常见焊接缺陷及检验方法解读课件.ppt

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1、常见焊接缺陷,May.2010,2010-1-11,一、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。,2010-1-11,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）,4,2010-1-11,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

2、致在焊接过程中出现裂纹：层状撕裂,5,2010-1-11,层状撕裂,焊接工艺的调整 接头形式的改善,6,2010-1-11,二、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）,7,2010-1-11,三 、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

3、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，射线探伤很难发现。,8,2010-1-11,四 、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。,9,2010-1-11,五、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

4、合要求 6 其他缺陷,2010-1-11,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: 粗心 .不同厚度的母材焊接 厚度过渡,预防: 改善工艺. 改变厚度过渡的过度角度。,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.,2010-1-11,咬边,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: 电流过大、 焊条角度不合适、电弧过长。,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: 选用较小的焊条、最好是打磨或挖凿后用低氢 焊条来补焊.,2010-1-11,焊瘤,定义:焊接过程

5、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。,13,2010-1-11,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）,14,2010-1-11,不规则的焊缝尺寸、形状,Concavity 凹陷,15,2010-1-11,Conve

6、xity 凸出,2010-1-11,其他缺陷,1 电弧擦伤 2 飞溅,17,2010-1-11,2010-1-11,二、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,19,2010-1-11,无损检验,射线检测超声检测磁粉检测渗透检测涡流检测,20,2010-1-11,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）,21,2010-1-11,射线的本质,X射线 射线 高频电磁波

7、 （光子）,22,2010-1-11,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）,23,2010-1-11,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。,24,2010-1-11,渗透检验的原理,1 毛细作用2 两平行板间的毛细现象,25,2010-1-11,声发射探伤技术,2010-1-11,

8、2010-1-11,2010-1-11,Removing a root pass by grinding,1. 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 an

9、gle. 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.,2010-1-11,2010-1-11,Excessive Concavity or Convexity,Definition: Concavity or convexity of a fillet weld which exceeds the specified allowable limits,Cause: Amp

10、erage and travel speed,Prevention: Observe proper parameters and techniques.,Repair: Grind off or weld on. Must blend smoothly into the base metal.,2010-1-11,Concavity,2010-1-11,Convexity,2010-1-11,Reinforcement,Excessive Insufficient Improper contour,The amount of a groove weld which extends beyond

11、 the surface of the plate,2010-1-11,Excessive 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 structural shapes).,Cause: Travel speed too slow, amperage too low,Prevention: Set amperage and

12、 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, Underfill may be up to 5% of metal thickness not to exceed 0.80mm/1/32” as long as the thick

13、ness 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 cause drooping of the open root puddle.,Prevention: Use proper welding technique. Use b

14、acking 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 Reinforcement,2010-1-11,Definition: When the weld exhibits less than a 1350 transition angle at the weld toe.,Cause: P

15、oor 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.,1350,Improper Weld Contour,2010-1-11,Overlap,Definition: When the face of the weld extends beyond the toe of the weld,Cause: I

16、mproper 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 into the base metal. Be careful of deep grind marks that run transverse to the load

17、. Also be careful of fusion discontinuities hidden by grinding. Use NDT to be sure.,2010-1-11,Overlap,Overlap 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.,2010-1-11,Burn-through (non-standard),Definiti

18、on: 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 sink, or by reducing welding parameters.,Repair: Will be defined by standard

19、s. Filling may suffice. Otherwise, removal and rewelding may be required. Some standards may require special filler metal and/or PWHT.,2010-1-11,Incomplete or Insufficient Penetration,Definition: When the weld metal does not extend to the required depth into the joint root,Cause: Low amperage, low p

20、reheat, 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.,2010-1-11,Incomplete Fusion,Definition: Where weld metal does not form a cohesive bond with the base metal.,Cause: Low amperage, ste

21、ep 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 extremely difficult to find.,

22、2010-1-11,Arc 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,Prevention: In difficult areas, adjacent areas can b

23、e 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.,2010-1-11,Inclusions,SlagWagontracks lines of slag along one or both side

24、s 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 either up or downhand positions.,Prevention: Increase amperage or preh

25、eat, grind out tight areas to gain access to bottom of joint, position electrode correctly.,Repair: Remove by grinding. Reweld.,Slag Inclusion,2010-1-11,Definition: Slang 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

26、 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 careful not to gouge other areas on the weldment.,Wagon Tracks (non-s

27、tandard),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 into the weld pool or touched with the fill rod, electrode split

28、.,Prevention: Eliminate the cause,Repair: Grind out and reweld,Tungsten Inclusion,2010-1-11,Inclusions,Fix when you see it. Otherwise grind out & fix when found to be unacceptable by non-destructive examinations.,2010-1-11,Whiskers, Grapes, or Excessive Push Through,UnsightlyInhibits material flow i

29、n pipingAre inclusionsCan break off in pipes and damage equipment downline,2010-1-11,Spatter,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

30、cause. Base metal can be protected with coverings or hi-temp paints or other means.,Repair: Remove by grinding or sanding.,2010-1-11,Arc Craters,Definition: A depression left at the termination of the weld where the weld pool is left unfilled.,Cause: Improper weld termination techniques,Prevention:

31、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.,2010-1-11,Cracks,LongitudinalTransverseCraterThroatToeRootUnderbead and Heat-affected zoneHotCold or delayed,2010-1-11,De

32、finition: 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 the cooling rates.,Repai

33、r: Remove and reweld,Longitudinal Crack,2010-1-11,Definition: A crack running into or inside a weld, transverse to the weld axis direction.,Cause: Weld metal hardness problem,Prevention:,Repair:,Transverse Crack,2010-1-11,Definition: A crack, generally in the shape of an “X” which is found in a crat

34、er. 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 termination and/or preheat to even out the cooling of the puddle,Repair:

35、,Crater Crack,2010-1-11,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 propagation.,Prevention: Correct initial cause. Increasing prehe

36、at 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 Crack,2010-1-11,Definition: A crack in the base metal beginning at the toe of the weld,Cause: Transverse shrin

37、kage stresses. Indicates a HAZ brittleness problem.,Prevention: Increase preheat if possible, or use a more ductile filler material.,Repair:,Toe Crack,2010-1-11,Definition: A crack in the weld at the weld root.,Cause: Transverse shrinkage stresses. Same as a throat crack.,Prevention: Same as a throa

38、t crack,Repair:,Root Crack,2010-1-11,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 Crack,2010-1-11,Definition: A crack in the weld that occurs dur

39、ing 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 Crack,2010-1-11,Definition: A crack that occurs after the metal has completely solidified,Cause: Sh

40、rinkage, 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 Crack,2010-1-11,Repairs to Cracks,Determine the causeCorrect the problemTake pre

41、cautions to prevent reoccurrenceGenerally required to repair using a smaller electrode,2010-1-11,Base Metal Discontinuities,Lamellar tearingLaminations and DelaminationsLaps and Seams,2010-1-11,Laminations,Base Metal DiscontinuityMay require repair prior to weldingFormed during the milling process,2

42、010-1-11,Lamination effects can be reduced by joint design:,2010-1-11,Delaminations,2010-1-11,Laps and Seams,A mill-induced discontinuity in which results from a lump of metal being squeezed over into the surface of the material. If beyond acceptable limits, must be removed and repaired or discarded

43、.,2010-1-11,Porosity,Single PoreUniformly ScatteredClusterLinearPiping,2010-1-11,Single Pore,Separated by at least their own diameter along the axis of the weld,2010-1-11,Uniformly Scattered Porosity,Typically judged by diameter and proximity to a start or stopoften caused by low amperage or short a

44、rc gap or an unshielded weld start,2010-1-11,Cluster Porosity,Typically viewed as a single large discontinuity,2010-1-11,Linear Porosity,being linear greatly affects the severity of this discontinuity,2010-1-11,Piping Porosity,Generally has special allowable limits,2010-1-11,Porosity,preheat will he

45、lp eliminatemay need an electrode with more deoxidizersUse run-on/run-off tapsrestart on top of previous weld and grind off lump,2010-1-11,Heat-affected zone microstructure alteration,add drawing of HAZ of groove weld with leaders to:grain refinementgrain growthhardened areassoftened areasprecipitat

46、e suseptable areas.,2010-1-11,Size 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 too time consuming and costly,2010-1-11,Ha

47、mmer marks,Stress risersUnsightlyUnnecessary,2010-1-11,REPAIR TECHNIQUES,May involve:different processdifferent proceduredifferent preheat/PWHTdifferent electrodesmaller electrode,2010-1-11,Only repair defects. Discontinuities are, by definition, acceptable. Repair is therefore unnecessary and not c

48、ost effective.,2010-1-11,Inspection Tools,2010-1-11,Measuring Weld Sizes,2010-1-11,Fibre Metal Fillet Gage,2010-1-11,Fibre Metal Fillet Gage,2010-1-11,Fibre Metal Fillet Gage,2010-1-11,Fibre Metal Fillet Gage,2010-1-11,Fibre Metal Fillet Gage,2010-1-11,Fibre Metal Fillet Gage,2010-1-11,Fibre Metal Fillet Gage,2010-1-11,Fibre Metal Fillet Gage,2010-1-11,Undercut Guage,Gal Gage Co.,2010-1-11,Palmgrin Guage,2010-1-11,Magnifying Glass,Used to read small scales,2010-1-11,2010-1-11,