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Drilling and tapping steel pipe for compressed air service

Just a Sparky

Just a Sparky

Hot Rolled
Joined
May 2, 2020
Location
Minnesota
I'm working up a bill of parts for a compressor discharge manifold. One of the unknowns I have is whether it is a safe and acceptable practice to drill and tap the wall of schedule 40/80 black steel pipe.

For context, this is a 1-1/4" pipe that will see a 100 PSI working pressure, 125-150 PSI pop-off. It would be getting 1/4", 3/8" and 1/2" NPT holes for pressure switch, relief valve, pilot valve, pressure gauge, etc. I could nipple a whole bunch of reducing tees together but that translates to added expense and screwing around in the form of trying to get all four to tighten up in the same orientation.

I can't find any engineering literature either in support of or opposition to this practice. Anyone in the know around here happen to have an authoritative 'go' or 'no-go' handy for this idea?

:reading:
 
I dont see a problem with tapping them in, but at 1 1/4" black pipe, 4 reducing Ts and 4 close nipples at home depot is like $30. Those wont be hard to line up when they are all together.

You could probably just purchase a manifold from supplyhouse.com. Or just purchase 2 crosses. That makes 4 ports.

Sent from my SM-G960U using Tapatalk
 
I don't think tapping into that diameter pipe is a viable option. The SOP would be a weld in tank flange, or at the very least..weld in the appropriate size nipple and screw your item into that. If you aren't adept at welding, reducing T's would work, although the finished product would look like hell! Nothing looks better than a welded 'tree'.

Your approach is not typical..most compressor installs would not require drilling and tapping into a pipe, ala-manifold. Have you given this a decent amount of thought?


Stuart
 
A lot of holes in line on samesideof pipe will weaken it a lot, and the wedging action of the tapered threads will act with the internal pressure to split it. Also the wall is very thin to expect enough thread engagement for a good seal. I would do as atomarc suggests and weld on nipples or half-couplings, or drill and tap a solid bar to make your manifold.
 
I think they use a flow drill for this sort of operation, it creates it's own boss on the inside of the pipe to support threads. For my shop I used stainless exhaust tubing with welded in half-couplings.
 
Just a Sparky said:
Anyone in the know around here happen to have an authoritative 'go' or 'no-go' handy for this idea?
Click to expand...

I'm no expert in strength of materials. But I would look at the wall thickness of the pipe and then look at how many threads you will
be able to get within that small dimension. Is it going to hold at your pressure setting? Or if it does have the strength to hold will
the small number of threads provide a good seal.

If you can get a stainless pipe instead of the black you won't be getting rust and scale in the pipe.
But if I remember correctly, I've seen manifolds made from aluminum square bars. Made one myself once.
 
Bondo said:
4 reducing Ts and 4 close nipples at home depot is like $30.
Click to expand...
And the chinese source guarantees them to leak when assembled.

I'd think like Ron and make a custom manifold from solid. It doesn't have to be flow through, you could only thread one end with the other blind.
 
Trouble is we're talking about a 1-1/4" feed-through manifold with enough spacing to accommodate pressure gauges, pressure switches, pilot valves, etc. That's a big chunk of metal. Several hundred dollars from anyone willing to make and sell a manifold that big. Also bigger than I care to try to drill, bore and thread on a Burke No. 4 & SB13 vs. $10/ea. for 4X US made reducing tees and some close nipples. Any kind of machined-from-solid manifold this size is going to be cost prohibitive.
 
I am sure there are charts for npt proof pull standards. For reference a 1/4 -28 in sch 60 is 2000 pounds. You have 100 x5(super safe margin) psi- over less than .25 square inches. You can run hydrolics level pressure and still be ok. Look at threaded zirk fittings and the pressure they handle.
Fine thread is stronger than nc.

Plastic push connects run fine with compressed air thru surgical tube. Coke soda fountains run high pressure co2- much smaller threaded manifolds holding that.

2 liter soda bottles can hold high pressure, with double lead thread plastic lid.

Be safe, not scared. 100 psi is not much (city water pressure is that).
 
Use one t and make a separate manifold .

This is our irrigation status panel, manifold inside, it is a solid with ports made as needed. This one is different from op.

Ours needed to monitor 5 things, 4 gages are standard so for mounting drilled and tapped a chunk of stock with port for gage and port for barb.

Mount stock and it holds gages, box hides the interconnecting hoses.

Op could do similar, bring a large line from his pipe via a t fitting then use either 3/4 pipe or make manifold to hold everything.

Allows for mounting in a "convenient place" where it can be better seen and serviced.View attachment 327477
 
memphisjed said:
Be safe, not scared. 100 psi is not much (city water pressure is that).
Click to expand...

I have seen an air pipe fail shooting across the shop, and an air/oil seperator blow up a few feet away from my face...100psi is Plenty to be scared about when cobbling a bunch of steel bits together. Pressurized liquid and pressurized gas will fail very differently.

Look at air ride parts possibly for a manifold configuration that would work at a reasonable cost? I'd find it hard to believe that you can't find some version of manifold that will work. Unless your budget is like $50 max...

Just a Sparky said:
One of the unknowns I have is whether it is a safe and acceptable practice to drill and tap the wall of schedule 40/80 black steel pipe.
Click to expand...

You can find lots of way's to justify something as "safe", but acceptable practice that is definitely not ime. Welded fittings would be the way to come off a pipe. I would say screw together a bunch of fittings to accomplish the goal is the best route if you can't justify more time or money for a proper manifold. Just my opinion.
 
memphisjed said:
I am sure there are charts for npt proof pull standards. For reference a 1/4 -28 in sch 60 is 2000 pounds. You have 100 x5(super safe margin) psi- over less than .25 square inches. You can run hydrolics level pressure and still be ok. Look at threaded zirk fittings and the pressure they handle.
Fine thread is stronger than nc.

Plastic push connects run fine with compressed air thru surgical tube. Coke soda fountains run high pressure co2- much smaller threaded manifolds holding that.

2 liter soda bottles can hold high pressure, with double lead thread plastic lid.

Be safe, not scared. 100 psi is not much (city water pressure is that).
Click to expand...


What city would that be? Water systems typically run 40-60 psi.
 
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