Weld Hydrogen Cracking Susceptibility MAT1 3 Project Overview

Weld Hydrogen Cracking Susceptibility MAT-1 -3

Project Overview Objective • Complete experimental trials to further develop an understanding of the factors promoting hydrogen cracking in weld metals – Develop hydrogen embrittlement curves for a range of dissimilar weld metals to define their material ductility and embrittlement indices. – Use chemical, microstructural, strength and ductility properties of each weld metal to develop empirical formulae to predict the material ductility and embrittlement indices • Project will make use of previously developed slow bend test procedure

Material Selection • Materials selection proposed based upon strength, toughness, chemistry, manufacturer, type Manufacturer ® Type AWS Classifcation Cellulosic E 8010 -P 1 Cellulosic E 8010 -G Lincoln Electric ® 8 P+ Shield-Arc® 70+ Lincoln Electric Shield-Arc HYP+ Cellulosic E 7010 -P 1 FOX CEL 70 P Cellulosic E 7010 -P 1 Lincoln Electric Excalibur Basic E 8018 -C 1 H 4 R Lincoln Electric Pipeliner LH-D 80 Basic E 8045 -P 2 H 4 R Lincoln Electric Excalibur 7018 MR Basic E 7018 -1 H 4 R Böhler Basic E 8045 -P 2 Lincoln Electric FOX BVD RP Shield-Arc 70+ Cellulosic E 8010 -G Lincoln Electric Pipeliner 6 P+ Cellulosic E 6010 Böhler FOX CEL 70 P Cellulosic E 7010 -P 1 Böhler FOX CEL+ Cellulosic E 6010 Lincoln Electric Pipeliner LH-D 80 Basic E 8045 -P 2 H 4 R Lincoln Electric Pipeliner 18 P Basic E 8018 -G H 4 Böhler Fox EV Pipe Basic E 7016 Böhler SG 3 -P GMAW ER 70 S-6 Lincoln Electric Phase 1 Böhler Phase 2 Electrode Name ® Pipeliner ® 8018 -C 1 MR Lincoln Electric, Pipeliner, Shield-Arc, Excalibur, MR, Jet-LH and Jetweld are registered trademarks of Lincoln Global, Inc. Böhler is a registered trademark of Voestalpine Edelstahl Gmb. H LIMITED LIABILITY COMPANY AUSTRIA Donau-City-Strasse 7 Vienna, AUSTRIA A-1220 5

Test Procedure Documentation • Documented weld specimen preparation and testing procedure and apparatus – Specimen dimensions including grooving – Fixture for welding – Welding parameters (electrode specific) to achieve filled groove based upon vendor recommended practice – Base material tensile testing – All weld metal tensile testing • Report includes Appendix written in AWS format for consideration as a recommended practice guide 6

Material Characterization • Base metal and weld metal stress strain curves captured Basic Electrodes – Aged 3 h at 150 o. C • Chemical analysis • Hardness testing • Microstructure assessment Cellulosic Electrodes 8

Material Characterization • Hydrogen effusion testing completed for all electrodes • Simulate Hydrogen Effusion – Observe similar behaviour for class 10

Hydrogen Cracking Susceptibility Testing • Preferred hydrogen cracking tests include notched 3 point bend specimens with known applied load Load or Displacement • Notched Specimen Slow Bend Load Displ.

Hydrogen Cracking Susceptibility Testing Slow Bend Hydrogen Cracking Susceptibility • Testing completed for all electrodes • Define critical deflection curves Pipeliner LH-D 80 (Basic Electrode)

Critical Hydrogen Curve Development Specimen deflections are converted to applied stress or strain knowing the specimen and loading geometry Charpy notch Force [k. N] • Nonlinear ANSYS FEM with 20 noded brick elements • Consider specimen geometry, materials and support contact weld Base metal Deflection [mm]

Critical Hydrogen Curve Development Strains perpendicular to the plane of the notch are used to characterize the cracking state • Reported from 0. 18 mm sub surface (Previously 0. 23 mm) Basic Pipeliner LH-D 80

Observed Correlations Higher hydrogen cracking susceptibility related to: • Lower elongation in the all weld metal tensile test – Lower elongation correlates with lower ductility indices • Carbon equivalent – Higher CE correlates with greater embrittlement indices (cellulosic electrodes) • Microstructures containing PF(I) intra-granular polygonal ferrite – Presence of PF(I) correlates with high hydrogen embrittlement susceptibility for cellulosic electrodes – Presence of PF(I) correlates with reduced hydrogen embrittlement susceptibility for basic electrodes • Welding heat input t 800 -500 – Increased cooling time through transition temperatures correlated with reduced susceptibility • Cellulosic electrode type – Showed stronger hydrogen susceptibility with increasing strength, hardness, and lower ductility than basic electrodes 18

Hydrogen Susceptibility Relationships Goal: Identify εcrit for different materials as a function of hydrogen concentration εcrit = A (Hconc)B Ductility Index A = f( ? ) Embrittlement Index B=f(? ) 19

Hydrogen Susceptibility: Cellulosic Electrodes Ductility Index ‘A’ A = 0. 2 CEIIW -0. 00055 E 50 -250 + 24. 72 Strong Correlations: CEIIW (negative), E 50 -250 (positive) Good Correlations: Reported %el. (positive) UTS, AF%, Mn% (negative) 21

Hydrogen Susceptibility: Cellulosic Electrodes Embrittlement Index ‘B’ B = -0. 0018*UTSTrue -0. 0000035*E 50 -250 + 1. 52 Strong Correlations: True UTS, E 50 -250 (negative) Good Correlations: Elongation (positive) YS, UTS, Resilience modulus (negative) 22

Basic Electrodes – Ductility Index ‘A’ Positive Correlations with: -Notch Hardness, Microstructure Constituents, Si% (positive) -Two relationships identified: -microstructure AF*(%) = AF(%) + 0. 65*FS -hardness (HV 10) 0. 14 HVnotch + 115 Si(%) - 62. 2 -Si demonstrates positive influence on ductility 24

Basic Electrodes – Ductility Index ‘A’ Close correlation between microstructure and the HV 10 hardness below the notch -Acicular ferrite (AF) + weighted fraction of FS, ferrite with second phases (aligned & non aligned) -Potential to develop a hardness and metallurgical assessment for weld procedure development 25

Basic Electrodes – Embrittlement Index ‘B’ Correlates with Ferrite with Aligned Second Phase. -Weight different microstructures based on theoretical susceptibility to embrittlement i. e. FS(NA) lower susceptibility than FS(A), while PF(I) & PF(G) are ductile structures B = -0. 0149 x {FS(A) + 0. 45*FS(NA) – 0. 46*PF(I + G)} - 0. 202 One Outlier: Excalibur 7018 MR -Widmanstatten structure from prior austenite GB -not observed with other materials tested 26

GMAW Electrode Similar Microstructure to Basic Electrodes -Low C, promotes ferrite along prior austenite GB -Concentrated heat source produces microstructure similar to a higher heat input SMAW Basic electrode weld -A slight increase in GMAW heat input would be expected to enhance development of ferrite structures -May produce lower residual stresses and hence in practice reduce susceptibility. Further investigation required to support hypothesis -Embrittlement Index predicted by microstructure relationship identified for basic electrodes 29

Conclusions • General… • 16 different consumables were tested, 13 unique • Microstructural trends observed for both cellulosic and basic electrodes and correlated to fracture morphology of slow bend samples • Cellulosic Electrodes • Susceptibility curves as a function of weld metal hydrogen content were able to be predicted with the CE of the electrode and mechanical properties • Increasing strength, hardness, modulus and CE contribute to increasing hydrogen cracking susceptibility • Weld procedure influences on susceptibility were identified for repeat test electrodes • Repeat electrode results suggest possibility of an embrittling threshold existing (combination of AF, UTS, HV 10) beyond which material becomes highly susceptible to all hydrogen contents 30

Conclusions (cont’d) • Basic Electrodes • Microstructure evolution showed correlation to the hydrogen susceptibility • Relationships between weld microstructure and hardness were found to correlate to hydrogen embrittlement susceptibility and may be beneficial for assessing weld procedure qualification testing • Welding procedure was found to influence the material properties and the susceptibility to hydrogen cracking • GMAW Wire • Insufficient data points to draw strong conclusions, however, microstructural characteristics and mechanical tests show similar performance to low hydrogen SMAW electrodes, but at lower attainable heat inputs 31

Recommended Future Investigation • Improve the fit of the developed hydrogen cracking susceptibility relationships based upon ductility and embrittlement indices: • • Evaluate the number of slow bend samples required to achieve a repeatable fit of the susceptibility curve used to define a materials performance in the presence of hydrogen; Evaluate the influence of varying welding parameters within manufacturer recommended ranges on the fit of the ductility and embrittlement indices. • Documentation and technical transfer of and testing procedures: • • Consider the transferability of the testing procedure to other test labs; and Consider assembly of a guidance note for the testing procedures. • Extension of the defined relationships and improvement of metallurgical basis for the observed susceptibility relationships: • Test the susceptibility of the weld HAZ to hydrogen embrittlement for material combinations that demonstrate low susceptibility in the weld; and

Recommended Future Investigation • Characterize additional materials to increase the correlation basis for the hydrogen cracking susceptibility curve relationships: • • • Perform additional tests using GMAW process to include commonly used filler materials; Perform additional GMAW welds to evaluate influence of common welding procedure variations (modified wave short circuit, spray transfer); and FCAW or metal-cored welding wires could be considered to consider their susceptibility. • Long Term Objectives to relate hydrogen cracking susceptibility to weldment design: • • Consider the relationship between critical strain to the strain observed in typical weld anomalies (e. g. lack of fusion, slag inclusions); and Relate or define upper bound hydrogen concentrations as a function of welding parameters and total diffusible hydrogen for typical electrode types and weld parameters.