Statistics analysis of TML UT measurements

[0707]

The selection of our thickness measurement locations (TMLs) is established in accordance with the API 570 guidelines.

Critical Piping circuits are selected in accordance with RECOMMENDED PRACTICE 571 Damage Mechanisms Affecting Fixed Equipment in the Refining Industry and API RECOMMENDED PRACTICE 580 Risk-based Inspection.

After the base line survey and the first inspection we calculate a corrosion rate based on the TML minimum thickness found in the circuit. With this corrosion rate we define the next inspection survey to define inspection frequency and estimation of the remaining life. After de third inspection survey we are in conditions to define a short term and a long-term corrosion rate, inspection frequency and a more accurate remaining life.

My question is:

Are there any guidelines for the statistics analysis of TML UT measurements?

A piping circuit section should be replaced when a TML of that section reaches the minimum calculated thickness or it should be given a statistics analysis of all TMLs within the whole critical piping circuit to preview the corrosion trend and pipe length replacement?

Comments on this subject should be appreciated
Regards

Luis Marques

 

[ndeguy]

This is the link to the HSE website:

http://www.hse.gov.uk/research/rrpdf/rr016.pdf

Good luck

 

[rustbuster]

It realy depends on the deterioration mode(s)predicted, the TML locations should be selected based on the expected damage as well as the technique(s) employed to monitor it.
I use both statistical and actual data, if your software system allows you to look at the data in variuos ways do so. TML data is indicative of the health of a system, verification of the damage mechanism is key understanding where and when to replace piping / equipment.