www.swan.ch ·
SWAN ANALYTISCHE INSTRUMENTE AG · CH-8340 Hinwil / SWITZERLAND · TEL. +41 44 943 63 00
Application Note: Measuring Hydrogen in Water Steam Cycle to Predict and Prevent
Potential Corrosion
Every year, corrosion costs the electric utility industry billions of dollars. International guidelines are
available for water chemistry control to minimize corrosion. Parameters such as pH, oxygen, iron,
hydrogen and others are directly related to corrosion control and used for monitoring corrosion.
International technical organizations and power plant chemists are working diligently to find a
suitable method to provide real-time corrosion trend monitoring in their process during
commissioning and normal operation.
Hydrogen monitoring in this case is becoming important in corrosion monitoring for water steam
cycle [1, 2, 3]. Corrosion occurs in the presence of water contact with iron at high temperature.
According to the Schikorr reaction (Eq. 1), hydrogen is released as a by-product during the formation
of the magnetite and hematite layer in the power plant. Therefore its concentration is a direct
measure of the rate of corrosion.
(Eq. 1)
During commissioning of a new power plant, commissioning engineers need the formation of
uniform iron oxides as a protective layer on the surface of the metallurgy to limit further corrosion of
the steel. However, some iron oxides are disrupted and formed again during operation. The
disruption and formation of the iron oxides layer will release hydrogen gas. Even though other
possible sources of hydrogen exist, measuring dissolved hydrogen concentration in the process will
provide valuable indication of an active corrosion rate in the system.
Various tests and research have been carried out to identify suitable sampling points for a
representative sample. Hydrogen concentration is commonly measured in the steam or feedwater[4]
to ensure that corrosion rates are kept at an acceptable level.
Guidelines for hydrogen levels are not well defined and may vary from plant to plant. Available
research indicates hydrogen levels occur at a few ppb (part per billion) during normal operation and
as much as several hundred ppb during commissioning. However, hydrogen values greater than
10ppb-50ppb under normal working condition may be an indication of permanent damage to the
boiler.
Graph 1 shows typical hydrogen measurement in a once-through superheated steam boiler. The
power plant is using oxygen treatment with ammonium as an alkalizing agent in the water steam
cycle. Dissolved hydrogen measurement tracking in superheated steam provides an indication of the
corrosion trend in the boiler. This information is very useful to plant chemists for corrosion
monitoring and control. The plant chemist could take the necessary action to mitigate corrosion.
Information in the graph indicates that the corrosion rate is under control.
Graph 2 shows hydrogen measurement in feedwater (economizer inlet). The graph indicates increase
of dissolved hydrogen in feedwater at various times. This indirectly represents increasing of corrosion
rate in the feedwater system. The dissolved hydrogen increase appears before corrosion is excessive.
Corrective action was taken to reduce and control corrosion in feedwater.
Eric CHAN, SWAN Analytische Instrument AG, Switzerland
Page 1 of 3
www.swan.ch ·
SWAN ANALYTISCHE INSTRUMENTE AG · CH-8340 Hinwil / SWITZERLAND · TEL. +41 44 943 63 00
Hydrogen Measurement in
Once-Through Superheated Steam Boiler
[µg/kg] H2
3.50
3.00
2.50
2.00
1.50
1.00
0.50
0.00
01.10.2012 13:12
01.10.2012 01:12
30.09.2012 13:12
30.09.2012 01:12
29.09.2012 13:12
29.09.2012 01:12
28.09.2012 13:12
28.09.2012 01:12
27.09.2012 13:12
27.09.2012 01:12
26.09.2012 13:12
26.09.2012 01:12
25.09.2012 13:12
25.09.2012 01:12
24.09.2012 13:12
24.09.2012 01:12
23.09.2012 13:12
23.09.2012 01:12
22.09.2012 13:12
Time
Graph 1: Online Hydrogen measurement in Superheated Steam for Once-Through Boiler in 1100MW
Lignite-Fire Unit Power Plant.
Hydrogen Measurement in Feedwater
[ug/kg] H2
1.00
0.90
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.00
27.07.12 00:00:00
26.07.12 00:00:00
25.07.12 00:00:00
24.07.12 00:00:00
23.07.12 00:00:00
22.07.12 00:00:00
21.07.12 00:00:00
20.07.12 00:00:00
19.07.12 00:00:00
18.07.12 00:00:00
17.07.12 00:00:00
16.07.12 00:00:00
Time
Graph 2: Online Hydrogen measurement in Feedwater (or Economizer inlet) in 660MW Coal-Fired
Unit Power Plant.
Eric CHAN, SWAN Analytische Instrument AG, Switzerland
Page 2 of 3
www.swan.ch ·
SWAN ANALYTISCHE INSTRUMENTE AG · CH-8340 Hinwil / SWITZERLAND · TEL. +41 44 943 63 00
References:
1. VGB Powertech; Feed Water, Boiler Water and Steam Quality for Power Plant/ Industrial
Plant; VGB-S-010-T-00; 2011-12.EN (formally VGB-R 450Le).
2. EPRI Technical Report 1012209; Fossil Plant Cycle Chemistry Instrumentation and ControlState-of-Knowledge Assessment; March 2007
3. Baldessari A.; An Introduction to Corrosion Monitoring; June 05; Protan S.A.
4. EPRI Technical Report 112024; Reference Manual for Online Monitoring of Water Chemistry
and Corrosion; Final Report; April 1999.
Eric CHAN, SWAN Analytische Instrument AG, Switzerland
Page 3 of 3