Thickness log
Your condition monitoring locations recorded once, your readings added each campaign, and the trends recalculated on their own.
Your data stays in this browser. Nothing is sent, but nothing is saved anywhere else either: clearing the cache or switching workstation makes it disappear. Export regularly.
Why a log rather than a spreadsheet
A thickness-tracking spreadsheet works perfectly as long as the person who built it is still there. It stops the day they move on, because no one else knows its logic. This log applies a fixed method: two rates calculated separately, a refusal to conclude below three readings, and the flagging of rising thickness readings.
What to know before using it
The data lives in your browser's local storage. It is sent nowhere, which keeps it confidential, but it is saved nowhere either. Clearing the cache, or changing workstation or profile, makes it disappear. Export to CSV regularly: it is the only safety net.
For the full method, see calculating a corrosion rate and measurement points: where to place them.
Definition
The thickness log is the register that keeps, measurement point by measurement point, the dated thickness readings of an equipment. Tied to a stable identifier owned by the operator, it makes it possible to track thinning over time, compute a corrosion rate and estimate a deadline. Its value rests on point identification: re-measuring exactly the same location from one campaign to the next.
Formula
Corrosion rate = (thickness1 - thickness2) / (date2 - date1), on the same measurement point. thickness1 is the older reading, thickness2 the most recent, the duration being expressed in years to obtain a rate in mm per year. Both a long-term rate (first and last measurement) and a short-term rate (two latest campaigns) are computed.
How to use this tool
- Place the points where degradation is expected according to the mechanism (elbows and downstream of valves for erosion, low points for general corrosion), not where access is easy.
- Give each point a unique, stable identifier owned by the operator, with a dimensioned sketch and a reference photograph.
- Record at each campaign the value point by point, the date, the technique and the measurement conditions; never reduce a campaign to its minimum thickness alone.
- Reconcile each new campaign with the previous one and compute the long-term and short-term rates on each point.
- Flag any thickness increase beyond the measurement uncertainty: it points to a point, technique or data-entry issue, never to metal growing back.
Worked example
On point A of a pipe, the recorded thickness was 12.0 mm in 2019 and 10.5 mm in 2024. The corrosion rate is (12.0 - 10.5) / (2024 - 2019) = 1.5 / 5 = 0.30 mm per year. If the minimum allowable thickness is 8 mm, the remaining margin of 2.5 mm gives a remaining life of about 8 years at this pace.
References
- API 570, in-service piping inspection code: measurement point plan and calculation of short-term and long-term corrosion rates.
- Inspectioneering, resource on condition monitoring locations and the use of readings over time.
Frequently asked questions
Where is my data stored?
In the browser of the workstation you are using, and nowhere else: nothing is transmitted. The downside is real: clearing the cache, changing workstation or profile makes the log disappear. That is why the CSV export exists, to be done at every campaign.
How many readings are needed for the trend to mean anything?
Two readings give a rate, three begin to give a trend. Below that, a discrepancy may come from the measurement itself: a different operator, a different instrument, a point relocated to within a few millimetres.
Why does the tool flag a thickness that goes back up?
Because metal does not grow back. An upturn indicates a poorly repositioned point, a change of instrument or couplant, or a data-entry error. Never an improvement. Until the discrepancy is explained, the series cannot be used.
Is this log enough to justify a decision before an inspection body?
No. It shows a change over time; it replaces neither a strength calculation, nor the minimum allowable thickness set by your technical manager or the competent body, nor the inspection plan.
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