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B31.2 Fuel gas piping (withdrawn in 1988 replaced by ANSI Z223.1)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)
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
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.
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.
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.
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