Welding Duplex steelsWelding Duplex steels

Project SNDC PHASE 1 OMANProject SNDC PHASE 1 OMAN

Mr. Anders ThörnqvistMr. Anders ThörnqvistM. Sc Met Engr, IWE, IWI-EM. Sc Met Engr, IWE, IWI-E

Introduction 1

What is Duplex Stainless What is Duplex Stainless Steel?Steel?

Low-carbon stainless steels Low-carbon stainless steels containing approx. equal parts of containing approx. equal parts of

ferrite and austeniteferrite and austenite

from a balance of ferrite formers from a balance of ferrite formers (Cr,Mo) with austenite formers (Cr,Mo) with austenite formers

(Ni,N) and heat treatment(Ni,N) and heat treatment

Introduction 2

What is Duplex Stainless What is Duplex Stainless steelssteels

• Duplex (DSS) steels are as previous Duplex (DSS) steels are as previous mentioned a combination of “ Carbon” mentioned a combination of “ Carbon” steels and “Stainless” steel.steels and “Stainless” steel.

• DSS microstructure is approximately DSS microstructure is approximately equal parts of Ferrite and Austenite.equal parts of Ferrite and Austenite.

• Duplex alloys exhibit some characteristics Duplex alloys exhibit some characteristics from both Ferritic and Austenitic steels. from both Ferritic and Austenitic steels.

• ffIntroduction 3

What is Duplex stainless What is Duplex stainless steels?steels?

• As a result of this combination of structures As a result of this combination of structures (steels) the welding procedure of Duplex (steels) the welding procedure of Duplex steels require different parameters than steels require different parameters than Ferritic and Austenitic steels.Ferritic and Austenitic steels.

• Attractive features off DSS steels are (as Attractive features off DSS steels are (as mentioned before, double Yield mentioned before, double Yield strength ,while maintaining ductility and strength ,while maintaining ductility and toughness in comparison of Austenitic steelstoughness in comparison of Austenitic steels

Introduction 4

Introduction 5

Duplex Stainless SteelDuplex Stainless SteelBase Metal Upper Right, Weld Metal Bottom Left

Source:The ESAB Group Introduction 6

Duplex SS – alloy 2205Duplex SS – alloy 2205

• Typically: 22 Cr, 5 Ni, 3 Mo, O.15 NTypically: 22 Cr, 5 Ni, 3 Mo, O.15 N

• Structure is austenite islands in ferritic Structure is austenite islands in ferritic matrix ~ 50/50 is idealmatrix ~ 50/50 is ideal

• Benefits in DSS from:Benefits in DSS from:

BCC 50%= Ferrite ,Body centered cubic BCC 50%= Ferrite ,Body centered cubic

FCC 50% = Austenite, Face centered FCC 50% = Austenite, Face centered cubiccubic

Introduction 7

Duplex SS – (cont.)Duplex SS – (cont.)

• Stress corrosion cracking resistance Stress corrosion cracking resistance substantially better than 304/316substantially better than 304/316

• Pitting & crevice cor. Resistance equal Pitting & crevice cor. Resistance equal or better than 316 in many mediaor better than 316 in many media

• Good resistance to erosion & abrasionGood resistance to erosion & abrasion

Introduction 8

DSS Welding - General DSS Welding - General RequirementsRequirements

• No preheat – 300F/ 150 C degrees inter-pass No preheat – 300F/ 150 C degrees inter-pass temperature typicaltemperature typical

• Heat input 15 to 65 kJ/in- 0.5 Kj-2.5 Kj mm.Heat input 15 to 65 kJ/in- 0.5 Kj-2.5 Kj mm.• To avoid high ferrite in welds, filler metals To avoid high ferrite in welds, filler metals

with higher nickel used ~ 2209 with 9% with higher nickel used ~ 2209 with 9% nickel( to high content of ferrite, reduces nickel( to high content of ferrite, reduces toughness and ductility)toughness and ductility)

• Avoidance of arc strikes, oxidation, grinding Avoidance of arc strikes, oxidation, grinding out of cratersout of craters

Introduction 9

Welding Processes UsedWelding Processes Used

• GTAW or TIGGTAW or TIG- manual- manual- orbital tube welding or automatic sheet- orbital tube welding or automatic sheet

• SAW-Submerged..SAW-Submerged..

• GMAW – MIGGMAW – MIG

• SMAW or covered electrodeSMAW or covered electrode

Introduction 10

Duplex SS - WeldingDuplex SS - Welding

• Q = Heat input is calculated by following Q = Heat input is calculated by following formula: U * I / V (mm/sec)formula: U * I / V (mm/sec)

U = VoltageU = Voltage

I = AmperageI = Amperage

V= Speed, travel speed of welding, V= Speed, travel speed of welding, mm /secmm /sec

Introduction 11

Duplex WeldingDuplex Welding

• Good results in DSS digester construction do not come by chance, but by adhering to a Good results in DSS digester construction do not come by chance, but by adhering to a good quality assurance program. good quality assurance program.

• Poor practices that are forgiven with carbon steel or austenitic stainless steel fabrication Poor practices that are forgiven with carbon steel or austenitic stainless steel fabrication can result in costly degradation of the superior physical and mechanical properties of DSS. can result in costly degradation of the superior physical and mechanical properties of DSS.

• While ASME Code requirements cover a certain level of quality, additional measures are While ASME Code requirements cover a certain level of quality, additional measures are warranted for DSS construction. warranted for DSS construction.

• Examples are the qualification of mill product materials and welding procedures to ASTM , Examples are the qualification of mill product materials and welding procedures to ASTM , and the follow-up testing of shop- and field-production weld coupons. and the follow-up testing of shop- and field-production weld coupons.

• Routine monitoring of welding heat input and interpass temperatures should also be Routine monitoring of welding heat input and interpass temperatures should also be performed. performed.

• Ferrite balance of welds can be made using a portable meter such as a Feritscope Ferrite balance of welds can be made using a portable meter such as a Feritscope Production joint fitup and intermediate steps in the welding process should be verified and Production joint fitup and intermediate steps in the welding process should be verified and documented by quality control.documented by quality control.

• The mill product material quality should be similarly monitored. Mills should give attention to The mill product material quality should be similarly monitored. Mills should give attention to material surface finish and post-fabrication cleaning. Additional information on material surface finish and post-fabrication cleaning. Additional information on specifications and testing of DSS is often required.specifications and testing of DSS is often required.

Introduction 12

Calculation Q-exampleCalculation Q-example

• Let’s say (simplified) that we are Let’s say (simplified) that we are measuring “critical data” from a welding measuring “critical data” from a welding sequence. Data such as Voltage, sequence. Data such as Voltage, Amperage, traveling speed.Amperage, traveling speed.

• Voltage , was measured to 10V, Voltage , was measured to 10V, amperage 82, travel speed 0.7 mm / amperage 82, travel speed 0.7 mm / sec.sec.

• Q= 10*82 / 0.7 = 1.17 kj/mmQ= 10*82 / 0.7 = 1.17 kj/mmIntroduction 13

GTAW Process - DSSGTAW Process - DSS

• Used for root passes and orbital weldsUsed for root passes and orbital welds

• Filler essential for ferrite-austenite Filler essential for ferrite-austenite balancebalance

• Ar + 20-40% He + up to 2.5% NAr + 20-40% He + up to 2.5% N22 to to

counter N loss from weld - no hydrogencounter N loss from weld - no hydrogen

• Backing gas to maintain weld N contentBacking gas to maintain weld N content

Introduction 14

Manual vs Automatic Orbital Manual vs Automatic Orbital Tube WeldingTube Welding

• Short projects may favor manual Short projects may favor manual weldingwelding

• Manual welders better able to Manual welders better able to accommodate poorer fit-up conditionsaccommodate poorer fit-up conditions

• Orbital welds have more consistent root Orbital welds have more consistent root weld beads and practically free from weld beads and practically free from heat tintheat tint

Introduction 15

Heat Tint? What is it?Heat Tint? What is it?

Introduction 16

The Sample Numbers refer to the amount of oxygen in the purging gas: The Sample Numbers refer to the amount of oxygen in the purging gas:

No.1- 10ppmNo.1- 10ppm No.2 - 25ppmNo.2 - 25ppm No.3 - 50ppm No.3 - 50ppm No.4 - 100ppm No.4 - 100ppmNo.5 - 200ppm No.6 - 500ppm No. 7 - 1000ppm No.8 - 5000ppm No.5 - 200ppm No.6 - 500ppm No. 7 - 1000ppm No.8 - 5000ppm No.9 -12500ppm No.10 -. 25000ppmNo.9 -12500ppm No.10 -. 25000ppm

Note: welds on type 304L SS showed no significant difference in heat Note: welds on type 304L SS showed no significant difference in heat tint colour from tint colour from type 316L.type 316L.

AWS D18.2 (1999):AWS D18.2 (1999): Heat Tint Levels on the Inside of Heat Tint Levels on the Inside of Welded 316L Austenitic Stainless Steel Tube Welded 316L Austenitic Stainless Steel Tube

Introduction 17

Heat Tint - Acceptance LimitsHeat Tint - Acceptance Limits

• Acceptable limits could vary with end Acceptable limits could vary with end application service, D18.1 or D18.2 application service, D18.1 or D18.2

• Typically # 5, 200 ppm and greater is Typically # 5, 200 ppm and greater is unacceptableunacceptable

• An acceptance level should be identified An acceptance level should be identified by number rather than ppm of oxygen or by number rather than ppm of oxygen or by workmanship standards for particular by workmanship standards for particular contractcontract

Introduction 18

Factors Influencing Heat TintFactors Influencing Heat Tint

• Oxygen in backing gas increases HTOxygen in backing gas increases HT

• Moisture in backing gas increases HTMoisture in backing gas increases HT

• Contaminants such as hydrocarbons Contaminants such as hydrocarbons increase discolorationincrease discoloration

• Hydrogen in backing gas decreases HT Hydrogen in backing gas decreases HT

• Metal surface finish can affect Metal surface finish can affect appearanceappearance

Introduction 19

Formation of Sigma phase & Formation of Sigma phase & Alpha phaseAlpha phase

Introduction 20

Sigma phase & Alpha phaseSigma phase & Alpha phase

• What is this??What is this??

• Sigma phase, an inter-metallic phase Sigma phase, an inter-metallic phase that occurs in DSS steels and reduces that occurs in DSS steels and reduces both Corrosion protection and lower the both Corrosion protection and lower the toughness of the steel. toughness of the steel.

• Sigma phase forms in the temperature Sigma phase forms in the temperature range of 700 C – 980 C.range of 700 C – 980 C.

Introduction 21

How to avoid Sigma Phase?How to avoid Sigma Phase?• Simplified we can say that the control of Simplified we can say that the control of

heat input (Q), will help us to reduce the heat input (Q), will help us to reduce the formation of this Phase.formation of this Phase.

• Heat input (Q) is in this case controlled Heat input (Q) is in this case controlled by the way we weld this material.by the way we weld this material.

• It is most important to follow all It is most important to follow all instructions regarding heat input and instructions regarding heat input and inter-pass temperature.inter-pass temperature.

• We will discuss this issue further, later on in the Education, control of Heat input-WPSWe will discuss this issue further, later on in the Education, control of Heat input-WPS

Introduction22

Alpha PrimeAlpha Prime• Alpha prime is an embrittling phase that also Alpha prime is an embrittling phase that also

occurs in the Ferritic, BBC phase of Duplex occurs in the Ferritic, BBC phase of Duplex steels.steels.

• Embrittiling occurs in the temperature range Embrittiling occurs in the temperature range 475 C, and the time to form this phase 475 C, and the time to form this phase various from minutes to hours.various from minutes to hours.

• In order to avoid this phase, same as the In order to avoid this phase, same as the Sigma phase we need to control Q, heat Sigma phase we need to control Q, heat inputinput..

Introduction 23

Welding QualificationsWelding Qualifications

• PQR-Procedure Qualification recordPQR-Procedure Qualification record• Welding Procedure Specification (WPS) Welding Procedure Specification (WPS)

- for each type of weld- for each type of weld• Performance Qualification - to test Performance Qualification - to test

welder’s abilitywelder’s ability• Preconstruction Weld Samples (PWS) - Preconstruction Weld Samples (PWS) -

3 welds made by each welder to aid in 3 welds made by each welder to aid in evaluating production weldsevaluating production welds

Introduction 24

DSS Welding & PreparationDSS Welding & Preparation

General:General:

Welders that have experience of Welders that have experience of welding Austenitic stainless steels welding Austenitic stainless steels should be able to apply their skills and should be able to apply their skills and technique acquired with these alloys to technique acquired with these alloys to DSS steels welding.DSS steels welding.

Introduction 25

DSS Welding & PreparationDSS Welding & Preparation

General:General:

The welding characteristics, puddle The welding characteristics, puddle manipulation, and viscosity of the two manipulation, and viscosity of the two families of alloys (Ferrite and Austenite) families of alloys (Ferrite and Austenite) are similar; however the puddle, control are similar; however the puddle, control of melt in DSS is more viscose's than of melt in DSS is more viscose's than Austenitic steels and therefore more Austenitic steels and therefore more difficult to weld by hand.difficult to weld by hand.

Introduction 26

Cleaning before WeldingCleaning before Welding

• The weld area to be cleaned before welding includes The weld area to be cleaned before welding includes the joint edges and about 40 mm beside the actual the joint edges and about 40 mm beside the actual weld area, closest to weld area. i.e. on each side, weld area, closest to weld area. i.e. on each side, inside- outside pipe.inside- outside pipe.

Introduction 27

Cleaning before WeldingCleaning before Welding

• Improper cleaning can cause weld defects such as Improper cleaning can cause weld defects such as cracks, porosity and lack of fusion.cracks, porosity and lack of fusion.

• The joint should be free of surface oxides such as The joint should be free of surface oxides such as might be left after thermal cutting.might be left after thermal cutting.

• Grinding, brushing or other mechanical means should Grinding, brushing or other mechanical means should be used in order to remove all paint, scales, oxid and be used in order to remove all paint, scales, oxid and dirt.dirt.

• Oil and grease compounds can be removed by Oil and grease compounds can be removed by suitable solvent cleaning, followed by a thorough suitable solvent cleaning, followed by a thorough rinse.rinse.

Introduction 28

Cleaning before WeldingCleaning before Welding

• There is a number of elements and There is a number of elements and compounds that can cause cracking, compounds that can cause cracking, reduce corrosion protection if not reduce corrosion protection if not removed!removed!

Introduction 29

Cleaning before welding & Cleaning before welding & toolstools

• Hand tools, such as wire brushed, used in fabrication Hand tools, such as wire brushed, used in fabrication of duplex steels should by all means be made from of duplex steels should by all means be made from stainless steel, stainless steel, and should be used exclusively on and should be used exclusively on duplex steels materialduplex steels material. .

• Grinding wheels etc, same procedure apply in this Grinding wheels etc, same procedure apply in this section, only grinding wheels suitable for grinding SS section, only grinding wheels suitable for grinding SS should be used to grind DSS.should be used to grind DSS.

• A good way to avoided confusion , mix up with A good way to avoided confusion , mix up with material etc, is to use a coloring system.material etc, is to use a coloring system.

Introduction 30

Cleaning before welding & Cleaning before welding & toolstools

• A very practical way to avoid mix up between A very practical way to avoid mix up between material is just to use this coloration system.material is just to use this coloration system.

• For example we can by a proper procedure designate For example we can by a proper procedure designate the the color green to be marked on all material used in color green to be marked on all material used in combination with DSS handling and welding. combination with DSS handling and welding. Everything from consumables to brushes.Everything from consumables to brushes.

• The actual marking is mostly done by the use of The actual marking is mostly done by the use of spray paint and applied “directly” to the object in spray paint and applied “directly” to the object in

questionquestion..

Introduction 31

DSS-Joints-Fit up DSS-Joints-Fit up

• In respect to welding duplex steels, a weld joint In respect to welding duplex steels, a weld joint design must facilitate full penetration.design must facilitate full penetration.

• The best way to prepare a bevel, weld edge The best way to prepare a bevel, weld edge preparation is to use machining rather then grindingpreparation is to use machining rather then grinding

• When grinding must be used, special attention should When grinding must be used, special attention should be given to the uniformity of the weld preparation and be given to the uniformity of the weld preparation and the fit-up in order to provide uniformity of the land the fit-up in order to provide uniformity of the land thickness or gap.thickness or gap.

• Any grinding burr should be removed to maintain Any grinding burr should be removed to maintain complete fusion and penetrationcomplete fusion and penetration

Introduction 32

DSS-Joints-Fit up DSS-Joints-Fit up

Introduction 33

What is an WPS?What is an WPS?

• A WPS is a document that describes how welding is to be carried out in A WPS is a document that describes how welding is to be carried out in production.  They are recommended for all welding operations and many production.  They are recommended for all welding operations and many application codes and standards make them mandatory application codes and standards make them mandatory

• What information should they include? What information should they include? •   Sufficient details to enable any competent person to apply the information and Sufficient details to enable any competent person to apply the information and

produce a weld of acceptable quality.  The amount of detail and level of controls produce a weld of acceptable quality.  The amount of detail and level of controls specified on a WPS is dependant on the application and criticality of the joint to specified on a WPS is dependant on the application and criticality of the joint to be welded. be welded.

•   For most applications the information required is generally similar to that For most applications the information required is generally similar to that recorded on a Procedure Qualification Record (PQR) or Welding Procedure recorded on a Procedure Qualification Record (PQR) or Welding Procedure Approval Record (WPAR), except that ranges are usually permitted on Approval Record (WPAR), except that ranges are usually permitted on thicknesses, diameters, welding current, materials, joint types etc. thicknesses, diameters, welding current, materials, joint types etc.

•   If a WPS is used in conjunction with approved welding procedures then the If a WPS is used in conjunction with approved welding procedures then the ranges stated should be in accordance with the approval ranges permitted by ranges stated should be in accordance with the approval ranges permitted by the welding procedure. the welding procedure.

Introduction 34

What is a WPS?What is a WPS?

•   However careful consideration should be given to the ranges specified to However careful consideration should be given to the ranges specified to ensure they are achievable, as the ranges given by welding procedure ensure they are achievable, as the ranges given by welding procedure standards do not always represent good welding practice.  For example welding standards do not always represent good welding practice.  For example welding positions permitted by the welding procedure standard may not be achievable or positions permitted by the welding procedure standard may not be achievable or practical for certain welding processes or consumables. practical for certain welding processes or consumables.

•   EN ISO 15609-1 (formally EN 288 Part 2)  European Standard For Welding EN ISO 15609-1 (formally EN 288 Part 2)  European Standard For Welding Procedure SpecificationsProcedure Specifications EN ISO 15609 Defines the contents of a Welding Procedure Specification in the EN ISO 15609 Defines the contents of a Welding Procedure Specification in the form of a list of information that should be recorded.  For some applications it form of a list of information that should be recorded.  For some applications it may be necessary to supplement or reduce the list. For example only in the may be necessary to supplement or reduce the list. For example only in the case of a procedure requiring heat input control would there be a necessity to case of a procedure requiring heat input control would there be a necessity to quote travel speed or run-out length for manual processes. quote travel speed or run-out length for manual processes.

•   ASME IX  American Boiler and Pressure Vessel CodeASME IX  American Boiler and Pressure Vessel Code QW 250 Lists the variables for each welding process, all the variables stated QW 250 Lists the variables for each welding process, all the variables stated should be addressed.  The range permitted by the WPS is dictated by the PQR should be addressed.  The range permitted by the WPS is dictated by the PQR or PQR’s used to qualify it.  or PQR’s used to qualify it. 

Introduction 35

What is a WPS?What is a WPS?• Typical Items That Should Be Recorded On W.P.S:- Typical Items That Should Be Recorded On W.P.S:-

    Common to all ProcessesCommon to all Processes        .         . • Procedure number Procedure number • Process type Process type • Consumable Size, Type and full Codification. Consumable Size, Type and full Codification. • Consumable Baking Requirement if applicable Consumable Baking Requirement if applicable • Parent material grade and spec. Parent material grade and spec. • Thickness range. Thickness range. • Plate or Pipe, Diameter range Plate or Pipe, Diameter range • Welding Position Welding Position • Joint Fit Up, Preparation, Cleaning, Dimensions etc. Joint Fit Up, Preparation, Cleaning, Dimensions etc. • Backing Strip, Back Gouging information.  Backing Strip, Back Gouging information.  • Pre-Heat (Min Temp and Method) Pre-Heat (Min Temp and Method) • Interpass If Required (Maximum Temperature recorded ) Interpass If Required (Maximum Temperature recorded ) • Post Weld Heat Treatment. If Required (Time and Temp) Post Weld Heat Treatment. If Required (Time and Temp) • Welding Technique (weaving,max run width etc.) Welding Technique (weaving,max run width etc.) • Arc Energy Limits should be stated if impact tests are required or if the material being welded is Arc Energy Limits should be stated if impact tests are required or if the material being welded is

sensitive to heat inputsensitive to heat input

Introduction 36

What is a PQR?What is a PQR?

• PQR's are not required if Standard Welding Procedures are used, see below for details. This PQR's are not required if Standard Welding Procedures are used, see below for details. This document contains details of the welding test, it must include details of all the parameters listed document contains details of the welding test, it must include details of all the parameters listed as variables in tables QW250 to QW265 for each process involved and all the destructive test as variables in tables QW250 to QW265 for each process involved and all the destructive test results. results.

• The relevant variables for each type of welding process are clearly defined in tables QW250 to The relevant variables for each type of welding process are clearly defined in tables QW250 to QW265. The left hand column of each table defines the section and paragraph where each QW265. The left hand column of each table defines the section and paragraph where each variable and its application to the table is explained in the code.  variable and its application to the table is explained in the code. 

• Welding VariablesWelding Variables

• Variables used in a welding procedure test are divided into 3 categories :- Variables used in a welding procedure test are divided into 3 categories :-

• Essential VariablesEssential Variables Are variables that have a significant affect on the mechanical properties of Are variables that have a significant affect on the mechanical properties of a joint. They must not be changed except within the limits specified by this code. e.g. Material a joint. They must not be changed except within the limits specified by this code. e.g. Material thickness range, Material Group etc. thickness range, Material Group etc.

• Non-Essential VariablesNon-Essential Variables Are variables that have no significant affect on mechanical properties. Are variables that have no significant affect on mechanical properties. They can be changed without re qualification of the PQR. They can be changed without re qualification of the PQR.

• Supplementary VariablesSupplementary Variables Are variables that have an affect on the impact properties of a joint. Are variables that have an affect on the impact properties of a joint. They are classed as Non-Essential if impact testing is not required They are classed as Non-Essential if impact testing is not required

• All variables listed as essential, non-essential or supplementary should be addressed on both All variables listed as essential, non-essential or supplementary should be addressed on both the WPS and the PQR. If any of the variables do not apply to the particular application then they the WPS and the PQR. If any of the variables do not apply to the particular application then they should be specified as not applicable.should be specified as not applicable.

Introduction 37

What is a PQR?What is a PQR?• Joint ConfigurationJoint Configuration

Either plate or pipe can be used for the test piece (plate approves pipe and vice versa ref. QW211), any welding Either plate or pipe can be used for the test piece (plate approves pipe and vice versa ref. QW211), any welding position approves all positions providing no impact tests are required ref. tables QW250 to QW265 and any joint position approves all positions providing no impact tests are required ref. tables QW250 to QW265 and any joint geometry approves all geometry's, e.g. single V, double V, U prep, backed or unbacked. geometry approves all geometry's, e.g. single V, double V, U prep, backed or unbacked.

• A butt or groove weld approves branch and fillet welds but not the converse, ref. QW202. Non pressure retaining fillet A butt or groove weld approves branch and fillet welds but not the converse, ref. QW202. Non pressure retaining fillet welds in pipe or plate can be tested but they must be double sided if plate and at least the dimensions illustrated in welds in pipe or plate can be tested but they must be double sided if plate and at least the dimensions illustrated in QW462.4a, ref. QW202.2c. Pressure retaining branch welds must be qualified by groove (butt) welds. QW462.4a, ref. QW202.2c. Pressure retaining branch welds must be qualified by groove (butt) welds.

• Material GroupingMaterial Grouping Materials are assigned P numbers in QW420; a test in one P number approves all materials listed under that P Materials are assigned P numbers in QW420; a test in one P number approves all materials listed under that P number, except where impact tests are required then approval is restricted to materials listed in the group number number, except where impact tests are required then approval is restricted to materials listed in the group number within the P number. Other P number groupings are permissible ref. QW424.1 for details. Ref QW 424.1 for further within the P number. Other P number groupings are permissible ref. QW424.1 for details. Ref QW 424.1 for further details. details.

• It is normally permissible if the material is not listed in QW422 to assign it to a P number which lists materials with the It is normally permissible if the material is not listed in QW422 to assign it to a P number which lists materials with the same metallurgical and mechanical properties although this is not in strict conformance with the code. Typically same metallurgical and mechanical properties although this is not in strict conformance with the code. Typically BS1501 151 430A low carbon steel could be regarded as P1 and stainless steels such as 316, 304 as P8. BS1501 151 430A low carbon steel could be regarded as P1 and stainless steels such as 316, 304 as P8.

• Note P5, 9 & 10 are divided into sub groups eg 5A,5B etc., Treat each sub group like a separate P Number Note P5, 9 & 10 are divided into sub groups eg 5A,5B etc., Treat each sub group like a separate P Number

• Dissimilar materials are acceptable providing they are compatible. For example P1 to P8, but this does not cover P1 Dissimilar materials are acceptable providing they are compatible. For example P1 to P8, but this does not cover P1 to P1 or P8 to P8. to P1 or P8 to P8.

• Note S numbers are for pipework to B31, a P number covers an S number but not the converse Note S numbers are for pipework to B31, a P number covers an S number but not the converse

Introduction 38

What is a PQR?What is a PQR?

• ConsumablesConsumables The ASME code uses its own specifications for consumables The ASME code uses its own specifications for consumables SFA. SFA. which is almost identical to the AWS which is almost identical to the AWS specification. specification.

• NOTE A change in consumable is only permissible providing it has the same F number and A NOTE A change in consumable is only permissible providing it has the same F number and A number (if applicable) as the P.Q.R.. number (if applicable) as the P.Q.R..     

• Thickness LimitsThickness Limits Thickness limits Groove welds. See QW451 for precise details.  Thickness limits Groove welds. See QW451 for precise details. 

• When Impact tests are required the minimum thickness approved is restricted.  See QW403.6 When Impact tests are required the minimum thickness approved is restricted.  See QW403.6 • More than one PQR may be required to qualify dissimilar thickness More than one PQR may be required to qualify dissimilar thickness • The thickness little The thickness little 't''t' of deposited weld metal for each process involved is approved from 0 to 2xt except:- of deposited weld metal for each process involved is approved from 0 to 2xt except:-

MIG/MAG (GMAW/FCAW) dip transfer weld of deposited thickness less than ½" approves maximum MIG/MAG (GMAW/FCAW) dip transfer weld of deposited thickness less than ½" approves maximum thickness of 1.1 x t only Ref: QW255 (QW403.10) thickness of 1.1 x t only Ref: QW255 (QW403.10)

• If any Pass in a single or multipass weld > ½" then the thickness approval equals  1.1xT If any Pass in a single or multipass weld > ½" then the thickness approval equals  1.1xT •

Dissimilar Thickness QW202.4:- The thicker and thinner part must be qualified, Except P8 and P4X the Dissimilar Thickness QW202.4:- The thicker and thinner part must be qualified, Except P8 and P4X the thinner part can be qualified if no Impacts and test coupon > 6mm thick. thinner part can be qualified if no Impacts and test coupon > 6mm thick.

• Thickness limits for fillet welds as per QW462.4a or QW462.4d qualify all fillet weld sizes on all base Thickness limits for fillet welds as per QW462.4a or QW462.4d qualify all fillet weld sizes on all base material thicknesses and all diameters in one testmaterial thicknesses and all diameters in one test

Introduction 39

What is a PQR?What is a PQR?

• Testing Requirements (Ref QW 463 for location of specimens)Testing Requirements (Ref QW 463 for location of specimens) • Unlike EN288 there is no requirement for any non-destructive testing such as radiography or MPI/DPI, Unlike EN288 there is no requirement for any non-destructive testing such as radiography or MPI/DPI,

although I would recommend radiography for butt welds.  although I would recommend radiography for butt welds.  • The testing requirement for groove welds are as follows:- The testing requirement for groove welds are as follows:- • Two Transverse tensile tests (QW150). Two Transverse tensile tests (QW150). • Two Root bends and Two face bends unless the plate thickness exceeds 3/8" then 4 side bends are Two Root bends and Two face bends unless the plate thickness exceeds 3/8" then 4 side bends are

required. All bend tests should be done to QW160 using the correct former ref. QW466 to an angle of 180 required. All bend tests should be done to QW160 using the correct former ref. QW466 to an angle of 180 degrees. Longitudinal (all weld) bend tests are not recommended unless the base/weld materials differ degrees. Longitudinal (all weld) bend tests are not recommended unless the base/weld materials differ markedly in bending properties.  See QW 466 for exceptions and precise details. markedly in bending properties.  See QW 466 for exceptions and precise details.

•The testing requirement for fillet welds on plate is 5 macro sections only, for Pipe fillet welds 4 macro The testing requirement for fillet welds on plate is 5 macro sections only, for Pipe fillet welds 4 macro sections. No fracture test requiredsections. No fracture test required

Introduction 40

Discontinuites- Weld defectsDiscontinuites- Weld defects

We will discuss common welding We will discuss common welding defects and cause, not only related defects and cause, not only related

to DSSto DSS

Hot Cracks

Cold Cracks

PORES

Lack of Fusion

Undercut

Misalignment

Arc strikes

Material Defects

Oxide inclusions

Pipe/Crater cracks

Hot CracksHot Cracks

Hot Cracks or Solidification cracksHot Cracks or Solidification cracks

• Formed under high temperatures, 1200Formed under high temperatures, 1200°°CC• ……under influence of shrinkage and tensions.under influence of shrinkage and tensions.• Crack is always formed in the middle if weldCrack is always formed in the middle if weld• Fillet weld is most sensitive for Cold CracksFillet weld is most sensitive for Cold Cracks• Can hide benith the surface.

Why Hot Cracks??Why Hot Cracks??

• High content of Carbon, sulfur, niob and phosforHigh content of Carbon, sulfur, niob and phosfor• Most sensitive in Root area and tack welding.Most sensitive in Root area and tack welding.• Welds geometry is also an important faktor • UCS: Units of crack susceptibilityUCS: Units of crack susceptibility• UCS: 230C+190S+75P+45Nb-12,3Si-5,4Mn-1UCS: 230C+190S+75P+45Nb-12,3Si-5,4Mn-1• UCS below or = 10 small riskUCS below or = 10 small risk• UCS over 30 big riskUCS over 30 big risk

ContinueContinue

• Big gaps in between welding objects, increase the Big gaps in between welding objects, increase the risk of Hot cracks.risk of Hot cracks.

• Concave weld bead, increase riskConcave weld bead, increase risk

What to do??What to do??

• Clean material.Clean material.

• Lower power supply, Heat Input.Lower power supply, Heat Input.

• Modify the groove.Modify the groove.

• Minimize gapMinimize gap

• Control the weld sequence.Control the weld sequence.

• Reduce the level mixture between base Reduce the level mixture between base material and filler material.material and filler material.