1. Weld Hydrogen Cracking Risk Management Guidance (MAT-1-1)
Oct 2018

2. Project Overview Background
PRCI and other organisations have funded research and development programs related to weld hydrogen cracking
Cracking test development
Hardness limit definition
Diffusible hydrogen delivery
Evaluation of hydrogen cracking delay time
Weldment hydrogen cracking susceptibility
Projects have produced results that can be used in developing or approving welding procedures, electrodes or consumables
Yet hydrogen cracking is still being observed in in-service welds and new construction

3. Hydrogen Cracking Guide
Project Objectives
Assemble an overview of what is known about hydrogen cracking

4. Guide Observations Hydrogen cracking theories differ
Suggest different mechanisms for crack formation
Can explain different cracking behaviours observed for different materials and the factors controlling susceptibility
The absorption and diffusion of hydrogen considered
The diffusion of hydrogen is describable to understand the time history of hydrogen concentration promoting cracking for electrode types
Susceptibility of each electrode type to hydrogen delivery was described along with hydrogen measurement techniques
Weld microstructure and chemistry considered
Factors affecting susceptibility in terms of hardness / hardenability
Carbon and carbon equivalent used to control hardenability

5. Guide Observations Hydrogen Cracking Susceptibility Testing Reviewed
Single pass, Go/No go testing
Material characterization/ranking testing
Sources of Stresses Reviewed
Residual, construction and role of material grade
Weld Procedure Qualification Testing Reviewed
Current tests, do preclude hydrogen cracking, but can reduce risk
Weld Inspection and Record Keeping
Inspection delay time remains an area for improvement

6. Weld Inspection Delay Time
Requested to add an appendix to the report to describe this work for fillet welds and girth welds

7. Modelling Matrix PRCI identified 20 cases of interest
6 Geometric Models (Wall thickness and electrode combinations)
Model
Case
Pipe
Consumable
 Minimum Preheat (F)
Ambient Temp
(F)
Max Interpass (F)
 Electrode Dia
(mm)
Dia
(in.)
Thickness (in)
Root
Hot
Fill & Cap A 1 12
0.25
E6010
E8010 P1 50
600 4 2 90 3
200 B 5
LH-D90 6 7 8 C 9
0.75 10 11 D 13 14 15 16 E 17 18 F 19 20

8. Modelling Matrix
BMT expanded modelling matrix to provide more comprehensive identification of trends
Approach similar to previous study for fillet welds (GRI-05/8759)
44 cases per model geometry
Input Condition
Modelled Values
Ambient Temperature (oC)
-40, -20, 0, 20, 32, 40
Wind Speed (km/hr)*
0, 7.5, 15, 22.5, 30
Preheat Temperature (oC)
10, 93, 150
Post Weld Heating Temperature (oC)
Ambient, 93, 150
Post Weld Heating Duration (min)
0, 30, 60
Diffusible Hydrogen Content Cellulosic (EXX10) Electrodes (ml/100g) 60
Diffusible Hydrogen Content Low Hydrogen (EXX45-H4R) Electrode (ml/100g) 4
Microstructural Trap Density, Vd
0.09, 0.11
*Windspeed was considered but was not found to produce notable influence

9. Modelling Approach 6 mm WT (0.25”) 3 Weld Passes 0.5 mm cell size
Air
6 mm WT (0.25”)
3 Weld Passes
0.5 mm cell size
Weld pass size estimated using Deposition Rate data provided by Lincoln Electric for different electrode types and sizes
3 Weld Passes
Base Metal

10. Modelling Approach 19 mm WT (0.75”) Cellulosic (E8010) Fill & Cap
4 mm dia electrode model ‘C’ shown
13 Weld Passes
1 mm cell size
10 Weld passes for 5 mm dia electrode model ‘E’ (not shown)
Low Hydrogen (E9045) Fill & Cap
4 mm dia electrode model ‘D’ shown
10 Weld passes
1mm cell size
9 Weld passes for 5 mm dia electrode model ‘F’ (not shown)

11. Evaluation of Min Inspection Delay Time
Time to reach peak Concentration In HAZ
Identify location requiring longest ‘time to peak’ hydrogen concentration in HAZ
Peak hydrogen corresponds to the time at which the highest risk of cracking exists (in absence of external loads)
Beyond this time, cracking risk diminishes as hydrogen concentration decreases
To compare cellulosic and low hydrogen electrodes procedures (different diffusible hydrogen contributions), the concentration of hydrogen used in combination with ‘time to peak’ to compare relative cracking risks
Concentration of Hydrogen In HAZ (ml/100g)

12. Predicted Time to Peak Hydrogen
Increasing thickness increases time to peak hydrogen (requ’d inspection delay)
Increasing preheat reduces the time to peak hydrogen
Sharp increase in time to peak hydrogen with decreasing ambient temperature
Cellulosic fill & cap proc. (Models A, C, E) have lower time to peak hydrogen

13. Cellulosic Fill & Cap Procedure
After Last Weld Pass
TTPH ~8.6 hr, 14 ml/100g
1 hr After Weld Completion
19 mm WT weld, 32°C Ambient, 93°C Min Preheat
Controlling location (TTPH) is adjacent to highest concentration region of weld
10 hr After Weld Completion
ml/100g

14. Low Hydrogen Fill & Cap Procedure
After Last Weld Pass
TTPH ~24 hr, 0.18 ml/100g
1 hr After Weld Completion
10 hr After Weld Completion
19mm WT weld, 32°C ambient, 93°C preheat
Controlling location (TTPH) is adjacent to final fill passes
Longer diffusion distance, lower concentration gradient produce longer time to reach peak hydrogen
ml/100g

15. Predicted Time to H4
Identify the time for weld and HAZ to reach maximum concentration of 4 ml/100g
Increasing time required for cellulosic Fill & Cap Procedures, particularly with increased thickness A vs B, C vs D, E vs F)
Identify cases where risk of cracking may persist after TTPH inspection delay (i.e. need to manage pipe movement)

16. Reducing Inspection Delay
60 min at 150°C produces significant reduction of TTPH supporting reduction in inspection delay time
60 min at 150°C diffuses to H4 threshold for 0.25” WT pipe and 0.75” WT with low hydrogen fill & cap proc.
Can combine hydrogen cracking mat’l susceptibility with model predictions
Identify when TTPH approach may be conservative, expand hydrogen analysis to consider susceptibility to external loads (release of rigging, back filling, ditching of pipe) particularly in near or below freezing construction environments

17. Model Summary 6 Geometric Models Evaluated
Consider effect of wall thickness and different electrode combinations
Range of environmental temperatures, welding preheat, post heat, hydrogen diffusivity of completed weld
Strong temperature influence on required inspection delay time using TTPH approach and required time for hydrogen concentration to fall to maximum of H4 across weld and HAZ
TTPH provides different inspection delay times for cellulosic fill & cap procedures vs low hydrogen fill & cap procedures
Inspection delays supported by TTPH assume constant microstructure and stress states
Additional consideration may be required for duration to external loading

18. Project Status Draft Final Report Delivered Comments Received
Significant comments
Desire to see more guidance on inspection delay time
Additional work accepted (no cost to PRCI) to perform hydrogen effusion (Inspection Delay Time Modelling)
Modelling of matrix weld procedures has been completed
Report has been updated to address comments
Not posted to PRIME Internal 2nd Review in Progress,
Report Annex draft completed for internal review by Oct 25
Final version of report to be posted to Prime Nov 9