Pressure equipment and process plant · reference card
Weld monitoring for pressure vessels
Thick-section, multi-pass, code-governed welding. The codes that apply, the four monitoring pain points that cost pressure-vessel fabricators most, and which Therness signal addresses each.
- Industry
- Pressure equipment and process plant
- Dominant processes
- Submerged arc welding on longitudinal and circumferential seams; Gas metal arc and flux-cored welding on nozzles and attachments; Gas tungsten arc welding for root runs on critical joints; Manual metal arc welding for repairs and site work
Pressure-vessel welding concentrates every condition that makes process evidence valuable: thick section, many passes, restrained joints, expensive parent material, and a code that defines acceptance in terms of variables recorded during qualification rather than in terms of what the finished bead looks like.
The economics follow from the geometry. A defect found by radiography in a heavy seam is not a grind and a re-run; it is an excavation, a repair procedure, re-examination, and often a schedule slip on a critical-path item. Anything that moves the moment of detection earlier is worth disproportionately more here than on light fabrication.
Two of the four pain points above are not defects at all but documentation failures — an interpass excursion nobody recorded, a heat input nobody measured. Both are perfectly survivable while the vessel is in the shop and both are expensive when they surface during an audit or an incident review, because at that point the only honest answer is that the data was never taken.
Governing codes
| Code | Why it applies |
|---|---|
| ASME BPVC Section VIII | The construction code for most vessels built to the ASME route; it sets acceptance and calls up the examination methods. |
| ASME BPVC Section IX | Qualifies the procedures and the personnel that Section VIII construction relies on. |
| ISO 3834-2 | The comprehensive quality-system requirements a fabricator declares in the European route. |
| EN 13445 | The harmonised unfired pressure vessel standard used to show conformity with the Pressure Equipment Directive. |
Monitoring pain points
| Pain point | Consequence | Signal that sees it |
|---|---|---|
| Interpass temperature drifts upward through a long multi-pass seam | The final runs are welded outside the qualified band, and the toughness argument for the joint no longer holds. | Non-contact interpass measurement on every pass rather than a spot check between two of them. |
| Heat input is computed from the figures on the procedure sheet, not from what happened | A production weld sits outside the range the qualification record supports while every display reads normal. | Arc energy computed per pass from measured current, voltage and travel speed. |
| Lack of fusion is buried and invisible until volumetric examination | Rework on a thick section is slow, and a repair on a repair carries its own qualification burden. | Cooling-signature anomalies and pool wetting evidence on the run that produced them. |
| Traceability is assembled after the fact from paper and memory | Audit preparation absorbs engineering time, and a gap in the trail is discovered when it is expensive to close. | Weld identifier, operator, timestamp and process record joined in one exportable record as the weld is made. |
What that means for the cell
- HeatCam IR-C thermal weld camera Continuous interpass and cooling measurement on long multi-pass seams, without a welder stopping to place a probe.
- WeldTrace parameter acquisition Measured current, voltage, wire feed speed and gas per pass, which is what a qualified range is actually compared against.
- Welding parameter monitoring The route for building audit-ready evidence that production stayed inside the qualification.
Questions from pressure equipment and process plant
Does pressure-vessel monitoring reduce the required radiographic examination?
No. The extent of examination is set by the construction code and the joint category, and no monitoring system changes it. What monitoring changes is how early a suspect weld is identified, which affects rework cost rather than examination scope.
Can interpass temperature be evidenced without touching the workpiece?
Yes, provided the surface emissivity is established and recorded. Non-contact measurement covers the whole run instead of a single point at a single instant, which is the gap a contact thermometer leaves on a long seam.
Bring the evidence forward, not the inspection
Therness measures what happens while the arc is running — parameters, thermal signature, per-weld records — so the problems on this page surface on the shift that made them.
