What the Macro Suggests
From the image:
- Fusion is occurring on the upper groove walls.
- Root area shows an unfused triangular gap / cold lap zone.
- Weld metal is flowing around the joint rather than penetrating fully to the root.
- This is typical when the arc cannot adequately reach the root face or root land.
Likely Causes
1. Amperage Too Low for Root Pass
82 A for first pass on a restrained joint with 50 mm thick tubesheet may be too low, especially if heat is rapidly absorbed by the heavy SA-516 tubesheet.
The tubesheet acts as a heat sink, pulling heat away from the root.
2. Groove Design / Root Land Too Heavy
If the groove has:
- narrow included angle
- excessive land/root face
- insufficient tube projection or mismatch
then penetration becomes difficult at lower amps.
3. Arc Position / Torch Angle
If arc is focused too much on filler or upper bevel edges rather than root corner, fusion at the bottom will be poor.
4. Travel Speed Too Fast
If moving too quickly on root pass, puddle bridges the opening before full fusion occurs.
Recommendations to Achieve Sound Root Penetration
A. Increase Root Pass Current Slightly
Try:
For 19.05 mm tube:
- Root pass: 90–100 A
- Hot pass: 100–110 A
- Cap: 105–115 A
For 15.85 mm tube:
- Root pass: 80–90 A
(Exact depends on wall thickness)
Use pulse GTAW if possible.
B. Modify Groove Design (Very Important)
Need better root accessibility:
Suggested:
- Increase included angle to 37.5° to 45°
- Reduce root face to 0.5 mm max
- Maintain small root gap if code allows
- Ensure tube stickout/projection consistent
Current geometry may be choking penetration.
C. Use Arc Focus Technique
For root pass:
- Keep tight arc length
- Direct arc into root corner
- Slight pause at sidewalls
- Minimal filler addition initially until keyhole/fusion established
D. Preheat Tubesheet Slightly
For SA-516 thick section:
- 80–120°C local preheat
This reduces heat sink effect and improves fusion without excessive amperage.
E. Back Purge / Internal Shielding
For SS304L tube root integrity, ensure argon purge inside tube.
Poor shielding can also contribute to cracking/oxidation.
To Avoid Cracks Simultaneously
Since you also had cracking concerns earlier:
Use:
- ER309LMo is correct choice
- Control interpass <150°C
- Avoid excessive restraint if possible
- Do not overweld
- Slightly higher heat with fewer passes is often better than cold multilayer welds
Cold welds can crack too.
My Best Practical Recommendation
Trial Procedure:
19.05 tube:
- Preheat tubesheet to 100°C
- Root pass 95 A DCEN
- 1.6 mm tungsten
- Tight arc
- Slow travel
- 3 passes total
If still incomplete:
- Slightly open groove angle.
Important Observation
You moved from cracking due to too much restraint/heat imbalance to lack of fusion due to overcorrection (too cold).
Now you need the balanced middle zone.
On Fri, May 1, 2026 at 7:55 AM PARAI Reaction Channel <saravanshyla@gmail.com> wrote:
--Dear Sirs,
As per my below mail history and your recommendation for low Amps to avoid high heat input,After performing the new MOCKUPs for 15.85, & 19.05 OD SS304L tubes to CS SA-516-70N tubesheet of 50mm with GTAW ER309LMO 1.6 Dia only of 3 passes for 19.05 ID tube, 82 A for 1st pass, 95A for 2nd, 100A for 3rd pass. Only 2 passes given for 15.85 OD tube.
We got incomplete penetration aa per the attached macro photo., almost for all the tube welds for both sized tube welds.
Please see the groove design for your reference.
Also, please give me suggestions to make sound complete penetration on root pass and to avoid cracks too.
Thanks and regards,Saravanan Sornam,Ansan city,S.Korea
On Thu, 16 Apr 2026, 2:51 pm 'Ahmed Osman' via Materials & Welding, <materials-welding@googlegroups.com> wrote:
--sure, 309LMO will be helpful as low carbon and MO are increasing delta ferrite for avoiding hot cracksalso reduce heat input for controlling dilution from CS sheet
Best Regards ,Ahmed Osman
On Thursday, April 16, 2026 at 08:32:05 a.m. GMT+3, PARAI Reaction Channel <saravanshyla@gmail.com> wrote:
--Dear Sir,
Thank you for your advice for root welding parameters.
Can i use ER309LMO instead of ER309 ?
Please confirm.
Thanks and regards,Saravanan Sornam,ANSAN,S.KOREA
On Thu, 16 Apr 2026, 12:06 pm Vanchinath S.A., <vanchinaths@gmail.com> wrote:
Weld root with 80-90 amps.Vanchi
--On Wed, 15 Apr, 2026, 7:18 pm PARAI Reaction Channel, <saravanshyla@gmail.com> wrote:
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.
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