GF Piping Systems pH Installation & Maintenance. GF Piping Systems 2 Agenda What is pH pH...

GF Piping Systems

pH Installation & Maintenance

2 GF Piping Systems

Agenda

What is pH

pH Electrode Construction

Installation Tips

Sensor Storage & Maintenance

pH Calibration

pH System Troubleshooting

3 GF Piping Systems

What is pH?

4 GF Piping Systems

What is pH?

Expressing Concentration in Terms of pH

pH is a Unit of Measurement Defined as the Negative Logarithm of Hydrogen Ion Activity

(concentration and activity are closely related)• pH = -log [H+]

– Example: if the hydrogen concentration is 1.0 x 10-4 moles/liter, the pH is 4.0

O2-

H+ H+

H+ O2-

H+

+

5 GF Piping Systems

What is pH?

pH measures the relative amount of hydrogen (H+) ions compared to hydroxide ions in an aqueous solution:

• H20 = H+ + OH-

In an aqueous (water based) solution, the concentration of hydrogen ions multiplied by the concentration of hydroxide ions is a constant number:

• Kw = [H+][OH-], Kw = dissociation constant for water• At 25ºC, Kw = 1 X 10-14; at 35ºC, Kw = 1 X 10-14

O2-

H+ H+

H+ O2-

H+

+

6 GF Piping Systems

What is pH? Acids and Bases

Acid dissolves in water to furnish H+ ions

HCl H+ + Cl-

Hydrochloric Acid

HNO3 H+ + NO3-

Nitric Acid

HF H+ + F-

Hydrofluoric Acid

Base dissolves in water to

furnish OH- ions

NaOH Na+ + OH-

Sodium Hydroxide

KOH K+ + OH-

Potassium Hydroxide

NH4OH

NH4+ + OH-

Ammonium Hydroxide

pH

7 GF Piping Systems

What is pH?

• pH is a measure of hydrogen ions in a water based solution

• It is expressed in hydrogen ion concentration: pH = -log [H+]

• Acids and bases added to water changes the amount of H+ ions.

pH Hydrogen Ion (H+) Hydroxyl Ion (OH-)Acid 0 1 0.00000000000001

1 0.1 0.00000000000012 0.01 0.0000000000013 0.001 0.000000000014 0.0001 0.00000000015 0.00001 0.0000000016 0.000001 0.00000001

Neutral 7 0.0000001 0.00000018 0.00000001 0.0000019 0.000000001 0.00001

10 0.0000000001 0.000111 0.00000000001 0.00112 0.000000000001 0.0113 0.0000000000001 0.1

Alkaline 14 0.00000000000001 1

8 GF Piping Systems

How is pH expressed?

• pH measurement is expressed on a scale of 0.0 to 14.0

• pH electrode will produce 59.16 mv per pH unit at 25 °C

• pH of 7.0 is neutral (H+ ions = [10-7] and OH- ions = [10-7])

• More hydrogen ions (H+) is considered an acid

• More hydroxyl ions (OH-) is considered alkaline (base)

pH

mV

Acids Bases

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

+414 +355 +296 +237 +177 +118 +59 00 -59 -118 -177 -237 -296 -355 -414

9 GF Piping Systems

pH Values of Common Items

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0

4.9 % H2SO4

Lemons

Oranges

Tomatoes

Beer

Milk

Pure Water

Blood

Crackers

4.0% NaOH

pHNaOH = Sodium Hydroxide

H2SO4 = Sulfuric Acid

10 GF Piping Systems

pH Electrode Construction


Traditional pH Sensors

A combination pH sensor consists of: Reference electrodepH electrode Temperature element

Reference electrode pH electrode

Temperature element


pH Sensing Electrode

Hydrogen sensitive glass Inert glass stemA silver/silver chloride wire Buffered electrolyte solution

Hydrogen sensitive glass bulb

Electrolyte Solution:

Silver/Silver Chloride Wire

Sol-gel (silica oxide layer) on both sides of glass

Glass membrane thickness 0.2-0.5 mm

Glass stem


Silver/Silver chloride wire

Front Porous Junction

2nd reference chamber: KCl Electrolyte

1st reference chamber: 3.5 M KCL

2nd Junction

Silver wire

Sealed barrier

Plastic tubing

Silver Chloride

3.5 M KCL

Sealed barrier

Traditional Reference Electrode


To make a pH measurement, a pH and a Reference electrode are required. A combination pH sensor consists of a pH electrode and a reference

electrode built into one body.– A pH sensor has a glass membrane which is sensitive to H+ ions– A reference sensor has a porous membrane with electrolyte on the inside

Electrode Construction

pH Sensor Reference Sensor = Combination Sensor

and


Temperature Measuring Elements

• Pt 100, Pt 1000, 3K Balco, etc…

• Glass error of 0.03 pH /per pH unit/per10 degree C

°C 2 3 4 5 6 7 8 9 10 11 12

5 .30 .24 .18 .12 .06 0 .06 .12 .18 .24 .30

15 .15 .12 .09 .06 .03 0 .03 .06 .09 .12 .15

25 0 0 0 0 0 0 0 0 0 0 0

35 .15 .12 .09 .06 .03 0 .03 .06 .09 .12 .15

45 .30 .24 .18 .12 .06 0 .06 .12 .18 .24 .30

55 .45 .36 .27 .18 .09 0 .09 .18 .27 .36 .45

65 .60 .48 .36 .24 .12 0 .12 .24 .36 .48 .60

75 .75 .60 .45 .30 .15 0 .15 .30 .45 .60 .75

85 .90 .72 .54 .36 .18 0 .18 .36 .54 .72 .90

0 pH error range

0.1 pH error range


pH and Sensor Calibration

pH• Theoretical slope; 59.16 mV/pH unit at 25C. • Calibrate in pH buffer solutions to determined

actual slope. • Slope indicates the true performance of the pH

glass. • A slope of 49 to 59 is typically acceptable for a

working electrode. • Below 49, the pH glass is bad.

Theoretical output

01

23

45

67

89

1011

1213

14

-500

-400

-300

-200

-100

0

100

200

300

400

500

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

pH value

mill

ivol

ts

177 mV

0 mV

3 pH units


Installation Recommendations


Preamplification

Preamplifiers are required for pH sensor

• Preamplifiers boost high impedance signals

• Preamplification allows separation for hundreds of feet


Installation Tips

Hints for Installing sensors with preamplifiers

• Mount electrodes in a location with ample clearance for removal for periodic cleaning and recalibration.• Choose a location that keeps the electrode glass completely submerged at all times.• Place the electrode tip in pH 4 buffer during system maintenance or storage to avoid dehydration and reduce chemical activity.• Be aware of mounting positions-some sensors must be mounted +/- 45 degrees of the vertical.


Installation – In-Line

In larger diameter tee’s watch for stack height of tee fitting, and flush style reducer bushings making sure sensor tip is in process

< 1.5”


Installation : In-Line

2 ½ in Tee

2 ½ X 1½ in

Flush style

reducer bushing

1½ X ¾ in

Flush style

reducer bushing

1 2


Installation : Submersion

and seal tape threads

Use “o”-ring lubricant


pH Sensor In-Line Installation

Caution: Air Bubbles

and Air Pockets

Caution: Sediment

and debris Build-up

Caution: Sensor

needs to stay wet


pH Calibration


pH Sensor Calibration

Two point calibration:Standardize / Slope

Single point calibration:Grab sample

pH 4 pH 7 pH 10


pH / ORP Sensor Calibration

Two Point Buffer Calibration

• Calibrate when:• The sensor is initially installed to insure proper functioning• pH sensor is replaced

• Calibration establishes sensor slope; ensures linear output Slope decreases with:

– age, coating, elevated temp.– pH glass erosion by abrasion, strong NaOH, KOH or HF – coating from grease and oils

Acceptable mV/pH slope is typically 49 mV/pH to 59 mV/pH– Theoretical pH/mV slope @ 25ºC is 59.16 mV/pH


pH Sensor Calibration

Single Point pH Calibration (Standardize)

To Perform a grab sample evaluation• Take sample at or near pH sensor installation point

• Analyze grab sample ASAP using a portable or laboratory analyzer (avoid temperature change)

• Change the reading in the instrument to match the portable or laboratory analyzer

• Single point standardization:• Compensates for minor coating of the pH electrode.

• Compensates for small offsets in the liquid junction potential


pH System Start-up

Recommendations for simple start-up:

• Place the sensor in 7.0 pH Buffer solution

• Wait 10 minutes for temperature to equilibrate and cal temp

• Using 4 and 7 pH buffers cal meter

• Use fresh off-the-shelf buffer

• Triple rinse and place in process

• Allow minimum time to equilibrate

• Repeat Buffer calibration in 24 hours.

• Determine appropriate cleaning and calibrating schedule for your

application. Try weekly and based upon observed results

increase or decrease frequency for desired results.


Sensor Storage & Maintenance


pH Storage & Care

• When storing boxed sensors, lay the sensor flat to maximize hydration of the reference surface. Keep the reference surface wet at all times. Store sensors at a stable room temperature.

• Remove storage boot that sensor is shipped in; keep boot and re-boot with pH 4 buffer to keep sensors wetted during storage and transportation.

• If the sensor dehydrates: Clean sensor, and soak the sensor tip in pH 4 buffer for 24 to 48 hours, then visually inspect the electrode for surface cracks, swelling, or discoloration. Severely dehydrated electrodes cannot be restored to reliable operation.

• Never expose electrode to temperatures below 0° C or allow it to dehydrate. These conditions may damage the electrode.


pH Storage & Care

Store between 10 and 30°CUse protective caps with potassium chloride KCl solution or pH 4 bufferDo not allow to dry out, else problems

Slow response High glass resistance To fix, re-hydrate for 24-48 hours in 4 buffer or KCl solution

Factors that decrease sensor lifetime• Heat• Extreme cold• Vibrations


Sensor Cleaning

Rinse with DI or warm tap waterSoak for a few minutes in one of the solutions below Rinse with DI or tap waterRe-hydrate in pH 4 buffer or KCl solution, 1-24 hoursGentle use of toothbrush is ok

Cleaning Solvent/Solution Application

Warm water & detergent For normal applications

Less than 5% HCl acid For coatings of lime and hydroxides

Acetone or isopropyl alcohol For coatings containing oils & fats

Dilute bleach, 1-5% For coatings with algae, bacteria or molds


Cleaning Frequency

Keep sensor reasonably clean to maintain accuracy

Frequency depends on… Process Accuracy required Experience with application


pH/ORP System Troubleshooting


Possible Problems in Existing Installations

• Electrode cleaning and calibration. Electrodes should be removed and cleaned on a regular maintenance schedule depending on the application.

• Faulty electrode. Sensor life is application specific. High temperature and chemicals shorten lifetimes.

• Faulty amplifier assembly• Electrical wire problems. Some environments can cause the wiring to

corrode and cause faulty connections.


Potential Measuring Problems-Troubleshooting

• Use simulator to check electronics• Use raw mV values to investigate sensors• Use buffers to gauge:

response timeaccuracystability

• Best Practice: Use logs to record maintenance intervals and events

• Check critical connections make sure they are dry

• Check seal areas

• Check sensor surfaces for breakage or fouling

• Clean sensor and calibrate; if the sensor cannot be calibrated, it is probably

time to replace it


Potential Measuring Problems

Reference Cell

pH Sensitive Glass

Heavy metals like Hg++, Cu+, Pb++, ClO4

- Penetrate the Liquid Junction and react with KCl

Br-, I-, CN-, S- compounds penetrate liquid junction and react with Ag+

pH Measuring Electrode: Internal solution and silver chloride (AgCl) wire is protected from outside elements.

Extreme pH or temperature values, harsh chemicals, and hairline cracks will affect the reading

Silver Chloride Billet

pH (glass)

Silver Chloride Billet

Porous Reference Junction

KCl solution

Oils, grease, dirt, from the outside and silver compounds formed on the inside will clog the reference junction

Reference Electrode: There are many elements that can affect the reference electrode.

What can Affect a pH Measuring or Reference Electrode Output?

Stray electrical currents



pH Measurement Electrode– Process coating– Mechanical failure – Chemical attack

pH Reference Electrode– Poisoning– Junction Blockage– Depletion– Ground Loops


pH Troubleshooting

Measuring Offset:

• Thoroughly decontaminate electrode with clean water

• Clean electrode tip in beaker of 5% HCl solution, < 30 seconds

• Thoroughly rinse off HCl residue with clean water

• Place electrode in beaker of fresh 7.0 pH Buffer solution

• Using electrode gently stir buffer for about 10 seconds.

• Wait for mV on controller to stabilize (should only need a few seconds)

• mV value on controller display should be 0 mV, +/- 50 mV

• Make note of mV value and retain for determining Span.

Example: mV value measured in 7.0 pH Buffer = - 10 mV

Caution: Always wear appropriate safety gear and exercise proper safety practices when working with or near liquids & chemicals


pH Troubleshooting / Maintenance

Measuring Span:

• Remove electrode from 7.0 pH Buffer solution

• Thoroughly rinse electrode with clean water

• Place electrode in beaker of fresh 4.0 pH Buffer solution

• Using electrode gently stir buffer for about 10 seconds.

• Wait for mV on controller to stabilize (should only need a few seconds)

• mV value on controller display should be +177 mV away from the

value measured in 7.0 pH Buffer, +/- 50 mV.

Example: Offset value was -10 mV, therefore Span value should be

+167 mV, +/- 50 mV (+117 to +217 mV)

Caution: Always wear appropriate safety gear and exercise proper safety practices when working with or near liquids & chemicals


pH Troubleshooting

Occurrence: Effect:• Natural aging mV slowly drift more positive• Clogged Reference Slow response in same direction• Coated pH Glass ORP Tip Erratic drifting multiple direction• Damaged pH Glass Short Span• Sodium Ion Error Reads low above 12.5 pH• Attacked Reference Large Offset (prematurely)• Depleted Reference Large Offset (over time)• Cracked Glass mV value always around +55, or 0mV• Shorted Wiring mV value always around 0 mV• Moisture intrusion Very wrong mV values, erratic, stuck• Glass pH Etched >2% HF, or >12.5 pH

Note: Offset problems are typically associated with Reference half Span problems are typically associated with Measurement half



Ground Loop Problems

Sensor picks up current from improperly grounded circuit, typically from pumps, motors, or other closely located electrically driven equipment

NOTE: Plastic piping can be a source of this problem because:1. It picks up current or static charges from liquid flow2. And/or it picks up electrical current from pumps and other

equipment but may not have grounding

Reference Element can be stripped, shortening sensor life Differential Sensors eliminate the issue of stripped reference element Symptoms include sensor reading drifting, noisy, or erratic Eliminating Ground Loops:

1. Find and Fix Grounding Problem2. Use a Solution Ground3. Use a Differential Sensor with Solution Ground


pH: Assessing pH Application (step 1)

pH / ORP application:

• Application (scrubber adjust, waste treat adj, process adj, effluent monitoring, etc)

• Process range e.g., 3 – 5 pH

• Desired process value range e.g., 7.5 – 9.5 pH

• Process conductivity

• Process temperature range• Solution chemistry (what, percentage)

• Solution quality (DI water, oils / grease, sludge, crystals, solids)

• Chemical compatibility of all wetted components

• Distance from sensor to indicator• Inline (pipe size, material, flow rate, pressure, recirculation or single pass)

• In tank (tank size, flow rate, type of mixing, retention time, flow through or batch)

• Reagent type and concentration• Chemical dosing (proportional, on/ off)


pH Things To Watch For

• Dry Glass / Junction (keep submerged in liquid)• Clogging of reference (avoid build-up of solids, oils/grease, salts, etc)• Coating of Glass (avoid build-up of oils/grease, solids, salts, etc)• Etching of Glass (avoid >2% hydrofluoric, caustics above 12.5 pH, etc)• Stray electrical currents (plating baths, poor grounding)• Chemical attack of Reference Fill (minimize exposure to mercury,

copper, lead, perchlorate, etc)• Chemical attack of Reference Element (minimize exposure to

bromine, ammonia, iodine, sulphur, cyanide, etc)• Moisture intrusion at back of pre-amp (properly seal seal

chemistry, condensate)• Moisture intrusion between electrode & pre-amp (select proper

“O”-Ring and lubricant to properly seal out chemistry)• Cracked Glass (mount in an easily accessible area for maintenance, away

from mixer blades, do not drop)


pH Things To Watch For - continued

• Controlling pH (should only be performed in tank or recirculation loop)• Retention time (in flow through tank, size the tank to allow at least 10

minutes for every 3 pH units of neutralization)• Improve pH adjustment (use proportionally controlled metering pumps,

and provide proper mixing)• Elevated Temperature (increases ionic activity, decreasing electrode

life)• Temperature fluctuations (cause pumping of fill solution, decreasing

electrode life)• Low conductivity solutions (deplete electrode fill solution, decreasing

electrode life)• Mounting angles (use plunger type electrodes for mounting greater than

70° from vertical, or less than 30° from horizontal)


pH Questions & Answers

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GF Piping Systems pH Installation & Maintenance. GF Piping Systems 2 Agenda What is pH pH...

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