ASTM D5540-94a(2003)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:D 5540–94a (Reapproved 2003)
Standard Practice for
Flow Control and Temperature Control for On-Line Water
Sampling and Analysis
This standard is issued under the fixed designation D 5540; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Terminology
1.1 This practice covers the conditioning of a flowing water 3.1 Definitions—For definitions of terms used in this prac-
sample for the precise measurement of various chemical and tice, refer to Terminology D 1129.
physical parameters of the water, whether continuous or grab. 3.2 Definitions of Terms Specific to This Standard:
This practice addresses the conditioning of both high- and 3.2.1 crud deposition—deposition on interior surfaces of
low-temperature and pressure sample streams, whether from sample tubing or other hardware of fine insoluble particles of
steam or water. iron oxides and other byproducts of metallic corrosion that are
1.2 This practice provides procedures for the precise control present throughout the system. The term “crud” is generally
of sample flow rate to minimize changes of the measured used for all types of fouling.
variable(s) due to flow changes. 3.2.2 sample conditioning—reduction of the temperature
1.3 This practice provides procedures for the precise control and pressure of a flowing sample from process conditions to a
of sample temperature to minimize changes of the measured controlled temperature and pressure, and maintenance of a
variable(s) due to temperature changes. constant flow rate both in incoming sample lines and through
1.4 The values stated in either SI or inch-pound units are to on-line analyzers.
be regarded as the standard. The values given in parentheses 3.2.3 sample cooler—a small heat exchanger designed to
are for information only. cool small streams of water or steam.
1.5 This standard does not purport to address all of the 3.2.4 temperature compensation—adjustment of the ana-
safety concerns, if any, associated with its use. It is the lyzermeasuredvalueforvariationintemperatureofthesample
responsibility of the user of this standard to establish appro- from a preestablished value by the use of electronic adjustment
priate safety and health practices and determine the applica- or data manipulation.
bility of regulatory limitations prior to use.
4. Summary of Practice
2. Referenced Documents
4.1 This practice covers the system design, operating pro-
2.1 ASTM Standards: cedures, and selection of equipment to help ensure the appro-
D 1066 Practice for Sampling Steam priate flow and temperature control for analysis of water and
D 1129 Terminology Relating to Water steam samples. This control is essential to ensure the accuracy
D 1192 Specification for Equipment for Sampling Water and repeatability of on-line analyzers. Variations in types of
and Steam in Closed Conduits analysis, sample characteristics, and their effect on sample
D 3370 Practices for Sampling Water from Closed Con- conditioning are included.
duits 4.2 The equipment and procedures described in this practice
D 3864 Guide for Continual On-Line Monitoring Systems are intended to represent current state-of-the art technology
for Water Analysis available from major manufacturers of sample conditioning
equipment. Refer to Practices D 1066 and D 3370, Specifica-
tion D 1192, and Guide D 3864 for additional information on
This practice is under the jurisdiction of ASTM Committee D19 on Water and
sampling.
is the direct responsibility of Subcommittee D19.03 on Sampling of Water and
Water-Formed Deposits, Analysis of Water for Power Generation and Process Use,
On-Line Water Analysis, and Surveillance of Water. 5. Significance and Use
Current edition approved Sept. 15, 1994. Published November 1994. Originally
5.1 Sample conditioning systems must be designed to ac-
approved in 1994. Last previous edition approved in 1994 as D 5540 – 94a.
commodate a wide range of sample source temperatures and
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
pressures.Additionally, efforts must be made to ensure that the
Standards volume information, refer to the standard’s Document Summary page on
resultant sample has not been altered during transport and
the ASTM website.
3 conditioning and has not suffered excessive transport delay.
Withdrawn.
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D 5540–94a (2003)
Studies have shown that sample streams will exhibit minimal diameter, the steam velocity may be too low to transport the
deposition of ionic and particulate matter on wetted surfaces at condensed portion of the steam along with the vapor. If the
specific flow rates (1–5). sample tubing has too small an inside diameter, the pressure
5.1.1 To ensure that the physical and chemical properties of drop may be excessive, reducing the quantity of sample
the sample are preserved, this flow rate must be controlled available at the sample panel. In the case of super-heated
throughout the sampling process, regardless of expected steam, significant ionic deposition can occur in the sample
changes of source temperature and pressure, for example, tubing transport as the steam desuperheats. This can affect
during startup or changing process operating conditions. sample analysis accuracy significantly. Superheated samples
5.2 The need to use analyzer temperature compensation should use a process to inject cooled sample into the sample
methods is dependent on the required accuracy of the measure- line at or near the nozzle outlet to desuperheat the sample so as
ment. Facilities dealing with ultra-pure water will require both to minimize deposition in the initial portion of the tubing run.
closely controlled sample temperature and temperature com- 6.4 Samples may become contaminated by products intro-
pensation to ensure accurate measurements. The temperature duced into the stream by the tubing, valves, or other associated
canbecontrolledbyaddingasecondortrimcoolingstage.The conditioning hardware. To minimize contamination of the
temperature compensation must be based on the specific sample, high-grade tubing, such asAISI Type 316 SS, must be
contaminants in the sample being analyzed. In other facilities used. Cobalt contamination from valve hardening material can
in which some variation in water chemistry can be tolerated, introduce significant error in transition metal analysis by ion
the use of either trim cooling or accurate temperature compen- chromatography.
sation may provide sufficient accuracy of process measure- 6.5 AirleakageintosamplelinescanaffectpH,conductivity
ments. This does not negate the highly recommended practice (specific, cation, and degassed), and especially dissolved oxy-
of constant temperature sampling, especially at 25°C, as the gen measurements.
most proven method of ensuring repeatable and comparable 6.6 The operation of a sample system includes periodically
analytical results. taking grab samples and adding and removing on-line analyz-
5.3 A separate class of analysis exists that does not require ers.Theaccuracyoftheanalysescanbeaffectediftheflowrate
or, in fact, cannot use the fully conditioned sample for accurate through any on-line analyzer changes because of these proce-
results. For example, the collection of corrosion product dures. The same is true if these actions change the flow rate in
samples requires that the sample remain at near full system the incoming sample line to the system.
pressure, but cooled below the flash temperature, in order to 6.7 Changingthetemperatureofthesampleflowingthrough
ensure a representative collection of particulates. Only some of an on-line analyzer can alter the accuracy of the analysis.
theprimaryconditioningcriteriaapplyinthiscase,asinothers. Sample temperature can change because of a change in flow
Temperature compensation is not applicable since the material rate through the heat exchangers, because of a change of flow
being analyzed is not in a liquid state. rate of the cooling water in the heat exchangers, or from a
change in temperature of the heat exchanger cooling water
6. Interferences
supply. Every effort should be made to ensure constant sample
temperature. The ideal sample temperature is 25 6 0.5°C
6.1 Samples can be degraded by the loss of ionic or
(77 6 1°F) because this is the standard for comparing readings
particulate components, introduction of contaminants by com-
of temperature-sensitive analyses.
ponents or leaks, changes of sample flow rate through an
analyzer, excessively long sample lines, sample temperature 6.8 Electronic compensation is able to compensate for the
deviations in sample temperature for a known chemical matrix
changes, and inaccurate temperature compensation of on-line
analysis equipment. (contamination). If an unknown source of contamination is
introduced, the analyzer may not be programmed, or program-
6.2 Studies (3–5) have shown that the loss of ionic and
particulate components is minimized by maintaining the water mable,torespondtothenewsolution.Anerrorisintroducedas
a result. The further the sample temperature deviates from
samplevelocityat1.8m/sinthesampletubingtransportingthe
sample. The turbulent flow at 1.8 m/s (6 ft/s) presents a stable 25°C (77°F), the greater the error.
6.9 In sliding pressure or cycling power plants, or both, in
condition of deposition and removal. Changes in sample flow
rate or flow rates beyond a median range of approximately 1.8 which sample inlet pressures vary, the sample flow methodol-
ogydetailedinthispracticeshouldbemodifiedtoautomatethe
m/s can upset this equilibrium condition.
6.3 Saturated steam and superheated steam samples present flow control process to ensure constant sample flow for
high-accuracy analysis.
difficulttransportproblemsbetweenthesourceandtheprimary
sample cooling equipment (4). Saturated steam samples with
7. Apparatus
transport velocities typically above 11 m/s (36 ft/s) provide
7.1 Sample Tubing— Tubing should be high quality such as
adequate turbulent flow to ensure the transport of most
AISI Type 316 SS and be sized to maintain appropriate flow to
particulates and ionic components. Excessively large or small
minimize sample analysis errors. The tubing inside diameter is
steam sample lines can affect the sample quality and quantity
the critical dimension. Heavy-wall tube with an appropriate
significantly. If the sample tubing has too large an inside
inside diameter size selected to provide proper flow rate (see
6.2) can be used for construction strength.
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