Advances in Welding for Sanitary Designs Richard E. Avery Consultant to the Nickel Institute May 17, 2004.

Advances in Welding forAdvances in Welding forSanitary DesignsSanitary Designs

Richard E. AveryRichard E. AveryConsultant to the Consultant to the Nickel InstituteNickel Institute

May 17, 2004May 17, 2004

Possible Materials Possible Materials

• 304L& 316L – used for vast majority of 304L& 316L – used for vast majority of applicationsapplications

• 6% Mo or super-austenitic SS6% Mo or super-austenitic SS

• Duplex stainless steelsDuplex stainless steels

• Ni-Cr-Mo nickel alloysNi-Cr-Mo nickel alloys

• Commercially pure titaniumCommercially pure titanium

Service ConsiderationsService Considerations

• 304L vs 316L – Mo (2-3%) in 316L 304L vs 316L – Mo (2-3%) in 316L improves pitting & crevice cor. resist.improves pitting & crevice cor. resist.

• Both sensitive to stress cor. cracking Both sensitive to stress cor. cracking over about 150over about 150ooFF

• Duplex SS good resist. to SCCDuplex SS good resist. to SCC

• Higher chlorides, low pH may require Higher chlorides, low pH may require 6% Mo SS or Ni-Cr-Mo or titanium6% Mo SS or Ni-Cr-Mo or titanium

Welding Processes UsedWelding Processes Used

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

• GMAW – MIG, pulsed arc modeGMAW – MIG, pulsed arc mode

• SMAW or covered electrodeSMAW or covered electrode

• Laser welding for manu. of welded Laser welding for manu. of welded tubingtubing

Typical Sanitary Piping SystemsTypical Sanitary Piping Systems

• Welded by gas tungsten arc welding Welded by gas tungsten arc welding (TIG)(TIG)

• Lines designed for CIPLines designed for CIP

• Inside of tube welds often not Inside of tube welds often not accessible for grinding or inspectionaccessible for grinding or inspection

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

In response to 3-A RequestIn response to 3-A Request

• AWS D18.1AWS D18.1Specification for Welding Austenitic Stainless Specification for Welding Austenitic Stainless Steel Tubing Systems in Sanitary (Hygienic) Steel Tubing Systems in Sanitary (Hygienic) ApplicationsApplications

• AWS D18.2AWS D18.2Guide to Weld Discoloration Levels on Inside Guide to Weld Discoloration Levels on Inside of Austenitic Stainless Steel Tubeof Austenitic Stainless Steel Tube

Goals of D18.1 & D18.2Goals of D18.1 & D18.2

• Guidance of judging root welds of tubes Guidance of judging root welds of tubes from OD appearancefrom OD appearance

• Guides for Procedure & Performance Guides for Procedure & Performance Qualification, Preconstruction Weld Qualification, Preconstruction Weld SamplesSamples

• Weld visual acceptance criteriaWeld visual acceptance criteria

• Illustration of weld discoloration levelsIllustration of weld discoloration levels

AWS D18 Committee WorkAWS D18 Committee Work• Members – equipment producers, users Members – equipment producers, users

& general interest groups& general interest groups• 36 weld samples, many with ID defects 36 weld samples, many with ID defects

– examined on OD & ID by 3-A – examined on OD & ID by 3-A inspectorsinspectors

• Tube with varying levels of weld Tube with varying levels of weld discolorationdiscoloration

• Tube with varying discoloration levelsTube with varying discoloration levels

Welding QualificationsWelding Qualifications

• Welding Procedure Specification Welding Procedure Specification (WPS) - for each type of weld(WPS) - 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 - 3 welds made by each welder to aid in evaluating production weldsin evaluating production welds

Visual Examination Visual Examination RequirementsRequirements

• OD of welds examined by welder & OD of welds examined by welder & inspector, to be consistent with WPSinspector, to be consistent with WPS

• Welds not meeting OD standards Welds not meeting OD standards examined by borescope or other examined by borescope or other suitable meanssuitable means

Visual Acceptance Criteria -Visual Acceptance Criteria -ID & OD ID & OD

• Welds full penetrationWelds full penetration

• No cracks, undercut, crevices, or No cracks, undercut, crevices, or embedded or protruding materialembedded or protruding material

• Offset not to exceed 10 %Offset not to exceed 10 %

Visual Acceptance CriteriaVisual Acceptance Criteriafor External, Non-Productfor External, Non-Product

Contact SurfaceContact Surface

These criteria give confidence These criteria give confidence that the inside weld surface is that the inside weld surface is acceptable without an internal acceptable without an internal

examinationexamination

Non-product contact surface - Non-product contact surface - Maximum concavityMaximum concavity

Non-product contact surface- Non-product contact surface- Maximum convexityMaximum convexity

Visual Acceptance Criteria for Visual Acceptance Criteria for Internal, Product Contact Internal, Product Contact

SurfaceSurface

• Max. concavity 0.012 in.Max. concavity 0.012 in.

• Max. convexity 0.012 in.Max. convexity 0.012 in.

• Oxide islands (slag spots), not greater Oxide islands (slag spots), not greater that 1/16 in. in diameter & 4 per weldthat 1/16 in. in diameter & 4 per weld

• No excessive heat-tint oxideNo excessive heat-tint oxide

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

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 and greater is unacceptableTypically 5 and greater is unacceptable

• 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

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

AWS D18.3 (Pending)AWS D18.3 (Pending)Specification for Welding Tanks, Vessels, Specification for Welding Tanks, Vessels,

and Other Equipment in Sanitary and Other Equipment in Sanitary (Hygienic) Applications(Hygienic) Applications

• Welding Procedure & Performance Qual.Welding Procedure & Performance Qual.• Visual Examination Acceptance Criteria:Visual Examination Acceptance Criteria:

- reject defects; cracks, lack of penetration - reject defects; cracks, lack of penetration etcetc- acceptable & unacceptable weld profiles - acceptable & unacceptable weld profiles prior to weld finishingprior to weld finishing- annex – Weld & Adjacent Zone Finishes – - annex – Weld & Adjacent Zone Finishes – WF-1 (as-welded) ~ WF-8 (ground flush & WF-1 (as-welded) ~ WF-8 (ground flush & electropolished)electropolished)

6% Mo or Superaustenitic SS6% Mo or Superaustenitic SS

• Typically: 21 Cr, 24 Ni, 6 Mo, 0.2 NTypically: 21 Cr, 24 Ni, 6 Mo, 0.2 N

• Areas for 6% Mo not handled by 316Areas for 6% Mo not handled by 316- high chlorides ~ over 1000 ppm- high chlorides ~ over 1000 ppm- low pH environments- low pH environments- where better pitting, crevice and stress - where better pitting, crevice and stress corrosion cracking resistance is corrosion cracking resistance is requiredrequired

Welding 6% Mo SSWelding 6% Mo SS

• Use over-alloyed filler metal – minimum Use over-alloyed filler metal – minimum of 9% Mo Ni-Cr-Mo alloyof 9% Mo Ni-Cr-Mo alloy

• GTAW welding procedures similar to GTAW welding procedures similar to that for 304/316 except:that for 304/316 except:- preferably avoid autogenous welds to - preferably avoid autogenous welds to avoid lower corrosion resistance avoid lower corrosion resistance - somewhat lower heat input and - somewhat lower heat input and interpass temperature interpass temperature

What are Duplex Stainless What are 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

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

Source:The ESAB Group

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

• Higher strength – YS 2 to 3 times 316Higher strength – YS 2 to 3 times 316- forming requires greater power- forming requires greater power- more spring-back during forming- more spring-back during forming

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

DSS Welding - General DSS Welding - General RequirementsRequirements

• No preheat – 300F interpass typicalNo preheat – 300F interpass typical

• Heat input 15 to 65 kJ/in.Heat input 15 to 65 kJ/in.

• To avoid high ferrite in welds, filler To avoid high ferrite in welds, filler metals with higher nickel used ~ 2209 metals with higher nickel used ~ 2209 with 9% nickelwith 9% nickel

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

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

Duplex SS - WeldingDuplex SS - Welding

• To avoid high ferrite in welds, filler To avoid high ferrite in welds, filler metals with higher nickel used ~ 2209 metals with higher nickel used ~ 2209 with 9% Niwith 9% Ni

• Avoid loosing N in weld – N backing Avoid loosing N in weld – N backing commoncommon

• Heat input 15 to 65 kJ/inHeat input 15 to 65 kJ/in

• Interpass temperature 300F typicalInterpass temperature 300F typical

Nickel Alloys & TitaniumNickel Alloys & Titanium

• Selectively used for their high corrosion Selectively used for their high corrosion resistant propertiesresistant properties

• Ni-Cr-Mo alloys – weldability comparable to Ni-Cr-Mo alloys – weldability comparable to austenitic SSaustenitic SS

• Commercially pure titanium – readily weldedCommercially pure titanium – readily welded- extra care to prevent contamination from - extra care to prevent contamination from atmosphere (oxygen, nitrogen)atmosphere (oxygen, nitrogen)

Summary – Welding for Food Summary – Welding for Food IndustryIndustry

• Technology well established for making Technology well established for making structurally sound weldsstructurally sound welds

• Greatest challenge is hygienic surface Greatest challenge is hygienic surface considerations, i.e.considerations, i.e.- welds free from surface defects- welds free from surface defects- surface finishes comparable to base metal- surface finishes comparable to base metal- control weld discoloration to levels - control weld discoloration to levels acceptable for end applicationacceptable for end application