NPT vs BSP

What kind of instrument?

How high is the pressure?

What is the pressurized media (gas, liquid, steam, etc.)?

Are there other fitting connections? Are they NPT or BSP? Try to standardize.

Hi

Instrument shall be mass flow meter with 1/4" NPT Thread

pressure shall be 20 Kg/cm2

Medium shall be H2 Gas

If the instrument is 1/4" NPT the fitting must be the same.

NPT and BSP are different. The thread form are different, NPT is deeper. The threads per inch are also different except sizes 1/2" and 3/4" (both 14 TPI) so with those sizes you might get away with male BSP in female NPT, but I wouldn't risk it.

In USA NPT , all over the world BSP .

no difference, the main concern is sealing mean, and a NPT male to a NPT female , and a BSP male to BSP female , there is one more distintion , NPTT and BSPT , the "T" mean Taper.

Either will be fine since, apparently, there are no requirements or specifications on this job.

Surly you would have included this information in your request for enlightenment.

Why don't you just ask all your questions in one thread?

Most of the plants I visited, use NPT. Check Schwagelock and Gyrolock connections. Both will do the the job BSP and NPT, but as far as I understand NPT is abot the standard for instrumentation. Use 316L 1/4 O.D. and apply the correct handling.

Both makes use a ferrule system that is designed for this work.

He's using a "Siemens Make MAS 2100 with 1/4" NPT process connection."

I think he doesn't understand a lot about the application and the threads he has to work with.

See Mass Flow Meter Installation

in both NPT and BSP the 1/4" refers to the inside diameter.

Correct for the thread side. The pipe (or tube) side however, ALWAYS refers to the OUTSIDE DIAMETER.

Tube sizes do refer to O.D.; pipe sizes do not, until 14" and over.

1/8" pipe = 0.405 o.d.
1/4" = 0.540
3/8" = 0.675
1/2" = 0.840
3/4" = 1.050
1" = 1.315
1-1/4" = 1.660
1-1/2" = 1.900
2" = 2.375
2-1/2" = 2.875
3" = 3.500
3-1/2" = 4.000
4" = 4.500
5" = 5.563
6" = 6.625
8" = 8.625
10" = 10.750
12" = 12.750

That is my understanding also.

... and for a given pipe size, the actual ID will depend on the pressure rating of the pipe.

For those not educated in the US, the distinction between tube and pipe may be difficult, especially for those having English as a second language.

There was a fairly long discussion of that here on CR4 not too long ago...http://cr4.globalspec.com/thread/77305

That is correct. We (in Europe) refer normally to pipe when metal and tube when flexible like PU, PE or PP, but different from e.g. a rubber hose. That must be a culture thing. English is no my native tongue. Sorry for that. Also thank you Tornado. I am learning every day.

There is no reason to express sorrow that English is not your first language! In fact you should be proud that you write English as well as you do.

The difficulty becomes even greater when spoken, and dialects become more obvious. I have no difficulty communicating with one British member of CR4 in writing, but have to pay really close attention to communicate with him orally, as I have done on several occasions.

I have not had the opportunity to speak directly with any CR4 members from India, but judging by my experiences with help desks there, I find their dialect of English extremely difficult to understand when spoken, while there is very little problem when written.

The history for these naming practices is perhaps murky. Hose is based on i.d. (at least in U.S. usage); other plastic tube such as the PU, PP, PE you mention are based on o.d.

Although pipe is named by (nominal) i.d., it is actually manufactured to the o.d.'s given previously. This allows for a few standard sizes of taps and dies. For greater pressures, the i.d. of the pipe decreases, while the o.d. of fittings increases. So at least the scheme makes sense, even if it seems weird at first.

Hi,

As a previous writer stated BSP and BSTPT are different and BSTPT is the equivilent of NPT. i.e it is a taper thread. Europe no longer uses taper threads on pipes etc. It is a poor system and relies on brute force. I would go the parallel thread route which in the states would be SAE. I doubt that you can get BSP in the states. I believe the parallel thread option is far superior no matter what the pressure.

Oliver Dunthorne

Just to correct your statement regarding the use of taper threads in Europe. Taper male treads (pipe ends etc) are used extensivly in Europe and the rest of the world. Correctly cut threads of either standard seal equally well. The choice is normally down to the local standard and how it is applied. Equipment exported from the USA tends to have pipe threads to the NPT standard regardless of the approved standard in the in the country of use. For example any gas fired plant imported into the UK with NPT threads shoukld be flagged up as "not to current standards" and would require a huge amount of paperwork and testing before the plant could be issued with a Certificate of Incorportation as required by the Provision of Work Equipment legislation.

If the OP is using an insertion meter he will be able to get the correct mounting adapter to suit his local standard thread which should probably be an NPTT in the USA and BSPT everywhere else. However he has already stated that he has an NPT thread so that is what he has. The absence of a T (taper) in his description suggest that it is likely to be a parallel thread and will require a suitably machined face on the mating fitting with an appropriate gasket or crush seal.

I assume he is going to mount the meter through an isolation valve (ball valve) to allow the meter to be removed for calibration etc without closing the line down as we would expect in the UK & Europe. The adapter should allow the meter measuring tip to be positioned in the meter manufacturers recomended insertion depth and facing the right way. As mass flow meters are basically hot wire meters orientation is critical.

I just checked briefly with one if my usual suppliers, and entering NPTT into the search field brings up only NPT. In my experience there is no such thing as an NPT thread that is NOT tapered. Double negative => All NPT threads are tapered. Please correct me with reference if I am mistaken.

From Wiki:

The taper rate for all NPT threads is ¹⁄₁₆ inch per inch (³⁄₄ inch per foot) or ³⁄₄ in/ft (62.5 mm/m) measured by the change of diameter (of the pipe thread) over distance.

I stand corrected. I assumed wrongly that the NPT standard was similar to the BSP & ISO7 standards where the taper & parallel threads are covered by the same standard.

That raises a question with me. The use of a taper male thread into a parallel female thread allows a degree of flexibility as to where the fitting tightens up thereby allowing tees and elbows to point in the right direction. With a taper/taper joint they tighten up were they do. How do you deal with that in the USA?

The pipes and fittings do flex somewhat, but with Teflon sealing/lubricating tape there is considerably more leeway in mating tapered fittings. Especially with brass fittings, it is nearly always possible to add a little more torque to get it pointing in the desired direction. I think somewhere in the distant past I have broken a pipe or fitting, but not for many years. Ocassionally, I have disassembled a joint and added a couple extra layers of Teflon tape to make it tighten a bit sooner.

I don't recall ever attempting to mate a tapered thread to a parallel one.

I have worked with about everything that has been used for instrumentation in Europe and the Middle East. Every day one of our engineers is connecting a measuring device in one or other refinery, gas plant, or chemical plant. They hook up into the process feed and in their toolbox are only stainless steel and bronze NPT connectors. The pipes they are using are 1/4" O.D. and this comes in 2 schedules. Sometimes they meet metric 6 mm O.D. pipe, also in 2 schedules. NPT is tapered (and conical) and does not come in cylindrical applications, unless on special demand. (and this is asking for troubles, because the female/male don't always match) In one of the posts the difference between the tread is explained too. Just the cutting angle of BSP and NPT is different (that is why the depth differs too). And he is right about the TPI count too. Tapered threads can connect tight without washers, BSP not. They have a cylindrical collar to handle this or fit tight to the bottom of a chamber. It is recommended to use always teflon tape or a liquid sealant on the tread, especially for stainless steel to keep the thread intact. BSP for instrumentation you will find in old installations and musea. Ask the suppliers how much BSP is sold. Your statement is correct. In our career we only used about 10 tons of these (very expensive) fittings worldwide. Makes you will find in my earlier post. Parker is also a supplier.

Pipe less than 14" is not named by O.D. For instance, 1/4" pipe is 0.540" O.D.

Thank you. See my post No 17. You have cleared this up for me.

They still do, however your size will fit either. I thought I belonged in a museum too but this is an excerpt of their recent catalogue.

http://www.swagelok.com/search/find_products_home.aspx?show_results=Y&item=4a0cf15d-0fea-47dd-baa8-07eab186b16c

I went to the Swagelock catalogue as you suggest and selected a brass elbow that was designated 5/8" tube and 1/2"npt male. If you do the same and order one you will see that that the HOLE size of the tube connection is 5/8" and the BORE size of the 1/2"npt pipe connection is 1/2" (nominally).

Jim.

Just to confuse us in Oz, we are now metric with 1/2" bsp being called 15mm; yes 15mm. 3/4" is now 19mm. Again these are approximations of the BORE size of the pipe.

In my experience the TUBE connectors using compression fittings have non standard threads for the nut doing the compression. i.e. Swagelock nuts will not fit Screwfix or Parker fittings. Also the type of collar that gets compressed is subject to patented designs and is not interchangeable, not even with older fittings from the same manufacturer. But I guess you know more about these notions than I do.

There is also a distinction to be made between NPT and NTPF....and no, the F doesn't stand for female.

In an NPT connection, a sealant is still required. In an NTPF connection a sealant is not required as the cut on the male threads is a little longer which results in a deformation of the thread tips and a metal to metal seal. NPTF is typically used on fire protection piping in the US. NPTF male connectors cannot be resued.