We'll be waiting with bated breath.
I didn't think there was much interest, but it is going to be a little while before I have enough time to write something more comprehensive.
When I have time here are some of the subjects I want to expand:
- basic cylinder stresses and cylinder stress calculations due to pressure (this is easy, it is covered 49CFR178.37 and other CGA documents).
- stresses due to secondary loads (some can be calculated, but many are hard to predict, it is a probability game)
- material properties and material conditions (for 3AA: AISI 4130 or similar, and the higher strength materials)
- difference between yield strength and ultimate strength and the importance of using a ductile material versus a brittle material, for pressure vessels
- How does material strength tends to affect ductility.
- material fatigue (low stress high cycles, versus high stress low cycles, metal coat hanger example)
- safety factors
- reasons for safety factors: secondary loads, manufacturing defects, imperfection introduced during service (including corrosion).
- risk calculations (again another probability game)
Differences between DOT code pressure vessels and ASME code pressure vessels? Basic answer is ASME have a higher safety factor and are normally heavier (not intended for transportation). They do not require regular testing and requalification. There is corrosion allowance in the material design for ASME cylinders, but not in DOT cylinders.
Basic pressure vessels as a structure designed to contain internal pressure are actually very simple and predictable, but then you add variables like manufacturing defects, condition changes due to corrosion, other external loads, etc. and it gets a bit more complicated.
The above is just a starting outline that I just wrote as a reminder of a few topics that I should touch on. This could easily become a very lengthy post. It takes me a lot of time to go through my references even when I remember where to find all the information. My memory is not that great and I can easily make mistakes when I rely on it.
When I write something like that is always very long, because I feel that it needs to be comprehensive. Otherwise, people like to argue the most stupid details if they are not clearly covered.
At this point I am busy with a number of projects, including our new regulator (the Argonaut) and several other projects, and it is alpine ski season up here.
The Argonaut:
http://www.scubaboard.com/forums/vi...totally-new-vintage-style-dh-regulator-2.html
I am also dealing with setting up a totally new computer... as expected this is taking longer than I wanted. Moving to windows 7 hasn't been as hard as I thought (I run AutoCAD, MathCAD, Solidworks, etc.), but it hasn't been without its issues.
---------- Post added January 11th, 2014 at 11:40 AM ----------
I guess as a scuba diver I'm willing to take risks where there is no documented failure to date. Certainly that is a lower risk than anything else we deal with diving? As an electrician I see changes made to the code book that are made to cover risks where there has never been a documented case of the thing happening. We have been using electricity, and scuba tanks, for a few years now and if something hasn't happened I'm willing to assume its risk of happening is a risk I'll not worry about.
I am getting the impression that according to your philosophy (maybe I am reading you wrong), we should always wait until someone gets killed or we have a disaster before we do something about it. Have you thought that maybe we will never see the incident because we have implemented safety measurements?
Believe or not, the majority of the safety codes (OSHA, NFPA, DOT, IBC, ASME, IEEE, etc. etc.) have been written in blood, but not all. Some have been extrapolation (from other disasters) or based on predictions based on analysis of risk. Risk analysis and predicting the future is not a precise science, but it is the best we have. And, it is the only tool we have to be proactive about avoiding future disasters.
Disasters are always a probability game and it is the consequence of several events that get combined in a particular way.
We rely on some previous experience to try to predict the future, but with very few small variations and we will have new events that have never happened before.
I am glad as a society (here in the US) we are a bit proactive about trying to avoid disasters, that is not always the case in some parts of the world.
Note: among some of my present work responsibilities involves the use of risk matrix analysis (for certain events involving potential structural failures). Many risk matrix tools have been developed to try to create a uniform method for evaluating risk. The DOD (Department of Defense) and the DON (Department of the Navy) uses them extensively.
I personally have a lot of reservations about our risk analysis tools, but at this point there is nothing better. Maybe someone is working on a reliable crystal ball...