Use the pump manufacturer's thermal limits as the controlling criteria. API 682 addresses mechanical seal systems; it does not supply a universal pump warm-up rate for this decision. API 610 likewise should not be treated as the source of a fixed rate here. Pump materials, liners, internal clearances, seal arrangement, and temperature distribution determine the permissible ramp.
Governing warm-up criterion
The term warm-up rate here means the change in a representative pump metal temperature divided by elapsed time. The term start-temperature difference means the absolute difference between that metal temperature and the liquid temperature the pump will receive at startup. These are separate limits: meeting the ramp limit does not prove that the pump is close enough to process temperature to start.
Rapid heating creates temperature gradients between the casing, liners, shaft, wear components, and seal chamber. Because these components do not heat or expand identically, the gradients can alter internal clearances, shaft alignment, and seal-face conditions. The manufacturer must translate the pump design into a maximum ramp and a maximum temperature difference at startup.
| Candidate criterion | Correct use | Decision |
|---|---|---|
| Manufacturer startup procedure | Design-specific maximum ramp and startup temperature difference | Controlling requirement |
50 °F/h |
Rate reported in some startup procedures | Use only when approved for the installed pump |
50 °F per 1/2 h |
Equivalent average rate of 100 °F/h
|
Do not misread it as 50 °F/h
|
100 °F/h |
Another reported pump requirement | Use only with the associated design approval |
Within 50 °F or 100 °F of pumping liquid |
Reported startup-difference criteria | Not interchangeable; select the documented value |
Check 1: Manufacturer thermal limits
Check 1: expect the pump startup procedure, datasheet, or approved operating instruction to state both the maximum heating rate and the permitted temperature difference before startup.
- Locate the instruction for the exact pump construction, not merely the seal family or service description.
- Record the maximum rate, its units, the temperature measurement location, and the reference liquid temperature.
- Record any different limit assigned to the casing, liner, seal chamber, or another component.
- Confirm whether the stated value is a maximum, a target, or an alarm threshold.
If both limits are present, proceed to Check 3 and test actual readings against them. If either limit is missing, proceed to Check 2. Do not convert 50 °F/h from prior practice into an API 682 requirement. A familiar field value remains installation-specific until the pump manufacturer or responsible engineering authority approves it.
Check 2: Construction-sensitive restrictions
Check 2: expect the bill of materials, sectional drawing, and manufacturer documentation to identify the casing, liner, shaft, internal wear components, and seal-chamber construction. This check determines whether a generic site practice is too aggressive.
Pumps with hard-iron liners require a slower warm-up than the common 100 °F/h example. No exact slower value is defined here; obtain it from the pump manufacturer for the installed liner and clearance design. The same decision rule applies whenever dissimilar materials, close running clearances, or construction-specific notes impose a more restrictive limit.
| Finding | Meaning | Next action |
|---|---|---|
| Exact construction has an approved thermal limit | The design restriction is known | Use that limit and proceed to Check 3 |
| Hard-iron liner is identified, but no rate is stated | A slower warm-up is required, but the allowable rate is unresolved | Obtain a written manufacturer limit before setting the procedure |
| Materials or clearances do not match the available procedure | The procedure may apply to another build | Resolve the document mismatch before heating |
| Construction record is unavailable | The thermal-growth basis is unknown | Identify the pump build from controlled records or manufacturer data |
Check 3: Measured temperature ramp
Check 3: expect time-stamped temperature readings from a representative pump metal location and the liquid source that will feed the pump. A single temperature reading cannot establish a rate.
For two successive readings, calculate:
Warm-up rate = (T2 - T1) / (t2 - t1)
Use hours for elapsed time when the limit is stated in °F/h. For example, a requirement written as 50 °F per 1/2 h equals 100 °F/h because . It is not the same requirement as 50 °F/h.
If every calculated interval remains at or below the approved maximum, proceed to Check 4. If any interval exceeds the limit, reduce or isolate the heating input according to the approved operating method, allow the temperature gradient to recover under manufacturer guidance, and restart the evaluation. Do not accept a low overall average that hides a short interval above the limit.
Recurring errors include measuring only the heating medium, using irregular timestamps, moving the temperature sensor between readings, and comparing local casing temperature with a remote process temperature that does not represent the liquid reaching the suction.
Check 4: Startup temperature approach
Check 4: expect the absolute temperature difference to meet the pump-specific startup limit:
Startup difference = |T_liquid - T_pump metal|
Reported procedures have used limits of within 50 °F or within 100 °F of the actual pumping liquid. Another reported requirement combines a 100 °F/h ramp with a final temperature within 100 °F of feed-drum temperature. Use feed-drum temperature only when it is the approved reference and represents the liquid the pump will receive.
If the difference is inside the documented limit, continue to the resolving procedure. If it is outside the limit, continue warming without exceeding the ramp limit. If the liquid temperature changes during warm-up, recalculate the difference from current readings; reaching a previously calculated target does not prove that the present difference is acceptable.
Resolving procedure and verification
- Enter the manufacturer-approved maximum warm-up rate and startup-temperature difference in the operating procedure. Include the specified measurement points.
- Place the pump in the manufacturer-approved warm-up configuration and begin logging pump-metal temperature, reference-liquid temperature, and timestamps.
- Calculate the rate over each logged interval. Regulate the heating input so each result stays at or below the approved maximum.
- Calculate the current startup-temperature difference. Continue controlled warming until the result is within the approved limit.
- Complete the pump and seal-system startup prerequisites defined by their controlled procedures, then start the pump.
Numbered verification checks:
- Check 1: expect each calculated ramp to be no greater than the manufacturer-approved maximum.
- Check 2: expect the sensor location and reference-liquid source to match the approved procedure.
- Check 3: expect the final absolute temperature difference to be no greater than the approved startup limit.
- Check 4: expect post-start leakage, vibration, and temperatures to remain within the pump, seal-system, and site acceptance criteria.
Frequently asked questions
Why does API 682 not give me a universal pump warm-up rate?
The allowable rate depends on pump materials, internal clearances, liners, and thermal growth. Use the exact pump manufacturer's startup instruction rather than assigning 50 °F/h as an API 682 value.
Why does 50 °F per half hour equal 100 °F per hour?
The rate is . Confusing this notation with 50 °F/h cuts or doubles the intended rate, depending on which value the procedure actually requires.
Why does the pump need a final temperature-difference limit?
A compliant heating rate can still leave the pump too far from the pumping-liquid temperature. Verify the separate manufacturer limit, which reported procedures have stated as within 50 °F or 100 °F.
Why does a hard-iron liner change the warm-up decision?
Hard-iron-lined pumps require slower warming than the reported 100 °F/h practice. Read the permitted rate from the manufacturer documentation for the exact liner and clearance design.
How do I verify the pump is ready to start?
Calculate every logged temperature ramp and confirm none exceeds the approved maximum; then calculate |T_liquid - T_pump metal| and start only when it is no greater than the manufacturer-approved difference.