8" super duplex

Date 03-14-2007 09:31

Sounds about right to me (10 hours) and if you had a series of fittings (flanges, tees, etc), might be more. IF it was a flange on a straight pipe on roller stands it could be done far below 10 hours, but as an average you'd be close imo.
hawk

By js55

Date 03-14-2007 13:31

A lot will depend upon your interpass requirements and whether or not you can use water to cool. If you have to wait upon ambient cooling it could take longer because once the BM recieves conducted heat from the weldment heat sink is reduced and cooling will take longer. If its a Super you do not want to cut corners on heat regime controls or someone will be cuttin a weld out before too long.

By welder5354 (**)

Date 03-15-2007 03:23

I understand that from some welders that the pulse mig process is a fast way to weld super duplex.
Have any of professional welders had the opportunity of using that process to weld duplex or superduplex with the GMAW pulse process. I understand it is a lot faster, then what happens to the heat input.

By aevald

Date 03-15-2007 05:56

Hello welder5354, a very basic and simple way to describe one of the possible benefits of the pulse process over standard GMAW would be to say that the weld can progress with a higher average amperage input and still be able to control the weld pool. From the theoretical end of this, picture a conventional GMAW process, particularly one that is being performed out of position, ie. vertical, horizontal, overhead, in order for this welding to end up with the proper profiles, penetration, etc. A much lower heat input would have to be used and in some cases this would not even allow for the welding to be performed correctly. Pulsing, in a simple explanation, allows part of the welding cycle to incorporate a relatively high amperage input and as the current transitions to the lower amperage input the puddle is allowed to freeze somewhat and the fluiditity of the pool is prevented from getting out of control and having excessive sag or other detrimental characteristics. Conventional GMAW at a theoretical setting of say 25 volts and 180 amps might yield a certain type of characteristic in a weld bead at a given travel speed. A comparably sized weld bead done with Pulsed GMAW might utilize a primary voltage of 32 volts and a background voltage of 22 volts which would yield an average voltage of roughly 26 volts and an amperage of say 220 amps(these are not actuals but somewhat illustrate the difference between the two processes), since this is pulsed it could very well give the operator a similar size weld bead, yet the travel speed might increase a considerable amount and the penetration might increase as well.
GMAW-P definitely has much more to it than the little bit that I described above. The various equipment manufacturers have done considerable work to make refinements and improvements to this process and almost all of them have come up with distinct variations that have led to both successes and failures. In the proper situation, there can be definite benefits to be gained from the process. I hope this has helped in some way.
I did want to include one other line of thought in regards to your comment on heat input. I believe Chuck Meadows could possibly shed the best light on this, however, I'm going to try to convey some information that I hope I have understood correctly. The duplex materials by the nature of their make-up, actually do better to some degree, with additional heat input during the welding process(to a small degree this could include preheats), the additional heat helps to minimize the formation of excessive carbide precipitants which can promote intergranular corrosion. If I got this part wrong, I'm sure that there will be plenty of others from the forum to correct me and I apologize before hand in that event.
Good luck and regards, aevald

By js55

Date 03-15-2007 13:57

Carbide precipitation is not as predominant an issue with duplexes in general and supers specifically because the carbon content is so low. The primary issue with heat input in DSS's is achieving as close to a 50/50 austenite/ferrite phase balance as possible. This means that the proper welding regime is more of a window of heat input as opposed to just minimizing the heat input in the manner of nickel alloys or super austenitics. Any additional heat input beyond that which is beneficial to phase balance threatens further partitioning of elements, for example Cr and Mo to the ferrite side and Ni and N to the austenite side, creating equilibriums that promote the formation of intermetallics such as Sigma, and Chi. Too low a heat input, besides circumventing phase balance may also promote the formation of CrN upon cooling due to the supersaturation of N in the untransformed ferrite phase which has been added to promote the formation of austenite.

By js55

Date 03-15-2007 13:59

N is also added to provide additional pitting resistance balance in the austenite phase since the Mo partitions to the ferrite phase.

By aevald

Date 03-15-2007 14:40

Hello js55, I knew if I threw a carrot out there I would get a very detailed and precise response. Thank you for the terrific clarification. Regards, Allan

By js55

Date 03-15-2007 14:56

I look forward to Chuck adding his comment as well. Duplex though quite easily weldable in most instances (if the proper procedures are followed), the metallurgy well estalbished, is still complicated to understand fully. The more input the better I say. Even if we've heard this stuff before. The Mantra will help it stick.

By chuck meadows (***)

Date 03-18-2007 00:25

Jeff and Allan,
You guys pretty much summed it up. I just got back from a bass tourney on famous Lake Fork here in Texas. Please show respect and don't ask me how I did...LOL..Y'alls answers were right on...

By welder5354 (**)

Date 03-18-2007 07:05

Thanks guys for all the info on the welding of dupex steels.
A few months back our facility had a welder and inspector do a procedure
on a duplex pipe for a contractor. Every time the welder stopped to position himself
the inspector would make the welder wait for the weld to cool to about 150 deg c.
before starting the welding again. My interpretation is that the welder should be able
to complete one full stringer bead (including stops and starts) on the circumference
of the pipe before letting the weld cool to the 150 deg. c. Am i right or wrong.

By chuck meadows (***)

Date 03-18-2007 13:00

Even in the Duplex grades, it is normal to measure the heat input after a complete revolution, and the recommended interpass temperature is 150C. Of course, extenuating circumstances might dictate otherwise, but constant waiting on interpass temps can cause uneven austenite/ferrite balances.

By chuck meadows (***)

Date 03-18-2007 13:07

Guys, the heat input for Super Duplex is much more restrictive than regular Duplex.For Super Duplex the heat input should be between 13,000-38,000 J/in and for the regular Duplex it is between 13,000-64,000 J/in. This is because Super Duplex is prone to sigma at a much quicker rate than Duplex.

By chuck meadows (***)

Date 03-18-2007 13:12

With respect, I would be leery of using water to cool the Super Duplex. Too rapid of a cooling rate will not allow the austenite for form properly and result in a high ferritic HAZ. Using proper heat inputs and interpass temperatures will normally be all that is needed to achieve the proper phase balance.

By js55

Date 03-19-2007 13:30

W5354,
Interpass temperature is exaclty that. "Inter" pass. There is no code justification for stopping in the middle of pass to enforce a controlled temp.
However, there may be metallurgical justification. If this is indeed the case then it should be reflected in the WPS. If it is not reflected in the WPS then the inspector had no justification for the restriction, and was demonstrating his ignorance of code intent.
I have seen exceptions to this rule to a certain extent for SAW, or machine GMAW, or machine FCAW, when the weld will be continuously rolled in a 1G and there are thermocouples attached to a recorder. In this case once the interpass temp limitation is violated then you must stop no matter where you are in the weld, unless an inspector is there to verify that you have not achieved your pass completion yet. In this case the 'interpass' terminology sorta breaks down.
The additional problem here is that you cannot wait for the intperass temp to be violated. You have to anticipate the violation because the thermocouple will generally be attached about a 1/2 inch or so from the weld toe, so the temp will continue to rise as the heat conducts outwardly until it reverses itself from extiguishing the arc. If you don't anticipate you will forced to explain why you were in the violation range for so long.

By welder5354 (**)

Date 03-19-2007 23:03

js55, u r correct when u say there is no justification for stopping in the middle of the pass.
The inspector was concerned that the temp would go above 150 deg. The inspector should realize that in order to weld the pipe the base material has to reach the melting point of the material in order to weld any joint. After all those stops and starts the weld failed. I suggested to the inspector, if he wanted to minimize the heat input; to weld from 6-3; 9-12; 6-9 and then 3-12 respectively and then let the joint cool to the 150 deg before starting the next stringer bead. Would i be correct in giving him this advise? The pipe was a 6" sch. 80 duplex.

By js55

Date 03-20-2007 13:30

The thing about interpass temps (mins and max's) that many don't understand (whether its nickels, SS's, Duplex, Grade 91, CrMo's, etc), is that it is intended as a minimum procedure standard. You have to have some form of control, but it doesn't mean that all of a sudden if you violate your interpass that you have irreversible metallurgical damage. Especially considering that there is really a built in 'fudge factor' with the establishment of interpass temp recommendations (not to mention the fact that I am assuming your PQR didn't demonstrate stopping in mid pass). Or at least should be. Once again, I am certainlynot advocating the willy nilly violation of procedures, as my point on the WPS/PQR demonstrates, but there is no replacing knowledge and sound engineering judgment.
I'll now step down off my soapbox.