4_常见焊接缺陷及检验方法

1、常见焊接缺陷常见焊接缺陷May.2010Volvo Construction Equipment2010-1-11一、焊接缺陷一、焊接缺陷 定义： 在焊接过程中，在焊接接头中产生的不符合标准要求的缺陷，称为焊接缺陷。 分类；依据GB641786,可将缺陷分为以下六类： 裂纹 孔穴 固体夹杂 未熔合和未焊透 形状缺陷 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、裂纹 依照裂纹产生的温度范围划分： 热裂纹：可分为 结晶裂纹 液化裂纹 高温失塑裂纹 （原因分析） 冷裂纹：主要产生于焊接热影响区 （氢的作用） 在热裂

2、纹：工件焊接后再次被加热 到一定温度下 （消应力热处理 多层焊 服役期）Volvo Construction Equipment42010-1-11母材中的夹层导致的裂纹母材中的夹层导致的裂纹 由于板材在轧制过程中出现夹层，导致在焊接过程中出现裂纹：层状撕裂Volvo Construction Equipment52010-1-11层状撕裂层状撕裂 焊接工艺的调整 接头形式的改善Volvo Construction Equipment62010-1-11二、气孔二、气孔定义：焊接熔池中的气泡在凝固时未能 及时溢出，而留下来所形成的孔穴。分类：依形状分 球形 条虫形 依分布分 孤立 均布 依来源

3、分 析出型 (分析原因) 反应型 （产生部位 原因） C+O=CO Fe+C=Fe+CO SiO2+2C=Si+2CO 防止措施：1 限制熔池中气体的溶入或产生。（具体措施） 2 排除熔池中已溶入的气体。 （具体措施）Volvo Construction Equipment72010-1-11三三 、固体夹杂、固体夹杂 1 夹渣 焊后残留在焊缝中的熔渣 形状 复杂 一般呈线状、长条状、颗粒状及其他形式。 部位 主要发生在坡口边缘和每层焊道之间非圆滑过渡的部位。横焊、立焊或仰焊比平焊多。 2 夹钨 钨极氩弧焊时，若钨极不慎与熔池接触，使钨的颗粒进入焊缝金属中。 在焊接镍铁合金时，形成钨合金，射线

4、探伤很难发现。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 焊接时母材金属之间应该熔合而未焊上的部分。 部位：单面焊的坡口根部、双面焊的坡口钝边。 危害：较大的应力集中，在其末端产生裂纹。 2 未熔合 焊缝金属与母材、焊缝金属与焊道金属之间未完全熔化结合的部分。Volvo Construction Equipment92010-1-11五、形状缺陷五、形状缺陷 形状缺陷包括： 1 错边、角变形 2 咬边 3 焊瘤 4 烧穿和下塌 5 焊缝尺寸、形状不合要求 6 其他缺陷 Volvo Construction Eq

5、uipment2010-1-11错边错边 定义：由于两个焊件没有对正而造成板的中心线平行偏差 成因成因: 粗心 .不同厚度的母材焊接 厚度过渡 预防预防: 改善工艺. 改变厚度过渡的过度角度。 修补修补: 打磨. 在错边不严重时可采用打磨的方法来处理 （板材）.管材内部错边较难处理.Volvo Construction Equipment2010-1-11咬边 定义定义: 由于焊接参数选择或操作不当，沿焊趾的母材部位产生的沟槽或凹陷 成因成因: 电流过大、电流过大、 焊条角度不合适、电弧过长。 预防措施预防措施: 清除焊缝两侧铁锈 焊接位置 立焊 仰焊时较易出现咬边的情况 修补修补: 选用较小

6、的焊条、最好是打磨或挖凿后用低氢 焊条来补焊.Volvo Construction Equipment2010-1-11焊瘤焊瘤 定义:焊接过程中，熔化金属流淌到焊缝之外未熔化的 母材上所形成的金属瘤。（图） 位置:焊瘤存在于焊缝表面，在其下面往往伴随着未熔 合、未焊透等缺陷。 危害:由于金属的堆积使焊缝的几何形状发生变化，造 成应力集中。Volvo Construction Equipment132010-1-11烧穿和下塌烧穿和下塌 定义：焊接过程中，熔化金属自坡口背面流出， 形成穿孔的缺陷。 烧穿易发生在第一道焊道及薄板对接焊缝或管子对接焊缝中。烧穿的周围常伴有气孔、夹渣焊瘤及未焊透等缺

7、陷。下塌：穿过单层焊缝根部，或在多层焊接接头中穿 过前道熔敷金属塌落的过量焊缝金属。（图）Volvo Construction Equipment142010-1-11不规则的焊缝尺寸、形状不规则的焊缝尺寸、形状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 电弧擦伤 2 飞溅Volvo Construction Equipment172010-1-11Volvo Construction Equipment201

8、0-1-11二、焊接检验二、焊接检验 焊接检验的分类： （1）破坏性检验 （2）非破坏性检验 （3）声发射检测Volvo Construction Equipment192010-1-11无损检验无损检验 射线检测 超声检测 磁粉检测 渗透检测 涡流检测Volvo Construction Equipment202010-1-11射线检测射线检测 射线探伤的实质 根据被检工件与其内部缺陷介质对射线的衰减不同，而引起的射线透照之后到达底片上的强度不同，从而造成底片“感光”程度不同将缺陷在底片上反映出来。Some examples (药皮、药渣、厚度方向缺陷不灵敏）Volvo Constructi

9、on Equipment212010-1-11射线的本质射线的本质 X射线 射线 高频电磁波 （光子）Volvo Construction Equipment222010-1-11超声波检测超声波检测 超声波检测：是利用超声波在物体中的传播、反射和衰减等物理特性来发现缺陷的一种探伤方式。 声波（人类的听觉） 次声波（地震、核武器） 超声波（0.510MHz）（图 Example） 探头 （45 平） 耦合剂 （探头不接触工件表面）Volvo Construction Equipment232010-1-11渗透检测渗透检测 渗透检测：利用带有荧光染料或红色染料渗透剂的渗透作用，显示缺陷痕迹的无

10、损检验方法。 用途：用于各种金属材料和非金属材料构件表面开口缺陷的检验。Volvo Construction Equipment242010-1-11渗透检验的原理渗透检验的原理 1 毛细作用 2 两平行板间的毛细现象Volvo Construction Equipment252010-1-11声发射探伤技术声发射探伤技术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