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| A '''welding defect''' is any flaw that compromises the usefulness of a [[wikt:weldment|weldment]]. There is a great variety of welding defects. Welding imperfections are classified according to ISO 6520<ref>BS EN ISO 6520-1: "Welding and allied processes — Classification of geometric imperfections in metallic materials — Part 1: Fusion welding"(2007)</ref> while their acceptable limits are specified in ISO 5817 <ref>BS EN ISO 5817: "Welding — Fusion-welded joints in steel, nickel, titanium and their alloys (beam welding excluded) — Quality levels for imperfections" (2007)</ref> and ISO 10042. <ref>BS EN ISO 10042: "Welding. Arc-welded joints in aluminium and its alloys. Quality levels for imperfections" (2005)</ref>
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In some situations this comes down to personal preference in regards to a handful of [http://Www.Harrietoneilllaw.com/node/582620 diverse issues]. To open a folding knife, it will either be spring assisted or manual. Most folks favor for their knives to be spring assisted but manual tactical knives are in basic a safer options. |
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| ==Major causes==
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| According to the [[American Society of Mechanical Engineers]] (ASME), welding defect causes are broken down as follows: 45 percent poor process conditions, 32 percent operator error, 12 percent wrong technique, 10 percent incorrect consumables, and 5 percent bad weld grooves.<ref>{{Citation | last = Matthews | first = Clifford | title = ASME engineer's data book | page = 211 | publisher = ASME Press | year = 2001 | url = http://books.google.com/books?id=7nIqrfROowQC&pg=PA211 | isbn = 978-0-7918-0155-0 | postscript =.}}</ref>
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| ===Hydrogen embrittlement===
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| {{Main|Hydrogen embrittlement}}
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| ===Residual stresses===
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| {{Main|Residual stress}}
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| The magnitude of stress that can be formed from welding can be roughly calculated using:<ref>{{Citation | last = Bull | first = Steve | title = Magnitude of stresses generated | publisher = University of Newcastle upon Tyne | date = 2000-03-16 | url = http://www.staff.ncl.ac.uk/s.j.bull/mmm373/WFAULT/sld012.htm | accessdate = 2009-12-06 | archiveurl = http://www.webcitation.org/5lpLTHRZo | archivedate = 2009-12-06 | postscript =.}}</ref> | |
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| :<math>E \alpha \Delta T</math>
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| Where E is [[Young's modulus]], α is the [[coefficient of thermal expansion]], and ΔT is the temperature change. For steel this calculates out to be approximately {{convert|3.5|GPa|abbr=on}}.
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| ==Types==
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| ===Cracks===
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| [[File:Welding cracks.svg|400px|center]]
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| Defects related to [[fracture]].
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| ====Arc strike cracking====
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| Arc strike cracking occurs when the arc is struck but the spot is not welded. This occurs because the spot is heated above the material's upper critical temperature and then essentially quenched. This forms [[martensite]], which is brittle and micro-cracks. Usually the arc is struck in the weld groove so this type of crack does not occur, but if the arc is struck outside of the weld groove then it must be welded over to prevent the cracking. If this is not an option then the arc spot can be postheated, that is, the area is heated with an [[oxy-acetylene torch]], and then allowed to cool slowly.<ref>{{harvnb|Rampaul|2003|pp=207–208}}.</ref>
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| ====Cold cracking====<!-- [[Cold cracking]] redirects here -->
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| Residual stresses can reduce the strength of the base material, and can lead to catastrophic failure through cold cracking, as was the case with several of the [[World War II]] [[Liberty ship]]s' hulls. Cold cracking is limited to steels and is associated with the formation of [[martensite]] as the weld cools. The cracking occurs in the heat-affected zone of the base material. To reduce the amount of distortion and residual stresses, the amount of heat input should be limited, and the welding sequence used should not be from one end directly to the other, but rather in segments.<ref name="cary">{{harvnb|Cary|Helzer|2005|pp=404–405}}.</ref>
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| Cold cracking only occurs when all the following preconditions are met:{{Citation needed|date=December 2009}}
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| * susceptible microstructure (''e.g.'' [[martensite]])
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| * [[hydrogen]] present in the microstructure ([[hydrogen embrittlement]])
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| * service temperature environment (normal atmospheric pressure): -100 to +100 °F
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| * high restraint
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| Eliminating any one of these will eliminate this condition.
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| ====Crater crack====
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| Crater cracks occur when a crater is not filled before the arc is broken. This causes the outer edges of the crater to cool more quickly than the crater, which creates sufficient stresses to form a crack. Longitudinal, transverse and/or multiple radial cracks may form.<ref name="raj128">{{harvnb|Raj|Jayakumar|Thavasimuthu|2002|p=128}}.</ref>
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| ====Fusion-line crack====
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| The following is an excrept from a research on Damage Behavior of Welded Joints with Defects on Fusion Line
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| Two kinds of welded joints damage models,with notch and crack on fusion line,were applied to '''analyse the influences of the mechanical property heterogeneity and geometric heterogeneity such as intensity matching, base metal rupture strain,base metal strain-hardening exponential and welding line width on the damage distribution and the relationship between damage parameter and rupture paremater'''. In addition, in the presence of entire damage zone method, the crack extension behaviors of the welded joints were investigated.
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| Base metal mechanical property has great effects on the damage distribution of the welded joints. On condition of similar load,the ''welded joints damage value increases with the decreasing base metal rupture strain and the increasing base metal strain-hardening exponential and intensity matching.''
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| For under-matched welded joints,the damage concentration zone of the welded joints near the notch will transfer from the welded metal side to the base metal side as the base metal rupture strain decreases and strain-hardening exponential increases. but for over-matched welded joints, the damage concentration zone will transfer from the base metal side to the welded metal side as the base metal rupture strain increases and strain-hardening exponential decreases.
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| On the other hand, the varied welded line width has little effect on the damage distribution of the welded joints.For the welded joints with crack on fusion line,when loaded and when the crack mouth opening distance reaches the same level,the maximum damage value in front of the crack increases as the base metal strain-hardening exponential and intensity matching increase,but decreases as the base metal rupture strain increases.
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| The establishment of the failure principle on the welded structure should take mechanical property heterogeneity into serious consideration. The numerical calculations of the crack extension behavior which is based on the entire damage zone viewpoint reveal that the '''crack extension path is parallel to the fusion line on condition of plane stress but on condition of plane strain the angle between the crack extension path and the fusion line is approximate 45°'''.The numerical calculations and analysis indicate that micro-damage parameter and macro -rupture parameter both can describe the stress-strain behaviors,and their relationship intensively relies on mechanical property heterogeneity. The investigation on the micro-damage parameter and macro -rupture parameter is undoubtedly supplement to the safety evaluation and life-span prediction of the welded joints,which is of great theory significance.
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| ====Hat crack====
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| [[File:Hat crack.svg|thumb]]
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| Hat cracks get their name from the shape of the cross-section of the weld, because the weld flares out at the face of the weld. The crack starts at the fusion line and extends up through the weld. They are usually caused by too much [[voltage]] or not enough speed.<ref name="raj128"/>
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| ====Hot cracking====
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| Hot cracking, also known as solidification cracking, can occur with all metals, and happens in the fusion zone of a weld. To diminish the probability of this type of cracking, excess material restraint should be avoided, and a proper filler material should be utilized.<ref name="cary"/> Other causes include too high welding current, poor joint design that does not diffuse heat, impurities (such as [[sulfur]] and [[phosphorus]]), preheating, speed is too fast, and long arcs.<ref>{{Citation | last = Bull | first = Steve | title = Factors promoting hot cracking | publisher = University of Newcastle upon Tyne | date = 2000-03-16 | url = http://www.staff.ncl.ac.uk/s.j.bull/mmm373/WFAULT/sld013.htm | accessdate = 2009-12-06 | archiveurl = http://www.webcitation.org/5lpX2E1S7 | archivedate = 2009-12-06 | postscript =.}}</ref>
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| ====Underbead crack====
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| An undercut crack, also known as a heat-affected zone (HAZ) crack,<ref name="raj126"/> is a crack that forms a short distance away from the fusion line; it occurs in [[low alloy steel|low alloy]] and [[high alloy steel]]. The exact causes of this type of crack are not completely understood, but it is known that dissolved [[hydrogen]] must be present. The other factor that affects this type of crack is [[internal stress]]es resulting from: unequal contraction between the base metal and the weld metal, restraint of the base metal, stresses from the formation of martensite, and stresses from the [[Precipitation (chemistry)|precipitation]] of hydrogen out of the metal.<ref>{{harvnb|Rampaul|2003|p=208}}.</ref>
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| ====Longitudinal crack====
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| Longitudinal cracks run along the length of a weld bead. There are three types: ''check cracks'', ''root cracks'', and ''full centerline cracks''. Check cracks are visible from the surface and extend partially into weld. They are usually caused by high shrinkage [[Stress (mechanics)|stress]]es, especially on final passes, or by a hot cracking mechanism. Root cracks start at the root and extent part way into the weld. They are the most common type of longitudinal crack because of the small size of the first weld bead. If this type of crack is not addressed then it will usually propagate into subsequent weld passes, which is how full centerline cracks (a crack from the root to the surface) usually form.<ref name="raj128"/>
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| ====Reheat cracking====
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| Reheat cracking is a type of cracking that occurs in HSLA steels, particularly [[chromium]], [[molybdenum]] and [[vanadium]] steels, during postheating. The phenomenon has also been observed in austenitic stainless steels. It is caused by the poor creep ductility of the heat affected zone. Any existing defects or notches aggravate crack formation. Things that help prevent reheat cracking include heat treating first with a low temperature soak and then with a rapid heating to high temperatures, grinding or [[peening]] the weld toes, and using a two layer welding technique to refine the HAZ [[crystallite|grain structure]].<ref>{{Citation | last = Bull | first = Steve | title = Reheat cracking | publisher = University of Newcastle upon Tyne | date = 2000-03-16 | url = http://www.staff.ncl.ac.uk/s.j.bull/mmm373/WFAULT/sld017.htm | accessdate = 2009-12-06 | archiveurl = http://www.webcitation.org/5lpXkrGfA | archivedate = 2009-12-06 | postscript =.}}</ref><ref>{{Citation | last = Bull | first = Steve | title = Reheat cracking | publisher = University of Newcastle upon Tyne | date = 2000-03-16 | url = http://www.staff.ncl.ac.uk/s.j.bull/mmm373/WFAULT/sld018.htm | accessdate = 2009-12-06 | archiveurl = http://www.webcitation.org/5lpYdb66E | archivedate = 2009-12-06 | postscript =.}}</ref>
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| ====Root and toe cracks====
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| A root crack is the crack formed by the short bead at the root(of edge preparation) beginning of the welding, low current at the beginning and due to improper filler material used for welding.Major reason for happening of these types of cracks is hydrogen embrittlement. These types of defects can be eliminated using high current at the starting and proper filler material. Toe crack occurs due to moisture content present in the welded area,it as a part of the surface crack so can be easily detected. Preheating and proper joint formation is must for eliminating these types of defects.{{Empty section|date=December 2009}}
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| ====Transverse crack====
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| A gap or break in the surface of a weld perpendicular to the weld axis that may be completely within the weld metal or may extend from the weld metal into the base metal. Excess hydrogen, an excessively strong weld metal, and high levels of residual stress result in transverse cracks.
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| ===Distortion===
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| Welding methods that involve the melting of metal at the site of the joint necessarily are prone to shrinkage as the heated metal cools. Shrinkage then introduces residual stresses and distortion. Distortion can pose a major problem, since the final product is not the desired shape. To alleviate certain types of distortion the workpieces can be offset so that after welding the product is the correct shape.<ref>{{harvnb|Weman|2003|pp=7–8}}.</ref> The following pictures describe various types of welding distortion:<ref>{{Citation | last = Bull | first = Steve | title = Welding Faults and Defects | publisher = University of Newcastle upon Tyne | date = 2000-03-16 | url = http://www.staff.ncl.ac.uk/s.j.bull/mmm373/WFAULT/sld010.htm | accessdate = 2009-12-06 | archiveurl = http://www.webcitation.org/5lpDLc6Iw | archivedate = 2009-12-06 | postscript =.}}</ref>
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| <gallery perrow=5 widths=130px heights=130px>
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| File:Welding shrinkage transverse.svg|Transverse shrinkage
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| File:Welding angular distortion.svg|Angular distortion
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| File:Welding shrinkage longitudinal.svg|Longitudinal shrinkage
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| File:Welding fillet distortion.svg|Fillet distortion
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| File:Welding neutral axis distortion.svg|Neutral axis distortion
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| </gallery>
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| ===Gas inclusion===
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| Gas inclusions is a wide variety of defects that includes ''porosity'', ''blow holes'', and ''pipes'' (or ''wormholes''). The underlying cause for gas inclusions is the entrapment of gas within the solidified weld. Gas formation can be from any of the following causes: high [[sulphur]] content in the workpiece or [[electrode]], excessive moisture from the electrode or workpiece, too short of an [[Arc welding|arc]], or wrong welding [[Electric current|current]] or [[Electrical polarity|polarity]].<ref name="raj126">{{harvnb|Raj|Jayakumar|Thavasimuthu|2002|p=126}}.</ref>
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| ===Inclusions===
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| There are two types of inclusions: ''linear inclusions'' and ''rounded inclusions''. Inclusions can be either ''isolated'' or ''cumulative''. Linear inclusions occur when there is [[slag]] or [[flux]] in the weld. Slag forms from the use of a flux, which is why this type of defect usually occurs in welding processes that use flux, such as [[shielded metal arc welding]], [[flux-cored arc welding]], and [[submerged arc welding]], but it can also occur in [[gas metal arc welding]]. This defect usually occurs in welds that require multiple passes and there is poor overlap between the welds. The poor overlap does not allow the slag from the previous weld to melt out and rise to the top of the new weld bead. It can also occur if the previous weld left an undercut or an uneven surface profile. To prevent slag inclusions the slag should be cleaned from the weld bead between passes via [[grinding (abrasive cutting)|grinding]], [[wire brushing]], or chipping.<ref>{{Citation | title = Defects/imperfections in welds - slag inclusions | url = http://www.twi.co.uk/content/jk43.html | accessdate = 2009-12-05 | archiveurl = http://www.webcitation.org/5lp4O9zyW | archivedate = 2009-12-05 | postscript =.}}</ref>
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| Isolated inclusions occur when [[rust]] or [[mill scale]] is present on the base metal.<ref>{{Citation | last = Bull | first = Steve | title = Welding Faults and Defects | publisher = University of Newcastle upon Tyne | date = 2000-03-16 | url = http://www.staff.ncl.ac.uk/s.j.bull/mmm373/WFAULT/sld007.htm | archiveurl = http://www.webcitation.org/5lnmtLCCy | archivedate = 2009-12-05 | postscript =.}}</ref>
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| ===Lack of fusion and incomplete penetration===
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| Lack of fusion is the poor adhesion of the weld bead to the base metal; incomplete penetration is a weld bead that does not start at the root of the weld groove. Incomplete penetration forms channels and crevices in the root of the weld which can cause serious issues in pipes because corrosive substances can settle in these areas. These types of defects occur when the welding procedures are not adhered to; possible causes include the current setting, arc length, electrode angle, and electrode manipulation.<ref>{{harvnb|Rampaul|2003|p=216}}.</ref>
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| Defects can be varied and classified as critical or non critical. Porosity (bubbles) in the weld are usually acceptable to a certain degree. Slag inclusions, undercut, and cracks are usually non acceptable. Some porosity, cracks, and slag inclusions are visible and may not need further inspection to require their removal. Small defects such as these can be verified by Liquid Penetrant Testing (Dye check). Slag inclusions and cracks just below the surface can be discovered by Magnetic Particle Inspection. Deeper defects can be detected using the Radiographic (X-rays) and/or Ultrasound (sound waves) testing techniques.
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| ===Lamellar tearing===
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| Lamellar tearing is a type of welding defect that occurs in [[rolling (metalworking)|rolled]] [[steel]] plates.<ref name="bull">{{Citation | last = Bull | first = Steve | title = Welding Faults and Defects | publisher = University of Newcastle upon Tyne | date = 2000-03-16 | url = http://www.staff.ncl.ac.uk/s.j.bull/mmm373/WFAULT/sld016.htm | archiveurl = http://www.webcitation.org/5ll21lW3L | archivedate = 2009-12-03 | postscript =.}}</ref> It has rarely been an issue since the 1970s because steel produced since then has less [[sulfur]].<ref name="still">{{Citation | last = Still | first = J. R. | title = Understanding Hydrogen Failures | url = http://www.aws.org/wj/jan04/still_feature.html | accessdate = 2009-12-03 | postscript =.}}</ref>
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| There is a combination of causes: non-metallic [[Inclusion (casting)|inclusion]]s, too much [[hydrogen]] in the material, and shrinkage forces perpendicular to the face of the plates. The main factor among these reasons is the non-metal inclusions, of which the sulfur is the main problem. Lamellar tearing is no longer a problem anymore because sulfur levels are typically kept below 0.005%.<ref name="still"/>
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| Some things that are done to overcome lamellar tearing are: reducing amount of sulfur in the material or adding alloying elements that control the shape of [[sulfide]] inclusions, such as [[rare earth element]]s, [[zirconium]], or [[calcium]].<ref name="ginzburg">{{Citation | last = Ginzburg | first = Vladimir B. | last2 = Ballas | first2 = Robert | title = Flat rolling fundamentals | page = 142 | publisher = CRC Press | year = 2000 | url = http://books.google.com/books?id=NeKG76F4KWUC&pg=PA141 | isbn = 978-0-8247-8894-0 | postscript =.}}</ref> A more drastic option is change the workpieces to [[casting (metalworking)|castings]] or [[forging]]s because this type of defect does not occur in those workpieces.<ref name="bull"/>
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| ===Undercut===
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| [[File:Welding undercut.svg|thumb]]
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| Undercutting is when the weld reduces the cross-sectional thickness of the base metal, which reduces the strength of the weld and workpieces. One reason for this type of defect is excessive current, causing the edges of the joint to melt and drain into the weld; this leaves a drain-like impression along the length of the weld. Another reason is if a poor technique is used that does not deposit enough [[filler metal]] along the edges of the weld. A third reason is using an incorrect filler metal, because it will create greater [[temperature gradient]]s between the center of the weld and the edges. Other causes include too small of an electrode angle, a dampened electrode, excessive arc length, and slow speed.<ref>{{harvnb|Rampaul|2003|pp=211–212}}.</ref>
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| {{clear}}
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| ==References==
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| {{Reflist|2}}
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| ===Bibliography===
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| * {{citation | last = Cary | first = Howard B. | last2 = Helzer | first2 = Scott C. | year = 2005 | title = Modern Welding Technology | location = Upper Saddle River, [[New Jersey]] | publisher = Pearson Education | isbn = 0-13-113029-3 | postscript =.}}
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| *{{Citation | last = Raj | first = Baldev | last2 = Jayakumar | first2 = T. | last3 = Thavasimuthu | first3 = M. | title = Practical non-destructive testing | publisher = Woodhead Publishing | year = 2002 | edition = 2nd | url = http://books.google.com/books?id=qXcCKsL2IMUC | isbn = 978-1-85573-600-9 | postscript =.}}
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| *{{Citation | last = Rampaul | first = Hoobasar | title = Pipe welding procedures | publisher = Industrial Press | year = 2003 | edition = 2nd | url = http://books.google.com/books?id=cie00sSLFqoC | isbn = 978-0-8311-3141-8 | postscript =.}}
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| *{{Citation | last = Moreno | first = Preto | title = Welding Defects | publisher = Aracne | year = 2013 | edition = 1st | isbn = 978-88-548-5854-1 | postscript =.}}
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| * {{citation | last = Weman | first = Klas | year = 2003 | title = Welding processes handbook | location = New York, NY | publisher = CRC Press | isbn = 0-8493-1773-8 | postscript =.}}
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| | |
| ==External links==
| |
| *[http://www.aws.org/wj/jan04/still_feature.html Understanding Hydrogen Failures]
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| *[http://www.ndt-ed.org/EducationResources/CommunityCollege/Radiography/TechCalibrations/RadiographInterp.htm Radiograph Interpretation - Welds]
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| {{DEFAULTSORT:Welding Defect}}
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| [[Category:Welding]]
| |
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The blade is 40 percent serrated and options two reliefs. The tanto edge is extremely sharp, and really thick. The Border Guard is created to be a rescue knife so I wanted to simulate its makes use of as a rescue knife The knife's weight and grip size make it easy to stab with. The sharp blade sliced by way of fabrics with ease. I learned this by stabbing an old chair to the hilt and ripping it across the length of the seat. Gerber is a knife business that needs no introduction and Bear Grylls has turn out to be a household name in survival, especially in finest multitools and survival equipment. When they combined and started producing a line of knives and tools that have earned rather the reputation. 12.125 7 ten 1095 Carbon Steel $ 4.five ALMAR ALS2K Sere 2000 Knife
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The Stone Cold Tanto is one particular of the tactical knives in the Black Label series released by Browning. It attributes a 5.7” stainless steel, tanto-point blade. The blade is partially serrated near the base. The knife has a solid pommel that has been pressure tested to make sure it remains tough even beneath intense pressure. This tanto was built to final for a extended time. The handle is grooved to let your fingers to rest effortlessly in them. It is wrapped with a durable desert camo paracord that makes gripping less difficult. A strip of cord is attached to the base of the manage to be employed as replacement, if required.
The Protected Keeper II can be used in either a punching or slashing motion. One of the wonderful items about this knife is that even a somewhat untrained user can efficiently wield this. Plus, it is next to impossible for any individual to disarm the user. About two thirds of the blade is a fine edge and one third serrated. Out of the box this blade is incredibly sharp and can shave the hair off of the back of my hand. The knife is well balanced and with the center of gravity falling proper under exactly where my 4 finger naturally wraps about the deal with. Getting applied lots of survival knives, I've discovered the best size to be around 9-11 inches in length. For example, my Blackbird SK-five survival knife pictured below is 10” in All round length with a 5” blade. p.s. WHO CARES ITS A Great KNIFE
SOG is a leader in knife manufacturing and their knives have won praise with numerous in the market. The SOG Flash II is an excellent reasonably priced option for the each-day-carry knife and looks comparable in look to the Benchmade Griptilian. It really is razor sharp with an AUS-eight stainless steel blade which is partially serrated and very durable. The Flash II utilizes spring assisted opening technologies which ensures a quick, smooth opening and the handle is glass-reinforced nylon which results in a lightweight but sturdy style. For added safety the knife contains a locking switch which will ensure the blade does not accidentally deploy.
There also shouldn't be any sharp corners or pinch points when holding the knife. The more comfortable it is in your hand, the better you will be able to wield it, especially under high pressure situations like those a police officer, military serviceman, or rescue professional will commonly be in. What Are the best handle materials for tactical knives? The opening mechanism , or deployment mechanism , is very important on a tactical pocket knife. For many people it's important that the blade can easily and quickly be opened with either hand and only requires one hand to open. This will be essential in those moments when you have to think quick and take action on the drop of a dime. Plain Edge Blade Pocket Folder Gladius A Victorinox Swiss Army knife
We only reviewed 5 leading tactical knife here, but there are a lot a lot more excellent knives waiting to be discovered. For example, if you are looking for the straight edge knife, make certain you verify out Spyderco ParaMilitary G-10 Plain Edge Knife It is 1 of the very best folding knife out there on the marketplace. For those hunting for excellent worth and trustworthy efficiency, Morakniv Bushcraft Carbon Fixed Blade Knife is the a single you can not miss. Of course, there are other popular excellent knives such as Zero Tolerance ZT0350TS and Cold Steel 27TLT Recon 1 Folding Knife , Both were reviewed in good detail. Now, It's Your Turn
Maybe the most crucial component of a tactical knife is it's functionality. Whether you are using it for each and every day operate or as a self-defence deterrent, you'll want the knife to be effortless to use. In some situations this comes down to personal preference in regards to a handful of diverse issues. To open a folding knife, it will either be spring assisted or manual. Most folks favor for their knives to be spring assisted but manual tactical knives are in basic a safer options.