Random Radiography

Date 05-25-2011 03:33

Hi all,
Have just read this very informative article written by Walt Sperko regarding random radiography in accordance with B31.3.

http://www.thefabricator.com/article/testingmeasuring/random-radiography?ID=1129

The scenario in the article describes the fabricator performing RT on 35-40 "lots" of piping welds and the owner stating it should have been approx 450 "lots".
The interpretation I get from the article is the owner required significantly more RT because the "lots" were multiplied tenfold.

This is where my confusion sets in.

Hypothetically, we have 10,000 groove welds on a refinery project.

If we break it into "process service systems" we have 50 lots with 200 welds per lot.
RT 5% of each lot = 10 welds per lot
50 lots x 10 welds = 500 welds subject to RT

If we break it into "piping line lists" we have 500 lots with 20 welds per lot.
RT 5% of each lot = 1 weld per lot
500 lots x 1 weld = 500 welds subject to RT

What am I missing here guys ?
Regards,
Shane

By js55

Date 05-25-2011 11:56

I haven't read Walt's article yet, but there needs to be full understanding ahead of time. Customers will try to get something for nothing and fabricators will try to get off as economical (cheap) as possible.
The problem is in the 'it should have been' statement.
I have spent hours in prejob meetings with customers determining exactly what a 'lot' is and explaining to them what exactly they will get.

By qcrobert (***)

Date 05-25-2011 15:25

Not missing anything Shane.

As the author concludes, there must be a clear, written understanding between the Client and Fabricator of what constitutes a "lot".

B31.3 specifies that the owner must evaluate his piping systems and assign fluid service categories as appropriate. If the owner doesn't designate a fluid service category, normal fluid service rules apply.

The extent of examination for fluid service categories is:

•Normal—5 percent random radiography of butt welds
•Category M—20 percent random radiography of butt welds
•High Pressure—100 percent radiography of butt and branch connections
•Severe Cyclic—100 percent radiography of all butt welds and branch connections
•Category D—Visual examination only

As JS mentioned, the contract must be clearly defined in pre-jopb meetings.