Non-destructive testing of helically welded pipes made of ...

Mariusz StachurskiNon-destructive testing of helically welded pipes made ofthermomechanically rolled materials used for sending ofcombustiblesAbstract: In the first part of the paper it has been presented the short informationon methods of fabrication of helically welded pipes used for transporting of combustibles.In the second one it has been given the NDT methods used during inspectionof the pipes in production plants. In the next parts it has been described the NDTmethods for steel pipes focusing first of all on visual, ultrasonic and radiographicones. The paper has been ended with the information about prospects of gas industrydevelopment in Poland and in the world.Keywords: welding, non-destructive testing, helially welded pipesIntroductionThe golden age of pipelines has comewith a permanently increasing demand forraw materials; the excavation of which is anenormously complicated undertaking. As oftoday, the best solution related to this typeof transportation is a subterranean grid ofmain pipelines made of steel pipes. Poland’sgas distribution system has approximately17 thousand kilometres of high-pressuregas pipelines and approximately 79 thousandkilometres of distribution network, 23 gaspumping stations, and approximately 4 thousand1 st and 2 nd degree pressure reducing andmeasuring stations. A growing consumptionof energy combined with a growing demandfor energy carriers, in particular for naturalgas, shapes the development of the network ofindustrial pipelines. Great distances betweenthe sources at which natural gas and oil areexcavated and the places of their consumptionrequire the construction of transit pipelinescharacterised by very high operatingparameters, e.g. gas pipelines with a diameterof over 1000 mm and pressure of 10 MPa.Such pipelines must be made of pipes characterisedby a strength of over 690 MPa(485MB, 555MB) and very good weldability.As a result, it is possible to observe thedevelopment of low-alloy steels (C 0.16%,Si 0.55%, Mn 1.9%), often with microadditionsof Nb, Mo, or Ti. Such pipes are obtainedby means of controller rolling referredto as thermoplastic or thermomechanicaltreatment. Pipes for the pipelines mentionedabove are produced following the regulationscontained in DIN standards or in their American(API5L) and European (EN 10208)counterparts. Large-diameter steel line pipesfor transporting liquid and gaseous fuels areused as the following:• seamless pipes (S), obtained by means ofhot or cold working methods,• welded pipes (W), produced by means ofelectric induction welding (EW) or buttwelding (BW) as well as submerged arcwelding (SAW) with a longitudinal weld(SAWL) or a helical weld (SAWH). Figure1 presents the process of welding pipeswith a helical weld (two-stage). Pipes candr inż. Mariusz Stachurski (Ph.D. Eng) - Bureau Veritas Poland ltd.No. 3/2013 BIULETYN INSTYTUTU SPAWALNICTWA37

also be welded using the combination ofgas-shielded welding of root runs andsubmerged arc welding of filling layers(COW) [1].First stage tack weld –MAG weldingSecond stage submerged arcwelding (with three automaticwelding machinessimultaneously)Fig. 1. Two-stage helical welding of pipes used by theGerman company of Salzgitter Mannesmann GrossrohrGmbH [5]This article presents non-destructive testingof thermomechanically rolled helicallysubmerged arc welded (SAWH) pipesL485MB and L555MB. These pipes were selectedas they are typical and manufacturedin many steelworks both in Poland and overseas.Following their manufacture the pipesundergo insulation application, usually withpolyethylene or polypropylene and are paintedinside with epoxy paints.Non-destructive testing used duringpipe manufactureGeneral informationThe basic purpose of non-destructive testing(NDT) is to assess the condition of a materialor welded joint and, on this basis, toissue an opinion related to the quality, durabilityand safe operation of a structure. Theeffectiveness and quality of non-destructivetesting depends on numerous factors:• personnel competence based on adequatetraining,• experience,• inspection procedures,• equipment,• environment in which testing is carried out,• psychological pressure, to which NDTpersonnel are exposed,• working time during the day,• equipment features,• supervision and how it is exercised,• applied standards, requirements andguidelines,• systems applied for the certification ofpersonnel, procedures and equipment [1].The basic NDT methods used in the productionof pipes are the following:• visual testing – VT,• radiographic testing of pipe ends – RT,• automatic fluoroscopic testing of a wholewelded joint,• ultrasonic testing of a burden material inthe form of a strip unwound from a coil(laminar imperfection test) – UT,• automatic ultrasonic testing of a wholewelded joint – UT,• manual ultrasonic testing of a welded jointon a pipe end – UT,• manual ultrasonic testing of a welded jointbeing repaired – UT.In addition, in order to determine preciselythe size of welding imperfections, alsoother NDT methods, i.e. penetration testing(PT) and magnetic particle testing (MT),can be used.The basic standard describing the selectionof testing manners and assessment criteriais standard PN-EN 10208-2 “Steel pipesfor pipelines for combustible fluids – Technicaldelivery conditions – Part 2: Pipes of requirementsclass B”. The standards describingtesting manners and assessment criteriaare the following:• PN-EN 10246-9 Non-destructive testingof Steel Tubes – Part 9: Automatic UltrasonicTesting of the Weld Seam of SubmergedArc Welded Steel Tubes for theDetection of Longitudinal and/or TransverseImperfections;• PN-EN 10246-10 Non-destructive testingof Steel Tubes – Part 10: RadiographicTesting of of the Weld Seam of AutomaticFusion Arc Welded Steel Tubes for theDetection of Imperfections;38 BIULETYN INSTYTUTU SPAWALNICTWANo. 3/2013

• PN-EN 10246-15 Non-destructive testingof Steel Tubes – Part 15: Automatic UltrasonicTesting of Strip/Plate Used in Manufactureof Welded Steel Tubes for the Detectionof Laminar Imperfections;• PN-EN 10246-16 Non-destructive testingof Steel Tubes – Part 16: Automatic UltrasonicTesting of the Area Adjacent to theWeld Seam of Welded Steel Tubes for theDetection of Laminar Imperfections;• PN-EN 10246-17 Non-destructive testingof Steel Tubes – Part 17: Ultrasonic Testingof Tube Ends of Seamless and WeldedSteel Tubes for the Detection of LaminarImperfections;• PN-EN ISO 10893-6 Non-destructivetesting of Steel Tubes – Part 6: RadiographicTesting of the Weld Seam ofWelded Steel Tubes for the Detection ofImperfections;• PN-EN ISO 10893-8 Non-destructive testingof Steel Tubes – Part 8: Automatic UltrasonicTesting of Seamless and WeldedSteel Tubes for the Detection of LaminarImperfections;• PN-EN ISO 10893-9 Non-destructivetesting of Steel Tubes – Part 9: AutomatedUltrasonic Testing for the Detection ofLaminar Imperfections in Strip/Plate Usedin the Manufacture of Welded Steel Tubes;Types of imperfectionsdetected during pipemanufactureResidual magnetismon pipe endsLaminar imperfectionon pipe endsLongitudinal/transverseimperfections in weldedjointLaminar imperfectionson pipe bodyLaminar imperfectionson strip edge wheretransverse weld wasmadeNon-destructive testingof weld in pipe ends(areas not tested previously)/ testing of areasbeing repairedTable 1. Non-destructive tests used in manufacture of pipes [2]Testing statusObligatoryOptionalObligatoryOptionalOptionalObligatoryTypes of tests, requirements and acceptance levelsGaussmeter using Hall effect or equivalent; max. 30 gausses,random testsUltrasonic testing according to PN-EN 10246-17 or PN-ENISO 10893-8, inspection area: max. 6 mm from pipe ends oncircumferenceUltrasonic testing according to EN 10246-9 or PN-EN ISO10893-11, acceptance level U2/U2H or calibration method”two lamb” (also for welds joining strip ends in helically weldedpipes)Radiographic testing according to PN-EN 10246-10 or PN-ENISO 10893-6, image quality class R1, used for T-type joints ofhelically welded pipesUltrasonic testing according to PN-EN 10246-15 or PN-ENISO 10893-9, acceptance level U2Ultrasonic testing according to PN-EN 10246-15 or PN-ENISO 10893-9 or alternatively ultrasonic testing according toPN-EN 10246-16 or PN-EN ISO 10893-8, acceptance levelU2Ultrasonic testing according to PN-EN 10246-9 or PN-EN ISO10893-11 for longitudinal imperfections, acceptance level U2/U2Hor (if not specified otherwise)Radiographic testing according to PN-EN 10246-10 orPN-EN ISO 10893-6, image quality class R1for longitudinalimperfectionsandUltrasonic testing according to PN-EN 10246-9, (PN-ENISO 10893-11) or radiographic testing according to PN-EN10246-10 (PN-EN ISO 10893-6) for transverse imperfectionsNo. 3/2013 BIULETYN INSTYTUTU SPAWALNICTWA39

• PN-EN ISO 10893-11 Non-destructive testingof Steel Tubes – Part 11: Automated UltrasonicTesting of the Weld Seam of WeldedSteel Tubes for the Detection of Longitudinaland/or Transverse Imperfections.The standards of the PN-EN 10246 serieshave been now replaced by the standardsof the PN-EN ISO 10893 series. The basicproduct standard PN-EN 10208-2 (version ineffect) still indicates older standards as thosein effect. As a result, all the greater productionplants continue to use these standards inthe manufacturing of pipes. For this reason,in all cases this study refers to both standardsas recommended for use. As far as ultrasonicmanual testing is concerned, the standardsapplied are the basic standards concernedwith the manner of the ultrasonic manualtesting of welded joints and their assessmentand are not discussed in this study. A detailedlist of non-destructive tests applied in pipemanufacture is presented in Table 1.The residual magnetism at the ends ofeach pipe, parallel in relation to the pipe axis,should not exceed 30 G (3mT). The measurementof magnetism should be carried out ona random basis on the butting face of the pipeend, by means of a calibrated meter (gaussmeter)using the Hall effect or by means ofequivalent devices.All non-destructive tests of welded jointsshould follow a hydraulic test of the pipe.Visual testing (VT)In accordance with the requirements ofstandard PN-EN 10208-2 each pipe shouldundergo a visual inspection of the entireouter surface. The inner surface of the pipeshould be inspected on each side of the pipeif its outer diameter is 610 mm or less and in100% of the entire inner surface if the outerdiameter of the pipe is 610 mm or greater.Visual testing should be carried out by adequatelytrained personnel and with properlighting of the surface being viewed (thelight intensity should amount to a minimumof 300 lx).Pipes should be free from imperfectionsas a finished product. The appearance of theouter and inner surfaces of the pipe should betypical for the production process and heattreatment applied. No surface imperfectionsrequiring removal should be visible.Below are presented manners of dealingwith imperfections detected on the outersurface:• imperfections with a depth equal to or below12.5% of a required wall thickness,which do not reduce the nominal thicknessof the pipe in the place of their occurrenceshould be treated as allowed imperfections(they can remain on the pipe surface or, inaccordance with the manufacturer’s decision,can be removed by cosmetic grinding);• imperfections with a depth exceeding12.5% of a required wall thickness, whichdo not reduce the nominal thickness of thepipe in the place of their occurrence areclassified as imperfections and should beremoved by grinding (after grinding it isnecessary to apply a proper NDT method,e.g. MT, in order to check the pipe surfaceafter grinding);• imperfections which reduce the nominalthickness of the pipe in the place of theiroccurrence should be treated as unallowedimperfections and repaired by welding orthe part of the pipe containing such imperfectionsshould be cut out (the requiredlength of the time should be maintained).If the aforesaid solution is impossible,a pipe with an unallowed imperfectionshould be rejected.Geometrical deformations of the cylindricalcontour of the pipe should not exceed thefollowing:• 3 mm (flattening, metal excess, coldformedindentations with gentle edges);• 6 mm (other indentations).40 BIULETYN INSTYTUTU SPAWALNICTWANo. 3/2013

Outer imperfections can be removed only bymachining or grinding. The thickness of apipe wall in the areas being repaired cannotbe less than the required nominal wall thickness.All machined/ground areas should gentlypass into the contour of the pipe [2].Ultrasonic testing (UT)Ultrasonic testing of strip (pipe body) forlaminar imperfectionsThe first type of ultrasonic testing usedduring pipe checks is testing for laminar imperfectionsof the strip surface. In this caseit is possible to accept ultrasonic testing carriedout at the sheet manufacturer’s or testa (flat-formed) material used in the productionof pipes, acting in accordance with therequirements of standards PN-EN 10246-15or PN-EN ISO 10893-9 and acceptance levelU2. Single laminar imperfections or laminarimperfections in groups exceeding acceptancelevel U2 are unallowed [2, 6, 11]. Anexample of a device for strip ultrasonic testingis presented in Figure 2.Fig. 2. Device applied in UT of strips for the presenceof laminar imperfections, used in the Salzgitter MannesmannGrossrohr GmbH compay, Germany [5]Ultrasonic testing for the detectionof longitudinal and transverse imperfectionsin welded jointsIn order to ensure full NDT of weldedjoints it is required that helically weldedpipes should undergo ultrasonic testingalong their whole length. The test objectiveincludes both longitudinal and transverse imperfections.Ultrasonic testing should be carriedout in accordance with the requirementsof standard PN-EN 10246-9 or PN-EN ISO10893-11 [2]. As a rule, UT of pipes followsthe completion of all the main operations ofa production process. In order to ensure thereliability of ultrasonic testing, pipes shouldbe sufficiently straight and free from foreignmatter.In order to detect longitudinal and transverseimperfections, helical welds shouldundergo ultrasonic testing. In both cases thetesting should be conducted in two oppositebeam propagation directions. During thetest the converter unit should remain in theproper position in relation to a weld so thatthe entire weld could be searched through. Asearching rate should not oscillate by morethan 10% than the adopted basic rate. Dependingon the thickness and roughness ofthe pipe surface, the frequency used in UTshould be contained within a 1 MHz÷15 MHzrange. The maximum width of each singleconverter, measured parallel to the mainaxis of the pipe, should amount to 25 mm.By means of an ultrasonic monitor connectedwith a marking and/or sorting system, theequipment should enable the classification ofpipes as accepted or rejected. If it is not possibleto test welds on pipe ends by means ofautomatic ultrasonic testing equipment, thetesting of pipe ends should be conducted bythe manufacturer using either manual ultrasonictesting or radiographic testing.Ultrasonic equipment for detecting longitudinalimperfections should be calibratedby means of four longitudinal grooves,No. 3/2013 BIULETYN INSTYTUTU SPAWALNICTWA41

two on the outer surface and two in the innersurface of pipe masters and/or by means ofa datum hole (Fig. 3). Converters used fordetecting transverse imperfections shouldbe calibrated by means of a hole and/or twogrooves transverse in relation to the weld,one on the outside and one inside a samplebeing tested. The decision whether to choosegrooves or a hole is at the manufacturer’sdiscretion.A reference groove should be of an”N-type” (Fig. 4). The sides of the grooveshould be parallel to each other and the bottomshould be perpendicular to the sides.Fig. 4. “N-groove” [3, 9].w – width, d - depthFig. 3. Arrangement of reference grooves and datum hole [3, 9]1. longitudinal outer grooves2. submerged arc made weld3. pipe master or pipe section4. right-through hole5. longitudinal inner groovesA test sample should have the same nominaldiameter, wall thickness, surface roughness,heat treatment state and similar acousticproperties (e.g. wave propagation velocityand wave damping coefficient) as the pipebeing tested. The manufacturer should havethe possibility of removing the inner and outerweld run in accordance with the pipe curvature.The outer and inner grooves as wellas the datum hole should be sufficiently distantfrom the pipe ends and from each otherso that clearly separate indications of signalscoming from the grooves and the hole can beobtained.Longitudinal reference grooves should belocated in the parent metal near the edge of theweld and in parallel to the weld run (Fig. 3).A reference groove should be electrodischargemachined or made with another method.The dimensions of reference groovesshould be the following:a) width, w, (Fig. 4) of a reference grooveshould not exceed 1.5 mm;b) depth, d, (Fig. 4) should be as specified inTable 2, subject to the following restrictions:◦◦minimum groove depth: 0.3 mm forpipes of categories U2 and U3 and 0.5mm for pipes of category U4;◦◦maximum groove depth: 2.0 mm forpipes of categories U2 and U3 and 3mm for pipes of category U4;c) depth tolerance for a reference grooveshould amount to ± 15% depth or ± 0.05mm, whichever value is greater;d) length of reference grooves should beequal to at least double width of each singleconverter, but not more than 50 mm.A datum hole should be drilled through thewall of a test sample, in the weld centre, perpendicularlyto the sample surface (Fig. 3).42 BIULETYN INSTYTUTU SPAWALNICTWANo. 3/2013

The diameter of the drill used to make the datumhole should be selected in accordance withTable 3. The diameter of a datum hole shouldbe checked and cannot exceed the nominal diameterof a drill by more than 0.2 mm.Table 2. Designation of acceptance level and relateddepth of reference groove [3, 9]AcceptancelevelGroove depth in % of nominalwall thicknessU2 5.0U3 10.0U4 12.5U5 15.0testing sensitivity by 3 dB (to compensateequipment indications), it is necessary tocarry out equipment calibration again aswell as to check all the pipes tested since theprevious calibration verification.Table 3. Designation of acceptance level and relateddrill diameter [3, 9]AcceptancelevelDrill diameterU2H 1.6U3H 3.2U4H 4.0The equipment should be calibrated sothat it would ensure (e.g. in three subsequentpasses of the test sample through the equipment)obtaining clearly distinguishable signalsof the reference standard. The peak valueof the amplitude of these signals shouldbe used for adjusting the level of the gate/alarm monitor in the equipment. The rateof the test sample travel in relation to theset of ultrasonic converters during the verificationof calibration should be the sameas during the tests of a product. Calibrationcan be verified by means of a semi-dynamicmethod. During the testing of pipes with thesame nominal diameter, wall thickness, andmade of the same steel grade, it is necessaryto verify the calibration of the equipmentat regular intervals. The equipment calibrationis verified by putting the pipe masterthrough the testing equipment. The verificationof calibration should be carried out atleast once every four hours as well as eachtime the equipment operator changes. Calibrationshould also be verified at the beginningand end of production. In addition, theequipment should be calibrated if any of theparameters set during the initial calibrationhave been altered. If while verifying calibrationduring production, calibration requirementsare not satisfied even after increasingFollowing testing, a pipe revealing signalsbelow the monitor/gate sensitivity thresholdshould be classified as meeting the requirements.And a pipe having signals equal toor greater than the monitor/gate sensitivitythreshold should be classified as questionedor, at the manufacturer’s request, shouldundergo another test. If during the subsequenttest of the same pipe no signal equalto or greater than the monitor/gate sensitivitythreshold was obtained, the pipe shouldbe regarded as meeting the requirements.Depending on the requirements of a productstandard, pipes questioned during testingshould be dealt with in accordance with oneor several following manners:a) Subject to an agreement between the purchaserand the manufacturer, the areawhich has been questioned should be testedby means of another NDT technique ormethod (usually radiographic), on the basisof agreed acceptance criteria;b) The questioned area should be cut out. Themanufacturer should guarantee that thewhole questioned area has been removed;c) The pipe should be classified as not satisfyingthe requirements [3, 9].Testing of helically welded pipes is carriedout for acceptance level U2/U2H, taking intoaccount the following inspection criteria:No. 3/2013 BIULETYN INSTYTUTU SPAWALNICTWA43

a) the maximum groove depth should amountto 2.0 mm;b) Using inner and outer longitudinalgrooves in the middle of the weld run forthe purpose of equipment calibration isunallowed;c) In the case of acceptance level U2, for thepurpose of detecting transverse imperfections,as an alternative to the datum holeone may use the inner and outer groovespositioned at a right angle and centredin the weld. In such a situation both innerand outer weld reinforcements shouldbe ground evenly with the pipe contour,in the direct vicinity and on both sides ofreference grooves. The grooves should besufficiently distant from each other in alongitudinal direction. They should alsobe sufficiently distant from any other reinforcements.Such an approach is necessaryto obtain a clear and distinguishableultrasonic signal response. In order to determinethe level of the gate/alarm of themeasuring equipment it is necessary to usethe complete amplitude of a signal fromeach of these grooves.d) For acceptance level U2 and by prioragreement, as an alternative to using referencegrooves for calibration purposes, itis possible to use inner and outer groovesof a constant depth and increase testingsensitivity using electronic methods (byincreasing dB amplification). In this case,also referred to as the „two lamb method”,the depth of grooves should be twice asbig as the length of an ultrasonic wave.A required increase in testing sensitivityshould depend on a pipe wall thickness. Themanufacturer should adequately assure thepurchaser that obtained testing sensitivity isbasically equivalent to that obtained whileusing grooves for acceptance level U2. Inthe case of helically welded pipes the entirelength of the weld joining strip edges shouldalso undergo ultrasonic testing. Testing sensitivityand parameters should be the same asduring the initial testing of the pipe helicalweld. In addition, cruciform joints, in whichthe weld ends of strip edges meet the helicalweld should undergo radiographic testing [2].Following the tests, the manufacturershould provide the ordering party with a reportcontaining at least the following information:a) reference to standards PN-EN 10246-9 orPN-EN ISO 10893-11 andPN-EN 10208-2;b) date of test report;c) acceptance level;d) declaration of conformity;e) product specification, i.e. steel grade anddimensions;f) type and details of testing technique;g) description of a master/standard [3, 9].An example of a device for UT of helicallywelded pipes is presented in Figure 5.Fig. 5. Automatic multichannel device for ultrasonictesting of helically welded pipe weld and strip-joiningweld used in the Salzgitter Mannesmann GrossrohrGmbH company, Germany[5]Laminar imperfections in strip area adjacentto welded jointIn such a case it is possible to accept ultrasonictesting carried out at steel sheet manufacturer’sor carry out post-weld testing atthe pipe manufacturer’s, following the requirementsof standard PN-EN 10246-16 orPN-EN ISO 10893-8 and acceptance level44 BIULETYN INSTYTUTU SPAWALNICTWANo. 3/2013

U2. The tests are conducted within a 15mmwidezone along both longitudinal edges of ahelical weld. In the case of transverse weldsjoining the edge of a strip testing is conductedalong areas adjacent to this butt weld. Requirementsconcerned with ultrasonic testingof laminar imperfections in the area adjacentto the weld are dealt with in standard PN-EN 10246-15 (PN-EN ISO 10893-9) or PN-EN 10246-16 (PN-EN ISO 10893-8). Singlelaminar imperfections or imperfections ingroups exceeding acceptance level U2 arenot allowed [2].Non-destructive testing of helically weldedjoints on pipe ends and in areas beingrepairedSections of welded joints on pipe endswhich cannot be tested by means of automaticultrasonic equipment and repaired areas ofwelds should undergo the following tests:a) in order to detect longitudinal imperfections– manual or semiautomatic ultrasonictesting using the same testing parametersand sensitivity as in the case of the automatictesting of the whole helical weld.Radiographic testing is also possible.b) in order to detect transverse imperfections– manual or semiautomatic ultrasonic testingusing the same testing parameters andsensitivity as in the case of the automatictesting of the whole helical weld. Radiographictesting is also possible.c) It is also necessary to carry out testingfor the laminar imperfections of the pipebody areas on pipe ends which cannot bechecked by means of automatic ultrasonicequipment. In such a case it is also possibleto carry out manual ultrasonic testingusing the same testing parameters andsensitivity as those used while testing areasadjacent to the weld. Laminar imperfectionswith a length ≥ 6 mm occurringin girth direction are unallowed if they arepresent 25 mm away from each pipe end;d) While carrying out manual ultrasonictesting a scanning rate should not exceed150 mm/s [2].Radiographic and radioscopic testing(RT)Another testing method used in the manufactureof helically welded pipes is radiographictesting, usually carried out on pipesafter the completion of all principal productionoperations. In order to ensure an appropriatetesting class, pipes intended for testsshould be sufficiently straight and free fromforeign matter impurities. The surfaces ofwelds and adjacent parent metal should befree from foreign matter and surface imperfectionsas they could impede the interpretationof radiograms. Grinding surfaces isallowed if it can ensure obtaining a surfacecondition acceptable for tests. If a weld reinforcementmust be removed, it is advisableto place markers (usually lead arrows) inorder to identify the weld location in a radiogram.In order to ensure the unambiguousidentification of a given weld section, eachsection should be provided with identificationsymbols (usually lead letters) so thattheir images can be visible in a radiogram.It is necessary to apply permanent markingon the pipe surface from the side of the radiationsource. This is done in order to providereference points for the accurate assignmentof each radiogram location. If it is impossibleto strike markers due to the type of aproduct and/or its intended operating conditions,it is necessary to provide other appropriatemeans of radiogram assignment, e.g.by marking with paint or preparing accuratesketches. In order to ensure that each part ofthe weld undergoes testing, during X-rayinga longer weld section with several films itis necessary that neighbouring films shouldoverlap over a minimum length of 10 mm.Longitudinal or helical welds of pipesshould undergo radiographic testing withNo. 3/2013 BIULETYN INSTYTUTU SPAWALNICTWA45

x-rays. The use of radioscopic methods is allowed(Fig. 6), yet only in cases when themanufacturer can demonstrate their appropriatesensitivity.Fig. 6. Example of device for radioscopic testingof welded jointsThere are two image quality classes, i.e.R1 and R2:• class R1 (class B): radiographic testingtechnique by means of X-radiation ofheightened sensitivity;• class R2 (class A): radiographic testingtechnique by means of X-radiation of normalsensitivity.For image quality class R1 it is necessaryto use at least fine-grained films (at least C4class), whereas for image quality class R2one should use at least medium-grained films(at least C5 class). For both image qualityclasses (R1 and R2), the thickness of frontintensifying screens should be between 0.02mm and 0.25 mm. Rear intensifying screenscan have other thicknesses. Fluorescent intensifyingscreens should not be used.The amount of backscattered and internalX-radiation should be limited to a minimum.When in doubt as to the efficiency of protectionagainst backscattered radiation, it is advisableto fix a characteristic sign (usually a1.5mm-thick letter B) behind the film holderor film frame and make a radiogram in a normalmanner. The density of the symbol imagein the radiogram lower than the backgrounddensity indicates that the protection againstbackscattered radiation is insufficient and thatadditional precautions should be used. A radiationbeam should be directed onto the centreof a weld section being tested and should beperpendicular to the pipe surface at this point.A length subjected to an assessment should beso that the thickness X-rayed at the ends of theusable length of a radiogram does not exceedthe thickness X-rayed in the radiogram centreby more than 10% for image quality classR1 and by more than 20% for image qualityclass R2. It is necessary to use a technique ofX-raying through one wall. If, due to the sizeof the object, such a technique cannot be used,it is allowed to use a technique of X-rayingthrough two walls (by prior agreement). Thedistance between the film and the weld surfaceshould be as small as possible.The minimum distance between the sourceand the sample ,f, should be selected usingappropriate formulas or diagrams. The conditionsof exposition should be so that thedensity of a radiogram in the tested area ofweld material free from imperfections is notlower than 2.0 for image quality class R1 (2.3for image quality class B) and not lower than1.7 for image quality class R2 (2.0 for imagequality class B).The quality of an image should be determinedusing an image quality indicator (IQI)made of mild steel, grade specified in standardsPN-EN 462-1 (PN-ISO 19232-1) and PN-EN 462-2 (PN-ISO 19232-2). An IQI shouldbe placed on the surface from the radiationsource side or next to the weld or, in the caseof a wire-type IQI – across the weld. Imagequality indicators should be placed from thefilm side only if the surface from the sourceside is inaccessible. In such cases it is necessaryto place a letter “F” next to an IQI andmake a note of this change of the procedure inthe test report [4, 10].46 BIULETYN INSTYTUTU SPAWALNICTWANo. 3/2013

sified as questioned. Questioned pipes shouldbe dealt with in one of the following manners:a) A questioned area should be levelled bymeans of an appropriate method. In orderto ensure that the imperfection has beenremoved entirely, after checking that theremaining thickness is still within a tolerancerange, the area should undergo anothercheck using magnetic particle testing orpenetration testing. Afterwards, the pipeshould be classified as passing the test. Ifthe recommended removal of the faultyarea has decreased the thickness belowthe acceptable value, the questioned areashould be repaired by welding carried outin accordance with an approved weldingprocedure specification. After that, the repairedarea should undergo radiographictesting following the requirements of PN-EN 10246-10 or PN-EN ISO 10893-6;b) A questioned area should be cut out. Themanufacturer should ensure that the wholequestioned section has been cut out;c) A pipe should be classified as failing tomeet the requirements.In required cases the manufacturer shouldwrite a test report containing at least the followinginformation:a) reference to PN-EN 10246-10 or PN-ENISO 10893-6 and PN-EN 10208-2;b) test report date;c) declaration of conformity;d) designation of a product providing gradeand dimensions;e) type of and detailed information about thetesting technique used;f) each deviation from specified procedures,agreed or not agreed;g) image quality class;h) operator’s name, signature and certificatenumber [4, 10].ConclusionIn recent years the manufacture of helicallywelded pipes has seen an intensive developmentowing to new gas pipelines underconstruction both in Poland and abroad. Theproduction of these pipes requires the use ofmaterials characterised by the highest mechanicalproperties in a given material group.NDT devices are usually provided with modernand recently developed technical solutions.Investment-related expectations forthe years to come make the manufacture ofwelded pipes the area of interest for investorsand manufacturers all over the world.References1. Michałowski, W., and Trzop, S., et al.(2006). Rurociągi dalekiego zasięgu. Warsaw:Wydawnictwo Fundacja Odysseum.2. PN-EN 10208-2:2011 Steel pipes forpipelines for combustible fluids - Technicaldelivery conditions - Part 2: Pipes ofrequirement class B3. PN-EN 10246-9:2004 Non-destructivetesting of steel tubes - Part 9: Automaticultrasonic testing of the weld seam ofsubmerged arc welded steel tubes for thedetection of longitudinal and/or transverseimperfections4. PN-EN 10246-10:2004 Non-destructivetesting of steel tubes - Part 10: Radiographictesting of the weld seam of automaticfusion arc welded steel tubes forthe detection of imperfections5. Presentation of Salzgitter MannesmannGrossrohr GmBH - Salzgitter 2012.6. PN-EN 10246-15:2002 Non-destructivetesting of steel tubes - Part 15: Automaticultrasonic testing of strip/plate used inthe manufacture of welded steel tubes forthe detection of laminar imperfections7. PN-EN 10246-16:2002 Non-destructivetesting of steel tubes - Part 16: Automaticultrasonic testing of the area adjacent tothe weld seam of welded steel tubes forthe detection of laminar imperfections8. PN-EN 10246-17:2002 Non-destructivetesting of steel tubes - Part 17: Ultrason-48 BIULETYN INSTYTUTU SPAWALNICTWANo. 3/2013

ic testing of tube ends of seamless andwelded steel tubes for the detection oflaminar imperfections9. PN-EN ISO 10893-6:2011 Non-destructivetesting of steel tubes - Part 6: Radiographictesting of the weld seam ofwelded steel tubes for the detection ofimperfections10. PN-EN ISO 10893-8:2011 Non-destructivetesting of steel tubes - Part 8: Automatedultrasonic testing of seamless andwelded steel tubes for the detection oflaminar imperfections11. PN-EN ISO 10893-9:2011 Non-destructivetesting of steel tubes - Part 9: Automatedultrasonic testing for the detectionof laminar imperfections in strip/plateused for the manufacture of welded steeltubes12. PN-EN ISO 10893-11:2011 Non-destructivetesting of steel tubes - Part 11: Automatedultrasonic testing of the weld seamof welded steel tubes for the detection oflongitudinal and/or transverse imperfectionsNo. 3/2013 BIULETYN INSTYTUTU SPAWALNICTWA49