ASTM D5540-94a(1999)

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
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Designation: D 5540 – 94a (Reapproved 1999)
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 3.2 Definitions of Terms Specific to This Standard:
3.2.1 crud deposition—deposition on interior surfaces of
1.1 This practice covers the conditioning of a flowing water
sample tubing or other hardware of fine insoluble particles of
sample for the precise measurement of various chemical and
iron oxides and other byproducts of metallic corrosion that are
physical parameters of the water, whether continuous or grab.
present throughout the system. The term 88crud” is generally
This practice addresses the conditioning of both high- and
used for all types of fouling.
low-temperature and pressure sample streams, whether from
3.2.2 sample conditioning—reduction of the temperature
steam or water.
and pressure of a flowing sample from process conditions to a
1.2 This practice provides procedures for the precise control
controlled temperature and pressure, and maintenance of a
of sample flow rate to minimize changes of the measured
constant flow rate both in incoming sample lines and through
variable(s) due to flow changes.
on-line analyzers.
1.3 This practice provides procedures for the precise control
3.2.3 sample cooler—a small heat exchanger designed to
of sample temperature to minimize changes of the measured
cool small streams of water or steam.
variable(s) due to temperature changes.
3.2.4 temperature compensation—adjustment of the ana-
1.4 The values stated in either SI or inch-pound units are to
lyzer measured value for variation in temperature of the sample
be regarded as the standard. The values given in parentheses
from a preestablished value by the use of electronic adjustment
are for information only.
or data manipulation.
1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
4. Summary of Practice
responsibility of the user of this standard to establish appro-
4.1 This practice covers the system design, operating pro-
priate safety and health practices and determine the applica-
cedures, and selection of equipment to help ensure the appro-
bility of regulatory limitations prior to use.
priate flow and temperature control for analysis of water and
2. Referenced Documents steam samples. This control is essential to ensure the accuracy
and repeatability of on-line analyzers. Variations in types of
2.1 ASTM Standards:
analysis, sample characteristics, and their effect on sample
D 1066 Practice for Sampling Steam
2 conditioning are included.
D 1129 Terminology Relating to Water
4.2 The equipment and procedures described in this practice
D 1192 Specification for Equipment for Sampling Water
2 are intended to represent current state-of-the art technology
and Steam in Closed Conduits
available from major manufacturers of sample conditioning
D 3370 Practices for Sampling Water from Closed Con-
2 equipment. Refer to Practices D 1066 and D 3370, Specifica-
duits
tion D 1192, and Guide D 3864 for additional information on
D 3864 Guide for Continual On-Line Monitoring Systems
sampling.
for Water Analysis
5. Significance and Use
3. Terminology
5.1 Sample conditioning systems must be designed to ac-
3.1 Definitions—For definitions of terms used in this prac-
commodate a wide range of sample source temperatures and
tice, refer to Terminology D 1129.
pressures. Additionally, efforts must be made to ensure that the
resultant sample has not been altered during transport and
This practice is under the jurisdiction of ASTM Committee D-19 on Water and conditioning and has not suffered excessive transport delay.
is the direct responsibility of Subcommittee D19.03 on Sampling of Water and
Studies have shown that sample streams will exhibit minimal
Water-Formed Deposits, Surveillance of Water, and Flow Measurement of Water.
Current edition approved Sept. 15, 1994. Published November 1994. Originally
published as D 5540 – 94. Last previous edition D 5540 – 94.
Annual Book of ASTM Standards, Vol 11.01.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 5540
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
can be controlled by adding a second or trim cooling stage. The conditioning hardware. To minimize contamination of the
temperature compensation must be based on the specific sample, high-grade tubing, such as AISI 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 Air leakage into sample lines can affect pH, 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. The accuracy of the analyses can be affected if the flow rate
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 Changing the temperature of the sample flowing through
ensure a representative collection of particulates. Only some of an on-line analyzer can alter the accuracy of the analysis.
the primary conditioning criteria apply in this case, as in others. 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
6.8 Electronic compensation is able to compensate for the
analyzer, excessively long sample lines, sample temperature
changes, and inaccurate temperature compensation of on-line deviations in sample temperature for a known chemical matrix
(contamination). If an unknown source of contamination is
analysis equipment.
6.2 Studies (3–5) have shown that the loss of ionic and introduced, the analyzer may not be programmed, or program-
mable, to respond to the new solution. An error is introduced as
particulate components is minimized by maintaining the water
sample velocity at 1.8 m/s in the sample tubing transporting the a result. The further the sample temperature deviates from
25°C (77°F), the greater the error.
sample. The turbulent flow at 1.8 m/s (6 ft/s) presents a stable
condition of deposition and removal. Changes in sample flow 6.9 In sliding pressure or cycling power plants, or both, in
which sample inlet pressures vary, the sample flow methodol-
rate or flow rates beyond a median range of approximately 1.8
m/s can upset this equilibrium condition. ogy detailed in this practice should be modified to automate the
flow control process to ensure constant sample flow for
6.3 Saturated steam and superheated steam samples present
difficult transport problems between the source and the primary high-accuracy analysis.
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
diameter, the steam velocity may be too low to transport the
6.2) can be used for construction strength.
7.2 Primary Sample Coolers—Heat exchangers, designed
to handle high-pressure and high-temperature samples and
The boldface numbers in parentheses refer to the list of references at the end of
this practice. provide efficient cooling with approach temperatures of below
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 5540
1°C (2°F), should be selected. Generally, AISI Type 316 SS is
an appropriate sample tube material; however, other material
selections may be necessary based on incoming sample tem-
perature and cooling water impurities, that is, chlorides.
7.3 Pressure Reducers—Pressure reduction is accomplished
with a variable orifice. A high-quality needle valve performs
well for source pressure less than 34.5 bar (500 psig). A
variable rod-in-tube device performs well for pressures 34.5
bar and greater because it is basically non-wearing and
minimizes sample dissociation during pressure reduction.
7.4 Pressure Regulating Device—To maintain constant
sample pressure at the inlet to each analyzer train, a variable or
fixed back pressure regulating valve or a head cup may be
used.
7.5 Secondary or Trim Sample Cooler—Similar to the
primary sample cooler, this heat exchanger should be a device
capable of maintaining a sample outlet temperature within
0.5°C (1°F) of the incoming cooling water temperature to
ensure constant outlet temperature, even with significant varia-
tions in sample flow or heat load.
7.6 Sample Flow Indicator(s)—A non-valved rotameter or
other flow indication device in the main sample line or flow
indication device, or both, in all branch lines (analysis, grab,
and bypass) is typically used. A method of measuring total
sample flow in accordance with recommended velocities must
NOTE 1—Fixed back pressure regulating valves (V4) are available and
be used (see 6.2 and 8.4 ).
eliminate the need to adjust back pressure and readjust the flow. This fixed
7.7 Temperature Indicator—A mechanical or electronic in-
pressure regulating valve provides the added benefits of acting as a sample
dication of sample temperature must be provided to help the
relief valve and grab sample discharge.
operator monitor sample conditions and confirm the efficiency
NOTE 2—In ultra-pure water applications, it is not uncommon for the
of the heat exchangers.
sample flow indicator (FI) to be placed in the sample bypass line and the
valved flow meter(s) (FICV) to be placed after the analyzer elements to
avoid the possibility of air inleakage, which could affect sample quality.
8. Procedure
FIG. 1 Schematic of a Typical Sample Line
8.1 Procedure for Establishing Constant Flow:
8.1.1 Confirm that the sample tube transporting the sample
is sized properly to ensure the sample velocities noted in 6.2
8.2.1 Temperature reduction and control of the sample is
and 6.3. Keep the sample lines as short as possible (particularly
best accomplished in two stages: primary and secondary
steam) to eliminate alteration of the sample prior to the primary
cooling. If only one stage of cooling is used, the temperature of
cooling point.
each sample will be constant with constant flow, but each
8.1.2 Flow control of the sample streams involves two
sample will have a different temperature because of different
stages. The first is reduction of the pressure from the source to
source temperatures and pressures supplied to the primary
a lower value and establishment of the desired flow in the
sample cooler. Using a second stage of cooling will bring the
incoming line. The second is maintenance of the reduced
temperature of all the samples to the same constant temperature
pressure at a constant value so that flow through the analyzers
(recommended at 25°C (77°F)). Refer to 6.7 and 6.8.
will remain constant.
8.2.2 Refer to the first stage of
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