ASME B31.3 5% X-Ray Requirement on Welds 2

[Engineer_M]

Hi,

Code says 5% of all welds must be x-rayed but it looks like its for normal service. My fluid service is liquid nitrogen, does anyone know how to determine the required x-ray %?

Thanks

 

[TiCl4]

Assuming you means B31.3, the code actually requires 5% NDT minimum for normal fluid service, which may be radiographic testing or ultrasonic testing. Be aware that for some materials (stainless steel in particular), normal ultrasonic is not kosher due to the dampening of the waves. For these metals, radiographic or phase-array testing are required (unless you have specific "standards" built for that pipe size, thickness, etc, which is typically more expensive for smaller projects than x-ray or phase array).

The code only requires a minimum of 5%. It is up to the owner to specify any additional requirements for normal fluid service.

There are other requirements in B31.3 (see table 323.2.2 for requirements for avoiding low temperature toughness tests) for cryogenic fluids. I suggest you fully read and understand the relevant sections before you make any determination on the QA/QC of the piping system.

 

[XL83NL]

If the owner has specified liquid nitrogen as Normal Fluid Service, then 5% as per Code requirements is what it is, yes.
Make sure to have a defined co-understanding of what shall be understood to be a designated lot.

Huub
- You never get what you expect, you only get what you inspect.

 

[LittleInch]

In ASME B 31.3 "Normal service" is actually everything not covered by either

Cat D ( non toxic, inert <150 psi and between -29 to 180C. So doesn't apply
Cat M - sometimes referred to a "lethal" service. Doesn't apply
High pressure - not stated, but usually implies > 5 or 10,000 psi
High purity - usually reserved for medical and food stuffs
High temp - not valid

How to determine this - READ THE CODE (I do assume you have a copy of the latest (2018). If not get your employer to buy one - you will find it very useful.



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

 

[SJones]

@LI will liquid nitrogen not be below -29 deg C and could a big spill not asphyxiate someone?

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[LittleInch]

Cat D is more than -29.

Lethal service means a few drops will kill you.

Hope I never work with stiff like that.

95% I would reckon is normal service.

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

 

[XL83NL]

Technically lethal service isn’t defined under B31.3. If the owner considers something as Cat M, it becomes Cat M. If the owner e.g. considers liquid nitrogen as such, then that is cat M, regardless if a few drops could kill you, or not.

Huub
- You never get what you expect, you only get what you inspect.

 

[LittleInch]

It might not "define it", but gives you good guidance. Nitrogen is 79% of what we breathe all day every day so whilst I am aware of its asphyxiating properties I don't think it really comes into the Cat M / lethal service category. IMHO.

(b) Category M Fluid Service: a fluid service in which
both of the following apply:
(1) [highlight #FCE94F]the fluid is so highly toxic that a single exposure to
a very small quantity of the fluid,[/highlight] caused by leakage, can
produce serious irreversible harm to persons on
breathing or bodily contact, even when prompt restorative measures are taken
(2) after consideration of piping design, experience,
service conditions, and location, the owner determines
that the requirements for Normal Fluid Service do not
sufficiently provide the leak tightness required to
protect personnel from exposure

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

 

[XL83NL]

I agree with LI, it's just that engineers should be aware of this, I think. Ive seen engineers call a fluid or medium cat M, which isn't technically correct.
We've had an occasion where something, that we thought of as not being very lethal, was considered cat M fluid service by the owner, and procured by them through us that way. This wasn't something explained easily, let alone the cost impact it had on the project.

Huub
- You never get what you expect, you only get what you inspect.

 

[LittleInch]

I think maybe someone doesn't realise that in the snip above, BOTH a and b need to apply.

It's called "Reading the Code" and sadly many people don't even have a copy of it never mind read it....

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