View Full Version : 7018 root
Are there situations where a 7018 root pass in pipe would be used, or where a code would call for it? Thanks for any input.
07-16-2005, 03:18 AM
I don't have any pipe cert but I read in the Lincoln book that lo-hi rod can be used for the root if there is a backup ring in the pipe. BTW I have never seen a backup ring, so I don't know what it's supposed to look like. But it seems like it would cause flow restriction in the pipe. Maybe that's why I've never seen them use in oilfields or plants.
07-16-2005, 05:30 AM
I'm no expert but I have never heard of using 7018 for root pass, also never saw or heard of a backing ring being used in process piping. I have saw backing rings used on sectional steel pipe pilings. These were being installed under/ very close to an exsisting pipe rack so a reg pile driver could not be uesd.. The pilings were like 12" pipe welded together every 6 to 8 ft. and drove on down. I do not recall what rod was used for these pilings.
07-16-2005, 09:26 AM
A long time ago when we used to build power plants in this country, backing rings were allowed in certain carbon steel (A53) piping (3" and larger) fitups that had been poorly prepped for butt welding. The prep usually consisted of a 37.5 degree bevel that was done in the field. These were thin rings, but wide enough to cover the root gap. Sometimes they had 3 small pins at 120 degrees apart to assist in getting the gap set properly and the pins would then be consumed during the welding process. Depending on the weld procedure, the root pass for this joint would be either TIGed using E70S2 or sometimes with 6010 stick, then welded out and capped with 7018. I don't recall if the root was ever run with 7018 on these but its possible. These type of joints/prep were eventually eliminated due to the ring causing corrosion/erosion problems inside the pipe. I can remember looking at the NDE x-rays done on these joints and one could easily see the backing ring in the x-ray. This procedure was eventually done away with and replaced with strictly an open butt, properly prepped 37.5 degree joint. The root was then TIGed with E70S2 only and no more 6010 stick root passes.
Also, on some heavy wall, high pressure, high chrome content pipe joints, the procedure would sometimes call out using a "consumable insert". These joints were usually J-bevel prepped from the factory (in constrast to the 37.5 degree field bevel in the above) and the insert was placed in the gap at the root. The insert was consumed in the root pass which consisted of TIGing with either E80S2 or E90S2 depending upon the chrome content of the pipe and then stick welded out with either 8018 or 9018 accordingly. These welds were usually pre-heated prior to welding, interpass temperatures were monitored closely and then were stress-relieved after successful NDE x-ray.
I think I'm giving my age away with this post....... :p
07-16-2005, 10:06 AM
I have ran root 7018 with backup on tests.
07-17-2005, 12:19 AM
it can and is done...you can take a U69 pipe test with 7018 as a root..i think they refer to it as a "chrome" ticket
07-17-2005, 12:31 AM
Makes sense to me. With the backup ring, you can crank up the 7018, get good penetration and not burn thru as compared to using 6010 with no ring. Sound about right??
07-17-2005, 09:27 AM
Been welding pipe for 20 + years and i have have never tested with a lo-hi root. Once took a plate test and we used 7018 as a root but without a backing bar.
07-17-2005, 10:07 AM
Typically you wouldn't use a E7018 / E8018 etc in a OPEN root ( without backing ) because of the possibility of lack of fusion. By design cellulosic electrodes like E6010 / E7010 have a dig aggresively and relatively low depostion ( high depostion in a vertical down can get you in trouble ). By definition a E7018 has iron powder in the coating ( kinda like a Jet rod ) to increase deposition
The problem now and in the future is much of the new pipelines are made of much higher strength material. There are now more X80 ( 80ksi yield strength ! ) , X100 even X110 . In these steels, hydrogen in the weld deposit content is the kiss of death
The typical cellulosic electrodes like E6010 ( Fleetweld 5P+ ) have hydrogen contents of 30 to 50 ( units are ml / 100g of weld metal ) . A typical low hydrogen stick electrode is 2 to 8 .....waaaaay less ). These new pipeline steels require low hydrogen deposits
This problem has led to the development and more use of low hydrogen root electrodes. One such electrode is the Lincoln Pipeliner 16P ( which is a E7016....a E7018 without the iron powder to reduce the deposition ). These electrode are designed to run vertical up ( vertical down use can lead to lack of penetration )
This has also lead to more use of MIG ( yes even in the field ) in the root because MIG by nature a low hydrogen process and handles open root welding well.
BTW the reason for the backing ring is not to crank up the amps to ensure good penetration compared to an open root, but rather you can now open up the gap / feather the edge to ensure you get to the ID of the pipe. Obviously if you just open up the gap without a backing ring using a stick electrode you would end up with more metal inside the pipe than in the joint. This is where MIG type processes lends itself well to excessive gaps . Typically if you are using backup ring, you can open the gap equal to the diameter of the electrode and most often with a feathered edge
Conclusion ( finally ! ), low hydrogen electrodes are used with a backup ring . Without a backup ring, a typical low hydrogen like a E7018 is not a good idea. The exeption to this rule are the low hydrogens that are designed for open root pipe welding...which are much harder to find
Truth of the matter is most pipe that is welded you don't really need a low hydrogen electrode anyways so why not just use the proper electrode for root pass....a E6010
07-17-2005, 12:38 PM
07-17-2005, 01:04 PM
[dsc] Here are back up rings for pipe. Smaw electrode 7018 for the root. If you need any more questions answered let me know i will help you. Hope this helps
07-17-2005, 02:55 PM
I have done pipe tests where your root pass was done with 7018 and the pipe was held at a 45 degree angle when doing the test.
07-17-2005, 05:05 PM
Jay, are the pins to keep gap between the pipes? Whats the rule for what the gap should be?
07-17-2005, 05:25 PM
Not trying to answer for the guy but I was told 1/8". Pipe must be beveled down to 1/8" at a 37 degree angle, gapped 1/8" and welded. Thats what I taught to do is what I do when I practice.
07-17-2005, 05:31 PM
For all sizes? Or is there a formula or chart?
07-17-2005, 05:39 PM
I'm pretty sure. I think it all depends on what the project calls for. Maybe different welding standards for different pipe. My pipe fitters book says that there has to be a 1/8" gap though. Maybe 3/32 - 1/8". I'll have to check.
07-17-2005, 06:25 PM
many many coupon makers feather the edge to a point and the welder will grind back the landing to whatever he likes....some use next to no landing and keep the gap close...some may go heavier on the thickness of the landing and make the penetration gap larger......answer...welders choice..so long as the bend is good in the test..do whatever turns your crank
07-17-2005, 09:04 PM
Open butt v with 7018 root is used a lot more in the Boilermakers than in process piping. I've never taken one but I have friends who have tested on it. It's much more common in Europe from what I hear.
The boilermakers that use it regularly say it's not bad once you get the hang of it.
07-17-2005, 10:39 PM
Ya,, I ran one like that a long time ago,,, maybe 20+ yrs. I am trying to remember the details but I think it was downhill root???. As I recall it was for Chicago Bridge and Iron anf despite the name they were more of a boilermaker outfit, tanking too and it was for some factory repair in a paper mill.
07-18-2005, 12:24 AM
Mike c the 45 degree test is the 6g test. Tom the gap is one GTAW 1/8'' for the gap for practise bent as an l in the bevel and taped on one side to the pipe. Then you tack pipe inbetween the tabs and make sure the pipe lays even over the other pipe and not lean more on one side than the other when you tack inbetween the bevels. When you tack inbetween the tabs you do one side and then straight across and tack the other side, like a criss cross pattern. Then you take the tabs and break them off. Hope this helps if you need any more questions let me know
07-18-2005, 04:42 PM
Been a long time since I was involved with that type of welding...
Depending on the specific weld procedure and the criticality of the specific joint, they wouldn't let us run stick on the root pass at all. We had to go with TIG (E70S2) on the root. They didn't want any of that 60k psi material in the weld. They would allow us to weld the root only and then would NDE/Xray the root to ensure all was ok before allowing it to be sticked out w/ 7018, then xrayed again when finished. I remember if you busted out more than a couple of times, they'd terminate ya.....
07-22-2005, 07:03 PM
I used to weld 70 80 9018 open root in a code shop all the time 7+ yrs on aircooled heat exchangers all the piping and headers were all open root all code work all x-ray or ut all position weld always left a beautiful crown on the i.d. all welding was done uphill .
07-29-2005, 12:18 PM
We certified for a project in South Africa on a recovery boiler. These were window welds and the window was supposed to be welded in with a E7018 root and fill. We all tested and certified, flew over and ended up using GTAW instead.
WIndow welds described (http://www.weldinginspectionsvcs.com/WindowWelds.htm)