[cuSetanta]

A certain leak rate is expected. Helium is a very small atom, and as such is used for leak testing of systems all the time. It is very good at finding gaps in a system.

Obviously the leaks here are a lot more serious. My experience of significant leaks in spacecraft propulsion would lead me to believe that there are welding issues. It can be very difficult to weld some of the materials used in these system, adding to the fact that they are all bound to be very thin walled. Cracks in welds can be hard to find, although I would expect every weld in a system like this to be X-ray inspected, and maybe also penetrant tested.

On the projects I have seen with issues like this, the main culprit has been steps in a procedure being skipped. Inspections signed off despite not being performed. I would highly doubt that this is the case here though, even with Boeings recent track record. Human spaceflight is treated different.

[hydrogen7800]

> It can be very difficult to weld some of the materials used in these systems.

Yes, lots of dissimilar metals welded together, using TIG, inertial/friction, electron beam, and probably other welding techniques.

>Cracks in welds can be hard to find, although I would expect every weld in a system like this to be X-ray inspected, and maybe also penetrant tested.

Indeed they are, and not just the welds. Any fracture critical component should have 100% nondestructive testing performed. This includes radiographic, liquid penetrant, helium leak test, etc., often all of the above. Like you, I would also be surprised if there were a single component or subsystem that was not subjected to these tests

[cameldrv]

All of that granted, isn't this stuff tested on the ground? I guess vibration from the launch must have cracked the welds or something, but I'd have thought that if this were a concern that the parts would have been tested in a vibration chamber.

[asadotzler]

It was tested on the ground. That's where they found the first of the five leaks, but launched anyway.

[cameldrv]

I'll be very interested to read the report when this is all over.

[cuSetanta]

It will have been tested extensively on ground. They will have identified leaks that are unreported in the media and there are those that have been reported.

I have no idea what went so wrong in this instance though. I am looking forward to reading some sort of report if it ever becomes available. Will be keeping an eye on the NASA Lessons Learned Library (https://llis.nasa.gov/).