Aws Module 9.ppt

MODULE 9- WELD AND BASE METAL DISCONTINUITIES

WELDING INSPECTION TECHNOLOGY

DIFFERENCE BETWEEN DISCONTINUITIES AND DEFECT

 DISCONTINUTIES – IS DESCRIBED AS ANY INTERRUPTION

IN THE

UNIFORM NATURE OF AN ITEM.

 DEFECT – IS A SPECIFIC DISCONTINUITY WHICH CAN IMPAIR THE SUITABILITY OF THAT STRUCTURE FOR ITS INTENDED PURPOSE.

DISCONTINUITIES  CRACKS – CRACKS ARE INIATED WHEN THE LOAD, OR STRESS, APPLIED TO A MEMBER EXCEEDS ITS TENSILE STRENGHT.

 GROUPING  HOT CRACKS – USUALLY OCCUR AS THE METAL SOLIDIFIES, AT SOME ELEVATED TEMPERATURE.

 COLD CRACKS – OCCUR AFTER THE METAL HAS COOLED TO AMBIENT TEMPERATURE.

 TYPES OF CRACKS  LONGITUDINAL – LYING IN A DIRECTION PARALLEL TO THE LONGITUDINAL AXIS.

 TRANSVERSE – LYING PERPENDICULAR TO THE WELD’S LONGITUDINAL AXIS.

 CETERLINE OR THROAT CRACK – EXTEND THROUGH THE WELD ALONG THE WELD THROAT, OR THE SHORTEST PATH THROUGH THE WELD’S CROSS SECTION.

 TOE CRACKS – CONSIDERED TO BE COLD CRACKS. - CAUSED BY EITHER THE TRANSVERSE SHRINKAGE STRESSES OF WELDING, SOME APPLIED SERVICE STRESSES, OR A COMBINATION OF THE TWO.

 CRATER CRACKS – OCCUR AT THE TERMINATION OFD WELD PASSES.  UNDERBEAD CRACK – LOCATED AT THE HEAT AFFECTED ZONE INSTEAD OF THE WELD METAL.

INCOMPLETE FUSION  A WELD DISCONTINUITY IN WHICH FUSION DID NOT OCCUR BETWEEN WELD METAL AND FUSION FACES OR ADJOINING WELD BEADS.

INCOMPLETE FUSION

INCOMPLETE FUSION

 INCOMPLETE JOINT PENETRATION – IT IS A CONDITION WHERE THE WELD METAL DOES NOT EXTEND ENTIRELY THROUGH THE JOINT

THICKNESS WHEN COMPLETE PENETRATION IS REQUIRED BY A SPECIFICATION.

INCOMPLETE JOINT PENETRATION

 INCLUSIONS – IS ENTRAPPED FOREIGN SOILD MATERIAL, SUCH AS SLAG, FLUX, TUNGSTEN, OR OXIDE.

 POROSITY – A “CAVITY-TYPE DISCONTINUITIES FORMED BY GAS ENTRAPMENT DURING SOLIDIFICATION”. TYPES OF POROSITY

 UNIFORMLY SCATTERED POROSITY – REFERS TO NUMEROUS AVITIES W/C OCCUR THROUGHOUT THE WELD IN NO PARTICULAR PATTERN.

 WORMHOLE POROSITY – ALSO REFERRED TO AS ELONGATED POROSITY OCCURING AT THE WELD SURFACE.

 PIPING POROSITY – THE MOST DETRIMENTAL CONDITION IF LIQUID OR GAS CONTAINMENT IS THE PRIMARY FUNCTION OF THE WELD BECAUSE IT REPRESENTS A MORE

SIGNIFICANT LEAK PATH POSSIBILITY.

 UNDERCUT – IS A SURFACE DISCONTINUITY WHICH OCCURS IN THE BASE METAL DIRECTLY ADJACENT TO THE WELD.

UNDERCUT

 UNDERFILL – IS A SURFACE DISCONTINUITY WHICH RESULTS IN A LOSS OF MATERIAL CROSS SECTION.

- RESULTS WHEN THERE IS NOT SUFFICIENT FILLER METAL DEPOSITED TO ADEQUATELY FILL THE WELD JOINT. - UNDERFILL AT THE WELD ROOT OF PIPE WELDS IS SOMETIMES REFERRED TO AS INTERNAL CONCAVITY OR “SUCKBACK”.

 OVERLAP – IS DESCRIBED AS THE PROTRUSION OF WELD METAL BEYOND THE WELD TOE OR WELD ROOT. - CONSIDERED TO BE A SIGNIFICANT DISCONTINUITY SINCE IT

CAN RESULT IN A SHARP NOTCH AT THE SURFACE OF THE WELDMENT.

 CONVEXITY – REFERS TO THE AMOUNT OF WELD METAL BUILDUP ON THE FACE OF THE FILLET WELD BEYOND THAT WOULD BE CONSIDERED FLUSH.

 CONVEXITY – BY DEFINITION, IS THE MAXIMUM DISTANCE FROM THE FACE OF A CONVEX FILLET WELD PERPENDICULAR TO A LINE JOINING THE WELD TOES.

CONVEXITY

 WELD REINFORCEMENT – IS DESCRIBED AS THAT WELD METAL IN EXCESS OF THE AMOUNT REQUIRED TO FILL A JOINT. FACE REINFORCEMENT

ROOT REINFORCEMENT

ACCEPTABLE AND UNACCEPTABLE TREATMENT OF EXCESS WELD REINFORCEMENT A. EXCESS WELD REINFORCEMENT REINFORCEMENT

FUSION WELD B. IMPROPER TREATMENT OF

REINFORCEMENT REMOVED BY GRINDING

C. ACCEPTABLE TREATMENT OF WELD REINFORCEMENT REMOVED BY GRINDING

 ARC STRIKES – RESULTS WHEN THE ARC IS INIATED ON THE BASE METAL SURFACE AWAY FROM THE WELD JOINT, EITHER INTENTIONALLY OR ACCIDENTALLY.

 SPATTERS – METAL PARTICLES EXPELLED DURING FUSION WELDING THAT DO NOT FORM A PART OF THE WELD.

 LAMINATION – RESULT FROM THE PRESENCE OF NONMETALLIC INCLUSIONS WHICH OCCUR IN STEEL WHEN IT IS BEING PRODUCED.

 LAMELLAR TEARING – DESCRIBED AS A TERRACE-LIKE FRACTURE IN THE BASE METAL WITH A BASIC ORIENTATION PARALLEL TO THE ROLLED SURFACE.

EXAMPLE OF LAMELLAR TEARING

LAMELLAR TEARING

 SEAMS AND LAPS – ARE BASE METAL DISCONTINUITY RELATED TO THE STEEL MAKING PROCESS. - THEY DIFFER FROM LAMINATION IN THAT THEY ARE OPEN TO THE ROLLED SURFACE OF THE METAL INSTEAD OF THE EDGE.

 DIMENSIONAL – DIMENSIONAL DISCONTINUITIES ARE SIZE AND/OR SHAPE IMPERFECTIONS.