JIC/AN installation best practice 3

[tooby-tube]

Hey everyone,

First time posting and really using this site so here is my obligatory apology if this question has already been asked and I missed it.

I am looking for best practice/standards for installing JIC/AN fittings (and if there are installation differences between the two fitting types). There are three steps of the installation process I have identified which I am looking for clarification and direction on. Google has largely failed to help clarify these points so here I am!

1. Should gaskets like SECO seals be used by default? At a previous place I worked we only used SECO seal gaskets on persistent leaks or very high pressure (think +5k psia) systems or helium systems. However, my current place wants gaskets on all joints. While I understand that this decreases the possibility of leaking in general, it feels unnecessary and creates another process during installation/maintenance (aka expensive) but I may be wrong.

2. Is anti-galling compound required for SS fittings? Again, at my previous place we usually did not use Krytox to prevent galling. In fact, we never talked about galling with 316SS fittings and I never heard anyone every mention it happening in their past. However, my current place wants Krytox on all fitting joints which again feels unnecessary and creates an additional process. Without knowing better, I would only use Krytox to lubricate a problematic joint which at that point the joint should either be fixed or just replaced.

3. Torque vs turn method on tightening. If running torques are known using a torque wrench seems good enough however I would rather default to the turn method for consistency of load in the joint but I would like another opinions.

If needing specifics, my use case is 0-3000 psia, helium and up molecule sizes with temperatures from -100C to 100C. Some systems will flow oxidizers.

Thanks everyone for their thoughts and pointing me to the different standards which I likely missed.
Cheers!

 

[TugboatEng]

Have you considered using Swagelok or a Swagelok clone for this? The SS fittings are silver plated for galling resistance. Tightening is by torque to angle. Correct assembly can be verified with a go-no-go gauge.

Flared stainless tubing is challenging. It has a lot of spring back which makes achieving the correct angle more difficult than other materials.

 

[LittleInch]

Interesting blog here, saying AN fittings are not the same thing.

Plus everywhere seems to be saying they are most commonly used for hydraulic systems, not gas.

https://info.myssp.com/blog/the-role-of-jic-fittings-what-they-are-advantages-and-applications

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[tooby-tube]

Have you considered using Swagelok or a Swagelok clone for this?

We have considered it a bit. The main reason we are staying away from swage is we can machine male & female AN fittings into our flight hardware fairly easily unlike swage so we have a lot of heritage with AN style fittings. Therefore, we apply AN to our ground support equipment and test stands even if swage would be a reasonable substitute. For now, we are tooled for AN and therefore will likely be sticking with it (just too much momentum to change easily).

Plus everywhere seems to be saying they are most commonly used for hydraulic systems, not gas.

You are right that JIC purpose is primarily for hydraulics so I should have been a bit more rigorous in my question sorry. AN fittings are defined by SAE AS4841 and AS4875 for use in aircraft and spacecraft. I was grouping JIC and AN together because I was assuming (probably incorrectly) that the installation best practices would be the same for the two fitting types.

Thanks for the quick responses!

 

[TugboatEng]

I don't know that there is any challenge to machining in Swagelok type fittings. The silver plating is on th but side so you don't need special treatment for your adapters.

If you must use flare, helium is inert so carbon steel should be acceptable and will provide better sealing. As a rocket these systems are usually one time use?

 

[Rex Hang]

ello and welcome to the community!

It's great that you're seeking best practices for installing JIC/AN fittings, and your questions are quite detailed. Here are some insights that might help:

Use of Gaskets like SECO seals:

SECO seals can be beneficial in high-pressure systems, and using them by default may provide an extra layer of security against leaks. However, the necessity can depend on the specific requirements of your system and the materials being transported.
If your current place insists on gaskets for all joints, it might be a precautionary measure to ensure a higher level of integrity in the system. It's essential to balance the cost with the potential risks and benefits.
Anti-galling compound for SS fittings:

The use of Krytox or other anti-galling compounds for SS fittings can be a preventive measure to avoid galling issues. While it might seem unnecessary in certain cases, it can contribute to the longevity and reliability of the fittings, especially in applications with temperature variations.
Considering your specific use case with temperatures ranging from -100C to 100C, the use of anti-galling compounds becomes more relevant to prevent issues like galling in extreme conditions.
Torque vs Turn method on tightening:

Both torque and turn methods have their merits. Using a torque wrench can provide a precise measure of the applied force, ensuring that fittings are tightened to the specified level. This is particularly important in applications with known running torques.
The turn method, on the other hand, can be practical for achieving consistent load in the joint. It may be a matter of personal preference and the specific requirements of your system. Ensure that whichever method you choose aligns with any industry or manufacturer guidelines for the fittings you're using.
It's always a good idea to consult relevant industry standards, manufacturer recommendations, and possibly involve your team or colleagues in the decision-making process. Additionally, you might want to explore specific standards such as those provided by organizations like SAE (Society of Automotive Engineers) for AN fittings or other relevant bodies in your industry.

 

[LittleInch]

An AI response?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[btrueblood]

Looks that way.

 

[EdStainless]

While there are subtle differences (making them non-interchangeable) between JIC and AN the process is the basically the same.
We did not use seals, but then we would not use AN for Helium or Hydrogen.
How often have you He leak tested AN fittings in He service?
If pressed, we used Swagelock (all and only) but 85% of the time these were welded.
We used Krytox on all SS threaded joints.
Even when people claimed that it would never be disassembled.
By using lube on all joints it kept the assembly procedure the same.
We used a deg-of-turn method, because that is just how we did it.
Some of our fittings (larger ones) even had basic tightening info etched on them.
We also had restrictions on the re-use of fittings.
Once flared fittings are re-tightened a few times they are not the same.
Places that we knew would be undone a lot had extra tube provided to allow for cutoff and re-flare during the lifetime.


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P.E. Metallurgy, consulting work welcomed