Goto BH to know more.
This is a very good question. The quick answer is that they are inexpensive! This is the ONLY benefit.
Merchant couplings are manufactured per ASTM A865 and are intended for use on steel pipe joints in accordance with ANSI B1.20.1. Sizes 1&#;8" NPS through 2" NPS are straight tapped unless otherwise specified. Larger sizes, like 2 1&#;2" NPS and larger, are always taper tapped.
The only reason for straight (NPS) threads is the low cost! Machining straight through NPS threads on a parallel inside diameter is much less costly than threading tapered pipe threads (NPT) as they must be tapped from each end. This increases the production cost significantly.
The question as to whether a proper seal will form between a tapered (NPT) pipe threaded into a straight tapped (NPS) threaded merchant coupling is often asked. There is no question, NPS couplings are less likely to form a watertight seal. Tapered threads seal better! The reason they seal better is because the threads seal on a much greater contact area compared to straight threads which stay the same width throughout, reducing the contact area between the mating parts.
Many consider merchant couplings to be little more than thread protectors. Merchant coupling are most often used to join pipes together in non-pressure related applications such as structural railings. While some choose to use them in low-pressure piping, they are less than ideal and typically they will not stand up well in situations where high pressure is involved. For this reason, merchant couplings have chamfered ends which not only help start the threading, but also are helpful for the welding of the connection when required. Depending on the application they may be required to be welded together after they are fastened to a pipe to ensure a positive seal.
The reason we offer NPS merchant couplings is due to the demand for low cost merchant couplings which are the industry standard.
Yes and no!
In steel up to the 2&#; size the answer is no!
In 2-1/2&#; and larger sizes &#; yes.
We do supply our ½&#; through 2&#; 304 and 316 stainless steel merchant couplings with NPT tapered threads.
https://boshart.com/product/merchant-coupling-3/?attribute_pa_size_size=2_size
https://support.boshart.com/are-merchant-couplings-the-same-as-wrought-steel-couplings
https://support.boshart.com/what-is-the-pressure-temperature-rating-for-your-series-gmc-blmc-blhmc-merchant-couplings
https://support.boshart.com/making-npt-connections
12:23 AM
is the standard cutting die with a 3/4-inch taper per foot (1 in 16) requirement + the FPN note referencing the ANSI/ASME B.1.20.1- an NPT (national pipe taper) as found on a typical plumbing threader/die or is it an NPSM (national pipe straight mechanical) which usually has to be specified + special ordered? should conduit threaded in the field have a taper thread or a straight thread? factory threads on conduit look tapered to me. i have heard NPSM (straight thread dies) also called conduit dies ; but is this really true? thanks
Re: NEC article 346-8 reaming + threading
12:47 AM
The standard thread for connecting conduit to threaded fittings, is the same as that used by pipe fitters. The straight cutting die is for lock nut connections only.
The length of the taper thread must not exceed the dimensions as stated in the ANSI standards. A thread longer than the standard dimension is a running thread, and a code violation, when making threaded connections.
Two, or more threads exposed, indicates a loose connection.
12:41 PM
i was under the impression that conduit threads were made to drain...
npt is a taper thread....pipe fitters, who use black pipe and galvanized etc., i thought used a straight thread to acheive a seal....
02:12 PM
The tapered thread on black pipe, etc. allows for a greater surface area to be in contact between the pipe and fitting. B.I. pipe comes with a "thread protector" on one end that is straight thread but looks like a coupling. If they're used, they usually leak like crazy. (A plumber I know had to redo the gas on 5 complete houses when the guy he sent out came back with a whole box of unused couplings on his truck)
Re: NEC article 346-8 reaming + threading
11:11 AM
Hazardous Location work and fittings require tapered threads. These must engage for at least 5 threads and also be wrench-tight without use of locknuts. This helps to minimize spread of flame into the surrounding(explosive) atmosphere by cooling the flame to the point of extinguishment by the time it would work its way through the path of the threads. Running threads (Electrical allthread?) are not permitted in these applications.
Re: NEC article 346-8 reaming + threading
12:55 PM
Redsy,
All field cut and threaded conduit requires taper threads, not just those in calssifed areas. Also because 346-8, the only time running thread time you can use running thread is if it is "factory" cut.
Don(resqcapt19)
03:50 PM
Quote
Originally posted by resqcapt19:
Redsy,
All field cut and threaded conduit requires taper threads, not just those in calssifed areas. Also because 346-8, the only time running thread time you can use running thread is if it is "factory" cut.
Don(resqcapt19)
Thanks.I don't have much experience with running threads myself, but I have seen all-threaded nipples of various lengths used with double locknuts & bushings at each end. Would this violate 346-8, if they were used in accordance with 346-9(b)? Or only if they were field-made? Also,in what lengths are these nipples commercially available.
Re: NEC article 346-8 reaming + threading
04:36 PM
I think that all thread comes in 36" lenghts. They can be used with double lock nuts and bushings. I've seen them many times used between panels.
Don(resqcapt19)
For more information, please visit thread protectors pipe.
Re: NEC article 346-8 reaming + threading
11:55 PM
well I swear that a few years back we had a contractor do a igid pipe job for us and the pipe dies he used had 3/4 re and which stood for electric rigid and the box that the dies were in had for rigid electric pipe only not to be used for regular piping or something along that line and when you put them up aganist regular pipe dies they were different and when using a thread guage on them u could see the difference in the threads I have always understood that rigid conduit threads and regular pipe threads are different not much but some now am I wrong
Re: NEC article 346-8 reaming + threading
03:18 AM
Doc,
The code requires them to be the same. I am aware of at least two manufacturers of small threading machines for conduit that can only cut straight threads. They say that they are code leagle, but I don't see how.
Don
03:34 AM
>
B.I. pipe comes with a "thread protector"
11:05 AM
We have always used NPT dies for our rigid.
The only other dies that I am aware of are NPT for Stainless Steel which can be used on softer metals but not vice- versa. Are there also special dies for aluminuminmumum?
11:54 AM
DSpark
Yes, the term I was referring to was Black Iron Pipe, which is correctly called Steel (pronounced "Crawfishing"). The term Iron is used also in this area by even the plumbers and pipefitters, although probably incorrectly.
. Q: What does the abbreviation IPS stand for, and why is it not SPS?
The thread protectors need not have any more warning on them than the plastic thread protectors on GRC or IMC, which don't say "not a bushing."
I can't see how any installation could be speeded up by having a coupling on the end installed by the factory, as you'd need to pull it off anyway to apply joint compound.
...I'll now shut up before my crawfish becomes a full-blown lobster...s
[This message has been edited by electure (edited 05-22-).]
04:12 PM
Quote
Originally posted by electure:
DSpark
Yes, the term I was referring to was Black Iron Pipe, which is correctly called Steel (pronounced "Crawfishing"). The term Iron is used also in this area by even the plumbers and pipefitters, although probably incorrectly.
. Q: What does the abbreviation IPS stand for, and why is it not SPS?
The thread protectors need not have any more warning on them than the plastic thread protectors on GRC or IMC, which don't say "not a bushing."
I can't see how any installation could be speeded up by having a coupling on the end installed by the factory, as you'd need to pull it off anyway to apply joint compound.
...I'll now shut up before my crawfish becomes a full-blown lobster...s
[This message has been edited by electure (edited 05-22-).]
Our mechanic (mechanical)says that it means "iron pipe size" and is used to designate another material, such as PVC, as an equivalent in dimension to iron pipe of the same nominal size.
Re: NEC article 346-8 reaming + threading
08:57 PM
>
The thread protectors need not have any more warning on them than the plastic thread protectors
I can't see how any installation could be speeded up by having a coupling on the end installed by the factory, as you'd need to pull it off anyway to apply joint compound.
12:22 AM
Thanks. I've always wondered why a PVC fitting would have IPS written on it. I called my plumber friend and he couldn't answer that one. He did say that you can tell the thread protectors because they fit real loosely, and go too far on to the thread before they purchase.(I suppose this is an acquired "feel" like us tightening a wirenut). Other than that, his only comment was "It'll leak". Good thing I'm not a plumber 'cause most of mine leak anyway.
Re: NEC article 346-8 reaming + threading
12:37 AM
I don't believe that I've ever seen black steel thread protectors, and I sure hope I didn't!
IPS - iron pipe size - is one standard of sizing pipes, and is common for schedule 40 PVC. The size refers the inside diameter.
CTS - copper tubing size - is another standard, and is also used for CPVC and some small diameter polyethylene pipe which have thin walls. Of course, CTS copper still has IPS threads.
SDR - standard dimensional ratio - is used for piping, but I've never seen it used to refer to threads. Perhaps if we used SI instead of "English" measurements we could have one system?
[This message has been edited by Dspark (edited 05-22-).]
06:33 AM
I have heard the steel 'thread protectors' called merchant couplings but I do not know what they are used for. Most I have seen have ended up in land fills. Now I am curious why they are included. Typical #150 couplings used for plumbing are cast and have a raised band on each end in addition to the threads not going all the way through.I have also heard IPS called NPS, Nominal . . . Goes with NPT??
Redsy,
There are also dies for plastic pipes and coated pipes.
Phil H
12:37 PM
Iron Pipe or Black Pipe or Black Iron Pipe is correct terminology. I retract my crawfish.
The couplings that are sold here (even at Home Cheapo) have thicker bands around the ends, and 2 longitudinal bands.
. DSpark, what application have you that wouldn't require that compound or sealant be applied to the threads?
06:00 PM
>
what application have you that wouldn't require that compound or sealant be applied to the threads?
If you are looking for more details, kindly visit 2 axis cnc.