any welding experts out there

I have been welding for many years and I like welding something that is a bit difficult
when I am arc welding vertical I weld upwards as all the welding books say
I have been watching pipeline welding on youtube which is very interesting but the pipes are welded downwards so can anyone explain the difference
 
Usually just the cover pass is done downward, the root and buildup would be done in the usual upward way. The exception would be thin wall pipe or such
 
Not trying to deny it but how would that
work when hot gasses would rise? Just
puzzling to me
 
I am a Pipefitter pipewelder and pipeline welding is all done downhill from the root pass to the cap. They have used HPPE rod which they call "hippy" rod. I'm not sure what they're using nowadays. Downhill is usually faster than uphill welding. Most of the pipeline welds are X-rayed 100%.
 
When I was a Certified welder in an industrial setting we had specifications that called for all pipe in a horizontal position was welded vertical up, all passes. That was the spec we tested on and had to follow. That was 20 plus years ago
 
I don't know if I qualify as an expert at anything,but I have been burning rods for over 40 years and here is what I know. Some electrodes can be run downhill,some can't. All certified welds are made under a particular code. Procedures for each code are set up in the welding spec for that code.Most of my certifications are under the ASME pressure vessel code. The procedures for these welds states that weld progression will be uphill.Most pressure vessel welds are made with some type of low hydrogen electrode-7018-8018-9018 etc.Weld progression must be uphill for these electrodes because of trapping slag. 100% X-ray welds do not allow for any slag inclusion in the weld. Pipelines are welded under another code that is governed by another procedure and it allows for down hill progression. These welds are generally made with 6010 or 7010 electrodes that have a very light flux coating and can be easily run downhill. The x ray requirements for these welds are generally not a stringent as the pressure vessel welds also. Some pipeline welds are also now made with MIG, downhill. Speed is one reason for downhill. Probably can make 2 or three welds to one versus uphill.Downhill concentrates less heat in one spot and less warpage is another.
 
This is my experience as well. I have worked on and been certified for work on pressure vessels as well, but have never worked on pipelines. But I have read some about it on welding sites and what you said seems to be the norm. One thing I found very interesting is a guy from some European country, I don't remember which, who posts about pipeline work there and they use all 6013 rod, I believe on ac current. His work is something to see too.
 

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