National Pipe Thread (NPT) Design Specs

The obvious question is how much pressure?

From a strength standpoint, I don't see a problem. That is my opinion, based solely on 50 years of being around mechanical stuff.

I don't know about code, but a deviation may be required to be signed off by an inspector or engineer.

450 psi is the test pressure. It's for a water tank.

Are 3/4" NPT steel plugs too expensive?

It's not a plug. It's an adapter that gets welded to various (7 - 86 gallon) pressurized water tanks. The tanks are pressure tested at 450 psi. Although working pressure is far less.

Please explain the purpose of this "adapter". How long is it, and where does the unfinished end go? Hopefully you're not going to use it to support the tank, nor are you going to bore a hole through it. It's much easier to use 3/4" inch steel pipe.

Yes, it supports the tank on the smaller models. Otherwise, it sits on a base and is plumbed to on the top of the tank.

The un-threaded end has a specially designed end for resistance welding it to the top of tank. It is actually cut from hex bar. I didn't mention it, so as not to complicate matters. But, I need a hex so it can be tightened with a wrench, so that people won't be tempted to tighten it by turning the tank, which could potentially break the weld. This is why I'm not using pipe; because of the hex.

My issue is that the hex called for is 1.062" hex (across the flats). This is an odd size, and therefore much more expensive. It also calls for a 1-1/16 wrench... or an adjustable wrench. A 1" wrench would be much more convenient, if possible.

The 1.063 hex is used, instead of 1.00" hex, because a 3/4" NPT has a 1.050 diameter at it's largest thread.

3/4" pipe also has a 1.050 outside diameter, but as mentioned, I need the hex for a wrench. Otherwise, I'd love to use pipe, and eliminate the boring out of the center.

Any creative design improvement suggestions would be welcome.

I feel this could be improved somehow, but I can't quite pinpoint how.

1.062" is not an 'odd' size; it's 27mm and from a brief trawl of pipe fittings 3/4" fittings are made from 27mm hex material so I would suggest that is what you use. If a job is worth doing, it's worth doing right

There are always allowances for thickness variation and corrosion in piping standards...The pipe material, the working environment and pressures, any coating processes, these are all variable factors....That's why pipe is sized for much higher pressure than actual maximum working pressure....and maintenance and inspection of the installation is required....

"Based on ASTM A53 Grade B or A106 Grade B Seamless ANSI 831.1, 1977 with allowances for connections and fittings reduces these working pressures approx. 25%"

https://ipspipe.com/wp-content/uploads/2015/06/Pipe_pressure_rating.pdf

What about going female...?

Yeah, I've considered that. She's very attractive, but the industry standard is male, coming off the tank.

I would try looking in a hydraulic fittings catalog. There are various types with hex flanges and the like.

It will all work out with a little thread tape or thread sealant. ??

Or will it?

I know I use 1-1/8" hole for a trace quattros pipe. A 1" would have me scratching my head.

..not sold on the idea. Test and get back.

Or.. send me a sample to test.

I AM Lookin for a good size second hand accumulator tank for my energy conversion project.

Any metal rod or pipe with threading, especially with coarse thread is most vulnerable for failures. In fact each 'V' groove, acts as a source of cut.

For cutting metal plates or structurals, before advent of machine cutting, a chisel and a hammer were used to make a 'V' shaped cut, and though the depth of such groove is much smaller than the width of the metal member, it was very easy to make it snap into two parts, with minimum force.

There was a stopper for a ratchet wheel drive, mounted onto the body, with a 1 1/2" diameter round bar, threaded into the female thread on the body, on which the moving stopper was moving freely. When some force was being exerted onto the stopper, due to some reason, the stopper was not engaging properly on the tooth of the ratchet wheel, and used to slip, with a large noise. Then I found that the axle, the 1 1/2" rod, was bent slightly at the exact spot, it came out of the thread, with a couple of threads, outside. I made a dozen such threaded rounds, and asked the workers to replace the bent rod. whenever such slippage occurred.

One night, I was called to the plant, to know that the ratchet wheel was slipping, and they had exhausted all the spare rods. Then, and then only, i made my brain work as to why that is happening. When I could diagnose the problem to be the threads remaining outside, i could get a solution too. There were a couple of bolts on either side of this stopper. I made just a half inch plate, fitted to the two bots on either side, and at the exact place, where the axle of the stopper was fitted, I made a hole of 1 1/2" dia, inserted the rod into it, and welded it to the plate. All this, I did it in the dead of the night, with the repair looking pretty shabby, with odd shaped plate, and poor welding done by me.

It worked for five long years, without any change, and there was never any slippage.

The point is, a 'V' shaped groove on any surface makes the material weak.

Nice story, welcome to the world of practical bodged engineering.

I don't know about codes for this, but I can tell you from practical experience that this won't fail IF IT FITS THE OTHER HALF OF THE CONNECTION.

We've got a couple of Ridgid 535 power threaders, which have adjustable dies. Very rarely will we just set them right at the indicated position and thread pipe- on a job we'll thread a piece, grab a box of fittings (which are never made in North America) and try it on a couple, and adjust the die to fit properly.

So, if the fitting seals properly with at least a full thread showing once tightened properly it will work (from my experience with up to 3,000lb fittings) on the smaller sized NPT fittings.

If this and IF that.

I was at a job where 3/4" IPT was being fitted with some new runny honey type of plumbers pipe thread compound was being used. It was easy to apply and set, but made a runny mess.. Complaints were voiced. It was easily cleaned up, but wasteful and messy compared to other products.

All was well except the union fittings that leaked a small drip because the fittings were treated and hand tightened while other work was being done. It was the runny compound that ran out of the well fitting union before it was completely tight.

After throwing away the big brand compound the unions were redone with something better.

I like and

it's not too thick or thin..

..aaand it adds a monster to the utility room which my parents definitely had.. still have in thiers.

Of course it will - that's what "too high" means, Mildred.