14 Replies Latest reply on Sep 20, 2017 1:47 PM by Edward Poole

    How to denote tapered pipe thread engagement

    Kevin Andrews

      I have a flange that I have designed to mate with a 4" male NPT (tapered). I have never had to designate anything other than standard threads before, so I am at a loss here. I had a simple callout notating " 4" NPT TAPERED " - my co-engineer marked it and said that I needed to indicate thread engagement as well.

       

      Based on this website: Normal Engagement Length of NPT Thread in Inches (A) - Technical Reference - Technical Literature - JGB Technical Inform…

      My engagement should be 1-1/8". However, when I look at previous models with similar design (same size NPT), they are seated at 7/8" - as well, my design has the unit seated at 7/8" as well.

       

      I know that this is really more of an engineering question vs. a Solidworks question, but I feel pretty sure that some of you are engineers (like myself) and can help answer this question.

       

      Then, just to keep it Solidworks related...how would you notate that on a drawing?

        • Re: How to denote tapered pipe thread engagement
          Kevin Andrews

          OK - I found one part of the answer (the main engineering part). The Machinery's Handbook states that the standard engagement length for the 4" NPT is 0.844" - which is over 1/4" different than what the previously shared website states. I went with the website because that is what my coworker uses.

           

          But still....how do you call it out on a drawing? Properly...

            • Re: How to denote tapered pipe thread engagement
              Newell Voss

              thread engagement is generally a standard indicated by your pitch callout and therefore does not need to be spec'd on your print.

              you are reading the chart wrong or your co-engineer is wrong. engagement and usable thread are different. since the tap is conical, eventually the thread will wash out to the point that it will not hold. a 4" pipe tap will generally have around 7/8 engagement based on a 8-pitch tap. It would display as "4-8 NPT".

              add it to your model using the hole wizard, then in your print use the hole callout feature and see what it gives you.

                • Re: How to denote tapered pipe thread engagement
                  Kevin Andrews

                  We have had issues where engagement was all over the place. For instance, the flange that I am using requires a 4-8 NPT. We have used similar flanges with the same thread and have had engagement happen at different points. It just so hapens that this engagement is critical for upper component mount holes...if that makes any sense.

                    • Re: How to denote tapered pipe thread engagement
                      Edward Poole

                      Kevin, yes, an unfortunate side effect, they'll never line-up perfectly...ever! your only choice would be to use a really good sealant that works with the medium you're conducting and spec the length of engagement for repeatability.

                        • Re: How to denote tapered pipe thread engagement
                          Kevin Andrews

                          Fortunately, and as I have noted above, I did find the answer I was looking for. And the supplied website was correct: for a 4" NPT, the engaged length is 1-1/8". This is the "final" engaged depth that I need.

                           

                          The Machinery Handbook gives a "hand tight" dimension (L1 if you look on p. 2009 of the 30th edition). Then you would go 1 to 2.5 turns past that to get it nice-n-tight.

                           

                          Unfortunately, I talked with our shop guy. He says they go "hand tight" and then, "we tighten the shit out of it"...I don't think "tighten the shit out of it" is a measurable torque value..but it is a common setting on these guys here.

                           

                          This is why we specify the full engagement depth. Then, if they "tighten the shit out of it", it will, more-than-likely, cause some damage. Then they have to pay for what they have destroyed. They usually only do this once or twice...(from what I have heard)

                            • Re: How to denote tapered pipe thread engagement
                              Edward Poole

                              I love the response...boy, I've heard that more than once LOL!!!!

                              • Re: How to denote tapered pipe thread engagement
                                John Stoltzfus

                                Kevin Andrews  wrote:

                                 

                                Fortunately, and as I have noted above, I did find the answer I was looking for. And the supplied website was correct: for a 4" NPT, the engaged length is 1-1/8". This is the "final" engaged depth that I need.

                                 

                                The Machinery Handbook gives a "hand tight" dimension (L1 if you look on p. 2009 of the 30th edition). Then you would go 1 to 2.5 turns past that to get it nice-n-tight.

                                 

                                Unfortunately, I talked with our shop guy. He says they go "hand tight" and then, "we tighten the shit out of it"...I don't think "tighten the shit out of it" is a measurable torque value..but it is a common setting on these guys here.

                                 

                                This is why we specify the full engagement depth. Then, if they "tighten the shit out of it", it will, more-than-likely, cause some damage. Then they have to pay for what they have destroyed. They usually only do this once or twice...(from what I have heard)

                                Awesome terminology from the guys putting their all into it..

                                 

                                With the pipe tap being tapered and all, there is another important element on have tight fitting threads and that depends on the sharpness of the tap and die, yeah you can crank it up and tighten the crap out of it, but if the threads galled and rough the fittings could still leak..

                                 

                                Made me think when I was younger, my Dad would always ask, is it tight, yes Dad it's really tight, he'd always say, go one more revolution..

                      • Re: How to denote tapered pipe thread engagement
                        Edward Poole

                        I use a mate plane tied to the length of engagement, you could use the mate dimension to call out the depth of engagement.

                        • Re: How to denote tapered pipe thread engagement
                          Christian Chu

                          Here is my quick ref.

                          and you can find all your needs in the machinery handbook

                          and use that info. to model you parts

                          • Re: How to denote tapered pipe thread engagement
                            David Matula

                            I would download the link below....and this catalog comes in handy for pipe. 

                            Hackney Ladish, Inc. - Catalog 55

                             

                            also the call out on the parts is usually just a simple 4" NPTF OR 4" NPTM.  I USUALLY GO WITH THE NPT.  THE VIEW SHOWS THE MALE OR FEMALE..

                            the Tolerance on the machined fittings is inconsistent between who runs the machines cause one day they will go plus a thread, and the next guy will go minus a thread...and they will pass the gauge test.