Dear PRC,
What you’re seeing is a fairly classic situation with tube-to-tubesheet mockups so before changing filler, it’s worth understanding the mechanism.
1) Are these hot cracks?
Yes—what you’re describing strongly points to solidification cracking (hot cracking).
Why:
- They appear at the root and sometimes surface
- Not detected by PT, but show up after macro etch → typical of tight, interdendritic cracks
- Occur randomly, not in every weld
- You’re using austenitic filler (ER309) on a dissimilar joint (likely carbon steel tubesheet + possibly SS tubes)
These are textbook indicators of hot cracking during solidification.
2) Likely causes in your case
Several contributing factors are probably overlapping:
a) Dilution from SA-516 Gr.70 (high carbon steel)
- Excess dilution into ER309 reduces ferrite in the weld metal
- Low ferrite (FN < ~3–5) → high hot cracking susceptibility
b) Fully austenitic weld metal
- If your weld metal solidifies as fully austenitic, it’s very crack-prone
c) Heat input / bead profile
- Your parameters (~145 A, 13 V, 2 passes, 1.6 mm wire) can produce:
- Narrow beads
- High restraint at root
- Segregation → cracking
d) Joint restraint
- Tube-to-tubesheet welds are highly restrained, which promotes hot cracking
e) Possible contamination
- Sulfur, phosphorus, or even minor surface contamination can aggravate cracking
3) Can you switch to ER309LMo?
Yes—you can, and in many cases it helps, but it’s not a guaranteed fix by itself.
Why ER309LMo may help:
- Mo improves resistance to solidification cracking
- Slightly better tolerance to dilution
- Often results in a more crack-resistant weld metal structure
However:
- The key factor is ferrite content, not just Mo
- If dilution is still high, even ER309LMo can crack
4) More effective corrective actions (important)
Instead of only changing filler, address the root causes:
✔ Control ferrite number (very important)
- Target FN 5–10 minimum
- If possible, check using FN meter or calculate via WRC-92 diagram
✔ Reduce dilution from tubesheet
- Use lower heat input at root
- Use stringer beads, avoid wide weaving
- Slightly reduce amperage if penetration is excessive
✔ Consider buttering approach (best practice in critical jobs)
- Butter tubesheet hole with SS (309/309LMo)
- Then weld tube → reduces dilution dramatically
✔ Root pass control
- Ensure:
- Proper fit-up (no excessive gap)
- Smooth root profile (avoid concavity)
- Avoid overheating small root area
✔ Interpass temperature
- Keep controlled (typically <150°C for this type)
✔ Cleanliness
- Ensure:
- No oil, moisture, or oxide
- Proper pickling/cleaning if needed
5) Why PT didn’t detect cracks
This is normal:
- Hot cracks are often:
- Very tight
- Subsurface or micro-cracks
- PT only detects open-to-surface discontinuities
Macro etching exposes them by revealing grain boundary separation.
6) Practical recommendation
Do this in order:
- Switch to ER309LMo ✔ (good step)
- Reduce heat input at root
- Ensure ferrite presence (FN ≥ 5)
- If still failing →
👉 adopt buttering technique (most reliable fix)
7) Bottom line
- Yes, these are hot cracks (solidification cracks)
- Yes, ER309LMo is a better choice, but not a standalone solution
- The real fix is controlling dilution + ensuring ferrite in weld metal
Regards,
Ashish Ranjan
+91 9555864374
Save a tree...Please consider your environmental responsibility. Before printing this e-mail message, ask yourself whether you really need a hardcopy.
"Confidentiality Warning: This message and any attachments are intended only for the use of the intended recipient(s), are confidential and may be privileged. If you are not the intended recipient, you are hereby notified that any review, re-transmission, conversion to hard copy, copying, circulation or other use of this message and any attachments is strictly prohibited. If you are not the intended recipient, please notify the sender immediately by return email and delete this message and any attachments from your system.
Virus Warning: Although the company has taken reasonable precautions to ensure no viruses are present in this email. The company cannot accept responsibility for any loss or damage arising from the use of this email or attachment."
Caution: The e-mail below is from an external source. Please do not open attachments or click links unless this email comes from a known sender and you know the content is safe. |
Dear Sirs,--
We have made 2 MockUp PQRs as per ASME Sec IX QW-193.
The Tube sizes are 19.05OD x2.11T and 15.88OD x2.11T, thetubesheet plate is SA-516-70, 50T.
Amps used Max 145, Volts Max 13, welded with GTAW AWS Class ER309 with 1.6mm Filler , 2 passes.
We found minor cracks on the weld root and some on the surface too, but not for all the 10 tubes welded, but randomly found these cracks
When we did PT after welding on the surface, no cracks were found. But found after Macro etching at the test lab.
Can I switch the filler to ER309LMo for this MockUp weld ?
Are these cracks called Hot cracks ?
Please give me some advice.
With best regards,Saravanan Sornam,Ansan city,S.Korea.
https://materials-welding.blogspot.com/
https://www.linkedin.com/groups/122787
---
You received this message because you are subscribed to the Google Groups "Materials & Welding" group.
To unsubscribe from this group and stop receiving emails from it, send an email to materials-welding+unsubscribe@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/materials-welding/CALV1rkLag0%3D-RPjKQhRB21ODF3eNenk1Ey71-xTpp5LFMvTj5w%40mail.gmail.com.
https://materials-welding.blogspot.com/
https://www.linkedin.com/groups/122787
---
You received this message because you are subscribed to the Google Groups "Materials & Welding" group.
To unsubscribe from this group and stop receiving emails from it, send an email to materials-welding+unsubscribe@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/materials-welding/CA%2BRvhZCRCJOkP7xnMq9OgJgGNSoTAUdD8tWiqQKS_xADWOrS0g%40mail.gmail.com.
Comments