Traditionally Uncommon Pipe Sizes

[2ndIntegral]

Hi All,

Could anyone lend some historic perspective as to why non-preferred (uncommon) pipe sizes are just that? The enduring tradition is that, for example, 1 ¼” (32), 2 ½” (65), 3 ½” (90), 5” (125) are indeed manufactured but are non-preferred and thus relegated to the “use only if you have to” decision pile.

The reason for asking is that line sizing and hydraulic analysis is slightly inconvenienced by the larger jumps in flow area. Skipping the “half” sizes on larger bores is less significant as the marginal increase in flow area naturally decreases with incremental increases in diameter. Quite the opposite for a jump from 4” to 6” whilst missing an intermediate 5”.

Are these pipe sizes uncommon due to tooling and jigging or simply rationalising of pipe options?

Regards

 

[pennpiper]

I think it would be very hard to determine why the "Odd" sizes became "Odd" and were dropped from common use.

Was there so little call for them because they were not made or were they not made because there was so little call?

I have a few antique technical books. One of them is a pipe and fitting catalog with prices published by the "Stockham Pipe & Fitting Co." dated June 1915. It lists flanged fittings in all the current standard nominal sizes from 2" to 16". It also includes 2-1/2", 3-1/2", 4-1/2" 5", 7" and 9". These last six being the "Odd" sizes.
You bought these fittings Faced and Drilled (for bolts) or Faced only (not drilled). A 6" Class 125 Flanged Cast Iron 90 degree elbow, faced only was $7.60 (US) and Faced & Drilled was $8.90 (US).

Today I think it would be rare to find ready quantities of pipe, valves, flanges and fittings in any of these "Odd" sizes. If you did find some of these items (or someone who would make them) I think the cost would be prohibitive. Certainly more than $8.90 each for a 6" flanged 90 degree elbow.

 

[unclesyd]

We use a lot of the odd sizes for jacketed piping in our polymer piping system. On our high throughput lines We use 5" sch 160 on the high pressure end to maintain a certain velocity in the transfer of the polymer. This is supposed to mitigate the production of a cross linked material, bad. We did use a OT of 3 1/2".
I can't ever recall any problem in procuring any piping material in CS.


pennpiper,
I've seen the catalogue you mention in the library at Stockham. I CO-OP'd at Stockham in the early 50's. At that time they still sold drilled and undrilled GI flanges.

 

[sjrfc2]

5, 7, and 9 NPS piping was still seen in late 50's early 60's in marine steam propulsion. Weight is a big deal for the marine plants. I came to the conclusion there was a max velocity and they'd use whatever size would get them beneath it since they took a penalty on weight going to the next larger size.