A temperature-indicating stick answers a narrower question than many welders expect: has the tested surface reached the stick's rated melting temperature? It does not select the correct preheat for the job, measure an entire weldment, or tell you how far above that temperature the metal has gone. Understanding that distinction makes a Tempilstik useful rather than misleading.

Start with the welding procedure specification (WPS) or the responsible welding specialist's instructions. Then select the indicator rating, measurement method, location, and timing needed for that job. The 250°F and 425°F products discussed below are buying examples, not a recommended welding-temperature range.

Read melting, not a color change

Markal's Tempilstik manufacturer documentation identifies melting as the temperature signal and explicitly says the stick's color is not part of its function. Do not wait for a particular color change, identify the temperature by the core's color, or confuse an ordinary layout crayon with a temperature indicator.

With the correct indicator used as directed, melting shows that its threshold has been reached at the checked surface. It does not mean the surface is exactly at that temperature or that the opposite side of a thick plate is equally hot. Treat it as a threshold indication, not a substitute for an instrument when the procedure requires an actual temperature reading or a recorded temperature history.

Read the marking on the stick and its package before use. The manufacturer identifies the part number, temperature, and lot code as traceability information. Keep those details readable and associated with the actual stick instead of relying on a remembered cap color.

Separate minimum preheat from interpass limits

Minimum preheat is a lower-temperature requirement before the specified welding operation. Interpass checks address the temperature between passes; the procedure may include a minimum, a maximum, or both. Reaching a minimum is not permission to ignore a maximum. Miller's preheat guidance explains that the WPS defines required temperatures and duration and that temperature must also be monitored between passes.

Before choosing supplies, write down the relevant limits and units exactly as specified. Ask whether the approved method permits threshold sticks, requires an instrument, or needs both. Have the responsible welding or inspection personnel resolve uncertainty about tolerances and acceptance criteria. Do not substitute the nearest stocked stick for a required rating without that review.

A stick that melts during a minimum-temperature check does not establish compliance with an upper limit. Likewise, an old melted mark is not a current reading after a pause while the weldment cools. Repeat checks at the required stages using the prescribed method rather than treating the first successful indication as valid for the rest of the job.

Where and when you check matter

A convenient exposed corner is not automatically the correct measurement point. SSAB's preheat and interpass guidance specifies measurement location, heated area, and waiting time for its steel products. Its instructions are product-specific; they should not be copied as a universal spacing or timing rule for other materials.

Use the applicable procedure and material guidance to establish where readings are required and when they must be taken relative to heating and the next pass. Confirm any requirements for the opposite surface, through-thickness heating, multiple locations, or temperature equalization. A local threshold indication alone cannot demonstrate all those conditions.

Prepare and contact the test surface according to the indicator instructions and the approved inspection method. Do not use melting caused by exposing the stick directly to a flame as evidence of the weldment's temperature. Keep indicator residue out of locations where the welding procedure or customer specification prohibits it, and follow any required cleaning instructions.

Two replacement ratings to verify before ordering

250°F indicator: Markal's 028019 manufacturer page identifies the 250°F / 121°C option. ArcWeld lists the Tempil 28019, 250°F surface-temperature indicator as a single indicator. Match the rating and unit to the approved requirement; this is not a general preheat recommendation for mild steel.

425°F indicator: The 028037 manufacturer page identifies the 425°F / 218°C option. The corresponding ArcWeld listing is the Tempilstik 28037, 425°F surface-temperature indicator. It is a different threshold, not a higher-performance version of the 250°F stick.

Do not buy the pair simply to create a 250–425°F working window. Whether either rating belongs in a preheat or interpass check depends on the specific procedure. When ordering for several jobs, separate the purchase lines by rating, unit, quantity, and application rather than requesting an unspecified box of temperature crayons.

When a result is unclear, stop guessing

An unclear indication should trigger an identification and method check, not automatic extra heating. Confirm that the stick's label matches the intended test, that you used the specified location and timing, and that the surface and application meet the instructions. Ask the responsible inspector or welding specialist to resolve conflicting results with an approved measurement method.

Do not infer a safe handling temperature from a high-rated stick that has not melted. Metal can still cause burns below that rating. Maintain appropriate gloves, eye protection, and hot-work controls. OSHA 1910.252 addresses welding protective equipment and fire prevention; its confined-space provisions also require warning other workers about hot metal after welding. A temperature check does not replace those protections.

Make the check repeatable across the shop

A useful job record identifies the WPS revision, material and thickness, required temperature limits, measurement method and locations, indicator rating and lot identification when required, check timing, and result. Record a threshold result as a threshold result; do not turn a melted mark into a fabricated numerical thermometer reading.

For the broader setup, see ArcWeld's thicker-steel joint preparation and multipass guide. Temperature control belongs alongside the specified joint, filler, pass sequence, and inspection requirements—not in place of them.

Before ordering a replacement indicator, send ArcWeld the required rating and unit, manufacturer part number, package quantity, and any job-specific purchasing requirement. Choose the product that supports the approved temperature-checking method. The goal is a reliable decision at the right place and time, not merely a mark that melts.