常見(jiàn)焊接缺陷及檢驗(yàn)方法

1、常見(jiàn)焊接缺陷常見(jiàn)焊接缺陷2010-1-11一、焊接缺陷一、焊接缺陷 定義： 在焊接過(guò)程中，在焊接接頭中產(chǎn)生的不符合標(biāo)準(zhǔn)要求的缺陷，稱(chēng)為焊接缺陷。 分類(lèi)；依據(jù)GB641786,可將缺陷分為以下六類(lèi)： 裂紋 孔穴 固體夾雜 未熔合和未焊透 形狀缺陷 其他缺陷。2010-1-11焊接缺陷的特征及分布焊接缺陷的特征及分布 一、裂紋 依照裂紋產(chǎn)生的溫度范圍劃分： 熱裂紋：可分為 結(jié)晶裂紋 液化裂紋 高溫失塑裂紋 （原因分析） 冷裂紋：主要產(chǎn)生于焊接熱影響區(qū) （氫的作用） 在熱裂紋：工件焊接后再次被加熱 到一定溫度下 （消應(yīng)力熱處理 多層焊 服役期）42010-1-11母材中的夾層導(dǎo)致的裂紋母材中的夾層導(dǎo)

2、致的裂紋 由于板材在軋制過(guò)程中出現(xiàn)夾層，導(dǎo)致在焊接過(guò)程中出現(xiàn)裂紋：層狀撕裂52010-1-11層狀撕裂層狀撕裂 焊接工藝的調(diào)整 接頭形式的改善62010-1-11二、氣孔二、氣孔定義：焊接熔池中的氣泡在凝固時(shí)未能 及時(shí)溢出，而留下來(lái)所形成的孔穴。分類(lèi)：依形狀分 球形 條蟲(chóng)形 依分布分 孤立 均布 依來(lái)源分 析出型 (分析原因) 反應(yīng)型 （產(chǎn)生部位 原因） C+O=CO Fe+C=Fe+CO SiO2+2C=Si+2CO 防止措施：1 限制熔池中氣體的溶入或產(chǎn)生。（具體措施） 2 排除熔池中已溶入的氣體。 （具體措施）72010-1-11三三 、固體夾雜、固體夾雜 1 夾渣 焊后殘留在焊縫中的熔

3、渣 形狀 復(fù)雜 一般呈線(xiàn)狀、長(zhǎng)條狀、顆粒狀及其他形式。 部位 主要發(fā)生在坡口邊緣和每層焊道之間非圓滑過(guò)渡的部位。橫焊、立焊或仰焊比平焊多。 2 夾鎢 鎢極氬弧焊時(shí)，若鎢極不慎與熔池接觸，使鎢的顆粒進(jìn)入焊縫金屬中。 在焊接鎳鐵合金時(shí)，形成鎢合金，射線(xiàn)探傷很難發(fā)現(xiàn)。82010-1-11四四 、未焊透和未熔合、未焊透和未熔合 1 未焊透 焊接時(shí)母材金屬之間應(yīng)該熔合而未焊上的部分。 部位：?jiǎn)蚊婧傅钠驴诟?、雙面焊的坡口鈍邊。 危害：較大的應(yīng)力集中，在其末端產(chǎn)生裂紋。 2 未熔合 焊縫金屬與母材、焊縫金屬與焊道金屬之間未完全熔化結(jié)合的部分。92010-1-11五、形狀缺陷五、形狀缺陷 形狀缺陷包括： 1

4、 錯(cuò)邊、角變形 2 咬邊 3 焊瘤 4 燒穿和下塌 5 焊縫尺寸、形狀不合要求 6 其他缺陷 2010-1-11錯(cuò)邊錯(cuò)邊 定義：由于兩個(gè)焊件沒(méi)有對(duì)正而造成板的中心線(xiàn)平行偏差 成因: 粗心 .不同厚度的母材焊接 厚度過(guò)渡 預(yù)防: 改善工藝. 改變厚度過(guò)渡的過(guò)度角度。 修補(bǔ): 打磨. 在錯(cuò)邊不嚴(yán)重時(shí)可采用打磨的方法來(lái)處理 （板材）.管材內(nèi)部錯(cuò)邊較難處理.2010-1-11咬邊 定義: 由于焊接參數(shù)選擇或操作不當(dāng)，沿焊趾的母材部位產(chǎn)生的溝槽或凹陷 成因: 電流過(guò)大、 焊條角度不合適、電弧過(guò)長(zhǎng)。 預(yù)防措施: 清除焊縫兩側(cè)鐵銹 焊接位置 立焊 仰焊時(shí)較易出現(xiàn)咬邊的情況 修補(bǔ): 選用較小的焊條、最好是打磨

5、或挖鑿后用低氫 焊條來(lái)補(bǔ)焊.2010-1-11焊瘤焊瘤 定義:焊接過(guò)程中，熔化金屬流淌到焊縫之外未熔化的 母材上所形成的金屬瘤。（圖） 位置:焊瘤存在于焊縫表面，在其下面往往伴隨著未熔 合、未焊透等缺陷。 危害:由于金屬的堆積使焊縫的幾何形狀發(fā)生變化，造 成應(yīng)力集中。132010-1-11燒穿和下塌燒穿和下塌 定義：焊接過(guò)程中，熔化金屬自坡口背面流出， 形成穿孔的缺陷。 燒穿易發(fā)生在第一道焊道及薄板對(duì)接焊縫或管子對(duì)接焊縫中。燒穿的周?chē)０橛袣饪?、夾渣焊瘤及未焊透等缺陷。下塌：穿過(guò)單層焊縫根部，或在多層焊接接頭中穿 過(guò)前道熔敷金屬塌落的過(guò)量焊縫金屬。（圖）142010-1-11不規(guī)則的焊縫尺寸、

6、形狀不規(guī)則的焊縫尺寸、形狀Concavity 凹陷152010-1-11Convexity 凸出2010-1-11其他缺陷其他缺陷 1 電弧擦傷 2 飛濺172010-1-112010-1-11二、焊接檢驗(yàn)二、焊接檢驗(yàn)1 焊接檢驗(yàn)的分類(lèi)： （1）破壞性檢驗(yàn) （2）非破壞性檢驗(yàn) （3）聲發(fā)射檢測(cè)192010-1-11無(wú)損檢驗(yàn)無(wú)損檢驗(yàn) 射線(xiàn)檢測(cè) 超聲檢測(cè) 磁粉檢測(cè) 滲透檢測(cè) 渦流檢測(cè)202010-1-11射線(xiàn)檢測(cè)射線(xiàn)檢測(cè) 射線(xiàn)探傷的實(shí)質(zhì) 根據(jù)被檢工件與其內(nèi)部缺陷介質(zhì)對(duì)射線(xiàn)的衰減不同，而引起的射線(xiàn)透照之后到達(dá)底片上的強(qiáng)度不同，從而造成底片“感光”程度不同將缺陷在底片上反映出來(lái)。Some exampl

7、es (藥皮、藥渣、厚度方向缺陷不靈敏）212010-1-11射線(xiàn)的本質(zhì)射線(xiàn)的本質(zhì) X射線(xiàn) 射線(xiàn) 高頻電磁波 （光子）222010-1-11超聲波檢測(cè)超聲波檢測(cè) 超聲波檢測(cè)：是利用超聲波在物體中的傳播、反射和衰減等物理特性來(lái)發(fā)現(xiàn)缺陷的一種探傷方式。 聲波（人類(lèi)的聽(tīng)覺(jué)） 次聲波（地震、核武器） 超聲波（0.510MHz）（圖 Example） 探頭 （45 平） 耦合劑 （探頭不接觸工件表面）232010-1-11滲透檢測(cè)滲透檢測(cè) 滲透檢測(cè)：利用帶有熒光染料或紅色染料滲透劑的滲透作用，顯示缺陷痕跡的無(wú)損檢驗(yàn)方法。 用途：用于各種金屬材料和非金屬材料構(gòu)件表面開(kāi)口缺陷的檢驗(yàn)。242010-1-11滲

8、透檢驗(yàn)的原理滲透檢驗(yàn)的原理 1 毛細(xì)作用 2 兩平行板間的毛細(xì)現(xiàn)象252010-1-11聲發(fā)射探傷技術(shù)聲發(fā)射探傷技術(shù)2010-1-112010-1-112010-1-11Removing a root pass by grinding1. Recreate the groove geometry as closely as possible.2. Use a saw or die grinder and 1.5mm/1/16” 3.0mm/1/8” cut off wheel to recreate root opening. Remember repairs are sometimes re

9、quired to be made with a smaller electrode.3. Open the groove angle. Be careful to leave the proper root face dimension. 4. Feather the start and stop to blend smoothly into and out of the existing weld.2010-1-112010-1-11Excessive Concavity or ConvexityDefinition: Concavity or convexity of a fillet

10、weld which exceeds the specified allowable limits Cause: Amperage and travel speed Prevention: Observe proper parameters and techniques. Repair: Grind off or weld on. Must blend smoothly into the base metal. 2010-1-11Concavity2010-1-11Convexity2010-1-11Reinforcement Excessive Insufficient Improper c

11、ontourFace ReinforcementRoot ReinforcementThe amount of a groove weld which extends beyond the surface of the plate2010-1-11Excessive Reinforcement Definition: Specifically defined by the standard. Typically, Reinforcement should be flush to 1.5mm/1/16”(pipe) or flush to 3.0mm/1/8” (plate or structu

12、ral shapes). Cause: Travel speed too slow, amperage too low Prevention: Set amperage and travel speed on scrap plate. Repair: Remove excessive reinforcement and feather the weld toes to a smooth transition to the base plate.2010-1-11 Definition: Specifically defined by the standard. Typically, Under

13、fill may be up to 5% of metal thickness not to exceed 0.80mm/1/32” as long as the thickness is made up in the opposite reinforcement. Not applied to fillet welds. Cause: On root reinforcement - Too little filler metal will cause thinning of the filler metal. In OH position, too hot or too wide will

14、cause drooping of the open root puddle. Prevention: Use proper welding technique. Use backing or consumable inserts. Use back weld or backing. Repair: Possibly simply increase the face reinforcement. If backwelding is not possible, must remove and reweld.Insufficient Reinforcement2010-1-11 Definitio

15、n: When the weld exhibits less than a 1350 transition angle at the weld toe. Cause: Poor welding technique Prevention: Use proper techniques. A weave or whip motion can often eliminate the problem. Repair: The weld face must be feathered into the base plate.1350Improper Weld Contour2010-1-11Overlap

16、Definition: When the face of the weld extends beyond the toe of the weld Cause: Improper welding technique. Typically, electrode angles and travel speed. Prevention: Overlap is a contour problem. Proper welding technique will prevent this problem. Repair: Overlap must be removed to blend smoothly in

17、to the base metal. Be careful of deep grind marks that run transverse to the load. Also be careful of fusion discontinuities hidden by grinding. Use NDT to be sure.2010-1-11OverlapOverlap is measured with a square edge such as a 152.4mm/6” rule. No amount of overlap is typically allowed. Amount of o

18、verlap not determined by codes.2010-1-11Burn-through (non-standard) Definition: When an undesirable open hole has been completely melted through the base metal. The hole may or may not be left open. Cause: Excessive heat input. Prevention: Reduce heat input by increasing travel speed, use of a heat

19、sink, or by reducing welding parameters. Repair: Will be defined by standards. Filling may suffice. Otherwise, removal and rewelding may be required. Some standards may require special filler metal and/or PWHT.2010-1-11Incomplete or Insufficient Penetration Definition: When the weld metal does not e

20、xtend to the required depth into the joint root Cause: Low amperage, low preheat, tight root opening, fast travel speed, short arc length. Prevention: Correct the contributing factor(s). Repair: Back gouge and back weld or remove and reweld.2010-1-11Incomplete Fusion Definition: Where weld metal doe

21、s not form a cohesive bond with the base metal. Cause: Low amperage, steep electrode angles, fast travel speed, short arc gap, lack of preheat, electrode too small, unclean base metal, arc off seam. Prevention: Eliminate the potential causes. Repair: remove and reweld, being careful to completely re

22、move the defective area. This is sometimes extremely difficult to find.2010-1-11Arc Strike Definition: A localized coalescence outside the weld zone. In laymens language. An area where an electric arc scarred the base metal caused by electrode arc or electric cable being pulled across base metal. Ca

23、use: Carelessness Prevention: In difficult areas, adjacent areas can be protected using fire blankets. Repair: Where applicable, arc strikes must be ground smooth and tested for cracks. If found, they must be remove and repaired using a qualified repair procedure and inspected as any other weld.2010

24、-1-11Inclusions Slag Wagontracks lines of slag along one or both sides of bevel Tungsten 2010-1-11 Definition: Slag entrapped within the weld Cause: Low amperage, improper technique, Trying to weld in an area that is too tight. Slow travel in Vertical Down or not positioning electrode correctly in e

25、ither up or downhand positions. Prevention: Increase amperage or preheat, grind out tight areas to gain access to bottom of joint, position electrode correctly. Repair: Remove by grinding. Reweld.Slag Inclusion2010-1-11 Definition: Slang term for a groove left at the toe of a root pass which becomes

26、 filled with slag and is trapped in the weld. Cause: The contour of the root pass is too high, or the weld toe is not bonded to the base metal Prevention: Use proper technique to deposit the weld root. Repair: Best repaired before applying the hot pass. Carefully grind the root pass face flat. be ca

27、reful not to gouge other areas on the weldment.Wagon Tracks (non-standard)2010-1-11 Definition: A tungsten particle embedded in a weld. (Typically GTAW only) Cause: Tungsten electrode too small, amperage too high, AC balance on +, Upslope too high, electrode tip not properly ground, electrode dipped

28、 into the weld pool or touched with the fill rod, electrode split. Prevention: Eliminate the cause Repair: Grind out and reweldTungsten Inclusion2010-1-11Inclusions Fix when you see it. Otherwise grind out & fix when found to be unacceptable by non-destructive examinations.2010-1-11Whiskers, Gra

29、pes, or Excessive Push Through Unsightly Inhibits material flow in piping Are inclusions Can break off in pipes and damage equipment downline2010-1-11Spatter Definition: Small particles of weld metal expelled from the welding operation which adhere to the base metal surface. Cause: Long arc length,

30、severe electrode angles, high amperages. Prevention: Correct the cause. Base metal can be protected with coverings or hi-temp paints or other means. Repair: Remove by grinding or sanding. 2010-1-11Arc Craters Definition: A depression left at the termination of the weld where the weld pool is left un

31、filled. Cause: Improper weld termination techniques Prevention: Pause at this point and allow to fill prior to breaking arc. Repair: If no cracks exist, simply fill in the crater. Generally welding from beyond the crater back into the crater.2010-1-11Cracks Longitudinal Transverse Crater Throat Toe

32、Root Underbead and Heat-affected zone Hot Cold or delayed2010-1-11 Definition: A crack running in the direction of the weld axis. May be found in the weld or base metal. Cause: Preheat or fast cooling problem. Also caused by shrinkage stresses in high constraint areas. Prevention: Weld toward areas

33、of less constraint. Also preheat to even out the cooling rates. Repair: Remove and reweldLongitudinal Crack2010-1-11 Definition: A crack running into or inside a weld, transverse to the weld axis direction. Cause: Weld metal hardness problem Prevention: Repair:Transverse Crack2010-1-11 Definition: A

34、 crack, generally in the shape of an “X” which is found in a crater. Crater cracks are hot cracks. Cause: The center of the weld pool becomes solid before the outside of the weld pool, pulling the center apart during coolingof the outside. Prevention: Use crater fill, fill the crater at weld termina

35、tion and/or preheat to even out the cooling of the puddle Repair:Crater Crack2010-1-11 Definition: A longitudinal crack located in the weld throat area. Cause: Transverse Stresses, probably from shrinkage. Indicates inadequate filler metal selection or welding procedure. May be due to crater crack p

36、ropagation. Prevention: Correct initial cause. Increasing preheat may prevent it. be sure not to leave a crater. Use a more ductile filler material. Repair: Remove and reweld using appropriate procedure. Be sure to correct initial problem first.Throat Crack2010-1-11 Definition: A crack in the base m

37、etal beginning at the toe of the weld Cause: Transverse shrinkage stresses. Indicates a HAZ brittleness problem. Prevention: Increase preheat if possible, or use a more ductile filler material. Repair: Toe Crack2010-1-11 Definition: A crack in the weld at the weld root. Cause: Transverse shrinkage s

38、tresses. Same as a throat crack. Prevention: Same as a throat crack Repair:Root Crack2010-1-11 Definition: A crack in the unmelted parent metal of the HAZ. Cause: Hydrogen embrittlement Prevention: Use Lo/Hi electrodes and/or preheat Repair: (only found using NDT). Remove and reweld.Underbead Crack2

39、010-1-11 Definition: A crack in the weld that occurs during solidification. Cause: Micro stresses from weld metal shrinkage pulling apart weld metal as it cools from liquid to solid temp. Prevention: Preheat or use a low tensil filler material. Repair:Hot Crack2010-1-11 Definition: A crack that occu

40、rs after the metal has completely solidified Cause: Shrinkage, Highly restrained welds, Discontinuities Prevention: Preheat, weld toward areas of less constraint, use a more ductile weld metal Repair: Remove and reweld, correct problem first, preheat may be necessary.Cold Crack2010-1-11Repairs to Cr

41、acks Determine the cause Correct the problem Take precautions to prevent reoccurrence Generally required to repair using a smaller electrode2010-1-11Base Metal Discontinuities Lamellar tearing Laminations and Delaminations Laps and Seams2010-1-11LaminationsBase Metal DiscontinuityMay require repair

42、prior to weldingFormed during the milling process2010-1-11Lamination effects can be reduced by joint design:2010-1-11Delaminations2010-1-11Laps and SeamsA mill-induced discontinuity in which results from a lump of metal being squeezed over into the surface of the material. If beyond acceptable limit

43、s, must be removed and repaired or discarded.2010-1-11Porosity Single Pore Uniformly Scattered Cluster Linear Piping2010-1-11Single Pore Separated by at least their own diameter along the axis of the weld2010-1-11Uniformly Scattered Porosity Typically judged by diameter and proximity to a start or s

44、top often caused by low amperage or short arc gap or an unshielded weld start2010-1-11Cluster Porosity Typically viewed as a single large discontinuity2010-1-11Linear Porosity being linear greatly affects the severity of this discontinuity2010-1-11Piping Porosity Generally has special allowable limi

45、ts2010-1-11Porosity preheat will help eliminate may need an electrode with more deoxidizers Use run-on/run-off taps restart on top of previous weld and grind off lump2010-1-11Heat-affected zone microstructure alteration add drawing of HAZ of groove weld with leaders to: grain refinement grain growth

46、 hardened areas softened areas precipitate suseptable areas.2010-1-11Size or dimension If it renders the part unusable, it is a defect. If it is outside the allowable limit, it renders the part unusable. Things dont have to be perfect, just within the acceptable tolerance. Working to perfection is t

47、oo time consuming and costly2010-1-11Hammer marks Stress risers Unsightly Unnecessary2010-1-11REPAIR TECHNIQUES May involve: different process different procedure different preheat/PWHT different electrode smaller electrode2010-1-11Only repair defects. Discontinuities are, by definition, acceptable.

48、 Repair is therefore unnecessary and not cost effective.2010-1-11Inspection Tools2010-1-11Fillet Weld Size - For equal leg fillet welds, the leg lengths of the largest isosceles right triangle that can be inscribed within the fillet weld cross section. For unequal leg fillet welds, the leg lengths of the largest right triangle that can be inscribed within the fillet weld cross sectionMeasuring Weld Sizes2010-1-11Fibre M