Thickness trending

Every thickness reading in an issued report is kept as data, per TML and per position, so that the next inspection can be compared with the last. From that NDT Intact works out corrosion rates and remaining life against a minimum thickness you enter, and shows them per TML, per project and, when the tracker is released, to the client. The figures are indicative: every view says how they are worked out.

TMLs and positions

A TML (a thickness monitoring location) is a joint of the tracker, like a weld: one identifier per asset, kept with the project's welds on the Tracker tab and matched the same way, so "TML-3" and "TML 3" are one TML. See the tracker.

Within a TML a report records readings at positions: a clock position, a grid cell, a named point, as typed. Positions are compared on their text, case and spacing aside, so "12 o'clock" in one report meets "12 O'Clock" in the next. The rates are worked out per position wherever the same position was measured in two inspections.

Where the readings come from

Readings are never typed into the trend. When a report is issued, every row of its thickness readings table that names a TML and gives a thickness becomes a reading: the position, the value in millimetres, the inspection date and, where the template has one instrument field, the instrument. A report in draft or in review contributes nothing.

A revision of a report replaces the readings of the report it corrects: those are stamped as replaced, and the revision's readings count instead. A withdrawal stamps the report's readings with nothing in their place. Replaced readings stay on the TML's page, marked Replaced, and are left out of every rate.

A report form in inches keeps its figures as written on the report; the trend converts them exactly to millimetres (25.4 to the inch), so inspections in both units meet on one line. See issuing a report.

The Thickness tab

The Thickness tab of a project lists every TML with its Last inspected, Lowest thickness and the position it was found at, Minimum, Rate used and Remaining life. The TMLs that need attention come first: those at or below their minimum, then the shortest remaining life, then the rest, and TMLs with no readings last. A TML appears when a report with its readings is issued or when you add it to the tracker.

Remaining life from switches between the greater rate (the default), the short-term rate and the long-term rate for the whole list; the choice is carried in the page's address so a link keeps it.

A TML's card

Open a TML and its card, Wall thickness, shows:

• The headline: Lowest thickness and where, Rate used with the short-term and long-term rates beside it, Remaining life and Minimum thickness.
• A line saying what was compared: position by position, minimum to minimum, one inspection so far, or no readings yet.
• A chart of the lowest reading of each inspection over time, with the minimum as a dashed line.
• By position: each position's first, previous and latest reading, its short-term and long-term rates, and Not measured in the latest inspection where that is so.
• Readings: every reading with its date, position, value and report, replaced ones included.
• Minimum thickness: the figure in force, who entered it and when, its basis, and the earlier entries.

How the figures are worked out

In words, for each position, from its readings in date order (one issued report is one inspection; a position measured twice in one inspection counts at its lowest):

• Short-term rate is the previous reading minus the latest, divided by the years between them.
• Long-term rate is the first reading minus the latest, divided by the years between them.
• Remaining life is the latest thickness minus the minimum, divided by the rate chosen.

The TML's headline is the most conservative combination: the lowest latest thickness among its positions, the highest rate among the positions that were measured before, and the remaining life from those two. The per-position table always sits behind it.

Where no position of the latest inspection was measured before (the points were named differently, or moved), the rates compare the lowest reading of each inspection instead, and the card says minimum to minimum. One inspection gives no rate: rates need two. Two inspections on the same day give none either.

A rate of zero or below reads No measurable loss and gives no remaining life. A TML at or below its minimum has a remaining life of nought and is flagged At or below the minimum.

The minimum thickness

NDT Intact works out no minimum and ships none. The figure comes from your calculation or your client, and is entered on the TML's card with Enter the minimum thickness: the Minimum thickness (mm) and its Basis, for example the design calculation and its revision, or the client's instruction.

• In your company, owners, admins and reviewers enter it, because the Level 3 holds the acceptance criteria.
• In the portal, a client user may enter it on a TML of a project whose tracker is released to them; the entry then reads Entered by the client.
• A new figure is a new entry; the latest counts and earlier ones stay on record with who entered them. Each entry is written to the activity log.

A report template's own minimum thickness field is report data and stays on the report; the TML's minimum is entered on the TML.

The spreadsheet

Export to Excel on the Thickness tab writes every TML with its line and component, number of inspections, last inspection, lowest thickness and its position, minimum, both rates, the rate used, remaining life and what was compared, with a note saying the figures are indicative and which rate the remaining life uses. The export is recorded in the activity log.

In the portal

Once the project's tracker is released to the client, the portal has the same Wall thickness list and the same card per TML, from current readings only, with the same formulas spelt out. The client sees replaced readings as replaced, never a draft's readings, and may enter a minimum as described above. See the client portal and showing the tracker to the client.

What the figures are, and are not

Every view says the figures are indicative. They are the arithmetic above over the readings of the issued reports, no more: no risk ranking, no inspection interval and no fitness-for-service judgement. The decision on what the trend means stays with your Level 3 and the asset owner.