4_常見焊接缺陷及檢驗方法

1、常見焊接缺陷常見焊接缺陷May.2010Volvo Construction Equipment2010-1-11一、焊接缺陷一、焊接缺陷 定義： 在焊接過程中，在焊接接頭中產(chǎn)生的不符合標(biāo)準(zhǔn)要求的缺陷，稱為焊接缺陷。 分類；依據(jù)GB641786,可將缺陷分為以下六類： 裂紋 孔穴 固體夾雜 未熔合和未焊透 形狀缺陷 其他缺陷。Volvo Construction Equipment2010-1-11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

2、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）Volvo Construction Equipment42010-1-11母材中的夾層導(dǎo)致的裂紋母材中的夾層導(dǎo)致的裂紋 由于板材在軋制過程中出現(xiàn)夾層，導(dǎo)致在焊接過程中出現(xiàn)裂紋：層狀撕裂Volvo Construction Equipment52010-1-11層狀撕裂層狀撕裂 焊接工藝的調(diào)整 接頭形式的改善Volvo Construction Equipment62010-1-11二、氣孔二、氣孔定義：焊接熔池中的氣泡在凝固時未能 及時溢出，而留下來所形成的孔穴。分類：依形狀分 球形 條蟲形 依分布分 孤立 均布 依來源

3、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）Volvo Construction Equipment72010-1-11三三 、固體夾雜、固體夾雜 1 夾渣 焊后殘留在焊縫中的熔渣 形狀 復(fù)雜 一般呈線狀、長條狀、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渡的部位。橫焊、立焊或仰焊比平焊多。 2 夾鎢 鎢極氬弧焊時，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，形成鎢合金，射線

4、探傷很難發(fā)現(xiàn)。Volvo Construction Equipment82010-1-11四四 、未焊透和未熔合、未焊透和未熔合 1 未焊透 焊接時母材金屬之間應(yīng)該熔合而未焊上的部分。 部位：單面焊的坡口根部、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。Volvo Construction Equipment92010-1-11五、形狀缺陷五、形狀缺陷 形狀缺陷包括： 1 錯邊、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 Volvo Construction Eq

5、uipment2010-1-11錯邊錯邊 定義：由于兩個焊件沒有對正而造成板的中心線平行偏差 成因成因: 粗心 .不同厚度的母材焊接 厚度過渡 預(yù)防預(yù)防: 改善工藝. 改變厚度過渡的過度角度。 修補(bǔ)修補(bǔ): 打磨. 在錯邊不嚴(yán)重時可采用打磨的方法來處理 （板材）.管材內(nèi)部錯邊較難處理.Volvo Construction Equipment2010-1-11咬邊 定義定義: 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 成因成因: 電流過大、電流過大、 焊條角度不合適、電弧過長。 預(yù)防措施預(yù)防措施: 清除焊縫兩側(cè)鐵銹 焊接位置 立焊 仰焊時較易出現(xiàn)咬邊的情況 修補(bǔ)修補(bǔ): 選用較小

6、的焊條、最好是打磨或挖鑿后用低氫 焊條來補(bǔ)焊.Volvo Construction Equipment2010-1-11焊瘤焊瘤 定義:焊接過程中，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。Volvo Construction Equipment132010-1-11燒穿和下塌燒穿和下塌 定義：焊接過程中，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接焊縫或管子對接焊縫中。燒穿的周圍常伴有氣孔、夾渣焊瘤及未焊透等缺

7、陷。下塌：穿過單層焊縫根部，或在多層焊接接頭中穿 過前道熔敷金屬塌落的過量焊縫金屬。（圖）Volvo Construction Equipment142010-1-11不規(guī)則的焊縫尺寸、形狀不規(guī)則的焊縫尺寸、形狀Concavity 凹陷凹陷Volvo Construction Equipment152010-1-11Convexity 凸出凸出Volvo Construction Equipment2010-1-11其他缺陷其他缺陷 1 電弧擦傷 2 飛濺Volvo Construction Equipment172010-1-11Volvo Construction Equipment201

8、0-1-11二、焊接檢驗二、焊接檢驗 焊接檢驗的分類： （1）破壞性檢驗 （2）非破壞性檢驗 （3）聲發(fā)射檢測Volvo Construction Equipment192010-1-11無損檢驗無損檢驗 射線檢測 超聲檢測 磁粉檢測 滲透檢測 渦流檢測Volvo Construction Equipment202010-1-11射線檢測射線檢測 射線探傷的實質(zhì) 根據(jù)被檢工件與其內(nèi)部缺陷介質(zhì)對射線的衰減不同，而引起的射線透照之后到達(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。Some examples (藥皮、藥渣、厚度方向缺陷不靈敏）Volvo Constructi

9、on Equipment212010-1-11射線的本質(zhì)射線的本質(zhì) X射線 射線 高頻電磁波 （光子）Volvo Construction Equipment222010-1-11超聲波檢測超聲波檢測 超聲波檢測：是利用超聲波在物體中的傳播、反射和衰減等物理特性來發(fā)現(xiàn)缺陷的一種探傷方式。 聲波（人類的聽覺） 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）Volvo Construction Equipment232010-1-11滲透檢測滲透檢測 滲透檢測：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

10、損檢驗方法。 用途：用于各種金屬材料和非金屬材料構(gòu)件表面開口缺陷的檢驗。Volvo Construction Equipment242010-1-11滲透檢驗的原理滲透檢驗的原理 1 毛細(xì)作用 2 兩平行板間的毛細(xì)現(xiàn)象Volvo Construction Equipment252010-1-11聲發(fā)射探傷技術(shù)聲發(fā)射探傷技術(shù)Volvo Construction Equipment2010-1-11Volvo Construction Equipment2010-1-11Volvo Construction Equipment2010-1-11Removing a root pass by gri

11、nding1. 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 required to be made with a smaller electrode.3. Open the groove angle. Be careful to leave the proper root face di

12、mension. 4. Feather the start and stop to blend smoothly into and out of the existing weld.Volvo Construction Equipment2010-1-11Volvo Construction Equipment2010-1-11Excessive Concavity or ConvexityDefinition: Concavity or convexity of a fillet weld which exceeds the specified allowable limits Cause:

13、 Amperage and travel speed Prevention: Observe proper parameters and techniques. Repair: Grind off or weld on. Must blend smoothly into the base metal. Volvo Construction Equipment2010-1-11ConcavityVolvo Construction Equipment2010-1-11ConvexityVolvo Construction Equipment2010-1-11Reinforcement Exces

14、sive Insufficient Improper contourFace ReinforcementRoot ReinforcementThe amount of a groove weld which extends beyond the surface of the plateVolvo Construction Equipment2010-1-11Excessive Reinforcement Definition: Specifically defined by the standard. Typically, Reinforcement should be flush to 1.

15、5mm/1/16”(pipe) or flush to 3.0mm/1/8” (plate or structural 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.Volvo Construction E

16、quipment2010-1-11 Definition: Specifically defined by the standard. Typically, Underfill 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 meta

17、l will cause thinning of the filler metal. In OH position, too hot or too wide will 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 i

18、s not possible, must remove and reweld.Insufficient ReinforcementVolvo Construction Equipment2010-1-11 Definition: 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

19、 problem. Repair: The weld face must be feathered into the base plate.1350Improper Weld ContourVolvo Construction Equipment2010-1-11Overlap Definition: When the face of the weld extends beyond the toe of the weld Cause: Improper welding technique. Typically, electrode angles and travel speed. Preven

20、tion: Overlap is a contour problem. Proper welding technique will prevent this problem. Repair: Overlap must be removed to blend smoothly into 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 s

21、ure.Volvo Construction Equipment2010-1-11OverlapOverlap is measured with a square edge such as a 152.4mm/6” rule. No amount of overlap is typically allowed. Amount of overlap not determined by codes.Volvo Construction Equipment2010-1-11Burn-through (non-standard) Definition: When an undesirable open

22、 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 sink, or by reducing welding parameters. Repair: Will be defined by standards. Filling may suffice. Othe

23、rwise, removal and rewelding may be required. Some standards may require special filler metal and/or PWHT.Volvo Construction Equipment2010-1-11Incomplete or Insufficient Penetration Definition: When the weld metal does not extend to the required depth into the joint root Cause: Low amperage, low pre

24、heat, 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.Volvo Construction Equipment2010-1-11Incomplete Fusion Definition: Where weld metal does not form a cohesive bond with the base metal.

25、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 remove the defective area. This is sometimes extre

26、mely difficult to find.Volvo Construction Equipment2010-1-11Arc 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. Cause: Carelessness Pr

27、evention: 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.Volvo Construction Equip

28、ment2010-1-11Inclusions Slag Wagontracks lines of slag along one or both sides of bevel Tungsten Volvo Construction Equipment2010-1-11 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

29、positioning electrode correctly in either 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 InclusionVolvo Construction Equipment2010-1-11 Definition: Slan

30、g term for a groove left at the toe of a root pass which becomes 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 apply

31、ing the hot pass. Carefully grind the root pass face flat. be careful not to gouge other areas on the weldment.Wagon Tracks (non-standard)Volvo Construction Equipment2010-1-11 Definition: A tungsten particle embedded in a weld. (Typically GTAW only) Cause: Tungsten electrode too small, amperage too

32、high, AC balance on +, Upslope too high, electrode tip not properly ground, electrode dipped into the weld pool or touched with the fill rod, electrode split. Prevention: Eliminate the cause Repair: Grind out and reweldTungsten InclusionVolvo Construction Equipment2010-1-11Inclusions Fix when you se

33、e it. Otherwise grind out & fix when found to be unacceptable by non-destructive examinations.Volvo Construction Equipment2010-1-11Whiskers, Grapes, or Excessive Push Through Unsightly Inhibits material flow in piping Are inclusions Can break off in pipes and damage equipment downlineVolvo Construct

34、ion Equipment2010-1-11Spatter Definition: Small particles of weld metal expelled from the welding operation which adhere to the base metal surface. Cause: Long arc length, severe electrode angles, high amperages. Prevention: Correct the cause. Base metal can be protected with coverings or hi-temp pa

35、ints or other means. Repair: Remove by grinding or sanding. Volvo Construction Equipment2010-1-11Arc Craters Definition: A depression left at the termination of the weld where the weld pool is left unfilled. Cause: Improper weld termination techniques Prevention: Pause at this point and allow to fil

36、l prior to breaking arc. Repair: If no cracks exist, simply fill in the crater. Generally welding from beyond the crater back into the crater.Volvo Construction Equipment2010-1-11Cracks Longitudinal Transverse Crater Throat Toe Root Underbead and Heat-affected zone Hot Cold or delayedVolvo Construct

37、ion Equipment2010-1-11 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 of less constraint. Also preheat to even out

38、 the cooling rates. Repair: Remove and reweldLongitudinal CrackVolvo Construction Equipment2010-1-11 Definition: A crack running into or inside a weld, transverse to the weld axis direction. Cause: Weld metal hardness problem Prevention: Repair:Transverse CrackVolvo Construction Equipment2010-1-11 D

39、efinition: A 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

40、weld termination and/or preheat to even out the cooling of the puddle Repair:Crater CrackVolvo Construction Equipment2010-1-11 Definition: A longitudinal crack located in the weld throat area. Cause: Transverse Stresses, probably from shrinkage. Indicates inadequate filler metal selection or welding

41、 procedure. May be due to crater crack propagation. 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 CrackVol

42、vo Construction Equipment2010-1-11 Definition: A crack in the base metal 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 CrackVolvo Construction Eq

43、uipment2010-1-11 Definition: A crack in the weld at the weld root. Cause: Transverse shrinkage stresses. Same as a throat crack. Prevention: Same as a throat crack Repair:Root CrackVolvo Construction Equipment2010-1-11 Definition: A crack in the unmelted parent metal of the HAZ. Cause: Hydrogen embr

44、ittlement Prevention: Use Lo/Hi electrodes and/or preheat Repair: (only found using NDT). Remove and reweld.Underbead CrackVolvo Construction Equipment2010-1-11 Definition: A crack in the weld that occurs during solidification. Cause: Micro stresses from weld metal shrinkage pulling apart weld metal

45、 as it cools from liquid to solid temp. Prevention: Preheat or use a low tensil filler material. Repair:Hot CrackVolvo Construction Equipment2010-1-11 Definition: A crack that occurs after the metal has completely solidified Cause: Shrinkage, Highly restrained welds, Discontinuities Prevention: Preh

46、eat, weld toward areas of less constraint, use a more ductile weld metal Repair: Remove and reweld, correct problem first, preheat may be necessary.Cold CrackVolvo Construction Equipment2010-1-11Repairs to Cracks Determine the cause Correct the problem Take precautions to prevent reoccurrence Genera

47、lly required to repair using a smaller electrodeVolvo Construction Equipment2010-1-11Base Metal Discontinuities Lamellar tearing Laminations and Delaminations Laps and SeamsVolvo Construction Equipment2010-1-11LaminationsBase Metal DiscontinuityMay require repair prior to weldingFormed during the mi

48、lling processVolvo Construction Equipment2010-1-11Lamination effects can be reduced by joint design:Volvo Construction Equipment2010-1-11DelaminationsVolvo Construction Equipment2010-1-11Laps and SeamsA mill-induced discontinuity in which results from a lump of metal being squeezed over into the sur

49、face of the material. If beyond acceptable limits, must be removed and repaired or discarded.Volvo Construction Equipment2010-1-11Porosity Single Pore Uniformly Scattered Cluster Linear PipingVolvo Construction Equipment2010-1-11Single Pore Separated by at least their own diameter along the axis of

50、the weldVolvo Construction Equipment2010-1-11Uniformly Scattered Porosity Typically judged by diameter and proximity to a start or stop often caused by low amperage or short arc gap or an unshielded weld startVolvo Construction Equipment2010-1-11Cluster Porosity Typically viewed as a single large di

51、scontinuityVolvo Construction Equipment2010-1-11Linear Porosity being linear greatly affects the severity of this discontinuityVolvo Construction Equipment2010-1-11Piping Porosity Generally has special allowable limitsVolvo Construction Equipment2010-1-11Porosity preheat will help eliminate may need

52、 an electrode with more deoxidizers Use run-on/run-off taps restart on top of previous weld and grind off lumpVolvo Construction Equipment2010-1-11Heat-affected zone microstructure alteration add drawing of HAZ of groove weld with leaders to: grain refinement grain growth hardened areas softened areas precipitate suseptable areas.Volvo Construction Equipment2010-1-11Size or dimension If it renders the part unusable, it is a defect. If it is outside the allowable limit, it renders the part unusable. Thi