Visual Inspection of Welds

 

Visual Inspection Of Welds (VT)

 

Visual Inspection Of Welds (VT) Failure Due To Brittle Cracking

 

Visual Inspection Of Welds (VT) Prerequisites

 As with any other non destructive inspection method, there are various prerequisites that should be considered prior to performing visual examination. Some of the more common attributes to consider are discussed as follows:

 

Visual Inspection Of Welds (VT)

Visu isua al Acuity Acui ty

One of the most obvious prerequisites is that the visual examiner should have sufficient visual acuity to perform an adequate inspection. Consideration should be given to near and far vision with natural or corrected vision.

 

Visual Inspection Of Welds (VT) Visu isua al Acuity Acui ty

 A documented periodic visual inspection of requirement of many codes & specifications andthe is generally considered good practice.  An eye examination by a qualified examiner is a prerequisite for the certification by AWS as a Certified Welding Inspector (CWI) or A Certified Associate Welding Weldin g Inspect Inspector or (CAW (CAWI). I). CSWI CSWIP P – Visua Visuall Inspect Inspector or or Welding Inspector.

 

Visual Inspection Of Welds (VT) Exp xpe eri rie enc nce e & Traini Training ng

 Another obvious prerequisite is that the visual inspector should have sufficient knowledge and skill to perform the examination successfully and meaningfully. Knowledge and skill can be imparted or obtained through the education and training processes. Both method can be formal (classroom) or on the job.

 

Visual Inspection Of Welds (VT) Sufficient time should be allowed for different individuals to properly grasp key points pertaining to:   

Joint Preparations Welding preheat

Int Interp erpass assnttem temper peratu ature Weld We ldme ment dist di stor orti tion on re  Welding consumables and other materials.  Additionally, sufficient exposure to the many types of workmanship variances should be allowed. 

 

Visual Inspection Of Welds (VT)

Certi rtific fica atio tion n Progr rogra amme

To provide assurance that visual inspectors are qualified (that is, sufficient prerequisites are obtained and maintained), it may be desirable to have visual inspection personnel formally certified. Certification is a testimony of qualification.

 

Visual Inspection Of Welds (VT)

Certi rtific fica atio tion n Progr rogra amme

The American Welding Society offers Certified Welding Inspector (CWI) and Certified Associate Welding Inspector (CAWI) programme. Other programme such as TWI / CSWIP also offers such programme.

 

Visual Inspection Of Welds (VT)

Safety

Visual inspectors should receive sufficient indoctrination on welding safety practices. There are many safety hazards present gases, potential fumes, ultraviolet light, heat, etc.). (electricity,

 

Visual Inspection Of Welds (VT) Fun undame dament nta als Of Visual Ins Inspecti pection on..

Many programme instituted by the manufacturer or fabricator to control quality of the products utilise visual examination as the primary, and in some instances the only, evaluation method of inspection. It can be an invaluable tool when properly applied. In addition to locating surface flaws, visual examination can be an excellent process control technique to help identify subsequent fabrication problems.

 

Visual Inspection Of Welds (VT) Visual examination is a method for identifying surface flaws and imperfections. Consequently, any conscientious quality control programme consisting essentially of visual inspection should include a continual sequence of examinations performed during all phases of fabrication. This will allow visual inspection of the exposed surfaces as they occur in the fabrication sequence.

 

Visual Inspection Of Welds (VT)

Discovery and repair of any defects at that time results in substantial cost reduction. It has been shown that a conscientious programme of visual before, during, and of after weldinginspection can resultoccurring in discovery of the majority all defects which would have been detected later using more expensive test methods.

 

Visual Inspection Of Welds (VT)

The effectiveness of visual inspection is improved when a at system is instituted which provides for coverage all phases of the welding process (before, during, and after welding). The sooner the examination process is introduced into the system, the better the coverage.

 

Visual Inspection Of Welds (VT) Insp nspe ecti ction on Prio riorr To We Weldi lding. ng.

Prior to welding, some typical action items requiring attention by the visual inspector include: • Re Rev vie iew w dra draw win ings gs and and sp spec ecif ific icat atio ion n • Chec Check k qual qualif ific icat atio ion n of pr proc oced edur ures es and and per perso sonn nnel el to to be utilised • Establish check points • Set Set up up a pl plan an fo forr the the re reco cord rdin ing g of of res resul ults ts • Re Rev vie iew w ma matter eria ials ls to be be ut utililis ised ed

 

Visual Inspection Of Welds (VT) Insp nspe ecti ction on Prio riorr To Weldi Welding. ng. • Ch Chec eck k for for ba base se me meta tall dis disco cont ntin inui uiti ties es

• Chec Check k ffit it-u -up p and and al alig ignm nmen entt of of wel weld d joi joint nts s • Check pr preheat, if required If the preliminary inspector pays close which attention to these items,particularly many problems might occur later can be prevented. It is very important that the inspector knows exactly what requirements are to be met. Governing construction specifications will provide these data.

codes

and

 

Joint Configuration

 

Visual Inspection Of Welds (VT) Hold Points. Point s.

Consideration should be given to the establishment of hold points or check points where an examination is to occur prior to the accomplishment of any further fabrication steps. This is of utmost importance on large construction projects or massive welded fabrications.

 

Visual Inspection Of Welds (VT) Weld ldin ing g Proce Proc edu dures res  Another preliminary step which should occur is to

ensure that the applicable welding procedures comply with the job requirements. The proper documentation of the qualification or certifications of the individual welders should be reviewed. The drawings and specifications will dictate what base metals are to be joined and what filler metal will be utilised.

 

Visual Inspection Of Welds (VT) Weld ldin ing g Proce Proc edu dures res For structural welding and other critical applications,

welding is normally carried out in accordance with qualified procedures which record the essential variables of the process and by welders qualified for the process, material, and position to be welded.  Additional procedural steps might be needed to accommodate certain materials. An example of a procedural step is that when low-hydrogen electrodes are specified, storage facilities as recommended by the manufacturer are required.

 

Visual Inspection Of Welds (VT) Base Materials.

Prior to welding, identification of the material type and a thorough examination of the specific base metal should be made. If a discontinuity, such as a plate lamination, is present and remains undetected, it may affect the overall structural integrity of the weldment. Very often, a lamination will be visible along plate edge, especially on a flame cut edge.

 

Visual Inspection Of Welds (VT) Joint Joi nt Fit-up. Fit-up.

For a weld, the most critical part of the base material is that area which has been prepared to accept weld metal in some form of joint shape. The importance of the joint fit prior to welding cannot be stressed enough. Therefore, the visual examination of joint fit-up is of highest priority.

 

Visual Inspection Of Welds (VT) Joint Joi nt Fit-up. Fit-up.

Items that may be considered prior to welding include:  Groove angle  Root opening      

Joint alignment Backing Consumable insert Joint cleanliness Tack welds Preheat

 

Visual Inspection Of Welds (VT) Joint Preparation / Fit-up

 

Visual Inspection Of Welds (VT) Joint Preparation

 

Visual Inspection Of Welds (VT) Preheating

 

Visual Inspection Of Welds (VT) Preheating

 

Visual Inspection Of Welds (VT) Jointt Fit-up. Join Fit-up.

 All of these factors could a direct bearing on the the resultant weld quality. If have the fit-up is poor, then weld will most likely be of substandard quality as well. Extra care taken during the joint assembly can greatly improve welding effectiveness. Sometimes, examination of the joint prior to welding will reveal irregularities within code limitations, but these becomes areas of concern and can be watched carefully during later stage.

 

Visual Inspection Of Welds (VT) Joint Joi nt Fit-up. Fit-up.

For example, if a T-joint for fillet weld exhibits an excessive root opening, the size of the required fillet weld should be increased by the amount of the root opening present. So, if the inspector knows that this situation exists, the drawing or weld joint can be marked accordingly, and final determination of weld size compliance can be correctly interpreted.

 

Jointt FitJoin Fit-up up - Exc Excess essive ive Gap

 

Visual Inspection Of Welds (VT)

Duri uring ng Weldi lding. ng.

During welding, there are a number of items which require control so that the resulting weld will be satisfactory. Visual examination is the primary method for controlling this aspect of the fabrication.

 

Visual Inspection Of Welds (VT) Duri uring ng Weldi lding. ng.

      

Some ofinclude: these aspects of fabrication which can be checked Quality of weld root bead Joint root preparation prior to welding the second side Preheat and inter Preheat interpass pass temp temperat erature ure Sequence of weld pass Subsequent layers for apparent weld quality Cleaning between passes Conformance with the applicable procedure; i.e. voltage, amperage, heat input, speed, etc.

 

Visual Inspection Of Welds (VT) Weld Roo oott Pass

Perhaps the most critical part of any root pass. Problems which exist at progression combine to make completion of the balance of the accomplish. Consequently,

many

defects

weld is the weld this point in the the successful weld difficult to

which

are

later

discovered in a weld associated with the weld root bead.

 

Visual Inspection Of Welds (VT) Weld We ld Root Pa Pass ss

 Another critical joint root condition exists whenever second side treatment is applied to a double welded  joint. This usually includes removal of slag and other irregularities by chipping, thermal gouging, or grinding. Once this removal process has been accomplished, examination of the excavated area prior to welding the second side is required. This is to assure that all discontinuities have been removed.

 

Visual Inspection Of Welds (VT) Pre rehe hea at & Interpa nterpass ss Tempera mperatur ture e

Preheat & inter Preheat interpass pass tempe temperatur rature e can be be critical critical and, and, if specified, be measured. The limits are often described as a minimum, a maximum, or as both.  Also, to help in controlling the amount of heat in the weld zone, the sequence and placement of the individual passes can be important.

 

Visual Inspection Of Welds (VT) Pre rehe hea at & Interpa nterpass ss Tempera mperatur ture e

The inspector should always be conscious of the extent and location of any distortion or shrinkage caused by the welding heat. Often, corrective measures can be taken as the welding heat progresses to alleviate the problem.

 

Visual Inspection Of Welds (VT) Betwe Betw een Layer Exami Examinati nation on

To evaluate the quality of the weld as work progress, it is prudent to examine each layer visually to judge its integrity. This also provides a check to determine if adequate cleaning is being accomplished between passes. This may help to alleviate the occurrence of slag inclusions in the final weld.

 

Visual Inspection Of Welds (VT)

Betwe Betw een Layer Exami Examinati nation on

Many of these items may be addressed in the applicable welding procedure. In that case, visual inspection performed during the welding is basically a check to determine id there is compliance with the requirements of the welding procedure.

 

Visual Inspection Of Welds (VT)  Aff t er Wel  A Weld ding.

Many people feel that visual inspection commences once the welding has been completed. However, if all the previously discussed steps have been taken before and during welding, this final phase of visual inspection will be accomplished easily. It will simply provideinaacheck to be sure have resulted satisfactory weld.that the steps taken

 

Visual Inspection Of Welds (VT) Some of the th e va vario rious us ite i tems ms whic w hich h require attentio attention n aft fte er we w eld ldin ing g ha h as be b een comp c omplete leted d are: are:  

Final weld appearance Final weld size

Weld length  Dimensional accuracy   Amount of distortion 



Post weld heat treatment.

 

Visual Inspection Of Welds (VT) Fin ina al Weld Weld Ins nspecti pection on

The basic purpose of final weld inspection is to assure the weld’s quality. Therefore, visual examination of several things are required. Most codes and specifications describe the extent of discontinuities that are acceptable, and many of these can occur on the surface of the completed weld.

 

Visual Inspection Of Welds (VT) Discontinuities Typical discontinuities in found in welds are: • Porosity • Incomplete fusion • In Inco comp mple lete te jo join intt pe pene nettra rati tion on • Undercut • Overlap • Cracks • Slag Inclusion • Exces ess sive re rein infforcem eme ent.

 

Weld Discontinuities

 

Visual Inspection Of Welds (VT) Weld Discontinuities

 

Visual Inspection Of Welds (VT) Discontinuities While code requirements may permit limited amounts of some of these discontinuities, cracks and incomplete fusion defects are not allowed. For structures exposed to cyclic or fatigue loading, the criticality of these surface discontinuities is increased. In conditions such as these, visual examination of the surface may be the most important inspection which can be performed.

 

Visual Inspection Of Welds (VT) Discontinuities The existence of undercut, overlap and improper contour results in stress raisers; fatigue loading can cause premature failures which propagate from these discontinuities. This is why, often the proper contour of a weld can be much more important than the actual weld size, since a slightly undersized weld, free from abrupt surface irregularities, could perform more satisfactorily than a weld of adequate size exhibiting a poor contour.

 

Visual Inspection Of Welds (VT) Discontinuities To determine if compliance has been attended, the examiner should check to see if all welds meet drawing requirements for size and location. Fillet size can be determined by using one or several types of weld gauges to provide a more efficient and accurate measurement of size. Groove

welds

should

be

measured

for

proper

reinforcement on both sides of the joint. Some conditions may require the fabrication of special weld gauges

 

Visual Inspection Of Welds (VT) Post We Weld ld He Heat at Treat Treat ment

Due to size, shape, or base metal type, post weld heat treatment may be specified in the welding procedure. This may involve only the application of heat at or near the interpass interpass tempe temperatur rature e range to provide provide a post weld weld condition that will aid in metallurgical control of the final weldme weldment nt proper properties. ties.affect Heating Heati ng at the interpa interpass ss temperature will not the microstructure.

 

Visual Inspection Of Welds (VT) Post We Weld ld He Heat at Treatm Treatment ent

Some conditions may require the accomplishment of a thermal therm al stress stress relief treat treatment. ment. Here Here,, the the weldme weldment nt is gradually heated at a prescribed rate to the stress relief rel ief ran range ge of 590 590ºº C to 650 650ºº C for for most most carb carbon on stee steel. l.  After holding at this temperature for one hour for each on once ce doftoba base se tome meta tall th thic ickn knes ess, s, a th then en olwe weld ldme ment nt is allowed allowe cool cool about 315º C at control contr rat rate. e.

 

Visual Inspection Of Welds (VT)

Fin ina al Dimensional Dimensio nal Examinatio Examination n

 Another measurement that affects the performance of a wewill weldm ldment ent is an its assembly, its dimensiona dimens ional accuracy. accura If a wel welded ded part not fit itl may becy. useless, even though the weld is of adequate quality.

 

Visual Inspection Of Welds (VT)

Welding heat will distort the base metal, and can alter overall component dimensions.

Therefore, after may be required requireddimensional to determin determine eexamination the weldment weldments’s s’s welding fitness fitnes s for its its intended use.

 

Visual Inspection Of Welds (VT) Disc iscont ontinu inuiti itie es & Defe Defects cts

 A discontinuity is defined as an interruption of the typical structure of a weldment, such as lack of homogeneity in the mechanical, metallurgical, or physical characteristics of the material or weldment.  A discontinuity is not necessarily a defect. Disc Di scon onti tinu nuit itie ies s are are re rejec jecta tabl ble e onl only y if if the they y exc excee eed d specification requirements in terms of type, size, distribution, or location.

 

Visual Inspection Of Welds (VT) Disc iscont ontinu inuiti itie es & Defe Defects cts

 A rejectable discontinuity is referred to as defects. By definition, a defect is a discontinuity whose size, shape, orientation, or location makes it detrimental to the useful service of the part in which it occur.

Discontinuities may bemetal foundofin the weldments. weld metal, heat affected zone, or base many

 

Visual Inspection Of Welds (VT)

Four basic weld joints are considered in this presentation:  

Butt T



Corner 



L ap

 

Visual Inspection Of Welds (VT) Disc iscont ontinu inuiti itie es & Defe Defects cts

Weld and base metal discontinuities of specific types are more common with certain welding processes and  joint details are used.  An example is the tungsten inclusion, which only occurs in welds made using gas tungsten arc welding.

 

Visual Inspection Of Welds (VT)

Disc iscont ontinu inuiti itie es & Defe Defects cts

Other conditions, such as high restraint and limited access to portions of a weld leadbase to a higher than normal incidence of joint, weldmay and metal discontinuities.

 

Visual Inspection Of Welds (VT) Porosity Porosity is characterised by cavity type discontinuities

formed by gas entrapment during solidification. discontinuity formed is generally spherical but mayThe be cylindrical. Often, porosity is an indication that the welding process is not being properly controlled, or the base metal or filler metal is contaminated, or that the base metal is of a composition incompatible with the filler metal or process.

 

Visual Inspection Of Welds (VT) Porosity

 

Visual Inspection Of Welds (VT) Porosity

 

Visual Inspection Of Welds (VT) Scattere cattered d Porosit Poros ity y

Scattered porosity is porosity widely distributed in a single weld bead or in several beads of a multi pass weld. Porosity will be present in a weld if the welding technique, or material used or the conditions of the weld preparation, entrapment.

lead

to

gas

formation

and

If weld cool slowly enough to allow gas to pass to the surface before weld solidification, there will generally be no porosity in the weld.

 

Visual Inspection Of Welds (VT) Clus luster ter & Line Li nea ar Porosity Porosi ty Cluster porosity is a localised group of pores. It often

results from improper starting welding pass. Conditions causing arc and blowstopping can alsoof result in cluster porosity. Linear porosity is a number of pores which are aligned. It often occur along the weld interface, the weld root, or an inter-bead boundary, and developed by contamination that causes gas to be liberated at those locations.

 

Visual Inspection Of Welds (VT) Linear & Clustered Porosities

 

Visual Inspection Of Welds (VT) Incomplete Fusion

Incomplete fusion is termed as fusion which does not occur over the entire base metal surfaces intended for welding and between all adjoining weld beads. Incomplete fusion can result from insufficient heat input or the improper manipulation of the welding electrode. While it is a discontinuity more commonly associated with weld technique, it could also be caused by the presence of contaminants on the surface being welded.

 

Visual Inspection Of Welds (VT) Incomplete Fusion

 

Visual Inspection Of Welds (VT) Incomplete Fusion

 

Visual Inspection Of Welds (VT) Incomplete Fusion

 

Visual Inspection Of Welds (VT) Inco ncompl mple ete Joint Joi nt Penetra netratio tion n

Incomplete joint penetration is defined as penetration by weld metal that does not extend for the full thickness of the base metal in a joint with a groove weld. Incomplete penetration may result from insufficient welding heat, improper lateral control of the welding arc, or improper  joint configuration. Some welding process have greater penetrating ability than others and would therefore be less susceptible this discontinuities, problem. Pipesince welds vulnerable totothese the are joint especially is usually inaccessible for welding from the root side.

 

Visual Inspection Of Welds (VT) Incomplete Joint Penetration

 

Visual Inspection Of Welds (VT) Undercut Undercut creates

a transition which should be evaluated for a reduction in cross section, and for stress concentrations or notch effect when fatigue is a consideration.

Undercuts, controlled within the limits of the specification, is not usually considered a weld defect. Undercut is generally associated with improper welding technique or weld parameters, excessive welding current or voltages or both.

 

Visual Inspection Of Welds (VT) Undercut

 

Visual Inspection Of Welds (VT) Undercut

 

Visual Inspection Of Welds (VT) Underfill

Underf Unde rfill ill is a dep depre ress ssio ion n on the the weld weld fa face ce or or root root surface extending below the adjacent surface of the base metal metal.. Underf Underfill ill is usually usually define defined d as a condition condition where the total thickness through a weld is less than the thickness of the adjacent base metal. It results from the failure of a welder or welding operator to completely fill the weld joint, and is rarely acceptable.

 

Visual Inspection Of Welds (VT) Underfill

 

Visual Inspection Of Welds (VT) Overlap

Overlap is the protrusion of weld metal beyond the weld toe, or weld root. It can occur as a result of poor control of the welding process, improper selection of welding materials prior to welding. If there are tightly adhering oxides on the base metal that interfere with fusion, overlap will often result. Overlap is notch, a surface that forms a mechanical is oftendiscontinuity considered rejectable.

 

Visual Inspection Of Welds (VT) Overlap

 

Visual Inspection Of Welds (VT) Overlap

 

Visual Inspection Of Welds (VT) Lamination Laminations are flat, generally elongated, base metal discontinuity usually found at the centre of wrought product.

Lamination cannon be destructively completely internal, and are then only detected by ultrasonic testing. They may also extend to an edge or end where they are visible at the surface and may be detected by visual, penetrant, or magnetic particle testing. They may also be revealed when exposed by cutting or machining operations.

 

Visual Inspection Of Welds (VT) Lamination Laminations are formed when gas voids, shrinkage cavities, or They non metallic inclusions in theto original ingot are rolled flat. generally run parallel the surface of rolled products and are most commonly found in bars and plates. Some laminations are partially forged welded along their interface by high temperature and pressure of the rolling operation. Tight laminations will sometimes conduct sound across the interface and, therefore, may not be fully evaluated / detected by ultrasonic testing.

 

Visual Inspection Of Welds (VT) Lamination

 

Laminar Tearing

 

Visual Inspection Of Welds (VT) Cracks Cracks form in the weld and base metal when localised stresses the at ultimate strength of the material. Cracking exceed may occur evaluated temperatures during weld solidification, or after solidification, when the weldment weldm ent has equal equalised ised in temper temperature. ature. Cracking is generally associated with stress amplification near discontinuities in welds and base metal, or near notches associated with the weld joint design. Welding related cracks are generally brittle in nature, exhibiting little plastic deformation at the crack boundaries.

 

Visual Inspection Of Welds (VT) Cracks Cracks can be classified as either hot cracks or cold cracks. Hot cracks develop at elevated temperatures. They form on solidification of the metal at temperature near the melting point. Cold cracks develop after solidification id complete.

Cracking associated with hydrogen embrittlement, commonly commo nly referr referred ed to as ‘’delay ‘’delay crackin cracking,’’ g,’’ is a form form of of cold cracking. Hot cracks propagate along grain boundaries and through grains.

 

Visual Inspection Of Welds (VT) Various Types Of Cracks

 

Visual Inspection Of Welds (VT) Crack Ori rie ent nta atio tion. n. Crack orientation may

be

termed

longitudinal

or

transverse, depending on the crack direction with respect to the weld axis. When a crack is parallel to the axis of the weld, it is called a longitudinal crack, regardless of whetherr it is whethe is a centerlin centerline e crack in the weld metal or or a toe crack in the heat affected zone of the base metal. Transverse cracks lie perpendicular to the weld axis. This may be limited in size and confined to the weld metal or they propagate from the weld into the adjacent heat affected zone and into the base metal.

 

Visual Inspection Of Welds (VT) Crack Orientati Orientation on..

In some weldments, transverse heat affected zone and not in thecracks weld. will form in the Longitudinal cracks in welds, made by machine welding, are commonly associated with high welding speed and are sometimes related to porosity that does not showed at the weld face. Welds having high depth to width ratios also be susceptible longitudinal cracking due tomay the resulting solidi ficationtopatterns. solidification

 

Visual Inspection Of Welds (VT) Longitudinal Verses Transverse Crack.

 

Visual Inspection Of Welds (VT)

Throat Cracks

Throat cracks are longitudinal cracks in the weld face in the direction of the weld axis. They are generally, but not always hot cracks.

 

Visual Inspection Of Welds (VT) Solidification Cracking

 

Visual Inspection Of Welds (VT) Solidification Cracking

 

Visual Inspection Of Welds (VT)

Roo oott Crack Cracks. s.

Root cracks are longitudinal cracks in the weld root. They are generally hot cracks.

 

Visual Inspection Of Welds (VT) Root Cracks

 

Visual Inspection Of Welds (VT)

Crater Cra ter Crack racks s

Crater cracks occur in the weld crater and are formed by improper termination of welding arc. A non standard term for crater cracks is star cracks though they may have other shapes. Crater cracks are shallow hot cracks usually forming a multi-pointed star-like cluster.

 

Visual Inspection Of Welds (VT) Crater Cracks Crack s

 

Visual Inspection Of Welds (VT) Toe Cr Cr ack Toe cracks are generally cold cracks. They initiate and propagate from the weld toe where restraint stresses are highest. Abrupt profile changes at the toe caused by excessive convexity or weld reinforcement can amplify stresses, making the weld toe a more likely area for cracking to occur. Toe cracks initiate approximately normal to the base metal surface. These cracks are generally the result of thermal shrinkage stresses acting on the weld heat affected zone.

 

Visual Inspection Of Welds (VT) Toe Cracks

 

Visual Inspection Of Welds (VT) Underbe nderbea ad & HAZ HAZ Cra racks cks

Und nder erbe bead ad an and d hea heatt af affe fect cted ed zo zone ne cr crac acks ks ar are e generally cold cracks that form in the heat affected zone of the base metal. Underb Unde rbea ead d an and d heat heat aff affec ecte ted d zone zone cra crack cks s can can be either longitudinal or transverse. They are found at regular intervals under the weld and also outline boundaries of the weld where residual stresses are highest.

 

Visual Inspection Of Welds (VT) Unde nderbe rbea ad & HAZ Cra racks cks

Underbead cracks can become Underbead become a serious serious problem when the following three elements are present 

simultaneously: Hydrogen



Crack-susceptible microstructure



Stress

 

Visual Inspection Of Welds (VT) Sla lag g Incl nclusi usion on Slag inclusion are nonmetallic solid material entrapped in weld metal or between weld metal and base metal.

Slag inclusion are regions within the weld cross section or at the weld surface where once-molten flux used to protect the molten metal is mechanically trapped within the solidified metal. This solidified slag represents portion weld’s cross section where the metal isanot fusedoftothe itself.

 

Visual Inspection Of Welds (VT) Sla lag g Incl nclusi usion on

This can result in a weakened condition which could impair the serviceability of the component. Although normally thought of being subsurface discontinuities, inclusions may also appear at weld surface. Like incomplete fusion, slag inclusions can occur between the weld and base metal or between individual In fact, slag inclusion are often associatedweld withpasses. incomplete fusion.

 

Slag Inclusion

 

Visual Inspection Of Welds (VT) Weld Rein info forc rce ement. Weld reinforcement is weld metal in excess of the quantity required to fill a groove weld. It is that amount of weld metal in a groove weld that is above the base metal surface.

 All weld reinforcement produces a notch effect at the weld toe. Weld reinforcement, when excessive, does not add to the strengththe of applied the weld but may act as a stress raiser to amplify stress.

 

Visual Inspection Of Welds (VT) Weld Rein info forc rce ement.

Greater reinforcements are associated with reduced re-entrant angles, which result in greater notch effect. Reinforcement which are excessive tend to produce significant notch effects at the toe of the weld, which acts as stress raiser and can produce cracking in service.

 

Visual Inspection Of Welds (VT) Excessive Reinforcement

 

Weld Profile

 

Visual Inspection Of Welds (VT) Conv onve exit xity y & Concavity Convexity is the maximum distance from the face of a convex fillet weld perpendicular to a line joining the weld toes. Like weld reinforcement, when the amount of this convexity is excessive, the notch created at the weld toe could result in toe cracking.

Concavity is the maximum distance from the face of a concave fillet weld perpendicular to a line joining the weld Concavity is only weld. considered detrimental when toes. it results in an undersize

 

Visual Inspection Of Welds (VT) Concave Fillet Weld

 

Visual Inspection Of Welds (VT) Convex Fillet Weld

 

Visual Inspection Of Welds (VT)  Arr c St  A Strr i k es

 An arc strike is a discontinuity consisting of any localised re-melted metal, heat affected metal, or change in the surface profile of any part of a weld or base metal resulting from an arc.  Arc strikes result when the arc is initiated on the base metal surface away from the weld joint, either intentionally or accidentally.

 

Visual Inspection Of Welds (VT)  Arr c St  A Strr i k es

When this occurs, there is a localised area of the base metal surface which is melted and then rapidly cooled due to massive heat sink created by the surrounding base metal.  Arc strikes are not desirable and often not acceptable, as they could lead to cracking during cooling process or under fatigue conditions.

 

Visual Inspection Of Welds (VT)  Arc Strikes

 

Visual Inspection Of Welds (VT) Spatter  Spatter consist of metal particles expelled during fusion welding that do not form a part of the weld. Those particles that are actually attached to the base metal adjacent to the weld are the most disconcerting form of spatter. Particles which are thrown away from the weld and base metal are,

by definition, spatter. Normally, spatter is not considered to be a serious flaw unless its presence interferes with subsequent operations, especially nonbe destructive or the serviceability of the part. It might indicative testing, of the welding process being out of control.

 

Visual Inspection Of Welds (VT) Spatter 

 

Visual Inspection Of Welds (VT) Inspection Equip quipme ment nt There are numerous inspection devices used by the welding inspector. The following are some of the tools & gauges / instruments most frequently used in visual welding inspection:  

 Ampere meter 



Temperature sensitive crayons (Tempilstiks) Surface contact thermometer (Pyrometer)



Weld gauge



Fiberscope & borescope Ferrite gauge

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Visual Inspection Of Welds (VT)  Am  A m p er ere e met m eter  er 

 An ampere meter of the test type is aflowing unique, portable instrument that willtong measure current in a circuit without making an electrical connection to it. This is an efficient way to verify the amperage that is being used during welding. By placing the jaws of the tong tester around can the be conductor carrying current , a reading in amperes obtained.

 

Visual Inspection Of Welds (VT)  Ampere meter 

 

Visual Inspection Of Welds (VT) Temp mpe eratu rature re Se Sens nsit itiv ive e Crayo rayons ns

Temperature sensitive crayons are frequently used to give an approximate temperature indication. A crayon mark is made across the metal in the area to be checked; check ed; for for exampl example e 100º 100º C crayon, crayon, the tempe temperatu rature re of the the piece piece will will be at at least least 100º 100º C when when the the crayon crayon mark melts. This measurement usually should be made within 25 mm of the weld on the base metal. Crayon marks should never be made directly on the

weld because of possible contamination.

 

Visual Inspection Of Welds (VT) Temperature Sensitive Crayons

 

Visual Inspection Of Welds (VT) Sur urface face Con Contact tact Thermo hermometer  meter  The surface thermometer provides a direct indication of the surface temperature of pipe or other joint members. The an electrical The instrument offers directpyrometer indication is of temperature. point of which the probe is placed on the work and the temperature is read from the digital scale. These type of instruments give a more accurate indication than the surface thermometer and crayons.

 

Visual Inspection Of Welds (VT) Surface Contact Thermometer 

 

Visual Inspection Of Welds (VT) Weld Ga Weld Gaug uge e The fillet weld gauge offers a quick means of measuring most fillet welds of 3.2 mm through 25 mm in size. It measures both convex and concave fillet welds. Mult ultipu ipurpo rpose se Gauge There are several multipurpose welding gauges available on the market today. A multipurpose gauge is capable of performing many measurements, such as measuring convex and concave fillet welds, weld reinforcement, and root opening.

 

Visual Inspection Of Welds (VT) Multipurpose Gauge

 

Visual Inspection Of Welds (VT) Taper Ta per Ga Gaug uge e The taper gauge is inserted into the opening of a joint to measure root opening (gap) The root opening is taken from the gauge at the point where the gauge becomes snug in the joint. Hi-Lo Ga Hi-Lo Gaug uge e The hi-Lo gauge, also called a mismatch gauge, is used to measure the internal alignment of a pipe joint. After the gauge has been inserted and for adjusted, the thumb screw is tighten, and the tool is removed measurement of misalignment.

 

Visual Inspection Of Welds (VT) Hi-Lo Gauge

 

Visual Inspection Of Welds (VT) Taper Gauge /Fillet Weld Gauge

 

Visual Inspection Of Welds (VT) Fiberscop iberscope e & Videosc Videoscope ope

These Thes e are are fi fibe bero ropt ptic ic in inst stru rume ment nts s ide ideal al fo forr examination where there is restricted access.

weld wel d

 A flexible fiberscope is basically an optical instrument. This allows the inspector to look into small holes and around corners. These units are also available with magnifying lenses, screen, and the resultimages stored. can be projected on a

 

Visual Inspection Of Welds (VT) Fiberscope

 

Videoscope

 

Visual Inspection Of Welds (VT) Ferri errite te Ga Gaug uge e The present of a small fraction of the magnetic delta ferrite phase in an otherwise austenitic (non magnetic) weld metal has a pronounced in the influence in the prevention of weld centerline cracking and fissuring. The amount of ferrite in as-welded weld metal is largely, but not completely, controlled by a balance in the weld metal composition between the elements. ferrite-promoting elements and the austenite-promoting

 

Visual Inspection Of Welds (VT) Ferrit Ferr ite e Gauge Gauge When welding austenitic stainless steel, with insufficient delta ferrite structure, the weld metal has a tendency to develop small cracks or fissures. This small fissures tend to be located transverse to the weld interface in the weld beads and base metal that were reheated to near the

melting point. Ferrite content of the weld metal is indicated in ferrite number (FN), and may be bracketed between two values. This provides control in most minimum ferritesufficient content or a ferrite rangeapplications is specified. where

 

Visual Inspection Of Welds (VT) Ferritescope

 

Visual Inspection Of Welds (VT) Lighting

The have while adequate illumination, eitherinspector natural should or artificial, performing visual inspection. This may be determined using a fine line, approximately 0.8 mm in width, drawn on a 18% neutral grey card. The card should be placed near the area under examination; if this fine line is distinctly visible, the inspector may consider this as a demonstration of adequate illumination.

 

Visual Inspection Of Welds (VT) Lighting Generally, a flashlight / torchlight will provide sufficient lighting. Some co Some code de sp spec ecif ify y min minim imum um fo foot ot ca cand ndle le / lux lux of illumination that are required while performing visual inspection; for example 15fc (16lx) for general examination and a minimum of 50fc *54 lx) for the

detection of small discontinuities.

 

Visual Inspection Of Welds (VT) Records.  As with any type of inspection, once completed, any defective area should be identified in some manner to assure that it will be located and repaired properly. Many methods are available, so specific conditions may dictate which marking system would be more effective. One method commonly used is to record the type, size and location of any defects so that they can be located, identified and repaired. Perhaps more effective, however, is the identification of the defective area by marking

directly on the part.

 

Visual Inspection Of Welds (VT) Records  An inspector should be able to maintain adequate records. Inspectors should be able to writ clear and concise reports so that superiors will have no difficulty understanding reasons for past decisions if they are reviewed later.

Inspection report should be concise, yet complete enough to be clear to a reader unfamiliar with the product inspected. In preparing the records, the most basic facts should be included even though they are well known and understood timelater. of writing, since they may not be rememberedatsothe clearly

 

Visual Inspection Of Welds (VT) Records. Thus, good records not only protect the inspectors who wrote them, they also help in adhering to a policy of uniform standards.  Any work performed under a specification or code that requires req uires inspection, examination or tests may also require records. However, whether required or not, the inspector should kept adequate records. It is also the inspector’s duty to examine all records for completeness and accuracy in accordance with specified

requirements and to make certain that they are available when needed.

 

Visual Inspection Of Welds (VT) Records.  Any records that require the fabricator’s signature should be prepared by the fabricator rather than the inspector. Records in as much detail as necessary. inspectorshould shouldbe comment on the general characterThe of the work, how well it stayed within prescribed tolerances, difficulties that occurred, and any defects.

 Any repair should be explained. Copies of these records should goes to all persons entitled to receive them, and a copy should be kept for the t he inspector’s own file.

 

Visual Inspection Of Welds (VT) Records.

It should be remembered that facts well known at the time of the writing may not be recalled so clearly, completely, or accurately later. Check lists can be used to document inspection points during fabrication. Lack of explanatory information and documentation can result in costly delays.