is too large on a groove weld root pass?

It may cause the arc to concentrate against the sides of the groove instead of the root. The slag can then roll down into the root opening and may be trapped under the metal of the root pass.

What section accordance to CSA 5.3.4 says about material preparation?

It recommends that weld repairs shall be made by suitably preparing the defective area, welding with low-hydrogen electrodes to an approved procedure, and grinding the completed weld smooth and flush with the adjacent surface to produce a workmanlike finish.

What is intergranular carbide precipitation?

It's a metallurgical condition resulting on a chromium depletion, mainly due to the precipitation of chromium carbides in the grain boundaries. Chromium carbides can be precipitated if the stainless steel is sensitized in the temperature range 550-850°C (1020-1560°F), for example during heat treatment or welding.

How a nick break test is done?

TO determine what internal fault is within a welded specimen, a notch is cut in both ends of a weld. This weakens the weld area, so when the specimen is placed on edge in a press and force is applied to one notch, a fracture develops between the two notches.

Name some mechanical properties that nay be defective?

Tensile strength Yield strength Ductility Hardness Fracture toughness (also known as impact strength)

When welding in accordance to CSA standard W59, which are the conditions and limitations to be applied?

The code standard located on 5.3 Preparation of materials; sections 5.3.1 and 5.3.4

What is incorrect joint preparation and fit-up fault?

The faults that occur prior to welding include the layout, cutting and forming of the material and fit-up operations.

What happens where stress flow lines are forced to go around a fault?

The lines are squeezed together. This causes a high concentration of stress at this point. At the same, the fault lowers the effective strength at the same point. Failure is likely at the point of high stress.

Remedies to avoid slag inclusion.

The majority of slag inclusions may be prevented by: -Proper preparation of the joint, -Correct filler metal selection, -Correct current settings, -Complete removal of slag between passes on multi-pass welds and -Proper welding techniques (angle, inclination and arc length).

What are the surface defects on structural defect that happen during welding?

The welder is directly responsible for these defects as a result of improper base metal preparation, incorrect technique or improper current settings, faulty or wet electrode or unsuitable base materials.Surface defects includes: -Surface porosity -Badly shaped surface ripples on the weld bead -Excessive spatter -Craters -Accidental striking of the arc on the material adjacent to the weld, called stray arc flashes or stray arc strikes

What is distortion or warpage?

The welding operation involves the application of heat to metal in localized sections of the fabrication. Stresses of sufficient magnitude may be set up (due to unequal thermal expansion and contraction) which an cause distortion of the structure.

How are the stress flow lines on an object with uniform dimensions and no defects are?

These lines are evenly spaced and run parallel to the general outline of the object being stressed.

What are structural defect that happen during welding?

These weld faults can occur if the welder does not follow welding techniques or weld procedures. Structural discontinuities can occur during welding and can be categorized as: -Surface defects -Internal defects

What are the other names for porosity?

They are also called pinholes, gas pockets, wormholes and piping.

What is structural discontinuities in the weld zone?

They are generally caused during the welding operation. This class of weld fault can be very serious because of high concentrations of stress that can ultimately lead to the failure of the weld while in service.

What are the causes of overlap?

This fault may be caused by: incorrect electrode angle, incorrect travel speed, excessive passes or layers or incorrect welding technique.

What is spherical fault, for internal defect?

This fault tend to be less serious unless they are present in large quantities or are positioned in line. These internal discontinuities can be in the form of: 1. Porosity 2. Slag inclusions 3. Other inclusions

What are the internal defects on structural defect that happen during welding?

This include slag inclusion, lack of fusion, necklace cracking and incomplete filled groove. Internal discontinuities fall into to general categories: spherical and laminar.

What is Slag Inclusion?

This term describes oxides and other non-metallic solids that are sometimes found as elongated or irregular shaped inclusions in welds. Slag is always produced by SMAW, FCAW, and SAW.

What are dimensional defects after welding?

Those are defects that occur after welding are a direct result of either incorrect weld procedure or the welder not following the weld procedure.

Which are the codes and standards established for the proper storage of filler metals?

To avoid moisture from this source, the consumables should be stored under controlled conditions. Various codes and standards establish procedures for the proper storage of welding filler metals: -CSA Standard W59, -ASME Boilers and Pressure Vessels Code and -AWS D1.1.

What are the remedies for overlap?

To avoid this fault, use these precautions. Use proper joint preparation. Maintain correct current settings. Use recommended welding techniques. Use recommended electrode angles. Do not over-weld.

What are the remedies for excessive concavity (insufficient throat or leg)?

To avoid this fault, use these precautions. Use proper joint preparation. Maintain correct current settings. Use recommended welding techniques. Visually inspect the weld to ensure it has sufficient, but not excessive reinforcement on completion.

Causes of convexity on a weldment?

Travel speed to slow Incorrect electrode angle Incorrect electrode or filler metal size Incorrect welding technique Insufficient current

The relativity associated with weld defect in type and quantity level of problems depends on?

Type of weld and service requirements. An imperfection deemed harmful in one case may be acceptable in another.

What are the effects of distortion or warpage?

Uncontrolled distortion can cause the welded components to be badly out of shape that extensive work is required to straighten them or the pieces may need to be replaced. Both alternatives can be very time-consuming and expensive.

Can undercut be corrected?

Undercut of the sidewalls of a groove does not the complete weld and should be corrected if possible. However, some construction codes and standards allow limited amount of undercut to remain in the weld. The amount of undercut allowed depends on its location relative to the direction of stress placed on the weld.

What is upset in welding?

Upset welding (UW) is a resistance welding process utilizing both heat and deformation to form a weld. A wide variety of shapes and materials can be joined using upset welding in either a single-pulse or continuous mode.

Another name for weld fault?

Weld defect and weld discontinuities

Testing methods for structural discontinuities in the weld zone?

Weld faults of this nature are often internal, so visual examination for these faults is ineffective. Non-destructive testing methods such as radiographic examination and ultrasonic testing are effective means of detecting internal structural discontinuities.

What are stress flow lines?

When any stress is applied to an object, imaginary lines of force run through the object.

Flame-cut surfaces on preparation methods:

When oxy-fuel cutting torch is not operated properly, notches and irregularities may occur. Quite often, slag may adhere to these notches and surfaces and, if it is not removed prior to welding, faults such as porosity, lack of fusion, slag entrapment and chemical composition defects may occur.

Stress flow lines are?

When you apply any type of stress to an object, imaginary lines of force known as stress flow lines run through the object. In an object with uniform dimensions and no defects, these lines are evenly spaced and run parallel to the general outline of the object being stressed.

What happens if a rapid changes in cross-section?

Where joints are to be made between parts of unequal thickness, failure to taper out rapid changes in a cross-section leads to severe notching effect and possible failure of the weldment.

What are the remedies for distortion or warpage?

You can control distortion by: 1. Ensuring accuracy during preparation and fit-up of the components. 2. Strict adherence to welding specifications and procedures 3. Using jigs, braces and supports when required.

What is hardness?

a material's ability to resist an indentation and permanently be deformed.