Re: [PSUBS-MAILIST] gas piping through hull

[Cliff Redus <cliffordredus@sbcglobal.net>]

Brent,

 

I don't have a good solution for the thread rust issue while using thread-o-let. I am just going to live with a bit of rust. You would have the same issue with externally threaded nipple that is welded unless it was SS.  I chose not to go with SS thread-o-lets because of the potential for galling when you have threaded connection and SS on SS.  I don't know off the top of my head of a SS vendor for thread-o-lets.
 

Cliff

 

----- Original Message ----
From: Brent Hartwig <brenthartwig@hotmail.com>
To: personal_submersibles@psubs.org
Sent: Tuesday, January 15, 2008 2:29:28 PM
Subject: RE: [PSUBS-MAILIST] gas piping through hull

Hello Cliff,

How do you plan to prevent rust leaking from the cast steel thread-o-let threads and interior void space between the inner and outer thread-o-lets?  I see a fair number of pressure vessels as well as older subs that have rust leaking out of there none stainless steel through hulls. Do you know of a good SS thread-o-let option?

Regards,

Brent

Date: Sun, 13 Jan 2008 06:36:00 -0800
From: cliffordredus@sbcglobal.net
Subject: Re: [PSUBS-MAILIST] gas piping through hull
To: personal_submersibles@psubs.org

Antoine,

 

Another option would be to use "thread-o-lets" which are forged pipe fittings with female thread that are welded on the side of hull.  A hole is drilled through the hull prior to welding on the thread-o-let.  There would be two thread-o-lets, one for each side.  3000 and 6000 psi thread-o-lets are readily available as they are used extensively on process vessels and connections for instrumentation on pipes. They are approved for ASME pressure vessels.  I used 3000 psi thread-o-lets for all of the thru hulls on my boat.  The advantage of a thread-o-let for a welded pipe nipple is that the joint is stronger and treads are protected. 

 

Cliff

----- Original Message ----
From: Antoine Delafargue <antoine.delafargue@gmail.com>
To: personal_submersibles@psubs.org
Sent: Saturday, January 12, 2008 10:50:36 PM
Subject: [PSUBS-MAILIST] gas piping through hull

Hello,

 

I am struggling on the design of gas piping through hulls for my 1atm 1 person sub project, if anyone could help:

 

-What is the best way to design gas through hulls (as close as ABS standards as possible) ?

 

a)  the one I am considering: circular thick SS plate welded on the end cap with various holes (O2, MP air, MBT, snorchel/vent) machined in it and threaded for setting ball valves directly on it. (actually 2 plates for full redundancy). that s the "threaded" i don t like.

 

b) same SS plates but swagelok tubes welded on it and connected to the valves. that s the "welded" i don t like

 

c) same SS plates with machined holes, filled with some off the shelf gas through hulls, linked to tubes and valves. not as simple: it implies a seal between the SS plate and the through hull.

 

d) individual off the shelf gas through hulls welded on the hull. But I could not find a reference in the Swagelok catalog.

 

e) other suggestion...

 

 

 

Thanks a lot,

 

Antoine