The Importance Of Chill Rings

Date 04-07-2007 00:50 Edited 04-09-2007 02:46

Thats a broad question, without specific incidence and specific code, I don't believe anyone can accurately answer the nature of your question.
I'll list some codes below to draw attention to the need for specificity in regards to piping code questions. The statement of "any description makes
the question so broad as to be un-answerable.
Mil STD-278/Navesea S9074-AR-GIB-010/278 requirements for fabrication welding and inspection, and casting inspection and repair for machinery,
piping, and pressure vessels.
Mil STD-22 joint design

AWS D1.1 Structural Welding code (as are most of the D series for one thing or the other, however, I don't think your going to find much for piping in them)

ASME code for pressure piping:
B31.1 Power piping
B31.2 Fuel gas piping (withdrawn in 1988 replaced by ANSI Z223.1)
B31.3 Process piping
B31.4 Pipeline transportation systems for liquid hydrocarbons and other liquids
B31.5 Refrigeration piping
B31.6 Canned in 1974 it was originally intended to be chemical plant code, ncorporated into B31.3
B31.7 Nuclear piping: short lived, requirements now reside in Section III sub sections NA,NB,NC, and ND
B31.8 Gas transmission and distribution piping systems. CFR 49 gives this one force of law. As with the nuclear codes, you can get yourself put in jail for screwing with this one.
B31.9 building services piping. not particularly well known or used.
B31.10 Cryogenic piping, draft was incorporated into B31.3
B31.11 Slurry piping systems
B31.12 yet to be released hydrogen piping system code. ((edit) looks like this one will be in this year(/edit))

As you can see B31.3 is the monster of the lot, second to it is B31.1 in overall usage. If your building assemblies, your going to get into the MSS standards, and a multitude of others.

I am not trying to be a smart A## here, so please don't take it that way. If you can give something more specific in regards to the code I'll be glad to help you if I can.

Regards,
Gerald

(edit) Something that may help. When looking in the codes, refer to AWS A3.0 standard welding terms and definitions. As defined by AWS 3.0:
chill ring. A nonstandard term when used for backing ring.
It may help you when researching to insert backing ring for chill ring. (/edit)

By tom cooper (**)

Date 04-07-2007 09:28

Hi Gerald-
Thanks for looking over my question. I didn't intend for it to be a Code or a specification question - it was more of a "weld joint physics" question. When the problem came up, we happened to be working on a Mil-Std 22 P-5 butt joint. I didn't specify that before because I didn't think too many here would be familiar with that spec ( I got a rush just from seeing you mention it in your reply!), and also the nature of my question could apply generally to any of the piping Codes.
Best Regards and thanks again for you interest.
Tom

By CWI555

Date 04-07-2007 17:51 Edited 04-09-2007 02:47

Depending on the welding process: Only ESW, EGW, EBW, and LBW requires the backing to be essential or supplementary essential. I think there may be something in regards to material.

By CWI555

Date 04-07-2007 23:51

It's been a few years, but I dug out the spec (mil std 22 / P5 Joint) in question. attached is the details of a P5 Joint. Note that it refers to it as a backing ring rather than a chill ring. (removable ring vs P6 non removable)
I think that should answer part of your question. To the relevant standard, your looking for the wrong word, you need to be looking at removable backing ring.
I gather in no way that your inserts are consumable, however if so MIL-I-23413C will apply.
Assuming again removable, b31.3 for instance will tell you for severe service split rings are not allowed, and I believe the mil std's will follow suit on that one.
A lot changes when you go to p4 or p6. so I won't address those as you've denoted a P5. I believe the material is susposed to be compatable in all cases for dilution reasons. Trying to find the specific chapter and vs in mil std would take more time than I have so I'll refere you back to the ASME B piping series which does address the matter. (b31.1, b31.3)

Regards,
Gerald

By medicinehawk (**)

Date 04-08-2007 18:30

So..............a chill ring is a backing ring to removed after welding and a consumable insert is not????
Interesting topic and while I have used consumable welding rings which become a permanent part of the weldment, I have not used chill rings, but have seen them used on flue/exhaust duct work, but not on process piping. Can someone clarify all this as I am confused.
Thanks,
Hawk

By js55

Date 04-09-2007 14:41

Pinned 'chill' rings are generally NOT used as removable rings. The pins are also there to help you gap. The rings are intended to provide a backing for the root pass and are intended to stay put. They are generally used in carbon steel and though I have never used alloy chill rings I suppose they exist. It would be important for the chill ring to match the alloy of the BM. Though insisting upon an exact match is probably not necessary since dilution would be of little concern, and many BM's achieve properties through specific heat treats, grain refinements, etc., and many weld metals overmatch the BM anyhow. For example E7018 used on 60ksi min pipe.
Service and sound engineering judgment also have to be considered. You would not wish to use chill rings in, for example a high velocity fluid service.
I do not remember if B31.1 mentions backing rings specifically but they would NOT be recommended for almost all power services.
I would not use them in corrosive services, especially where crevice corrosion is a threat.
My opnion would be though that in general there is little difference between chill rings and matching BM backing if the backing doesn't pose any particualr problems.

By js55

Date 04-09-2007 14:44

And FYI, consumable inserts are intended to be fully consumed by the GTAW process without the use of additional filler metal, and are actually a root pass in themselves. They are the filler metal.
The come in a variety of designs.

By js55

Date 04-09-2007 15:05

Tom,
Keep in mind your WPS has essentially no service relevence, and neither do your backing rings. In other words, your WPS does not know what pressures, temperatures, or medium is involved. Its adequacy must be decided by sound engineering practice. And if your backing 'backs', it has served its function.

By 803056

Date 04-09-2007 20:45

I believe the terms "chill ring", "land" are simply a slang terms that has been adopted by pipefitters and others in the welding industry. The rings are no more and no less than simple backing. For the most part, they are left in place after the weld is completed.

The rings that are purchased are typically thinner than the thicknesses recommended by AWS D1.1 or MIL-STD-22D. The welders typically use lower amperage settings with the purchased backing rings (chill rings) to prevent burn-through.

Some piping codes require the procedure to be qualified with backing if it is to be used in production. In some cases, their use is prohibited as is the case with ASME B31.3 for high pressure service.

It is not the intent of the "chill ring" to cool the molten weld metal quickly. It simply acts as a dam to hold the molten weld metal in place until it solidifies. The mass of the backing would have to be substanial in order to provide any "real" chilling or quench affects on the weld puddle. Even the backing thicknesses recommended by AWS D1.1 and MIL-STD-22D are not massive enough to create any quenching affects.

The backing should be chemically similar to the base metal being welded to ensure the proper chemistry of the diluted weld in the root pass. After all, the chemistry is going to influence the mechanical properties and corrosion properties of the joint. Any dissimilar metals (chemistry) in the wetted area can result in galvanic corrosion. The fit should not leave any excessive "gaps" between it and the underside of the base metal to minimize the tendency to have problems with burn-through and slag inclusions if a flux is involved.

Best regards - Al

By js55

Date 04-09-2007 20:59

Al,
I always thought that the slang 'chill' ring had the potential for confusion. Sounds too much like heat sink chill devices. But you're right they do not do much as a chill effect. I remember welding, and testing, with the things many moons ago. The whole trick is not to burn though. You have to stay off em or you will blow a hole.

By 803056

Date 04-09-2007 21:12

Hello JS;

And no one likes a big nasty hole in the ring!

There's nothing like first hand experience when it comes to welding. You can talk about it all day, but if you've done it, you'll never forget it.

Al

By js55

Date 04-09-2007 21:24

Al,
LMAO!!
Yeah and there is no repairin those buggers either.
We'll, technically you can, but its not allowed. Blow a hole and you may as well grab your lunch pail, because your headin out the gate.

By tom cooper (**)

Date 04-10-2007 00:35

Gentlemen all,
Thanks for these ideas and information. I think you're 100% right that referring to these as "chill" rings caused us to assume more was going on with the heat flow than could be possible. Your point is well taken that the rings would have to be much heavier to provide useful quenching.

Al-
You mentioned "fit" only in connection with danger of burning through, BUT I was thinking we had to provide a tight fit to minimize oxides forming on the underside of the root (GTAW, A106 pipe). We came up with that conclusion based on our alternate requirement to use purging gas ONLY if we weld an open butt, never when we use the backing rings.
Any merit to this idea? If so, how tight is tight enough on a backing ring fit?

Thanks again.

By js55

Date 04-10-2007 13:28

Tom,
I'm not sure why you even bother with GTAW over a chill ring, unless I misunderstood you. You can go straight to SMAW or FCAW and not even mess with GTAW.
And if your welding carbon steel there isn't much point to purging, so I wouldn't concern myself with oxides either, unless of course there is something specific and demonstrated with your intended service that would cause them to be problematic.
As for tight, I would say that if the ring provides backup and your welders don't have burn through problems your good to go. The tightness of the fit is a welding functional issue. So if its working, its fine.

By 803056

Date 04-10-2007 16:00

Hello Tom;

Again, I can only speak from my experience and that is limited compared to some of the folks responding to the questions asked.

I have used the backing rings with SMAW, not GTAW or FCAW. The reasons are that the purchased rings are typically too thin for FCAW and not needed if GTAW is used.

The welder usually welds the root with a single pass. A gap between the ring and the bevel face and root side of the base metal increases the volume of weld metal needed to make the root bead. It requires the welder to linger at that spot to fuse the ring and to "fill" in the volume caused by the space between the ring and the underside of the base metal. As the welder lingers, heat is building up and burn-through rears its ugly head. A tight fit minimizes the time required to weld the two bevel edges and the ring and minimizes the chance of burning through the ring. The space also provides a void that can entrap slag between the backing ring and the underside of the joint. In some cases, the edge of the bevel is melted away and internal undercut can result, i.e., on the underside of the base metal.

Backing rings are not the best choice if corrosion is a major concern. The space between the backing ring and the underside of the base metal is ideal for crevice corrosion. As for oxides on the back side, there will be some oxide formation on the back side of the backing ring because there is no backing (purge) gas to prevent oxidation. Higher heat input due to decreased travel speed will cause more oxidation, again a good arguement to minimize any spaces between the ring and the underside of the base metal.

Best regards - Al

By js55

Date 04-10-2007 16:10

Tom,
An explanation of chill ring practice just doesn't get any better than Al's.

By 803056

Date 04-10-2007 20:25

Thanks JS.

Al

By js55

Date 04-10-2007 20:40

No sweat Al. You clearly have done more than your fair share of those %&#$ rings.

By tom cooper (**)

Date 04-10-2007 23:53

Whew!! This is just world class information on backing rings you guys have put down here. I searched many nights on the internet looking for this kind of stuff and came up empty every time. You should write an article for publishing. I think maybe spreading this interesting info and your experiences on the lowly backing ring could help a lot of younger folks out here.

Can you believe I have one last question - both of you guys have said we do not need backing rings with GTAW; Our guys say they have more control with GTAW in the root, then finish off with SMAW. What are we missing that you guys can easily weld an open butt w/o backing? Are you guys not leaving an gap between pipe ends when TIGing?

How many times can I say thanks, but thanks again.
Tom

By 803056

Date 04-11-2007 02:56

Open root using GTAW is performed thousands of time a day. The level of "quality" and the base metals being welded will dictate whether gas backing (purge) is required.

There are several methods used to weld open root pipe joints. AWS has several "Recommended Practices" that may be worthwhile to purchase.

One method is to utilize a root opening and root face that are approximately the same as the filler metal diameter. The filler metal is "laid" in the root and fused to each side of the root edge. Low amperage and a short arc are maintained with sufficient heat to achieve fusion. The gas nozzle (cup) can be "walked" to help control the weld puddle.

The other method is to use no root opening. The root face is reduced to about 0.03 inch. This works best if the pipe can be counterbored and machined to produce a U-groove. The welder fuses the root adding enough filler metal to build up a slight root bead. More heat, i.e., amperage is required to achieve the joint penetration necessary. Typically, 40 to 50 amps is sufficient to penetrate the 0.03 root face. I like this technique when a purge gas, usually argon, is used. The tight fit minimizes gas leakage and there is no "shrinkage" to contend with as there is when a root opening is utilized and the tacks are small. With a tight fit, the tack welds do not have to resist the shrinkage and contraction forces developed as the welder makes the root pass. Another advantage is that the tack welds do not have to be feathered by grinding. This technique is more expensive to prepare, but I recommend it when the welders have limited experience with open root pipe welding.

Good luck - Al

By swsweld (****)

Date 04-11-2007 03:11

Backing rings can be welded w/GTAW. It is much slower. SMAW is the most common process to use for quality and production. As stated earlier, a consumable insert can be used instead of open butt groove for GTAW process. One more tip with either choice of backing; all of the rings that I have used have a split. A good practice is to tack the split so that the welder doesn't blow through while performing the root pass. I always positioned the split approx 10 oclock to 12 oclock if welding 5-G so gravity helps with penetration. This is just a suggestion but tacking the split is necessary.
It has been 15 yrs since I welded a "chill" ring. Just a thought on where the term "chill" got started, it is possible that they were used on chill water pipes for cooling(Air Conditioning) purposes. They are typically low pressure systems.
We are doing three different preengineered preinsulated heating/cooling distribution systems at Fort Bragg, NC and two of them specify open butt welding(E-6010 and E-7018) is what we normally use although I have tigged the roots. But the last job we were awarded states in the specs that split welding rings shall be used for field joints on pipes above 2 inches to assure proper alighment, complete weld penetration, and prevention of weld splatter reaching the interior of the pipe. This is from the Army Corp. of Engineers. This is the first job using rings at Ft. Bragg. Don't know why they want rings all of a sudden. I thought they were detrimental is many situations, turbulance, erosion of ring over years. It is odd that pipe from one job ties into the other job that is not using rings. Specs are almost identical except for the ring difference and the fact that the ring job is 100% RT and the open butt job is 10% RT. It take more skill for the open butt root pass. Another section of the specs says that split rings may be used. This is Medium temp hot water pipe 250max psi. Seems like too much pressure for backing rings. Code is ASME B31.1 pipe is A 106/A 106M.
We will begin welding in about six weeks.

By js55

Date 04-11-2007 13:44

Tom,
I might add on the GTAW open root issue that my preferred method is to prep the pipe with a 'feather' or 'knife' edge, easily done either by plasma, oxy-acetylene, or abrasive methods. Gap slightly less than the diameter of the rod (and I mean slightly, since the gap will have a tendency to close up on you) so that you can rest the rod against the bevels (good for guys with less experience) and then just walk the cup over the top watching the puddle 'drop' or 'lay in" as it melts of the end, making sure to point the GTAW arc right at the edges of the bevel as you oscillate to ensure fusion.
If you watch a GTAW weld from the back side the puddle will swirl as the arc moves back and forth. You want that swirl to flow from bevel edge to bevel edge. Keep the rod at about 15deg from the tangent slightly tipping it up as you tie into your tacks. In fact, if you are unable to grind your tacks you can tip your rod to perpendicular, hold for a second at the tack start achieve great tie ins.
Slightly widen your oscillation as you tie in your tack because you will have a little more metal available now.
And as a tip for guys starting out(or even old hands); if your welding 5G, which is most common, don't close up your gap to the top on the first side. Leave about an inch or so from the top tack. Weld up the other side. Now you have a window you can shine a flashlight in to inspect your root. Then, when you close, light up on the top tack actually running downhill from the top. You can do this without requal for 15deg from top dead center, and your welder can turn up the current a bit and help ensure better fusion on a portion of the weld they may not be able to see once its closed.

PS: Ask as many questions as you need. Its no problem.

By CWI555

Date 06-28-2007 04:58

Interestingly enough, I had to look this up again and answered my own question. (old age=feeble mind) In effect Tom an article has been written here in the forum for anyone aware of how to use the search function. It's one of the more valuable tools superceded only by minds such as Chucks.

Regards,
Gerald

By tom cooper (**)

Date 06-28-2007 16:07

Gerald-
It must be a seasonal thing because I too am reliving some nightmares with backing rings. I can't find the article you are talking about. Can you post the link please?
Thanks