Maintenance & Reliability · SOP
Boiler Water Chemical Dosing And Alkalinity Testing
A precise technical standard for performing chemical dosing and wet-chemistry alkalinity testing on industrial steam boilers. Covers sampling protocol, titration endpoints, and pump calibration to maintain ASME water chemistry guidelines.
Estimated Time
45 min
Difficulty
Advanced
Regulation
ASME / CSA B51
Version
1.0
Purpose
To define the exact sequence of operations for safely handling, preparing, and administering chemical treatment (oxygen scavengers, scale inhibitors, pH adjusters) to industrial boiler systems. This procedure ensures precise P & M alkalinity and pH levels are maintained within manufacturer-specified ranges, directly preventing tube fouling, caustic embrittlement, silica carryover, and steam contamination.
Scope
This procedural directive applies to all Low-Pressure (LP) and High-Pressure (HP) steam boilers, including fire-tube and water-tube designs, operating in continuous or batch mode. It covers the responsibilities of stationary engineers, shift supervisors, and certified water treatment technicians. This specification explicitly excludes cooling tower, closed-loop chiller, and wastewater treatment protocols.
Safety Precautions
- Lockout/Tagout chemical feed pump circuit breaker at the motor control center (MCC). Verify zero energy state with a contact voltmeter. Attach personal LOTO hasp. Only the authorized employee who applied the lock may remove it.
- Don full-face shield (ANSI Z87.1), neoprene or nitrile gloves (18 mil minimum), and a Tychem or PVC chemical-resistant suit when handling or transferring caustic soda (NaOH), amines, or sulfite-based oxygen scavengers. An emergency eyewash/shower must be within a 10-second travel path.
- Contain all chemical drips and boiler water sample waste. Neutralize any caustic spill with a 10% citric acid solution immediately. Dispose of all treatment chemicals, test sample water, and used PPE per local environmental regulations and the facility's SPCC plan.
Required Tools & Materials
- Chemical treatment drums (oxygen scavenger, scale inhibitor, neutralizing amine)
- Chemical dosing pump (diaphragm or piston type) with calibration cylinder
- Boiler water sample cooler (required if sample temp exceeds 80°C) and 1L HDPE sample bottle
- Alkalinity test kit: 0.02 N sulfuric acid (H2SO4), phenolphthalein indicator, bromocresol green indicator
- pH meter calibrated with pH 7.0 and 10.0 buffer solutions, or high-range pH test strips (8–12)
- Conical flask (125 mL), graduated cylinder (50 mL), and digital burette (0.01 mL resolution)
- Deionized rinse water in a wash bottle
- Log sheet and tablet for CMMS entry (ServiceGrid)
Procedure: Step-by-Step
1
Pre-Job Hazard Assessment: Review the Safety Data Sheet (SDS) for each chemical being dosed. Confirm LOTO isolation points on the chemical feed pump. Verify that all required PPE is serviceable and that the eyewash station passes its activation check.
2
Boiler Water Sample Collection: Open the sample valve slightly and let water run for 2–3 minutes to fully purge the sample line. Fill the 1L HDPE bottle, rinsing it twice with boiler water before collecting the final sample. Pass the water through a sample cooler if the line temperature exceeds 80°C. Cap the bottle and allow it to cool to 25°C ± 2°C in a water bath.
3
pH Measurement: Rinse the pH electrode with deionized water and gently blot dry. Immerse the electrode in the cooled sample and swirl gently. Wait for the pH reading to stabilize (typically 30–60 seconds). Record the pH value. Acceptable operating range for most industrial boilers is pH 10.5 to 11.5. If using test strips, compare the color change against the chart within 15 seconds.
4
P Alkalinity Test (Phenolphthalein Indicator): Using a graduated cylinder, measure exactly 50 mL of the cooled sample and transfer it to a clean conical flask. Add 3–5 drops of phenolphthalein indicator. If the solution turns pink, titrate slowly with 0.02 N H2SO4 while swirling constantly, until the pink color just disappears (colorless endpoint). Record the volume of acid used. Calculate: P-Alk (ppm as CaCO3) = mLs of acid × 20.
5
M Alkalinity Test (Bromocresol Green / Methyl Red Indicator): To the same colorless sample from the P test, add 3–5 drops of bromocresol green indicator. The solution will turn blue. Continue titrating with the same 0.02 N H2SO4 until the color changes sharply from blue to a greenish-yellow. Record the total volume of acid used from the start of the P test. Calculate: M-Alk (ppm as CaCO3) = total mLs of acid × 20.
6
Assessment & Dosing Calculation: Compare the measured P-Alk, M-Alk, and pH values against the boiler manufacturer's water chemistry limits. Determine the required chemical adjustment. For example, if pH is below 10.5, calculate the volume of 50% caustic soda solution needed to raise the system pH based on the boiler water volume and feedwater flow rate. Enter the calculated values into the chemical dosing pump controller.
7
Chemical Dosing Pump Calibration: Verify the dosing pump is fully primed and that the suction line is free of air. Perform a calibration check using a graduated cylinder (bucket test). Measure the pump's actual output (mL/min) against the required setpoint. Adjust the stroke length or stroke speed to match the calculated dose requirement.
8
Documentation & CMMS Update: Immediately record all test results (pH, P-Alk, M-Alk, calculated chemical dose, final pump setting) in the shift log and/or directly into the CMMS (ServiceGrid). If any critical limit is exceeded, generate a flagged work order for immediate engineering review.
9
Housekeeping & Spill Containment: Ensure all chemical drums are bung-tight and stored in the secondary containment area. Wipe down any drips or residue from the dosing pump, sample station, and workbench. Dispose of all used titration samples, rinse water, and chemically-soiled PPE according to the facility's hazardous waste disposal protocol.