Uncommon Pipe Sizes

cmaverick

Hi all. I was just wondering what the most uncommon pipe sizes are that are generally skipped? For instance, I think 5" is skipped. What about 3"? Are there any others?

Also, WHY are some skipped?

Thanks!!

mattmia2

The are skipped because the change in area isn't that much so there would be many fewer cases where you could use the skipped size rather than having to go up to the next common size.

KC_Jones

5" isn't skipped we buy it all the time, same with 3" After 6" I believe it is every 2", so 6, 8, 10, 12 14, etc.

The only one I've heard about that used to be made as is essentially gone is 3 1/2"

EdTheHeaterMan

I actually remember purchasing 2-1/2" pipe for a steam boiler job in the 1980s. I made a 3" header and needed to adapt to the 2.5" existing main pipe. It ran for about 6 feet before it was reduced to 2" after 3 radiator takeoffs. no 3" x 3" x 2.5" tee available so I used a bushing. I think is was my second steam job completed by myself. (my design... I had a helper with me for the grunt work) I would never have taken the job if I did not take a Steam Seminar taught by @DanHolohan

Thanks Dan!

Mr.Ed

DanHolohan

Thanks, Mr. Ed! You made my day. 

JohnNY

We use 2-½" pipe frequently between boilers and Fire Suppression systems. It's a common size in the Weil-McLain I&O manuals and FS trunk lines. We also came across two boilers this year with headers piped in 3-½" pipe. We had a fabrication shop make transition fittings for us. In another case we had to buy a 3-½" coupling and a 3-½"x 3" bushing, two fittings $600.

EBEBRATT-Ed

2 1/5 is very common and so is 3, 4, 5, 6,

3 1/2" you still see in old buildings

I ran into 7" but only once in an old apartment building

retiredguy

I used to run into 3 1/2" and 7" pipe on occasion but only in very old buildings.

JUGHNE

The 1955 building I work on has 5-4-3 1/2-3-2 1/2-2 sizes.
Some where in the steam main are eccentric reducers for all these reductions.

JUGHNE

Also, I have wondered why 1 1/4" was developed....the only 1/4 size I have seen.
And why 21' in the standard length of iron pipe? Old truck bed maximum length?

DanHolohan

21' is the longest length that could hold the heat to produce a good weld along the seam while also allowing the pipe to form its shape.

EBEBRATT-Ed

The older I got the more I liked 10 footers.

You can order the pipe in special lengths. We used 40 footers on one job

DanHolohan

I'm thinking of the contractor who told me he had one end of a 21-foot length of pipe on his shoulder when the helper dropped the other end on the concrete. I forget what size it was, but I suppose it didn't matter at that point.

cmaverick

Thank you all for the responses! What a great group!

DavidBranch

I am a retired plumber. I was an apprentice and we had a job at a beer warehouse. It was my first day on the job and the journeyman had called in sick. The yard with all the pipe was fully stocked and all the trenches were dug. I was installing the no-hub cast iron waste pipe in the office area. I looked at the plans and figured out where everything went so I started to string out the pipe for the mains. I hauled about 20 lengths of heavy, cast iron pipe from the yard, up and over mounds of dirt then I got the fittings. I threw the first 4” wye into the ditch next to the pipe I’d just lugged in…and that’s when I discovered that cast iron pipe also comes in 5”.

DanHolohan

Good one, David!

rick in Alaska

I was under the impression that steel pipe came in 21 foot lengths because that is the length that would fit between 2 stories in a building. But, I am not sure about that.
As far as the guy dropping one end of a 21 footer, I guess it would depend on the pipe, and the guy. When I did fire sprinkler work, our pipe was schedule 10. I would carry two 21 footers on my shoulders without much problem. We laughed at the plumbers on the job who had three guys to carry one of their 4" pipes, until we had to help them once. They were using schedule 80 I believe.
Rick

EBEBRATT-Ed

There was a guy in the union with me and older than me he was really crusty.

There was a story about him I don't know if it's true (wasn't their) that he somehow got a 21 foot stick of 4" #40 on his shoulder and came walking across the job site with it. (i think that's like 215 lbs).

He started yelling a couple of guys went over to help. He wouldn't let them touch the pie he just wanted them to open a door so he could continue on!!!!

JUGHNE

But the odd 1 1/4" size?

The only explanation I heard of was from a long passed uncle who was talented in many areas including water wells.

He thought it may have been developed for well drilling. Virtually every shallow well jet pump and all windmill pump cylinders that I have seen use 1 1/4" pipe.

DanHolohan

This is from PMEngineer magazine (2006)

A question was put to the PM Engineer (PME) staff (one of SUPPLY HOUSE TIME'S sister magazines) asking how nominal pipe size came to be. Here is the answer provided by PME Editorial Director Julius Ballanco.

The person directly responsible for the nominal pipe size was a gentleman by the name of Robert Briggs. Briggs was the superintendent of the Pascal Iron Works in Philadelphia. In 1862, he wrote a set of pipe specifications for iron pipe, and passed them around to all of the mills in the area.

Realize that in 1862, this country was engaged in the Civil War. Each pipe mill made its own pipe and fittings to its own specifications. Briggs tried to standardize the sizing, which would also help the war effort. The pipe and fittings would be interchangeable between mills. This was rather novel in 1862.

The pipe standards went on to become known as the “Briggs Standards.” They eventually became the American Standards, and finally the standards used for modern day pipe.

The current ASTM A53 Steel Pipe Standard uses basically the Briggs Standard for pipe sizes 1/2 inch through 4 inch. You will notice that after 4 inches, pipe starts to get closer to the actual dimension used to identify the pipe.

So, you are probably asking, where did the sizes come from? Well, they were the sizes of the dies used in Pascal Iron Works. Briggs made everyone adjust to him. Hence, the name “nominal” pipe size came about, meaning “close to” or “somewhere in the proximity of” the actual dimension.

EBEBRATT-Ed

Interesting

I got another one.

Copper tubing is sold in nominal sizes type M, L, K for plumbing and heating. There is also DWV copper tubing for plumbing drain, waste and vent.

DWV, M,L,,K all have the same OD (for a given size) the wall thickness varies

In air conditioning & refrigeration the same tubing (yes, ac tubing is cleaned and dehydrated) is sold in OD sizes (which to me makes more sense and the way all copper should be sold)

so 1/2" nominal =5/8 OD,
3/4 nominal= 7/8" OD etc etc etc

So 1/2" nominal L tubing is exactly the same as 5/8 ACR except the ACR is cleaned and dehydrated.

And ACR has an oddball size like 3/4" OD (which I herd was something Carrier insisted on)

Just wondering why it all is not sold as OD tubing which would be less confusing

Did Robert Briggs get his paws into copper tubing as well? LOL

Don't think they were making standardized copper tubing in the 1860s


This has cause me issues in the past. I have sent apprentices to pick up soft copper tubing at a supply house. Depending on what the supply house stocks

If I want 1/2" nominal size the correct marking on the box is 1/2" nominal

But some supply houses stock ACR tubing and he comes back with 1/2" OD.

BenDplumber

As a young apprentice I was asked to take off a piping extension to a new wing being installed in a old school building. Popped a couple ceiling pads found what by sight i thought was a 4" domestic cold water main in the ceiling, no problem a couple of slip couplings, tee, valve and short piece of pipe....well it was 3 1/2" k hard copper. Hard and expensive lesson learned. Check the circumference.

JUGHNE

Or get a "Pocket Rocket" measuring gauge, well worth the investment.
Used to be sold here.

BenDplumber

Any number of ways to check circumference I use a wrap-a-round for welders and fitters. But I could always use a new tool!!

JUGHNE

The "Rocket" will read nominal iron pipe sizes from 1/8 up to 16".
Also give you the actual diameter of any round object.
Decimal to fractions conversion and also a 14" ruler when unfolded.

Nominal copper is always 1/8" over actual OD. 1/2" plumber copper is 5/8" OD.

This you learned with your 3 1/2" copper adventure.

BenDplumber

"Nominal" means just that. And just so we're clear the outside diameter "may" be the same however the inside diameter is different depending on schedule or " type" size. I learned a long time ago that the words " always and never" shouldn't be used in the pipe trades. As industrial pipefitter the internal diameters and wall thickness are the parameters we work from...with the engineers blessing of course. As EBEBRATT-ED said if you're looking for " icemaker" tubing at the supply house it " may" be called 1/8" or 1/4" depending on who you talk to.

EBEBRATT-Ed

@BenDplumber

We have all been fooled by a piece of odd pipe more than once I am sure.

3 1/2" is probably one of the more common"old sizes" that can screw things up. 5" can look like 6" or 4" from a distance.

Of course 1 1/4 & 1 1/2 " pipe can be tough. I never had a problem with those unless the pipe was painted, that always threw me off

problem is in the last few years since I got my last pair of glasses I can't tell 1/2 from 3/4 or 3/4" from 1" some kind of distortion or something lol

ChrisJ

What pisses me off is how in plumbing we go by ID, but in refrigeration we go by OD because, why not make life more interesting.

PC7060

CPVC is another tricky one. Needed 2” schedule 80 for a job and the supply house delivered 2” CPS.  Apparently they switch size standards over 1”.  Best part is the counter guy telling me 2” pipe is 2” pipe!  The manager had to get a grey haired retired plumber from another counter over to explain pipe sizing standards to them. 

pecmsg

EBEBRATT-Ed said:

Interesting

I got another one.

Copper tubing is sold in nominal sizes type M, L, K for plumbing and heating. There is also DWV copper tubing for plumbing drain, waste and vent.

DWV, M,L,,K all have the same OD (for a given size) the wall thickness varies

In air conditioning & refrigeration the same tubing (yes, ac tubing is cleaned and dehydrated) is sold in OD sizes (which to me makes more sense and the way all copper should be sold)

so 1/2" nominal =5/8 OD,
3/4 nominal= 7/8" OD etc etc etc

So 1/2" nominal L tubing is exactly the same as 5/8 ACR except the ACR is cleaned and dehydrated.

And ACR has an oddball size like 3/4" OD (which I herd was something Carrier insisted on)

Just wondering why it all is not sold as OD tubing which would be less confusing

Did Robert Briggs get his paws into copper tubing as well? LOL

Don't think they were making standardized copper tubing in the 1860s


This has cause me issues in the past. I have sent apprentices to pick up soft copper tubing at a supply house. Depending on what the supply house stocks

If I want 1/2" nominal size the correct marking on the box is 1/2" nominal

But some supply houses stock ACR tubing and he comes back with 1/2" OD.

3/4" refrigeration tubing is needed for Oil return to the compressor. If the suction line is too large there's not enough velocity to move the oil with it.

Erin Holohan Haskell

JUGHNE said:

Or get a "Pocket Rocket" measuring gauge, well worth the investment.
Used to be sold here.

We still have them here: https://heatinghelp.com/store/category/tools
Thanks!