常见焊接缺陷及检验方法解读课件

1、常见焊接缺陷May.2010一、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。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）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2010-1-114层状撕裂焊接工艺的调整 接

2、头形式的改善2010-1-115二、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）2010-1-116三 、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

3、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。2010-1-117四 、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。2010-1-118五、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 2010-1-119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

4、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.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.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

5、 成应力集中。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）2010-1-1113不规则的焊缝尺寸、形状Concavity 凹陷2010-1-1114Convexity 凸出2010-1-1115其他缺陷1 电弧擦伤 2 飞溅2010-1-1117二、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）声发射检测无损检验射线检测超声检测磁粉检测渗透检测涡流检测201

6、0-1-1119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）2010-1-1120射线的本质X射线 射线 高频电磁波 （光子）2010-1-1121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）2010-1-1122渗透检测渗

7、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。2010-1-1123渗透检验的原理1 毛细作用2 两平行板间的毛细现象2010-1-1124声发射探伤技术2010-1-1125Removing 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 recreat

8、e 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 dimension. 4. Feather the start and stop to blend smoothly into and out of the existing weld.Excessive Concavity or ConvexityDefinition: Conc

9、avity or convexity of a fillet weld which exceeds the specified allowable limits Cause: Amperage and travel speedPrevention: Observe proper parameters and techniques.Repair: Grind off or weld on. Must blend smoothly into the base metal. ConcavityConvexityReinforcementExcessive Insufficient Improper

10、contourFace ReinforcementRoot ReinforcementThe amount of a groove weld which extends beyond the surface of the plateExcessive ReinforcementDefinition: 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 shape

11、s). Cause: Travel speed too slow, amperage too lowPrevention: 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.Definition: Specifically defined by the standard. Typically, Underfill may be up to 5%

12、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 cause drooping of the

13、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 ReinforcementDefinition: When the weld exhibits less th

14、an a 1350 transition angle at the weld toe. Cause: Poor welding techniquePrevention: 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 ContourOverlapDefinition: When the face of the weld extends

15、 beyond the toe of the weldCause: 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 into the base metal. Be careful of deep grind mar

16、ks that run transverse to the load. Also be careful of fusion discontinuities hidden by grinding. Use NDT to be sure.OverlapOverlap 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.Burn-through (non-standar

17、d)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 sink, or by reducing welding parameters.Repair: Will be defined by s

18、tandards. Filling may suffice. Otherwise, removal and rewelding may be required. Some standards may require special filler metal and/or PWHT.Incomplete or Insufficient PenetrationDefinition: When the weld metal does not extend to the required depth into the joint rootCause: Low amperage, low preheat

19、, 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.Incomplete FusionDefinition: Where weld metal does not form a cohesive bond with the base metal.Cause: Low amperage, steep electrode angles,

20、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.Arc StrikeDefinition: A

21、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: CarelessnessPrevention: In difficult areas, adjacent areas can be protected using fire blankets.Repai

22、r: 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.InclusionsSlagWagontracks lines of slag along one or both sides of bevel Tungsten Definition: Slag entrapped wit

23、hin the weldCause: 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 preheat, grind out tight areas to gain access to bottom of joint,

24、position electrode correctly. Repair: Remove by grinding. Reweld.Slag InclusionDefinition: 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 the root pass is too high, or the weld toe is not bonded to the base metal

25、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-standard)Definition: A tungsten particle embedded in a weld. (Typically GTAW on

26、ly)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.Prevention: Eliminate the causeRepair: Grind out and reweldTungsten InclusionInclusionsFi

27、x when you see it. Otherwise grind out & fix when found to be unacceptable by non-destructive examinations.Whiskers, Grapes, or Excessive Push ThroughUnsightlyInhibits material flow in pipingAre inclusionsCan break off in pipes and damage equipment downlineSpatterDefinition: Small particles of weld

28、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 paints or other means.Repair: Remove by grinding or sanding. Arc Crat

29、ersDefinition: A depression left at the termination of the weld where the weld pool is left unfilled.Cause: Improper weld termination techniquesPrevention: 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

30、 the crater back into the crater.CracksLongitudinalTransverseCraterThroatToeRootUnderbead and Heat-affected zoneHotCold or delayedDefinition: 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 str

31、esses in high constraint areas.Prevention: Weld toward areas of less constraint. Also preheat to even out the cooling rates.Repair: Remove and reweldLongitudinal CrackDefinition: A crack running into or inside a weld, transverse to the weld axis direction.Cause: Weld metal hardness problemPrevention

32、:Repair:Transverse CrackDefinition: 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 fi

33、ll, fill the crater at weld termination and/or preheat to even out the cooling of the puddleRepair:Crater CrackDefinition: A longitudinal crack located in the weld throat area.Cause: Transverse Stresses, probably from shrinkage. Indicates inadequate filler metal selection or welding procedure. May b

34、e 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 CrackDefinition: A crack in

35、 the base metal beginning at the toe of the weldCause: Transverse shrinkage stresses. Indicates a HAZ brittleness problem.Prevention: Increase preheat if possible, or use a more ductile filler material.Repair: Toe CrackDefinition: A crack in the weld at the weld root.Cause: Transverse shrinkage stre

36、sses. Same as a throat crack. Prevention: Same as a throat crackRepair:Root CrackDefinition: A crack in the unmelted parent metal of the HAZ.Cause: Hydrogen embrittlementPrevention: Use Lo/Hi electrodes and/or preheatRepair: (only found using NDT). Remove and reweld.Underbead CrackDefinition: A crac

37、k 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 CrackDefinition: A crack that occurs after the metal has completely solidi

38、fiedCause: Shrinkage, Highly restrained welds, DiscontinuitiesPrevention: Preheat, weld toward areas of less constraint, use a more ductile weld metalRepair: Remove and reweld, correct problem first, preheat may be necessary.Cold CrackRepairs to CracksDetermine the causeCorrect the problemTake preca

39、utions to prevent reoccurrenceGenerally required to repair using a smaller electrodeBase Metal DiscontinuitiesLamellar tearingLaminations and DelaminationsLaps and SeamsLaminationsBase Metal DiscontinuityMay require repair prior to weldingFormed during the milling processLamination effects can be re

40、duced by joint design:DelaminationsLaps 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 limits, must be removed and repaired or discarded.PorositySingle PoreUniformly ScatteredClusterLinearPipingSi

41、ngle PoreSeparated by at least their own diameter along the axis of the weldUniformly Scattered PorosityTypically judged by diameter and proximity to a start or stopoften caused by low amperage or short arc gap or an unshielded weld startCluster PorosityTypically viewed as a single large discontinuityLinear Porositybeing linear greatly affects the severity of this discontinuityPiping PorosityGenerally has special allowable limitsPorosity preheat will help eliminatemay need an electrode with more deoxidizersUse run-on/run-off tapsrestart on top of previous weld and grind off l