Extend Of Exposed Thread In Thread Joint Of Pipe 4

[mmbguide]

hello

Design Code ASME B31.3

We have threaded joint in Galv. pipe 6" but, about 2 centimeter of thread of pipe remain out of coupling and assume that some of them shall be sea welded and my concern is exposed thread of pipe. what shall I do? can I grind the thread to remove exposed thread or is not necessary? if seal weld had been required, is it necessary to grind all exposed thread of pipe?

thank you all

 

[moltenmetal]

Can't view your pictures.

Using NPT threads beyond 2" NPS is rare. I have some 8" NPT threaded flanges in my office, which were removed from a burner assembly we received. They were a shock, as I'd never previously seen an NPT joint beyond 3" NPS, and that's in 28 years working with piping professionally.

You can't seal weld galvanized pipe...not without removing the zinc first. And even if you do this, you will likely damage the zinc in the bore where it matters most.

The likely mating components are cast or ductile iron, also not weldable.

Exposed threads are no problem- they're normal. You are required to discount the wall thickness available in the pipe design by the full depth of the threads anyway.

Protect the threads with a spray cold galvanizing compound (i.e. zinc-rich paint) and be done with it.

 

[mmbguide]

 

[racookpe1978]

Why do you want to seal weld the threaded, galvanized joint? It is very, very difficult to properly weld a threaded joint under any circumstances. Exposed threads are expected for threaded joints - why do you suspect the number of threads visible is incorrect?

How did you verify the original tightness/torque of the original assembly of the threaded couplings?

 

[mmbguide]

Thank you all.

I agreed that exposed thread is correct but I was looking for a general rule for that.

but second problem is that, when one of them needs seal weld and because of weld size which is 10 mm Max. what shall I do with rest of exposed thread? is it possible to grind them to minimum wall thickness or not?

thank you

 

[moltenmetal]

Leave the rest of the exposed threads alone. Remove excessive thread sealant where it's loose and nonadherent, and coat the exposed threads with something for corrosion protection, and move on.

 

[bimr]

I agreed that exposed thread is correct but I was looking for a general rule for that.

The chart in the link shows the standard dimensions of NPT threaded pipe.

NPT THREAD DIMENSIONS

 

[MJCronin]

This looks a lot like electrical conduit ..... Is there a fluid or is there wires in these "pipes"

Electrical conduit does not use ASME B31.3 for a design code ...

MJCronin
Sr. Process Engineer

 

[Compositepro]

Are those hemp fibers used to seal the thread? If so you probably have a great deal of sealant on the threads which is preventing the parts from screwing together as much as they should be. Also, be aware that electrical conduit fittings look like pipe fittings but they use straight threads and not tapered threads as do pipe threads for containing pressure. A pipe coupling will be threaded from both ends and there is a very visible discontinuity in the threads at the middle where the threads meet. An electrical coupling has one continuous thread all the way through and it is required that the joint be electrically continuous to carry any ground currents, so you cannot use sealants that will break the electrical continuity.