Duties of Welding Inspector Before Welding 1. Safety: Safety: To check all operations are carried out in complete compliance with local company or National safety law i.e (permits to work are in place) 2. Documentation: Documentation : To check, a) Specif Specifica icatio tion n (yea (yearr & reisi reision) on) !) "orr "orrec ectt rei reise sed d draw drawin in#s #s.. c) $eldin# procedure specifications ($%S) & welder approals ($T) d) "ali!ration certificates of weldin# e'uipment ancillaries ancillaries & all inspection inspection instruments. e) aterial & consuma!le certificates. *. Welding process & ancillaries: ancillaries : To check weldin# e'uipment & all related ancillaries (ca!les, re#ulators, oens, 'uiers etc.) +. Incoming Consumables: Consumables: To check all pipe plate & weldin# consuma!les for sie, type & condition. -. Marking out preparation & set up: up : To check, a) "orrect "orrect method method of cuttin# cuttin# weld preparat preparations. ions. (%rehe (%reheat at for thermal thermal cuttin# cuttin# if applica! applica!le) le) !) "orrect "orrect preparatio preparation n (releant (releant !eel an#les, an#les, root face, face, root #ap, #ap, root radius, radius, land land etc.) c) "orrect "orrect preweldi preweldin# n# distortio distortion n control. control. (Tackin#, (Tackin#, !rid#in#, !rid#in#, /i#s, /i#s, line line up clamps clamps etc.) d) "orrec "orrectt prehea preheatt applied applied prior prior to to tack weld weldin# in#.. e) 0ll tack tack weld weldin# in# to to use moni monitor tored ed & inspec inspectio tion. n.
During Welding a) !) c) d) e) f) #)
To check, %reheat %reheat alues alues (heatin# (heatin# method, method, location location & control) control) n process process distortio distortion n control control (se'uenc (se'uence e or !alanced !alanced weldin#) weldin#) "onsuma!le "onsuma!le control control (speci (specificat fication, ion, sie, sie, conditio condition n & any special special treatme treatments) nts) %rocess %rocess type & all all related related aria!le aria!le parameters parameters (olta# (olta#e, e, ampera#e, ampera#e, trael trael speed) speed) %ur#in# %ur#in# #ases #ases (type, (type, pressure pressure flow & control control method) method) $eldin# $eldin# conditio conditions ns for root run run hot hot pass pass & su!se'ue su!se'uent nt run & interrun interrun cleanin cleanin#. #. inimum inimum or maimum maimum interpa interpass ss temperatu temperature re (temperatur (temperature e & controlli controllin# n# method) method)
After Welding a) 3isual inspection of the welded /oint (includin# dimensional check) !) N4T re'uirements (method & 'ualification of operator) operator) c) To identify repairs from assessment of isual of N4T reports d) %ost weld heat treatment (%$5T) (%$5T) (5eatin# method & temperature recordin# system) e) To reinspect with isualN4T after %$5T %$5T (if applica!le) applica!le) f) 5ydro test procedures (for pipelines or pressure essels) essels) Repa Re pair irs s: To check, a) 6caa 6caatio tion n proced procedure ure (app (appro roal al & eecu eecutio tion) n) !) 0pproal 0pproal of the N4T %rocedures. %rocedures. c 7epair procedure. procedure. c) 6ecut 6ecution ion of of appro approed ed rewe reweldi ldin# n# proce procedure dure.. d) To reinspec reinspectt the repair repair area area with isual isual inspect inspection ion & approed approed N4T method) method) e) To su!mit su!mit inspectio inspection n reports reports & all related related documents documents to the " departme department. nt. 0fter all , responsi!ilities of weldin# inspector are, o obser!e all obser!e all actions related to weld 'uality throu#hout production. This will include a final isual inspection of the weld area. o record all record all production inspection points record showin# all identified weld imperfections. o compare all compare all reported information with the acceptance leels criteria & clauses with the applied application standard.
Nick break tests : 8sed to assess root penetration & fusion in dou!le sided !ut welds & the internal faces of sin#le sided !utt welds. Test is carried out for a welder approal test. The specimen is normally cut !y hacksaw throu#h the weld faces to a depth stated in the standard. t is then weld in a ice & fractured with a hammer !low from the rear. 9nce fracture has !een made then !oth fractures are inspected for imperfections. 0s we are checkin# weld 'uality, test is 'ualitatie mechanical test.
Micro Testing enerally performed ma#nifications #reater than 1;< 4etermine micro structural constituents, presence of inclusions, presence of microscopic defects, nature of crackin# etc. 7e'uire fine #rindin# & polishin# to produce a mirror finish. %ictures of micro specimens are called photomicro#raphs .
Macro Testing enerally performed usin# ma#nifications 1;< or lower. 4etermine depth of fusion, depth of penetration, effectie throat, weld soundness, de#ree of fusion, presence of weld discontinuities, weld confi#uration, num!er of weld passes etc. Some macro specimens need only !e rou#h #round !ut mostly fine #rindin# & een polishin# pictures of macro specimens are called photo macro#raphs
MANUAL METAL ARC PRCE!! "MMA# 1) Mode of "peration : anual 2) #rinciple of "peration:0rc is struck !etween short flu !onded metal electrode & the work piece. =oth the electrode & work piece surface melt to form a weld pool. Simultaneously meltin# of flu coatin# on the rod will form a #as & sla# which protects the weld pool from the surroundin# atmosphere. 9ne of the weld run is completed the sla# must !e chipped off. *) Basic $%uipment re%uirement a) Transformer rectifier (constant current (droppin#) characteristic) !) %ower %ower return ca!les c) 6lectrode holders. d) 3isor with lens e) 6lectrode f) 6lectrode oen (!akes up to *-; ") #) 5oldin# oen (temp. up to 2;; ") +) Arc striking: The arc is struck !y strikin# the electrode on the surface of the plate & withdrawin# it a small distance. aintain short, constant arc len#th. -) Weld refining & cleaning : 7efinin# & cleanin# compounds within the !onded flu. >) #rocess !ariable parameters a) 9"3 (9pen "ircuit 3olta#e) 7e'uirement to initiate or rei#nite the arc & chan#e with type of electrode !ein# used. 0rc olta#e chan#es with chan#e in arc len#th. !) "urrent : Type & alue of current will !e determined !y the choice of electrode classification, diameter, material type, thickness & weldin# position. c) %olarity : 0"4"? (6lectrode ? or & polarity reersi!le or strai#ht) or electrode coatin# !ein# used. d) @ull electrode specification & diamter : Should !e correctly written on electrode & electrode !o. e) 6lectrode preuse: =asic coated electrodes (i) should !e !aked at *-; " for 1 5r. (ii) 5eld in holdin# oens at 1-; " (iii) @inally in a heated 'uier (around A; "; with welder for weldin#. f) Speed of trael: 5i#h dependant on the skill of a welder. A) Consumables: "ore solid wire !etween *-; & +-;mm & 2.->mm diameter, coered with !onded flu coatin# core wire #enerally low 'uality steel. 6lectrodes are #rouped dependin# on the main constituent in their flu coatin#. The common #roups arc =asic B "alcium car!onate & calcium f luoride (6lectrode no. endin# with-,>&C) "ellulosic B "ellulose (6lectrode no. endin# with ; &1) 7utile B Titania (6lectrode no. en din# with 2,*, &+) C) ypical imperfections i) Sla# inclusions : %oor weldin# techni'ue & insuf ficient inter run cleanin#. ii) 5ydro#en cracks : ncorrect electrode type or !akin# procedure. D) Ad!antages i) 7an#e of consuma!les. ii) 0ll positional. 1;) Disad!antages i) 5i#h leel of #enerated fumes. ii) 5ydro#en control 11) #ositional capabilities : 0ll positional !ut depend on consuma!le type. °
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TUN$!TEN INERT $A! "TI$# WELDIN$ PRCE!! 1) Mode of "peration anual !ut can !e semiautomatic 2) #rinciple of operation: Small diameter solid wire and shieldin# #as (inert #as) is used. The arc is produced !etween a nonconsuma!le electrode (tun#sten) & the work piece. 9perator must control the arc len#th & also add filler metal into the weld pool *) Basic e%uipment re%uirements: a) Transformer 7ectifier (constant current (droopin#) characteristic) !) 5ead 5ose assem!ly. c) %ower return ca!le. d) Torch head assem!ly e) as cylinder, hoses, re#ulators, flow meter. f) 3isor with lens. #) @ume etraction. +) Arc Striking : The arc strikin# (scratch start) the core wire onto the plate an d withdrawin# cause contamination of the tun#sten and weld metal to work on this hi#h fre'uency arc is used cause interference. To work on this, lift arc is used where the electrode is touched on to the plate & is withdrawn sli#htly. -) Arc and Weld S'ielding: nert #as (pure ar#on & helium) is used to shield arc & weld. as cutoff delay is used to shield weld metal at the end of a run. >) Weld refining & Cleaning: 3ery clean hi#h 'uality drawn wire is used. () #rocess !ariable parameters a) 3olta#e : "han#es with chan#e in arc len#th & type of #as !ein# used. !) "urrent : "han#es with chan#e in tun#sten diameter. Slope in & slope out controls the current at the start & end of the weld. c) %olarity : 4" Be for steels , 0" for 0luminum. d) nert as type: %ure #ases ar#on & helium are used. Nitro#en added for copper weldin#. iture (0r? 5e) #ies #ood #as coer & penetration. e) as @low rate : Should !e correct for #ien /oint desi#n & position as #ien in approed weldin# procedures. f) %ur#in# : %ur#in# #as pure ar#on used to reduce atmospheric root oidation. #) Tun#sten type : Thoriated tun#sten for 4" and irconated tun#sten for 0". Too fine erte an#le will melt the tun#sten tip. $ith 0", the tun#sten end is chamfered & forms a !all end durin# aluminum weldin# Consumable : 5i#h 'uality drawn wire & inert #as (pure ar#on or helium or miture of !oth) a) ypical imperfection Tun#sten inclusions: "aused !y a lack o f welder skill, too hi#h current & incorrect erte an#le. "rater pipes : "aused !y poor weld finish techni'ue or incorrect use of cu rrent decay. a. $eldroot oidation : f usin# insufficient #as cutoff delay or pur#e pressure. !) Ad!antages a) 5i#h 'uality weld !) 0ll positional c) Eow inner run cleanin# b) Disad!antages a. Small ran#e of consuma!les. !) 5i#h oone leels. c) Eow productiity #ositional capabilities: 0ll positional.
Metal Inert Gas (MIG) Welding Process %Metal Active Gas (MAG) Welding Process 1. Mode of "peration : Semiautomatic 2. %rinciple of 9peration : "opper coated or uncoated small diameter solid continuous wire from a spool & shieldin# #as (0r#on ? "92) is used. 0rc is produced !etween a metal electrode wire & the work piece to form a weld pool. *. Basic e%uipment re%uirements a) Transformer 7ectifier (constant olta#e (flat) characteristic) !) 5ead hose assem!ly c) $ire liner d)%ower return ca!le e) $ire feed unit, wire spool f) as cylinder, hoses, re#ulators, flow meter #) 3isor with lens i) @ume etraction. +. Arc Striking: The arc is struck in three different metal transfer modes. !) 4ip transfer : The wire short circuits the arc & the molten metal formin# on the wire is transferred !y the wire dippin# into the weld pool. ii) Spray transfer : The wire does not make contact with the weld pool. The molten metal at the tip of the wire transfers to the weld pool in the form of spray of small droplets. iii) %ulsed transfer : 8ses pulses of current to fire a sin#le #lo!al of metal across the arc #ap. -. Arc & Weld s'ielding : "ylinder fed inert actie #as shield for arc & weld. >. Weld refining & cleaning : 3ery clean, hi#h 'uality drawn wire. (. #rocess !ariable parameters 9"3 (9pen "ircuit 3olta#e): 7e'uire to initiate or rei#nite the arc. 4epend on type of #as !ein# used & type of transfer achiea!le. "urrent $ire feed speed ($@S): ncreasin# the wire feed speed automatically increases the current in the wire. %olarity : 4" Be (6lectrode positie B 7eersi!le) as type : iture of ar#on & "o2 (-2;F) to #et #ood penetration, sta!le arc, ery little spatter. as flow rate : 0de'uate to #ie #ood coera#e oer solidifyin# & molten metal to aoid oidation & porosity. nductance: "auses a !ackpressure of olta#e to occur in the wire & operates only when there is a chan#e in current. 7educe leel of spatter. 6lectrode diameter: (enerally produced in ;.>;.C;.11.21.+&1.>mm diameter. "ontact tipdrie roller & liner sies =oth should !e of correct sie for the wire !ein# used. Eoss in contact !etween the wire & contact tip will reduce current pick. "ontact tip should !e replaced re#ularly. The drie roller pressure is only hand ti#ht /ust to drie the wire. Einer should !e of correct type & sie for the wire. $ire @eed Speed ($@S) : ncrasin# the wire feed speed automatically increases the current in the wire. Consumables : 5i#h 'uality drawn wire & inert actie #as. ypical imperfections i) =urn throu#h : ncorrect metal transfer mode. ii) Solica inclusions : "aused !y poor inter run cleanin#. Ad!antages i) aterial thickness ran#e !) 5i#h productiity (of) c) "ontinuous electrode Disad!antages i) Small ran#e of consuma!les !) 5i#h oone leels c) %rotection for site workin#. #ositional Capabilities 4ip B 0ll positional Spray B @lat only %ulse B 0ll positional
!ub&erged arc 'elding process
Mode of "peration: 8sually automatic !ut it can !e semiautomatic. #rinciple of "peration: ranular flu & !are solid wire is used. 0rc is su!mer#ed hence no isi!le si#n of arc. 0rc melts the electrodewire, flu & some !ase meta l to form weldpuddle. Basic e%uipment re%uirements: i) Transformer rectifier (constant olta#e( flat )characteristic) ii) 5ead5ose assem!ly iii )%ower return ca!lei i) $ire feed unit ) @lu hopper deliery recoery system i ) 7un onoff ta!s ii) Tractor carria#e iii) @ume etraction. Arc Striking: $ire contact is made !y the adancement of the wire !y mechanical drie. Arc & Weld s'ielding: ranular flu uses to #enerate protectie #ases & sla#, & to add alloyin# elements to the weld pool. Weld refining & cleaning: 7efinin# & cleanin# compounds within the flu #rocess !ariable parameters: a) 9"3 (9pen "ircuit 3olta#e): 7e'uired to initiate or rei#nite the electric arc. !) 0rc 3olta#e: "han#es with arc len#th. 0rc is su!mer#ed any chan#es in arc len#th will chan#e in weld metal composition . c) "urrent $@S ($ire @eed Speed): ncreasin# the wire feed speed automatically increases the current in the wire. d) %olarity: 0"4" ? . e) @lu type & sie:i) @used flues: acidic type. 0##lomerated flues (=onded flues): !asic type. The shape of the flu is #ranular f) 6lectrode wire type & diameter: 5i#h 'uality wire in 2.+ B > mm diameter in coils. Ear#e diameter reduces penetration. #) 6lectrode wire flu specification: "omposition & #radin# is selected to suit the electrode & parent metal. h) $ire @eed Speed( $@S): ncreasin# the wire feed speed automatically increases the current in the wire. Consumables: 5i#h 'uality drawn wire & #ranular flu. ypical *elding imperfections: (i) "enterline cracks : 4eep & narrow welds. (ii) Shrinka#e caities: caused !y a weld depth width ration of G *2 Ad!antages (i) 5i#h productiity (ii) No isi!le arc li#ht Disad!antages (i) 7estricted in positional weldin# ) 3aria!le compositions (0rc len#th) #ositional Capabilities: @lat only, !ut may !e 53 !utt welds.
La&ellar Tearing Eocation : %arent aterial Steel Types : 0ny steel type Suscepti!le icro structure : Eow throu#h thickness ductility Eamellar tears are terrace like separations in the !ase metal. They are caused !y shrinka#e stresses in the throu#h thickness direction of the plate /ust !elow 50H.Eamellar tears can cause a serious failure. icro impurities such as sulphides & silicates which occur durin# steel manufacture, causes this poor throu#h thickness ductility this may lead to lamellar tearin#. #re!ention of +amellar earing a) "heckin# the chemical analysis & for laminations with 8T & %T on plate ed#es. !) "han#e of weld desi#n c) 8se weld metal !utterin# layers d) inimie restraint f) 8se pre formed ITJ piece for critical /oints.
()drogen Cracking Eocation
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50H Eon#itudinal $eld metal Transerse or Eon#itudinal Steel type : 0ll hardena!le steels 5SE0 steels & T steels Suscepti!le microstructure : artensite 0lso referred to as cold crackin#, delayed crackin# or 50H crackin#. 5ydro#en crackin# may occur in the 50H or weld metal, dependin# on the type of steel !ein# welded. 5ydro#en may !e a!sor!ed into the arc from water on plates, moisture in the air, paint or oil on the plates or the !reakdown of #as shieldin# etc. f the 50H or weld has some harden a!ility then the chances of hydro#en crackin# is more.
The four minimum critical factors & their values, where hydrogen cracking is likely to occur, arc considered to be : a) 5ydro#en content: G 1-ml1;; #m of deposited weld metal !) 5ardness : G*-; 3%N c) Stresses : G ;.- of the yield stress d) Temperature : K*;; " #re!ention of 'ydrogen Cracking a) 8se a low hydro#en process & electrode !) aimise arc ener#y. c) inimise restraint d) 6nsure plate is dry & free from rust, oil, paint or other coatin#s. e) "ontrol interpass temperature f) 6nsure weldin# is carried out under controlled enironmental conditions. #) 6nsure preheat is applied. h)8se a constant & correct arc len#th. °
!olidification Cracking Eocation Steel types Suscepti!le microstructure
: $eld center ( lon#itudinal ) : 0ll : "olumnar #rains ( n the direction of solidification ) 0lso called hot crackin# occurs durin# solidification of welds in steel, hain# hi#h sulphur content or contaminated with sulphur. 0nother cause is the depth width ratio of the weld which refers to as deep narrow welds. Therefore if we hae a com!ination of deep narrow welds with a hi#h incidence of sulphur then we are increasin# the chances of hot crackin#. 4urin# weldin#, sulphur in or on the plate may !e remelted will /oin with the iron to form ironsulphides. ron sulphides are low meltin# point impurities, which will seek the last point of solidification of the weld, which is the weld centerline. #re!ention met'ods for solidification cracking a) 8se low dilution processes !)8se hi#h man#anese consuma!les c)aintain a low car!on content d) inimie restraint stress e) Specify low sulphur content of plate f)7emoe laminations #) Throu#h cleanin# of preparation h)inimie dilution
Inter*Cr)stalline corrosion cracking or Weld Deca) "!ensiti+ation# Eocation : $eld 50H ( lon#itudinal ) Steel types : 0utenitic stainless steels Suscepti!le microstructure : Sensitised #rain !oundaries 4urin# weldin# of austenitic stainless steels when heated to the weldin# temperature a portion of !ase metal reaches temperatures in -;; D;; " ran#e & with this temperature ran#e the chromium & car!on present in the metal com!ine to form chromium car!ides. These chromium car!ides typically found alon# the #rain !oundaries of the structure. This result of their formation is the reduction of the chromium content within the #rain itself ad/acent to the #rain !oundary called L chromium depletionM 7esultin# reducin# the chromium content !elow that desired. 0fter such an effect we can say that the stainless steel has !een sensitied that is to say it has !ecome sensitie to corrosion. f no further treatment is #ien, corrosion will appear parallel to the weld toes, within the 50H. This corrosion will occur only when the weld is su!se'uently put in serice. This s commonly known as weld decay. #re!ention of *eld decay in stainless steel a) 8se parent material with a car!on content !elow ;.;*F a) To add sta!iliin# elements such as nio!ium & titanium to the plate & electrodes to sta!ilie the steel. !) aimum interpass temperature controls applied c) 0fter weldin# heatin# to 11;; " & 'uenchin#. °
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(eat Treat&ent of !teels, 0ll heat treatment are !asically cycles of three elements, which are a ) 5eatin # !) 5oldin # & S oakin # *)"oolin#. 5eat treatments #ien to metals are as follows. 1) 0nnealin# 2) Normaliin# *) 5ardenin# +) Temperin# -) Stress 7eliein#. >) %reheatin#. The methodssources that may !e used to apply heat to a fa!rication may include: i) @lame !urners heaters preheatin#. ii) 6lectric resistance heatin# !lankets B %reheatin# & %$5T. iii) @urnaces B 0nnealin#, Normaliin#, 5ardenin#, Temperin#. The tools use to measure the temperatures of furnaces & heated materials may include: a) Temperature indicatin# crayons (tempil sticks) B preheatin#, %$5T. !) Thermocouples B 0ll heat treatments. c) %yrometers (9ptical, resistance, radiation) B @urnace heat treatments. d) Se#ar cones B @urnace heat treatments. 1) Annealing: The term annealin# #enerally means to !rin# a metal or alloy to its softest or most ductile natural condition. 0nnealin# is a heat treatment process that may !e carried out on steels, & most metals to re#ain the softness ductility. n steels we can carry out two kinds of annealin#: a) @ull annealin# (includin# solution annealin#) !) Su! critical annealin# n full annealin# of steels the steel is heated a!oe its 8"T (8pper "ritical Temperature) & allowed to cool ery slowly in a furnace for 1 hour eery for eery 2-mm of thickness. The furnace is then turned off & the steel remains in the furnace to cool. This produces a lar#e or course #rain structure that is soft & ductile !ut has ery low tou#hness. The 8"T ran#e of plain car!on steels is !etween A2*D1; ". n su! critical annealin# the steel is heated to temperatures well !elow the lower critical temperature (A2* ) 2) ,ormali-ing enerally used for steels. The steel is heated a!oe its 8"T & soaked for 1 hour for eery 2-mm of thickness. 9nce the soakin# time finished the steel is remoed from the furnace to cool in still air. This produces a much finer #rain structure than annealin# & althou#h the softness & ductility is reduced, the stren#th & hardness is increased. *) ardening The steel is heated a!oe its 8"T & soaked for 1 hour for eery 2-mm of thickness. 9nce the soakin# time has finished the steel is remoed from the furnace to 'uench in a coolin# medium. =rine is considered to !e the fasted coolin# media followed !y water & then oil. This produces a fine #rain martensitic structure that has ery hi#h hardness & stren#th, thou#h ductility is almost ero, with ery low tou#hness. +) empering: Temper means to !alance. $hen temperin# steel we re!alance the properties of ecessie hardness & !rittleness !y decreasin# the hardness & increasin# the leel of tou#hness. The steel is reheated after hardenin# & the !alance of hardness to tou#hness is ad/usted as the temperature is increased from 22; A2* ". 0t A2* " all martensite has !een tempered remoin# !rittleness & returnin# the ductility. The fine structure is retained #iin# hi#h stren#th & further improin# the tou#hness. -) Stress Relie!ing or #W: The purpose of stress reliein# is to reliee internal elastic stress that has !ecome trapped inside the weld durin# weldin#. n stress reliein# the steel may !e heated !etween 2;;D-; dependin# on the steel type. 4urin# stress reliein# yield point is ery important yield point is the point where steel can no lon#er support elastic strain & !ecomes plastically deformed (i.e) %lastic strain occurs. This means that the steel will no lon#er return to its ori#inal dimension. $hen steel is heated the yield point is suppressed, which means that the elastic strain will now start to !ecome plastic strain. The hi#her the temperature then #enerally the more elastic strain will !e conerted to plastic strain. >) #re/'eating %re heat is used a) To control the structure of the weld metal & 50H on coolin#. !) To improe the diffusion of #as molecules throu#h on atomic structure. c) To control the effects of epansion & contraction. n this the steel is heated to a temperature dependant on the type of steel !ein# heated treated, !ut normally less than *-; ". %reheatin# used to control the formation of 52 cracks. °
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Materials Inspection 0ll materials arriin# on site should !e inspected for Sie "ondition Type Specification Some imperfections associated with plate are as follows: a) Eaminations: "ontain impurities & ma/or inclusions in the in#ot. $hen rolled out these ma/or inclusions may eist throu#hout the plate thickness cause laminations. !) Se#re#ation !ands: 9ccur in the center of the plate & are low meltin# points impurities such as sulphur or phosphorous. "annot !e detected !y N4T. "an only !e found on etched surfaces. c) Eaps: "aused durin# rollin# when oerlapped metal does not fuse to the !ase material due to insufficient temperature & or pressure.
#late Inspection should !e checked for condition of the plate. "orrosion, mechanical dama#e, laps & lamination should !e checked. Type & specification should !e stamped on plate should !e checked for dimensions (len#th, width) & Thickness of the plate. 9ther checks need to !e made such as heat treatment condition, distortion, tolerance, 'uality stora#e & identification. #ipe Inspection
"orrosion, mechanical dama#e, wall thickness, 'uality, laps, and laminations. Type & specification should !e stamped on pile. Should !e checked for dimensions (inside, outside diameter of pipe, len#th & thickness of pipe, whether seam or seamless other checks also need to !e made such as heat treatment condition, distortion, tolerance, 'uantity, identification & stora#e.
Mec-anical Testing 1) arness ests : 5ardness is the a!ility of a material to resist indentation. Test is used to check the leel of hardness across the weld. Types of hardness test are a) 7ockwell scale B mpressin# a diamond or steel !all !) 3ickess pyramid 3%N B mpressin# a diamond c) =rinell =5N B mpressin# - or 1;mm diameter steel !all d) Shore Scwerescope B easures resilience ost of the hardness tests are carried out !y i) mpressin# a !all or a diamond into the surface of a material under a fied load. ii) Then measurin# the resultant indentation & comparin# it to a scale of units (=5N3%N etc.) 5ardness sureys are #enerally carried out across the weld also at the weld /unction fusion one. 2) oug'ness ests : Tou#hness is the a!ility of a material to a!sor! impact ener#y & resist fracture. Test is used to check the resistance to impact loadin#. Types of tou#hness test are, a) "harpy 3 (oules) B Specimen weld horiontally in test machine, notch to the rear !) od (@tl!s) B Specimen held ertically in test machine, notch to the front. c) "T94 or "rack Tip 9penin# 4isplacement testin# (mm) n charpy 3 & od test, the fracture tou#hness is assessed !y the amount of impact ener#y a!sor!ed !y a small specimen of 1;mm2 durin# fracture !y a swin#in# hammer. The notch is 2mm deep, ;.2- root radius & notch +- . *) ensile test: 8sed to measure tensile stren#th (N mm2) (4uctility as 6F). Stren#th is the a!ility of a material to resist a force (normally tension). Types of tensile tests are: a) Transerse tensile test & !) 0ll weld metal tensile test a) rans!erse tensile test: i) 7educed section: 8sed to test the stren#th of the weldment ii) 7adius reduced section: "an !e used to assess the stren#th of the weld metal. . !)All *eld metal tensile test : 8sed to test weld metal for 8TS, yield point & elon#ation or 6F Transerse tensile test are taken across the weld . n reduced tensile test the specimen is first cut & then reduced. n radius reduced tensile test the weld metal is turned down .0ll weld metal tensile test are carried out !y electrode manufacturers to determine weld metal stren#th & also ductility as elon#ation (6F).0fter fracture, the pieces are placed !ack to#ether & the elon#ation is calculated as 6F. +) Macro $0amination tests : used to check the internal leel f 'uality in the weld. 0 macro specimen is normally cut from a stopstart position in the root or hot pass of a welder approal test. The startstop position is marked out durin# a welder approal test !y the weldin# inspector. 9nce cut the specimen is polished usin# finer #rit papers & polishin# at D; to preious polishin# direction for smooth surface. t is then etched in the acid solution, which is normally -1;F nitric acid in alcohol ("ar!on steels). 0fter etchin# for the correct time, the specimen is then washed & dried. 0 isual inspection should !e carried out at all sta#es. @inally a report is then produced on the isual findin#s, then compared & assessed to the leels of acceptance in the application standard. acro samples may !e sprayed with clear lac'uer after inspection, for stora#e purposes. °
°
-) ) Bend est: . 4uctility is the a!ility of a material of plastically deform under tension. =end test is used to check weld ductility & fusion in the area under stress. n !end test the former is moed throu#h a #uide (#uided !end test) or rollers, & the specimen is !end to the desired an#le Types of !end test are: a)@ace !ends !)7oot !ends c)Side !ends d)Eon#itudinal !ends @ace !end B The face of the specimen is in tension & root is in compression. 7oot !end B The root of the specimen is in tension & face is in compression. Side !end B 0ny side of the specimen is in tension & other side is in compression. enerally !end tests are carried out for welder approal tests, thou#h they may also !e used durin# procedure approal. =end test is 'ualitatie method of mechanical testin#. >) 1illet *eld fracture tests : 8sed to check root fusion in fillet welds. This test is carried out for welder approal test. The specimen is normally cut !y hacksaw throu#h the weld face to a depth of 12mm. t is then fractured with a hammer !low from the rear. 9nce the fracture has !een made !oth fractured surfaces are inspected for imperfections. @inally the line of root fusion is o!sered for continuity. 0ny strai#ht line would indicate a lack of root fusion & as per most of the standards this is, sufficient to fail the welder. 0 s we are checkin# weld 'uality, test is 'ualitatie mechanical test. A) ,ick break tests: 8sed to assess root penetration & fusion in dou!le sided !ut welds & the internal faces of sin#le sided !utt welds. Test is carried out for a welder approal test. The specimen is normally cut !y hacksaw throu#h the weld faces to a depth stated in the standard. t is then weld in a ice & fractured with a hammer !low from the rear. 9nce fracture has !een made then !oth fractures are inspected for imperfections. 0s we are checkin# weld 'uality, test is 'ualitatie mechanical test.
WELDIN$ IMPER.ECTIN!: $eldin# imperfections are material discontinuities caused !y, or durin# the process of weldin#. "an !e classified into the followin# #roups. 1"racks,2 as pores & porosity * Solid inclusions + Eack of fusion - Surface & profile > echanical dama#e Aisali#nment. 1. Cracks : 9ccur in welded materials. To occur crack there are three criteria that must !e present a) @orce !) 7estraint c) 0 weakened structure. Typical types of cracks are: 5ydro#en cracks Solidification cracks Eamellar tears aterials causin# crack durin# weldin# can !e ealuated under the term welda!ility. aterials, which welded !y common weldin# processes, is called welda!ility. "racks are classed as planer imperfections as they #enerally hae len#th & depth. 2. 2as #ores & #orosity: as filled caities smaller than 1.>mm diameter, which are created durin# solidification. %orosity are #as pores K1.>mm diameter, which are #enerally #rouped to#ether. 0 sin#ular #as filled caity O or G 1.>mm diameter is termed as L!low holeM. %orosity is mainly produced when weldin# improperly cleaned plate, or when usin# damp weldin# consuma!les. Shrinka#e caities are created durin# solidification of welds of hi#h depth: width rate. This may occur when the d: ration is G2:1. 0lso called hot plastic tear with sharp ed#es & is treated as a crack. *. Solid inclusions: include metallic & nonmetallic inclusions that may !e trapped in the weld durin# the process of weldin#. ay !e caused !y a) Eack of welder skill (incorrect weldin# techni'ue) !) %oor manipulation of the weldin# process, or electrode. c) ncorrect parameter settin#s, i.e) olta#e, current, trael speed. d) a#netic arc !low. e) ncorrect positional use of the process or consuma!le f) ncorrect interrun cleanin#. +. +ack of 1usion: is a lack of union !etween two ad/acent areas of material. 0 serious imperfection as produce areas of hi#h stress concentration. This may caused !y a) Eack of welder skill (incorrect weldin# techni'ue) a) %oor manipulation of the weldin# process, or electrode. !) ncorrect parameter settin#s i.e) olta#e, ampera#e, trael speed. c) a#netic arc !low. d) ncorrect positional use of the process, or consuma!le. e) ncorrect interrun cleanin#. -. Surface & #rofile enerally caused !y poor weldin# techni'ues. Su rface or profile imperfections are as follows. a) ncompletely filled #roe: ay !rin# the weld !elow its desi#n throat thickness. Spatter: Not a ma/or factor !ut should !e cleaned off !efore inspection as it mask other imperfections. "an cause micro crackin#. 0rc Strikes (Stray arc or Stray @lash) can cause seeral types of cracks to occur. Normally !e N4T inspected & then re'uired. ncomplete root penetration: "an cause !y too small a root #ap, insufficient current or poor weldin# techni'ue. =ul!ous or irre#ular contour : "auses sharp stress concentrations at the toes & may also contri!ute to oerall poor toe !lend. rre#ular !ead width: s a surface imperfection. Should !e re#ular alon# its linear len#th. 8ndercut: 4epression at the toe of a weld. "aused !y incorrect weldin# techni'ue, too hi#h current & the weldin# position. Seerity can !e measured !y its len#th depth & sharpness. 7oot concaity (Suck !ack): "aused when usin# too hi#h a #as !ackin# pressure in pur#in#. 0lso produced when weldin# with too lar#e a root #ap & depositin# too thin a root !ead. 6cess penetration =urn throu#h: "aused !y usin# too hi#h a weldin# current & or slow trael speed, lar#e root #ap &or small root face for the current or process !ein# used. 0ccompanied !y !urn throu#h, which is a local collapse of the weld puddle causin# a hole or depression in the final weld root !ead. 7oot 9idation: ay take place when weldin# reactie metals such as stainless . steels with contaminated or inade'uate pur#in# #as flow. >. Mec'anical Damage Surface material dama#e caused durin# the manufacturin# process. 4ama#e can !e caused !y rindin#, "hippin# , 5ammerin# , =reakin# of welded attachments !y hammerin# usin# needle #uns to compress weld cappin# runs can cause local stress concentrations & should !e repaired prior to completin# the / o!. A. Misalignment Two forms of misali#nment a) Einear misali#nment. !) 0n#ular misali#nment.Einear misali#nment can !e controlled durin# weld set up !y tackin#, !rid#in#, clampin# etc. 6cess weld metal hei#ht is always measured from the lowest plate to the hi#hest point of the weld cap. 0n#ular misali#nment can !e controlled !y !alance weldin#, offsettin# or use of /i#s, clamp etc.
MMA WELDIN$ / .UNCTIN! . ELECTRDE CATIN$ ".LU0# 1. 2. *. +. -. >. A. C. D. 1;.
To assist arc i#nition To improe arc sta!iliation. To produce a shieldin# #as to protect the arc column. To refine & clean the solidifyin# weld metal. To form a sla#, which protects the solidifyin#, weld metal. To add alloyin# elements. To control hydro#en content of the weld metal To form a core at the end of the electrode, which directs the arc. To reduce the coolin# rate. t acts as a deoidiin# a#ent.
1! 234 !pecification E 56 33 1 627 8 ( 6 -1 **
6lectrode Tensile & Pield Stren#th (TS-1;>-;Nmm2,, PS*C;Nmm 2,) Tou#hness 2C & +A oules @irst di#it 2C, Second di#it +A Testin# temperature : 2; " 6lectrode "oatin# B = for =asic 6lectrode efficiency $eldin# position B 2 for all positions ecept ertical down 6lectrical parameters B 9 for 4" polarity as recommended & 0" in 9"3 ( 9pen circuit olta#e) not recommended. Eow hydro#en potential (0fter !akin#) °
= 1>; 2 9 5
1!En 944 !pecification E 92 3 6Ni 1 5 9 (5 6 +> * 1Ni
6lectrode Tensile & Pield stren#th (TS -*;>C;Nmm2 , PS +>;Nmm2) Tou#hness +A oules (* for *; ") 0ny li#ht alloyin# composition. (n B 1.+, Ni B ;.>1.2) = @lu coatin# type (==asic) 6lectrical parameters & efficiency (0"?4", 7ecoeryF G12- K 1>;) + $e ldin # posit io n (+ for flat !utt & fillets) 5 Eow hydro#en potential (after !akin#) °
-
AW! A 5,6 : A5,5 !pecification E ;7 6 ; $ 6 C; 1 1C
6lectrode Tensile Stren#th 1;;; (TS C;;;;), PS >C B C;;;;) $eldin# position (1 for all positions) 6lectrode coatin# Q electrical characteristic (1C for !asic ?2-F @e powder, 0" or 4"?) Eow alloy steels ( Ni, "r,o& 3)
.lu
4) Agglo&erated .lu
5+RAS",IC $SI,2 Ad!antages 1. @errous & nonferrous alloys can !e tested. 2. "an easily detect lack of sidewall fusion. *. No ma/or safety re'uirements. +. %orta!le with instant results. -. 0!le to detect su!surface defects. easures depth & throu#h wall etent. >. "an test heay wall thickness /o!.
1. 2. *. +. -.
Disad!antages 5i#h operator skill leel. 4ifficult to interpret 7e'uires cali!ration. No permanent record (unless automated) Not easily applied to comple #eometry.
RADI"2RA#IC $SI,2 Ad!antages 1. 2. *. +. -.
%ermanent record. ost materials can !e tested. 4etects internal flaws. ies a direct ima#e of flaws. @luoroscopy can #ie real time ima#in#.
1. 2. *. +. -.
Ad!antages Eow operator skill leel. 0pplica!le to nonferroma#netic materials. Eow cost. Simple, cheap & easy to interpret. %orta!ility.
Disad!antages 1. Skilled interpretation re'uired. 2. 0ccess to !oth sides re'uired. *. Sensitie to defect orientation (possi!le to miss planner flaws) +. 5ealth haard. -. 5i#h capital cost.
#$,$RA, $SI,2
1. 2. *. +. -.
1. 2. *. +. -.
Disad!antages "areful surface preparation re'uired. Surface !reakin# flaws only. Not applica!le to porous materials. No permanent record. %otentially haardous chemicals.
MA2,$IC #ARIC+$ $SI,2 Ad!antages Disad!antages %recleanin# not as critical as with 4% 1. @erroma#netic materials only. $ill detect some su!surface defects 2. 4ema#netiation may !e re'uired. 7elatiely low cost. *. 4irect current flow may produce arc Simple e'uipment. strikes. %ossi!le to inspect throu#h thin coatin#s. +. No permanent record. -. 7e'uired to test in two directions.
Residual !tresses : Distortion esidual stresses are defined as those stresses remaining inside a material after a process has been carried out. The process used is welding & the stresses are caused by the heat of welding producing load expansion & contraction to take place. These stress es causes stress corrosion. !racking to occur also affect dimensional stabilit y. The amount of contraction is controlled by : The volume of weld metal in the "oint# the thickness, heat input, "oint design. $ffsetting may be used to finali%e the position of the "oint. n plates or pipes arc prevented from moving by tacking, clamping or "igging etc. The movement caused by welding related stresses is called distortion, Three basic directions of distortion are i' (ongitudinal ii' Transverse iii' )hort transverse A high percentage of residual stresses can be removed by heat treatments. The peening of weld faces *with the use of a pneumatic needle gun' will only redistribute the residual stress.
WELDIN$ !A.ET= : $eldin# inspector hae to ensure that the safe workin# practices are strictly followed. Seeral area where safety in weldin# re'uires arc as follows: . 1) $eldin# cuttin# process safety. 1. 6lectrical safety. 2. $eldin# fumes & #ases (use & stora#e of #ases) *. Safe use of liftin# e'uipments. +. Safe use of hand tools & #rindin# machines. -. eneral weldin# safety awareness. 3)Welding 6 cutting process safety: a)7emoin# any com!usti!le materials from the area. "heckin# all containers to cut or welded arc fume free (permits to work etc) a' %roidin# entilation & etraction where re'uired. b' Reepin# oil & #rease away from oy#en. c' 0ppropriate %%6 is worn at all times. d' 2) $lectrical Safety : a)
6nsure that insulation is used where re'uired & that ca!les & connections are in #ood condition. 0ll electrical e'uipment must !e re#ularly tested & identified. 7)2ases & 1ume Safety: ases & fumes may come from electrodes, platin#, !ase metals & #ases used in & produce durin# the weldin# process. 4an#erous #ases include oone, nitrous oides & phos#ene, which are etremely poisonous & will result in death when oer eposure occur. "admium chromium & other metallic fumes are etremely toic & will result in death if oer eposure results. 8)+ifting $%uipments: t is essential the correct liftin# practices are used for slin#in#. Should !e re#ularly inspected. "are should !e taken for cuttin# corners, as it is more dan#erous. 4onJt stand !eneath a load when liftin# is #oin# on. 9)and tools & grinding mac'ines: 5and tools should always !e in a safe & sericea!le condition & should always !e used in a safe & correct manner. 8se cuttin# discs for cuttin# #rindin# discs for #rindin# only. :)2ene ral *elding safety a*areness: =e aware of the haards in any weldin# /o! & always minimie the risk. 0lways refer safety adisor if any dou!t eists.
Cutting Processes All thermal cutting processes must satisfy two functions to used a cutting + gouging process. . A high temperature *capable of melting the materials being cut' -. A high velocity *capable of removing the molten materials in the cut' Plasma Cutting : tili%es the temperatures reached from the production of the plasmas from certain types of gases. /itrogen gas plasma can reach a temperature of over -0,000 ! but temperature of air plasma is much lower. There are two different types of plasma cutting process which are: Transferred arc *sed cutting conductive materials' /on1transferred to arc *sed for cutting non conductive materials' Arc cutting & gouging . Temperature attained by an electric arc can be used in cutting processes. There are three types of processes, the main differences being in the consumables & the gas used in producing the velocity required. !onventional cutting + gouging electrodes. $xy1arc cutting + gouging. Arc 2 air cutting + gouging. Conventional cutting / gouging electrodes : The consumables consist of a light alloy central core wire, which is mainly to give rigidity & a heavy flux coating, which provides elements that produce arc energy. The arc is truck in a conventional way to 33A welding, however the melts the base material, which is then pushed away by using a pushing action with the electrode. OxyArc cutting / gouging! equire a special type of electrode holder. The consumables arc tubular in section & arc coated with a very light flux coating. The arc is struck & compressed oxygen may be activated at the torch head. The heat of the electric arc melt the base metal or alloy & the velocity to remove it is provided by the compressed oxygen. This process is generally used for decommissioning + scrapping plant as the cut surface is generally not consistent. Arc " Air cutting / gouging! sed for gouging old welds removing materials. The consumable is a copper coated carbon electrode. The gas used is compressed air. The process is basically a 4melt & blow process5. The main disadvantage is high level of noise °
produced & the volume of fumes generated. The coat face will require dressing. A safety precaution is to use correct ear protection & breathing supply system.
1lu0es for Submerged arc *elding 1) 1used flu0es : @used flues are mied to#ether & !aked at a ery hi#h temperature where all the components !ecome fused to#ether. $hen cooled the resultant mass resem!les a sheet of !lack #lass, which is then puleried into small particles. These particles a#ain resem!le small silers of !lack #lass. They are hard, reflectie, irre#ular shaped, & cannot !e crushed in the hand. @used flues tend to !e of the acidic type produce comparatiely low 'uality weld metal in terms of the mechanical properties of tensile stren#th & tou#hness. -' Agglomerated #luxes : Agglomerated fluxes are a mixture of compounds that are baked at a much lower temperature & are essentially bonded together by bonding agents into small particles. The recognition points of these types of fluxes is easier, as they are full, generally sound granules, that are easily crushed & can also be very brightly colored as coloring agents may be added in manufacture as a method of identification unlike fused fluxes. Agglomerated fluxes tend to be of the basic type & will produce weld metal that is of much higher quality in terms of strength & toughness
Residual Stresses & Distortion 7esidual stresses are defined as those stresses remainin# inside a material after a process has !een carried out. The process used is weldin# & the stresses are caused !y the heat of weldin# producin# load epansion & contraction to take place. These stresses causes stress corrosion. "rackin# to occur also affect dimensional sta!ility. The amount of contraction is controlled by :
The olume of weld metal in the /oint the thickness, heat input, /oint desi#n. 9ffsettin# may !e used to finalie the position of the /oint. n plates or pipes arc preented from moin# !y tackin#, clampin# or /i##in# etc. The moement caused !y weldin# related stresses is called distortion, Three !asic directions of distortion are i) Eon#itudinal ii) Transerse iii) Short transerse 0 hi#h percenta#e of residual stresses can !e remoed !y heat treatments. The peenin# of weld faces (with the use of a pneumatic needle #un) will only redistri!ute the residual stress.
