Re: [MW:17973] PQR for Welding Weldox 700

Dear Rudolf:

Now that's the information I needed.
At the beginning I thought you have the usual HAZ toughness problem but this one is different.

There are a few reasons for such high hardness values in root pass, including:

• Alloying elements in this filler metal (1.75% Ni and 2.0% Mn) 
• Your thickness is 35mm so heat sink is high
• Root pass geometry causes stress concentration
  

That means you have to increase Heat input and/or preheat.

But you can't increase preheat so much otherwise you will jeopardize HAZ toughness so PWHT will be essential. There is no other way...!!!

I recommend include back gouging (grinding is better) in your WPS (if you have access in the actual work). Gouging shall be done with low heat input, followed by grinding.
This is to remove this problematic root pass.

Good Luck

Ramin Kondori

Sr. QA/QC Engineer

SINOPEC

r.kondori@petroyada.com
+98-2123592322
+98-9132150320

On Tue, Jun 18, 2013 at 2:56 PM, Rudolf <rudolf_jude@yahoo.com> wrote:

Hi Ramin, 

Thanks for your reply. Yes you are right the impact values at 1mm and 5 mm at fusion line is over 150 joules. It is only at the weld metal that it has dropped to single digit. The hardness at root pass weld metal and HAZ is around 350 to 400 HV. The parameters are all fine. Checked with Esab. 

The parameters are given in my first query. 

Am really confused. Why and how it has happened. I have religiously monitored the inter pass temp with temp stick and digital thermometer. Continuously checked V and A using tong meter. Checked gas flow at regulator. 

Thanks and regards 

Rudolf 

Sent from my iPhone

On 18 Jun, 2013, at 4:51 PM, Ramin Kondori <raminkondori@gmail.com> wrote:

Dear Rudolf:

Are you saying that your specimens did not fail in HAZ (or fusion line) and weld metal specimens failed...?

If "weld metal" impact test has failed, most probably it has something to do either with your filler metal or welding process (or power source settings, technique etc.).

Are you using recommended welding parameters...?
Please check with the ESAB page to ensure you are using proper power source settings (http://www.esabna.com/us/en/products_catalog.cfm?Product_ID=265).

Normally, the problem with welding of Quench & Tempered steels like Weldox-700 is that impact toughness drops in HAZ (and/or fusion line). Of course that's when you select suitable filler metal and welding process and technique. Below table shows that you should not have any problem with weld metal specimens. In other words if you use recommended parameters, you should get these results (for weld metal only). If you have not, then you are missing something.

Typical Mechanical Properties (Weld Metal)

As Welded 75% Ar / 25% CO2

Yield Strength: 110 ksi, 760 MPa

Tensile Strength: 120 ksi, 830 MPa

Reduction in Area: 54%

Elongation in 2": 19%

Stress Relieved 8 hrs. @ 1150°F (621°C) 75% Ar / 25% CO2

Yield Strength: 108 ksi, 745 MPa

Tensile Strength: 116 ksi, 800 MPa

Reduction in Area: 56%

Elongation in 2": 19%

Charpy V-Notch Properties (Weld Metal)

Testing Temperature 0°F (-18°C)

As Welded 75% Ar / 25% CO2 : 40 ft-lb, 54 J

Stress Relieved 8 hrs. @ 1150°F (621°C): 29 ft-lb, 39 J

Testing Temperature -20°F (-29°C)

As Welded 75% Ar / 25% CO2 : 36 ft-lb, 49 J

Stress Relieved 8 hrs. @ 1150°F (621°C) : 27 ft-lb, 37 J

Testing Temperature -60°F (-51°C)

As Welded 75% Ar / 25% CO2 : 26 ft-lb, 35 J

Stress Relieved 8 hrs. @ 1150°F (621°C) : 21 ft-lb, 28 J

That was about "weld metal" but HAZ is another issue here.
PWHT is necessary since it will restore toughness of the HAZ. I don't know why that manufacturer has told you that PWHT is not mandatory. When you have impact requirements, PWHT is essential for restoring toughness in HAZ of QT steels.

I have seen this issue before and by changing the process to Pulsed GMAW the problem solved.
Pulsed GMAW lowers the heat input and you have more control on transfer mode.
I recommend you to do the same. 

Good Luck

Ramin Kondori

Sr. QA/QC Engineer

SINOPEC

r.kondori@petroyada.com
+98-2123592322
+98-9132150320

On Tue, Jun 18, 2013 at 11:48 AM, Rudolf <rudolf_jude@yahoo.com> wrote:

Dear Mr. Ramin

Thanks for your valuable feed back. But am afraid I have checked with SSAB manufacturer of this plate and am told that PWHT is not mandatory unless the design calls for. 

However I agree with you regarding the transfer method.

The heat input has been very low as the welding speed was good, but. This too fast may also be the reason for insufficient slag covering over the weld puddle and exposure to atmosphere. 

Another possibility may be the low heat input the heat has immediately dissipated to the base metal and the plate has served as a heat sink thereby leading to a hard micro structure. 

Regards

Rudolf

Sent from my iPhone

On 18 Jun, 2013, at 2:03 PM, Ramin Kondori <raminkondori@gmail.com> wrote:

Dear Rudolf:

Of course it will fail...
This is a Q&T steel...
Along with heat input control, a 35 mm Thick Weldox-700 plate shall definitely require stress relief after welding.

But be careful...

The holding temp shall not exceed that of base metal during manufacturing.
do not apply stress relieve at 600, 620 or so...
Check the plate certificate and you will find the heat treatment parameters there, the PWHT temp shall not exceed the tempering temperature of your weldox-700 plate.

Try to keep heat input around 1.0 KJ/mm. Lower heat input is better.

You are using FCAW...

Not saying that it is wrong but sometimes in Q&T steels, you have to use pulsed arc or spray transfer to get good impact results and for this reason, MIG works better (in case you failed with FCAW).

Good Luck

Ramin Kondori

Sr. QA/QC Engineer

SINOPEC

r.kondori@petroyada.com
+98-2123592322
+98-9132150320

On Sat, Jun 15, 2013 at 6:02 PM, rudolf <rudolf.jude@gmail.com> wrote:

Dear Community Members.

We have done a PQR coupon for welding Weldox 700E. The material Thickness was 35 mm. Double V Groove Butt Joint. 2G position. Code AWS D1.1

The following parameters were followed

Process = FCAW

Electrode wire = Esab Dual Shield II 110 

Gas = 80 % Argon 20% Co2

Gas Flow = 20 lpm

Preheat to 103 C

Interpass temp around 150 C

Current Settings 

DCEP CV

Amps 200 amps 24 Volts for root pass 

Amps 180 to 160  24 Volts for hot, fill and capping.

The heat input recorded was between .8 to 1.5 kj/mm

The wire feed rate was 10 m/min

We did a charpy test on weld metal however it failed.

The results were average of 8 kj absorption at -40 C

At 1mm and 5mm from fusion line the absorption was 80 to 130kj

Intend to do a re charpy test @ -18 C.

Though the client has not specified Charpy requirements and specifications. Wanted to do it for future requirements if any.

Request you to please share your opinion,

WHAT COULD BE THE REASON THE CHARPY @ WELD METAL IS SO LOW, and in the absence of specific requirements for CVN what should be the impact values.

AWS D1.1 does not state any values for Yield strength above 355 MPA, but leaves the onus on the client to specifiy.

Please advise.

Thanks

Rudolf

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