ASTM D6502 Standard Test Method for Measurement of On-line Integrated Samples of Low-Level Suspended Solids and Ionic Solids in Process Water by X-Ray Fluorescence (XRF)

Get Certified ASTM D6502 Testing for Reliable Process Water Corrosion Monitoring

Traditional corrosion-product sampling typically integrates a water sample over days and reports a single average value that masks short-term variations within the process. ASTM D6502 provides a time-resolved corrosion-product profile instead of relying only on a long-term averaged concentration. Plant operators use the resulting data to trace where corrosion products originate and how they move through the system, giving them a faster basis for operational response than a periodic lab sample allows.

The scope of ASTM D6502 includes-

• Material type: Process water from electricity-generating plant steam and water circuits that are sampled continuously through an on-line monitoring system.
• Purpose: Determination of low-level suspended solids and ionic solids concentration in flowing process water to form a continuous corrosion-product profile rather than a single integrated measurement.
• Properties evaluated: Concentration of multiple metals simultaneously, including titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, mercury, and lead, among others, within the XRF detector’s emission-energy range.
• Testing method: A technician operates a system that isolates a continuous flow of process water through a membrane filter for suspended solids and a resin membrane for ionic solids, followed by XRF analysis of the metals retained on the membranes to determine the concentration for the sampling period.
• Results: Metal concentrations in SI units that can be reliably reported at below 1 part per billion (ppb) for most metals.
• Test limitations: The procedure for the operation, calibration, and data analysis specific to the on-line monitoring system under review; laboratory analysis of discrete samples is outside the scope of this test method and is detailed in other relevant industry standards.
• Use conditions: The monitoring system operates from a flowing process-water stream and alternates between phases of accumulating a sample and analyzing the sample by XRF; the length of these phases can vary depending on the requirements of the monitoring program.
• Applications: Continuous corrosion-product monitoring, elucidation of corrosion-product source and transport mechanism, and supporting plant integrity and efficiency.

What are the Uses of ASTM D6502 Testing?

ASTM D6502 delivers a continuous corrosion-product profile that no grab sampling program can provide. The test method-

• Establishes a time-resolved concentration profile for multiple metals in the process water simultaneously.
• Detects corrosion product transients that a long-interval averaged sample would miss entirely.
• Supports operators in identifying the source of the detected metals and their transport mechanism throughout the plant.
• Tracks corrosion-product concentrations that can contribute to deposition on heat-transfer surfaces and affect plant efficiency.
• Provides more frequent monitoring data than long-period integrated sampling followed by separate analysis. 
• Feeds corrosion-management programs with data frequent enough to correlate against operational changes.
• Supports plant integrity assessment alongside other water-chemistry monitoring methods.

Which materials can be tested under ASTM D6502?

ASTM D6502 applies to process water within the steam and water circuits of electricity-generating plants. This standard test method is designed for continuous sampling of process water from flowing streams within the plant that contain suspended particulate corrosion products and ionic dissolved metals. An engineer seeking to assess a system’s corrosion risk using ASTM D6502 should first establish the relevant metal species within the process water, identify the concentration range needed for the application, and consider the characteristics of the flow stream available for sampling.

Why is ASTM D6502 Important?

Corrosion products transported within a power plant’s water circuit impact not only the corrosion risk of the system components but also the efficiency of the facility. Whereas a grab sample integrates over days and provides operators with an average value of the corrosion-product concentration, irrelevant to the mechanisms of metal entry to the process stream. ASTM D6502 continuously monitors and reports the concentration of metals in the process stream, enabling operators to correlate changes to particular events. Additionally, by detecting metal deposits forming on the surface of plant equipment, ASTM D6502 helps operators determine and address areas of concern before they affect the integrity of the facility.

ASTM D6502 Testing Process and Data Collection

An analyst determines the water circuit and metal species pertinent to the monitoring program of the facility. An operator installs the analyzer, establishes the flow of the process water, and sets the sampling interval using the control panel. The system then continuously accumulates the suspended and ionic metals on the membrane filters, analyzing the material by XRF to determine the concentration for the sampling interval. A technician monitors the filter status and replaces the membrane filter when the system indicates that the filter has reached its end of service. The analyst interprets the concentration trends across the sampling intervals and records the data along with the system and operating conditions.

Common Challenges and Troubleshooting

Filter blockage from excessive particulate buildup restricts flow and can distort the accumulation interval, so a technician should track flow rate and replace filter media before restriction becomes excessive. Calibration drift in the XRF detector changes reported concentrations over time, so regular calibration checks against known reference standards are worthwhile. Inconsistent flow rate through the system changes the effective sample volume per interval and skews the calculated concentration, so a technician should confirm flow stability throughout the run. Interference between metals with overlapping XRF emission energies can complicate identification at low concentrations, and an analyst should account for that when interpreting results near the detection limit. A technician should also verify that the resin membrane and filter media match the metals and concentration range the monitoring program targets.

• The technician records the system identification, sampling point, sampling interval, and flow rate for the monitoring program.
• The analyst reports the concentration of each monitored metal in micrograms per liter (µg/L), based on XRF measurement of the material accumulated on the filter or resin membrane.
• The report presents the results as a time-resolved profile of metal concentration, since the on-line monitoring is designed to follow changes over time rather than report a single number.
• The report notes any filter replacement events and the reason for replacement, since these mark breaks in the continuous accumulation record.
• The analyst compares the concentration profile against normal plant operating baselines to identify corrosion-product transients or trends.

Link to ASTM D6502