Pipe Threads

M

Thread Starter

Mark Hill

Hi all;

Anyone know the difference between BSP and NPT ?
Will I cross thread a BSP if I thread it onto an NPT?

Mark Hill
 
W
Here's a site for BSP pipe data:
"http://homepages.tesco.net/~A10bsa/bspgo.htm":http://homepages.tesco.net/~A10bsa/bspgo.htm

Here's a site for NPT pipe data including compatibility with other threads.
"http://www.dent-mfg.com/threadsizes.htm":http://www.dent-mfg.com/threadsizes.htm

The answer is, BSP is not interoperable with NPT.::

Walt Boyes
Contributing Editor
Flow Control Magazine
---------SPITZER AND BOYES, LLC-------------
"Consulting from the engineer
to the distribution channel"
www.spitzerandboyes.com
[email protected]
21118 SE 278th Place
Maple Valley, WA 98038
253-709-5046 cell 425-432-8262 home office
fax:801-749-7142
--------------------------------------------
 
R

Robert Holman

Mark,

BSP is British Standard Pipe thread. It is one thread more per inch than NPT. Since there is not a metric pipe thread BSP is used as the de facto metric pipe thread. Check the "Machinery's Handbook" for more details.

Regards,
R. Holman
 
Thanks Walt
I searched all over the place and couldn't find this much info. Looks like my two pipes aren't compatible.

Mark
 
Walt is absolutely right in saying that they are not interoperable. However, it is probably the most abused mismatch of threads in industry because both have the same angle and in some sizes the same pitch. This doesn't make them the same thread because the diameters, rounding, tolerances etc also have to be the same. NPT is a tapered thread. BSP includes tapered and parallel. Some people use the straight BSP sockets in sizes where the pitch is the same. This allows either NPT or BSP fitted instruments to be screwed into the socket and I have even seen it specified in some company standards. For example, using thermowells with NPT male threads in BSP female fittings. BUT.... what is the pressure rating under these circumstances? When a tapered male thread is fitted to a straight female thread it doesn't have the same engagement as tapered/tapered. In fact in the mismatch only
one thread will have full engagement. Beware.... the consequences can be a disaster.

Vince Dooley
 
W
I cannot emphasise enough what Vince Dooley wrote.

Non-interoperable means non-interoperable. If you do put NPT into a BSP socket, for example, and you have a bad result (as in somebody gets injured, or property gets damaged, or both) you should not be surprised when your insurer refuses to cover the damage claims.

Yeah, yeah, I know. Vince is also right when he said that this is probably the most abused mismatch of threads in industry worldwide. But just because lots of people do it doesn't mean that it works, or is safe.

I have seen it done a lot in hydraulic lines. UNDER HIGH PRESSURE! Dumb.

Don't do it. Don't let anybody who works for you do it, or anybody you work with either.

If you have ISO9000 certification in your plant, it is one of the easiest ways to get an informed auditor to flunk you.

Walt Boyes
Contributing Editor
Flow Control Magazine

---------SPITZER AND BOYES, LLC-------------
"Consulting from the engineer
to the distribution channel"
www.spitzerandboyes.com
[email protected]
21118 SE 278th Place
Maple Valley, WA 98038
253-709-5046 cell 425-432-8262 home office
fax:801-749-7142
--------------------------------------------
 
Thanks for all the helpful info Vince.

I don't think my problem is quite that critical.
No pressure involved.
I'm trying to mount an open channel ultrasonic transducer on a piece of pipe.
The transducer is reportedly fitted with 1" BSP threads (male I assume) and I'd like to thread it into a 1" NPT.

Your thoughts ?

Mark Hill
 
I have threaded NPT into BSPP, depends on the size. It will only go in two turns max. You cannot apply much pressure. It will leak and it is dangerous if you do apply pressure.

I have only done this for temporary testing purposes, as it sounds like you are doing. You also can't torque it very much or you will ruin the threads. The best solution is to look up the thread in a Machinist's Handbook and have some adapters made.

Good Luck.
 
Both threads will be tapered but the 1 inch BSP will have 11 threads per inch and the NPT fitting will have 11.5. BSP is very common in many parts of the world. It should be fairly easy to buy a fitting but if not maybe you could ask the meter
supplier to provide a matching fitting or ask them to provide the meter with an NPT thread.

Vince Dooley
 
Thanks Vince and Walt.

I'll ask the manufacturer to provide me with a nipple for BSP/NPT conversion.

Mark
 
Make some simple test I think it will work. I've got some expirience with 1/8 male BSP (parallel and tappered) and 1/8 female NPT it works.

regards
 
W
In that case, since it isn't load bearing, dope it up really good and thread it in a couple of threads until it binds. It will work.

Walt Boyes
 
BSPT is a british standard and a 55° thread angle NPT is a US standard and a 60° thread angle

they are 2 totally differant threads. anyone who tries mating these threads is very uneducated.
 
FYI although the threads do not fit each other in terms of the angles, from what little experience I have, only 1/2" BSP & NPT threads are compatible.
 
B
1/2" BSP and NPT threads are just compatible enough to get you into trouble.

In other words, you can take up about 2 turns before the threads lock - a slack fitter will say it's good enough and leave it. However, the result is by no means pressure tight and will blow - sooner rather than later if the pressure is high enough.

Bruce.
 
K

Kevın Smıth

> FYI although the threads do not fit each other in terms of the angles, from
> what little experience I have, only 1/2" BSP & NPT threads are compatible.

No sıze NPT thread ıs compatible wıth a BSP thread. the angle of the threads are 55 degrees for NPT and 60 degrees for BSP, plus the pıtches are dıfferent except for the 1/2' and 3/4'.
 
Not correct. BSP threads are parallel, BSPT threads are tapered.

> Both threads will be tapered but the 1 inch BSP will have
> 11 threads per inch and the NPT fitting will have 11.5. BSP
> is very common in many parts of the world. It should be
> fairly easy to buy a fitting but if not maybe you could ask
> the meter

>supplier to provide a matching fitting or ask them to
>provide the meter with an NPT thread.
 
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