using DCSP for E6010 root pass

By welder_guy2001 (***)

Date 05-09-2003 01:53

it could be an error. If you've ever tried a cellulose rod on DC- you know it runs like crap.

By GOKHANYAMAN (*)

Date 05-10-2003 18:08

I do not think that is an error. Some welders, using E6010 electrodes with DC - . Of coourse its not as good as DC+, but its used.
The electrode manufacturer also advise the E 6010 with DC- or +

By George-kh (**)

Date 05-12-2003 07:07

gokhan
at least you agreed me. nobody believed to use DC-.
as I mentioned above the two companies suggest DC- just for root pass and DC+ for balance.
do you know why?

By Tim Buyle (**)

Date 05-12-2003 12:24

MMA welding :

DC+ or DCRP : electrode positive --> deep penetration, high dillution
DC- or DCSP : electrode negative --> low penetration, low dillution

So, for root welding DC- is often preferred to control the penetration !

By GOKHANYAMAN (*)

Date 05-12-2003 13:17

Tim,

I agree with you in that wiev.
Also, if the manufacturer advise to use DC+ or DC- and your PQR's mechanical results are satisfactory. then DC- can be used.
For pipeline 30" API 5L X 65 pipe root pass, E 6010 (Bohler) DC- using now.

Moreover, I have a question that what should be max. weld pass weave width with single pass???

By JTMcC

Date 05-12-2003 16:15

What is the wall thickness of your pipe? When the wall gets over .500", we generally go to a multiple bead cap when welding downhill. Going uphill with Ho Hi rod, it's however wide the welder can go and still look good and make X-ray! : ) Thats with the standard U.S. bevel of 60 degrees or a little more. What part of the world are you in and what type of bevel do you use?

regards,
JTMcC.

By GOKHANYAMAN (*)

Date 05-13-2003 10:23

jIM,

For Capping pass, I agree with you multiple passes are good. However My question is related filling passes except for cap passes.

I am working in Azerbaijan, in fact the stiation is that;

24" LTCS pipe with wall thickness of 33 milimeters and "V" type weld bevel with ~ 60 degrees. E 7018-1 electrode with UpHill position. So, What is the max. limitations for passes under cap (filling) 15..20.. or 25 milimeters.
As I remember (from ASME B31.3 may be) 3 times electrode diamater which used (for example, 4.0 mm electrode *3 = 12 mm, weld pass weave width). But I coul not find it now.
Asme sec . IX advised that weld pass weave width may be 2 or 3 times of electrode dia.
Related standards are ASME Sec IX and ASME B 31.3

Regards,
Gokhan

By JTMcC

Date 05-15-2003 16:29

Gokhan,

I don't know what ASME says about width of uphill 7018 pass, I thought someone would have commented on that by now. I don't see anything in API about it.
Is this a cross country pipeline or in plant piping?
What product will the completed pipe transport?
Just curious.
regards,
John

By George-kh (**)

Date 05-14-2003 05:00

Dear JTMcC
I’m not involved to this job now days; I’ve just studied OERLIKON and BOHLER catalogues.

By Tim Buyle (**)

Date 05-13-2003 06:55

I have some literature for you :

look at www.esab.com

follow the link "ESAB knowledge center" , look for handbooks ; you can download a 65 page handbook on pipe welding for free.

By George-kh (**)

Date 05-14-2003 05:05

Thank you Tim
I’ve down loaded it before and it neither explained about DC-, nor suggest DC- !!!!!!

And in your previous answer, you’ve mentioned that in SMAW, DC- has more penetration comparing to DC+. It’s true when using an electrode that can be used in DC- and DC+, E6013 for example.
But E6010 can be used just in DC+ and if you use it in DC- you will have a lot of spatters. These spatters are because of arc turbulence, in other words arc plasma jet is not concentrated and I believe concentration of arc has much more influence in penetration comparing to heat distribution (1/3 in plus pole and 2/3 in minus pole). An example is comparing plasma welding and TIG welding. Plasma has much more penetration just because of arc concentration.
What’s your idea?

By Tim Buyle (**)

Date 05-15-2003 10:02

The welding arc is a very complex phenomenon.
You should make a difference between an arc in wich metal is transported (MMA, GMAW, ...) and a true electric arc (GTAW).

Penetration, heat distribution etc. describing the GTAW arc is totally different compared to a MMA or GMAW arc. An arc in wich metal drops are transferred, there are also magnetic forces around the metal drops, causing penetration once they are projected in the weld pool !

In other words : you can not explain the difference in penetration between GTAW (DC- causes penetration) and MMA/GMAW (DC+ causes penetration) based on heat distribution generated at each electric pole.
If you want to know all details, look for welding physics handbooks !

There's even a contradiction :

(1) Tungsten will give penetration on DC- and will not melt
(2) a wire will give penetration on DC+ , but if you want a high deposition rate, you should make it DC- (wire melts, tungsten not) ...
Conclusion : it's all about physiscs , there's no such thing as a welding arc , every arc has its little differences resulting in strange conclusions.
Also generated gasses in MMA, shielding gas in GMAW will have an effect on the characteristics of the arc !

It's so complex to describe.
Stick to the rules of thumb and try something to raed about arc physics. I am not sure you will get any smarter ...it's very boring stuff.

By billvanderhoof (****)

Date 05-16-2003 05:03

Do you have a title and author to recommend?
Bill