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Interpass temperature timer
Interpass control fails on bookkeeping far more often than on physics. The welder measures, the number is fine, the next pass goes in — and three hours later nobody can say what the joint was at before pass seven, or how long it had been standing when the arc was struck. This page is the small piece that usually goes missing: a stopwatch between passes and a list of what was measured, when, and against which limit.
Type the maximum your procedure imposes, log each reading as you take it, and the page keeps the interval, the margin and the excursions. The interval clock and one subtraction are the only arithmetic on this page, nothing is assumed about your material, and the log itself is never uploaded or stored — it lives in this tab until you export it.
One subtraction, and a record of what was measured when
Interval = tthis reading − tprevious reading
Margin = Tmaximum − Tmeasured
Times from this browser's clock, in minutes. Temperatures in °C, or in °F with the unit toggle; the margin is a difference, so it converts as an interval and never carries the 32° offset.
There is deliberately no third equation. Interpass temperature is a measured quantity, not a derived one: the value comes from an instrument applied to the component, and the limit comes from the welding procedure specification. What a page can honestly add is the arithmetic nobody wants to do with gloves on — how long since the last pass, how much room is left below the ceiling, and which readings broke it.
The standards behind the practice are named rather than reproduced. EN ISO 13916 deals with how preheating, interpass and preheat maintenance temperatures are measured, which is where the questions of location and timing belong. EN 1011-2 deals with how a preheat regime for ferritic steels is arrived at, which is usually where the minimum in the field above came from. Codes such as ASME Section IX and AWS D1.1 treat preheat and interpass temperature as procedure variables, so changing them is changing the procedure — the exact classification, and every acceptance value, stays in the code and in your WPS.
How to run interpass control with a pass log
From the numbers on the WPS to an exportable list of what was measured, when, and against which limit.
- Copy the window off the WPS. Enter the maximum interpass temperature the procedure imposes and, if it names one, the minimum preheat or interpass temperature. Both fields start empty because neither number is assumed here — they are project decisions carried by the procedure.
- Set a warning band if you want one. The band is how far below the maximum you want to be told that the next pass will probably carry the joint over. It is a temperature difference, and zero turns it off.
- Measure where and when the procedure says. Take the reading before striking the next arc, at the point and after the delay the procedure fixes. Change the point or the delay and you have changed the measurement, not just the number.
- Log the reading. Pressing the log button timestamps the entry, freezes the limits that were in force alongside it, and starts the interval clock. The clock keeps running so you can see how long the joint has been waiting.
- Export the log before you leave the page. The CSV carries every entry with its local time, its UTC timestamp, the temperature, the limits in force, the margin and the interval since the previous reading. Nothing is stored in this page, so a reload clears it.
- The log lives in this tab and nowhere else. It is not saved, not uploaded and not recoverable after a reload. Export the CSV at the end of a run, or at any point you would be unhappy to lose. The export carries a local time and a UTC timestamp for every entry so it can be reconciled with another record later.
- An entry keeps the limits that were in force when it was made. Changing the maximum halfway through a run does not rewrite history: earlier entries still show, and are still judged against, the number that applied to them. That is the behaviour a review expects, and the reason the maximum is stored per entry rather than read once at export time.
- The minimum matters as much as the maximum. A joint that has fallen below the preheat the procedure requires is as far outside the window as one that has overheated, and it is the easier of the two to miss on a long wait. Where that minimum comes from is the job of the preheat temperature calculator.
- Waiting is not free. Letting a joint cool further than it needs to shortens the cooling time of the next pass: a joint that starts colder carries the weld zone from 800 °C to 500 °C faster. A shorter t8/5 hardens the heat-affected zone and raises its sensitivity to hydrogen cracking — the mirror image of running too hot, not the same mechanism. The t8/5 cooling time calculator puts a number on that side of it, and the heat input calculator on how much energy each pass is adding in the first place.
- Which instrument you use changes the number. A contact probe and a radiometric reading on the same joint disagree for good reasons, and the delay after the arc stops matters as much as the instrument. The comparison is worked through in the interpass measurement methods guide and, for cameras specifically, in infrared interpass monitoring.
- Sampling is the weak point this page cannot fix. A log is only as complete as the readings somebody remembered to take. Continuous thermal measurement removes that dependency, which is what HeatCam IR-C and the wider in-process monitoring platform exist to do.
- Sources for what this page computes. The interval is the difference between two timestamps read from this browser's clock, and the margin is the subtraction shown above; there is no other formula, and no constant taken from anywhere. The practice around those two numbers is governed by EN ISO 13916 for how preheating, interpass and preheat maintenance temperatures are measured, by EN 1011-2 for how a preheat regime for ferritic steels is arrived at, and by whichever fabrication code the contract invokes — commonly ASME Section IX or AWS D1.1 — for how preheat and interpass temperature are treated as procedure variables. Those documents carry the acceptance values, and none of them is reproduced here: the limit this page checks against is the one you typed off your own WPS.
For the limits themselves and how they are arrived at by material group, read interpass temperature limits and control.
Questions engineers ask about this calculation
What has to be written down next to an interpass temperature reading for it to count as a record?
A bare number proves nothing, because it cannot be attributed. A usable entry carries the value and its unit, the time it was taken, the joint or run it belongs to, the point on the component where the instrument was applied, the method or instrument used, and who took it. EN ISO 13916 is the standard that deals with how preheating, interpass and preheat maintenance temperatures are measured, and it is the reference a procedure normally points at for location and timing; ISO 3834 is what turns those readings into records the quality system keeps. Anything missing from that list is a gap somebody will find during a review, and by then the joint is welded.
Is a spot check between passes enough, or does interpass temperature need continuous measurement?
A spot check is evidence about one instant at one point. On short runs with a steady cadence and modest heat input, sampling before each pass is defensible and is what most procedures ask for. It stops being defensible when heat accumulates faster than the sampling interval — thick multi-pass joints, heavily restrained assemblies, layer-on-layer deposition — because the joint then spends most of its life unobserved, and the reading that mattered is the one nobody took. The honest test is whether you could show the limit held for the whole pass sequence, not just at the moments somebody happened to be standing there with a probe.
What should a welder do when a reading comes back above the WPS maximum interpass temperature?
Stop, and do not strike the next arc. Let the joint cool, then measure again at the same point after the delay the procedure names — a reading taken too soon after the arc reads the surface flash rather than the joint. Record the excursion as it happened and never overwrite it: whether the metal already deposited is acceptable is a concession decision for the quality system, not one for the shop floor. Forced cooling is only an option if the procedure allows it, because blowing air or water at a joint changes the cooling rate the procedure was qualified on, which is a different variable with its own consequences.
Can a browser stopwatch serve as the quality record for interpass control?
No, and it is worth being blunt about it. A page like this one is a working aid: it does the arithmetic, keeps the readings in order, and gives you an exportable list at the end of a run. It has no traceable clock, no calibrated instrument behind the temperature, and no link to the identity of the joint. The record has to come from the calibrated instrument, the person who used it and the quality system that stores the result. Use the export as an aide-memoire and as an input to the real record, never as the record itself.
A reading proves one instant. A thermal record proves the whole pass sequence.
HeatCam IR-C measures the joint without touching it and keeps looking between passes, so interpass compliance stops depending on somebody being free to take a reading at exactly the right moment.
