Visual inspection and Weld Discontinuities- Causes and Remedies

Visual inspection and Weld Discontinuities- Causes and Remedies

Oleh : Bayu Nurwinanto

Basic Safety Precautions

Burn Protection. Molten metal, sparks, slag, and hot work surfaces are produced by welding, cutting, and allied processes. These can cause bums if precautionary measures are not used. Workers should wear protective clothing made of fire-resistant material. Pant cuffs, open pockets, or other places on clothing that can catch and retain molten metal or sparks should not be worn. High-top shoes or leather leggings and fire-resistant gloves should be worn. Pant legs should be worn over the outside of high-top shoes. Helmets or hand shields that provide protection for the face, neck, and ears, and a head covering to protect the head should be used. In addition, appropriate eye protection should be used.

Electrical Hazards. Electric shock can kill. However, it can be avoided. Live electrical parts should not be touched. The manufacturer’s instructions and recommended safe practices should be read and understood. Faulty installation, improper grounding, and incorrect operation and maintenance of electrical equipment are all sources of danger.

All electrical equipment and the workpiece should be grounded. The workpiece lead is not a ground lead. It is used only to complete the welding circuit. A separate connection is required to ground the workpiece. The workpiece should not be mistaken for a ground connection.

Fumes and Gases. Many welding, cutting, and allied processes produce fumes and gases which may be harmful to health. Avoid breathing the air in the fume plume directly above the arc. Do not weld in a confined area without a ventilation system. Use point-of-welding fume removal when welding galvanized steel, zinc, lead, cadmium, chromium, manganese, brass, or bronze. Do not weid on piping or containers that have held hazardous materials unless the containers have been inerted properly.

Compressed Gas Cylinders. Keep caps on cylinders when not in use. Make sure that gas cylinders are chained to a wall or other structurai support.

Radiation. Arc welding may produce ultraviolet, infrared, or light radiation. Always wear protective clothing and eye protection to protect the skin and eyes from radiation. Shield others from light radiation from your welding operation.

Visual Inspection Notes

Visual Inspection is a very effective inspection method, and it should be the primary method included in any effective Quality Control Program. It has been shown repeatedly that, “Visual inspection, conducted by properly trained inspectors, results in the discovery of the vast majority of those defects which would only be discovered later by some mom expensive nondestructive test method.” While visual inspection is limited to materials’ surface-only examination, it often detects the most damaging defects. Visual inspection [abbreviated “VT’ by the American Society for Nondestructive Testing (ASNT)] of welded components requires inspectors to have a broad knowledge of many technologies, including welding, destructive testing, nondestructive testing, and metallurgy, as well as the correct terminology for each.

it is important to distinguish between the words ‘discontinuity’ and ‘defect’. Discontinuity refers to “An interruption of the typical structure of a material, such as a lack of homogeneity in its mechanical, metallurgical, or physical characteristics; a discontinuity is not necessarily a defect.” A defect refers to “A condition, or conditions, that render a

part unable to meet applicable minimum acceptance standards or specifications.” All defects are discontinuities, but not all discontinuities are defects. A defect can be considered a ‘rejectable discontinuity.

 Cracks

A crack is defined as “A fracture type discontinuity characterized by a sharp tip and a high ratio of length and width to opening displacement.” Cracks are usually considered the most severe discontinuity because of their tendency to propagate under stress. Cracks are usually further described by their location geometry, time of occurrence, or common usage terms; see figure below for AWS crack terminology.

NO	LEGEND
1.	CRATER CRACK
2.	FACECRACK
3.	HEAT-AFFECTED ZONE CRACK
4.	LAMELLAR TEAR
5.	LONGITUDINAL CRACK
6.	ROOTCRACK
7.	ROOT SURF ACE CRACK
8.	THROAT CRACK
9.	TOE CRACK
10.	TRANSVERSE CRACK
11.	UNDERBEAD CRACK
12.	WELD INTERFACE CRACK
13.	WELD METAL CRACK

Types of cracks often include the following prefixes: base metal, cold, crater, delayed, face, heat-affected zone, hot, hydrogen, intergranular, lamellar tear, longitudinal, quench, root, service induced, stress corrosion, throat, toe, transgranular, transverse, underbead, weld metal, and others.

Crack detection can be achieved visually if the crack is present on the surface and is of sufficient size to be visible to the eye. Smooth, clean surfaces, oblique angle lighting, and a lox power magnifier are extremely helpful during visual inspection for surface cracking. If the surface cracking cannot be found visually, the next step is the use of the Penetrant Test method (a)M.ag netic Particle Testing (MT) can also be used, but is limited to testing magnetic base materials. Ultrasonic Testing (UT), Eddy Current Testing (ET), and Radiographic Testing (RT) are required for the detection of subsurface cracking. Refer to the AWS Welding Inspection Technology materials for more details regarding IT, MT, UT, ET, and RT.

Cracking can be caused by a multitude of conditions, but the more common causes are: embrittlement of the base or weld metal caused by too-rapid cooling and the formation of brittle martensite, weld shrinkage stresses, insufficient root bead size, poor joint design, nonmatching filler metals, and corrosive environment. See following chart for specific causes and recommended remedies.

Repairs to cracks include the following general requirements :

• Locate crack extent and orientation.
• Grind to remove completely; confirm with NDT. Do not weld over (on top of) cracks.
• Weld using proper procedure, including preheat if required, use small diameter electrodes and stringer bead progression.
• NDT finished weld and base metal.

Note : The above procedures may not result in a suitable repair of stress corrosion cracking, which may require replacement of the affected part or parts.

COMMON CAUSES AND REMEDIES OF CRACKING
Causes: Weld Metal Cracking	Remedies: Weid Metal Cracking
Highly rigid joint	Preheat Relieve residual stresses mechanically (peening) Minimize shrinkage stresses using backstep or block welding sequence
Excessive dilution	Change welding current and travel speed Weld with covered electrode neeative: butter the ioint faces prior to welding.
Defective electrodes	Change to new electrode; bake electrodes to remove moisture.
Poor fit-up	Reduce root opening; build up the edges with weld metal. Increase root opening.
Small weld bead	Increase electrode size; raise welding current; reduce travel speed
High sulfur base metal	Use filler metal low in sulfur
Angular distortion	Change to balanced welding on both sides of joint
Crater cracking	Fill crater before extinguishing the arc; use a welding current decay device when terminating the weld bead
Causes: Heat-Affected Zone	Remedies: Heat-Affected Zone
Hydrogen in weiding atmosphere	Use low-hydrogen welding process; preheat and hold for 2 hour after welding or postweld heat treat immediately
Hot cracking	Use low heat input; deposit thin layers; change base metal and/or filler metal.
Low ductility	Use preheat; anneal base metal prior to welding.
High residual stresses	Redesign weldment; change welding sequence; apply intermediate stress-relief heat treatment.
High hardenabilit	Preheat; increase heat input; heat treat without cooling to room temperature.
Brittle phases in the microstructure	Solution heat treat prior to welding

Inclusions

Inclusions are defined as “Entrapped foreign solid material, such as slag, flux, tungsten, or oxide.” The inclusions may be found as single particles, aligned particles, or clustered particles. Slag inclusions are frequently found on the weld surfaces, or along the toes of the weld due to improper cleaning techniques. Tungsten inclusions are usually subsurface. Examples of inclusions are shown below. Inclusions on the surface can be

detected by VT; subsurface inclusions require UT or RT.

Slag Inclusions (darkened areas)

Repairs of inclusions on the surface require removal by gouging or grinding, welding if required, and reinspection by appropriate NDT method. Subsurface inclusions require removal by gouging or grinding, followed by weld repair and reinspection.

Common Causes and Remedies of Slag Inclusions
Causes	Remedies
Failure to remove slag	Clean surface and previous weld bead
Entrapment of refractory oxides	Power wire brush the previous weld bead
Tungsten in the weld metal	Avoid contact between the electrode and the work use larger electrode
Improper joint design	Increase groove angle of joint
Oxide inclusions	Provide proper gas shielding
Slag flooding ahead of the welding arc	Reposition work to prevent loss of slag control
Poor electrode manipulative technique	Change electrode or flux to improve slag control
Entrapped pieces of electrode covering	Use undamaged electrodes

Incomplete Fusion

Incomplete fusion is defined as “A weld discontinuity in which fusion did not occur between weld metal and  faces or adjoining weld beads.” Incomplete Fusion (IF) can occur on both groove welds and fillet welds. The term specifically applies to fillet welds where the weld does not extend to the joint root. See the figures below.

Detection of incomplete fusion using VT is possible if the discontinuity location is visible on the surface; oblique angle lighting and lox magnification aid the inspector. Generally, If is subsurface and is found using UT or RT methods. Repairs of incomplete fusion require removal of the discontinuity by gouging or grinding, followed by weld repair and final inspection.

Repairs of incomplete fusion require removal of the discontinuity by gouging or grinding, followed by weld repair and final inspection.

Common Causes and Remedies of Incomplete Fusion
Causes	Remedies
Insufficient heat input, wrong type or size of electrode. improper joint design, or inadequate gas shielding	Follow correct welding procedure specification
Incorrect electrode position	Maintain proper electrode position
Weld metal running ahead of the Arc	Reposition work, lower current, or increase weld travel speed
Trapped oxides or slag on weld groove or weld face	Clean weld surface prior to welding

Incomplete Joint Penetration

Incomplete joint penetration is defined as “A joint root condition in a groove weld in which weld metal does not extend through the joint thickness.” Note rhat it applies to groove welds only, norfillet welds. Examples of incomplete joint penetration (UP) are shown in the following figures.

Incomplete joint penetration can easily be found by VT if the root of the groove weld is visible; oblique angle lighting assists in its detection. For groove welds with the root not visible, UT or RT are required for detection.

Repairs for IJP, when access to the root of the groove weld is possible :

• Gouge or grind root to an oval, open shape, permitting access to root.
• Weld, followed by appropriate NDT method.

Repairs for IJP, where access to the root is not possible:

• Gouge or ground from the weld face to remove entire-weld down to joint root.
• Weld, followed by appropriate NDT method.

Common Causes and Remedies of Incomplete  Joint Penetration
Causes	Remedies
Excessively thick root face or insufficient root opening	Use proper joint geometry
Insuffcient heat input	Follow welding procedure specification
Slag flooding ahead of welding arc	Adjust electrode or work position
Electrode diameter too large	Use smaller electrodes in root or increase root opening
Misalignment of second side weld	Improve visibility or backgouge
Failure to backgouge when specified	Backgouge to sound metal if required in welding procedure specification
Bridging or root opening	Use wider root opening or smaller electrode in root pass

Overlap

Overlap is defined as “The protrusion of weld metal beyond the weld toe or weld root.” Examples are shown below for fillet and groove welds.

Detection of overlap is usually found by VT if the surfaces are visible to the eye: oblique lighting and lox magnification are helpful. PT and MT may be required to inspect questionable areas.

Repairs include removal of overlap by gouging or grinding as a minimum, and may require weid repairs to the gouged or ground areas, followed by reinspection using appropriate NDT method.

Common Causes and Remedies of Overlap
Causes	Remedies
Slow travel speed	Increase travel speed
Poor electrode manipulation	Additional welder training
Gravity effects	Additional welder training

Porosity

Porosity is defined as “Cavity-type discontinuities formed by gas entrapment during solidification or in a thermal spray deposit.” The porosity may be surface or subsurface, a single cavity, aligned, or clustered, and is represented by the following figures.

Repairs of porosity consist of removal of the affected area by gouging or grinding, weld repair, followed by reinspection by the appropriate NDT method.

Common Causes and Remedies of Porosity
Causes	Remedies
Excessive hydrogen, nitrogen, or oxygen in welding atmosphere	Use low-hydrogen welding process; filler metals high in deoxidizers; increase shielding gas flow
High solidification rate	Use preheat or increase heat input
Dirty base metal	Clean joint faces and adjacent surfaces
Dirty filler wire	Use specially cleaned and packaged filler wire, and store it in clean area
Improper arc length, welding current, or electrode manipulation	Change welding conditions and techniques
Volatization of zinc from brass	Use copper-silicon filler metal; reduce heat input
Galvanized steel	Remove zinc prior to welding Use E6010 electrodes and manipulate the arc heat to volatilize the zinc ahead of the molten weld pool
Excessive moisture in electrode covering or on joint surfaces	Use recommended procedures for baking and storing electrodes Preheat the base metal

Undercut

Undercut is defined as “A groove melted into the base metal adjacent to the weld toe or weid face and left unfilled by weid metal.” Examples are shown in the following figures.

Detection of surface undercut is easily found by VT using oblique lighting. ‘Catching a thumbnail’ in the undercut groove is also helpful in its detection. Measurement of undercut can be accurately determined using an undercut gauge shown in the following figure. Internal undercut on groove welds where access to the root is not possible requires UT or RT methods.

Set bottom of gage on base material. Set point on bottom of undercut. Read depth on scale at pointer. Locking screw can be tightened to hold reading for future reference.

Repairs to undercut usually require light grinding and additional welding to replace the base metal removed during the undercutting and repair grinding.

Common Causes and Remedies of Undercut
Causes	Remedies
Excessive welding current	Reduce welding current
Excessive travel speed	Reduce travel speed
Electrode manipulation	Additional welder train

Weld Profiles

Visual inspection is very useful in determining the adequacy of weld profiles; the actual welds are compared with code or specification requirements regarding convexity or concavity for fillet welds, and face and root reinforcement for groove welds. The following profiles are found in AWS D1.1, Structural Welding Code. Additionally, fillet weld sizes can be determined using fillet weid gages,

(A) DESIRABLE FILLET WELD PROFILES

(E) ACCEPTABLE FILLET WELD PROFILES

Note: Convexity, C. Of A Weld Or Individual Surface Bead With Dimension W Shall Not Exceed The Value Of The Following Table :

Maximum Convexity Of Fillet Welds
WIDTH OF WELD FACE OR INDIVIDUAL SURFACE BEAD, W	MAX CONVEXITY, C
W ≤ 5/16 in. (8 rnm)	1/16 in. (1.6 mm)
W > 5/16 in. TO w < 1 in. (25 mm)	118 in. (3 mm)
W ≥ 1 in.	3/16 in. (5 mm)

(C) UNACCEPTABLE FILLET WELD PROFILES

(D) ACCEPTABLE GROOVE WELD PROFILE IN BUTT JOINT

BUTT JOINT- BUTT EQUAL THICKNESS PLATE

BUTT JOINT (TRANSITION) - UNEQUAL THICKNESS PLATE

Note: Reinforcement R Shall Not Exceed 1/8 In. (3 mm)

(E) UNACCEPTABLE GROOVE WELD PROFILES IN BUTT JOINTS

EXCESSIVE REINFORCEMENT

INSUFFICIENT THROAT

EXCESSIVE  UNDERCUT

OVERLAP

Dimensional Considerations

An important aspect of VT is the measurements for size, geometry, and assembly of welded structures. The manufacturing drawings will show the required lengths, widths, thicknesses, diameters, etc., of the various components, as well as weld sizes. The inspector should determine the dimensional tolerances for each of the measurements specified, and consider them during component measurement for conformance. If the tolerances are not stated, the inspector should ask for clarification. Often, these tolerances are noted as 'minimums."maximums,' or a dimensional range such as "1 .500 - 1.750 inches." The inspector should also be aware that measurements can be given in the US. Customary units, or in the S.I. or metric units.

Dimensional Defects

Incorrect Joint Preparation

• Incorrect joint penetration subject to visual inspection, generally before welding is started. includes out-of-tolerance
• welding bevel or groove dimensions, base metal misalignment, and undesirable weld joint fit up conditions.
• Included in the requirements for weld joint preparation shall be inspection for removal of scale, paint, oil, etc., from the weld joint.                 
• Partial penetration weld joint preparations shall be visually inspected prior to welding to assure proper weld throat dimensions.

Incorrect Weld Size       

• Incorrect weld size subject to visual inspection includes undersized fillet weld leg dimensions and underfilled groove weld throat dimensions.
• Fillet weld size shall be determined by means of a fillet weld gage.

Incorrect Final Dimensions

Incorrect final dimensions subject to visual inspection include all conditions of dimensional inaccuracies, distortion, and lack of conformity to design requirements.

Standard Location of Elements of a Nondestructive Examination Symbol

The elements of a nondestructive examination symbol shall have standard locations with respect to each other as shown in the following figure.

Standard Location of Elements