Hydro Runner Blade Crack Repair CA6NM Welding

[TFR1]

thread338-322423

Hi From NZ,
We have a very similar situation to the one in the referenced thread except that we have 14 out of 15 blades cracked, the cracks appear to start at the trailing edge on the edge of the weld that attaches the blade to the crown ( hub )of the runner, the welds were done with E309L during manufacture.
Our intended repair is to remove a section of the trailing edge and weld in an insert that is designed to move the welds away from the high fatigue stress area. the blades are about 6 to 10mm thick at the trailing edge at the crack locations.
Due to the difficulty of doing a full PWHT we are developing a weld procedure with no PWHT using the temper bead process using all GTAW or GTAW root with SMAW fill and 410 filler metal, we are doing weld tests with 20mm thick plate to check the metallurgy and hardness of the HAZ and weld metal.
There has been some discussion over what preheat and interpass temperatures should be used, from what I have seen in various publications it appears that low preheat and interpass temperatures in the order 100 to 150 deg C and then slow cool after welding, usually this is then followed by PWHT to obtain optimum properties which we are not intending to do, but there has a been a suggestion here that a much higher preheat and interpass temperature should be used in the order of 280 degC, in combination with this higher preheat and interpass temperature the suggested process is to

Weld an initial layer of weld on the weld prep faces using the temper bead technique,
Then allow the weld to cool to below 100 degC,
Then dress off half of the weld thickness, (purpose of this is to help with the tempering of the HAZ when the next layer is welded)
Then reheat to 280 degC and complete the rest of the weldment using the temper bead technique with an interpass temperature of about 280 degC,
After the welding is completed slow cool the weld at 50 degC/hr to 100 degC and then allow to slow cool under insulation.

What are your thoughts.

To brimstoner,
I note in the other referenced thread you have had alot of experience with this material, are you able to let me know from your experience what you found was a good interpass temperature to use.

Thank you
Cheers
Tim

 

[EdStainless]

What is the C level in your material?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[TFR1]

Carbon content currently unknown, i believe a couple of small samples have been taken for analysis, they are actually the result of laminations in the plate that came out as part of the crack excavation.
Cheers
Tim

 

[arunmrao]

ER410NiMo is the preferred alloy commonly used for weld repairs .You will be lucky, if the Carbon content is about 0.03%,higher amounts can lead to cracking. I have seen few contractors use AWS 310 grade welding consumables as fewer cracks are seen after weld repair.

I have provided a few links, hope they are useful.


Supplement 8 High Alloy Data Sheets Corrosion Series

https://www.sfsa.org/sfsa/pubs/hbk/s7.pdf

Supplement 8 High Alloy Data Sheets Corrosion Series

https://www.sfsa.org/sfsa/pubs/hbk/s8.pdf

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[EdStainless]

I fail to see how running a temper bead is any easier than doing localized PWHT. I am assuming that this is lower carbon material and a temper is all that is required.
A picture would be helpful, if you put an insert in then one edge of it must still be where the existing crack is. You can spread out the load a bit, but won't part of you joint still be in the same location?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[metengr]

I don't believe the half bead technique is necessary, and agree with arunmrao on filler metal choice. Instead, I would use a smaller diameter wire/rod for the first layer with at least 50% bead overlap followed by increasing the heat input or wire/rod size for the second and remaining layers until full. With no PWHT, I would recommend a preheat of 450 deg F with a slightly higher interpass temperature.

 

[weldstan]

In addition to the above, consider using a higher strength nickel base alloy filler more closely matching the CA6NM if PWHT cannot be performed.

 

[TFR1]

Hi,
Thank you for the replies,

Yes we are using ER410NiMo wire for the GTAW and Metrode 13.4.Mo.L.R 2.5mm electrodes for the SMAW. Thank you for the links.

Temper bead while not as good as PWHT is easier to do for localised repairs on a hydro runner, a complicating factor is that the runner has a soft coating on it for erosion control that is very difficult to remove using abrasive methods as tends to melt and clog up rather than be abraded away. This would need to be removed over a much larger area if the runner was to be PWHT, it would be a very time consuming job. Plus there is a some concern about the effects of PWHT on the existing E309 welds, plus due to the complexity of the shape it would be difficult to achieve consistent temperatures.

The half bead ( grinding ) is being specified by the metallurgist, already using 1.6mm filler wire for the initial layer and 2.5mm filler wire and electrodes and following the 50% overlap principle, 450 F ( 232 C ) is higher than most information that I have read, granted that the recommendations have had the welding followed by PWHT.

Metallurgist is suggesting a Preheat of 280 C and interpass of around 300 C which seems high to me as there will be very little Martensite formation to then be tempered during the welding, Martensite will mainly form as part of the final cool down. For this welding I believe we should be using a preheat of around 100 C with an interpass of around 150 C max 200 C.

metengr, I presume your comment regarding increasing the heat input for the second layer is to help with the tempering the HAZ.

Yes there was a little bit of thought on using nickel base filler such as Inconell 82 or even using E309L but would still have the issue of a hard HAZ.

Still keen to hear from brimstoner on his experience with runner manufacture.

Cheers
Tim

 

[EdStainless]

The matensite will form cooling down to 1600F (875) from the weld temperature.
You normally need to try to reach normalizing temp during your next weld pass, but with your low C (I hope that it is about 0.03%) then very little martensite will form, and what does will be lean in C.
This is why the call for such high preheat and interpass temps, your 100C pre and 150C interpass seam low to me.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube