Friday, January 1, 2010

DEADLINE EXTENSION - PLEASE RESPOND - TG 020 Ballot

For those of you who signed up to vote on the proposed revision of the "NACE Standard TM0497-2002 - Measurement Techniques Related to Criteria for Cathodic Protection on Underground or Submerged Metallic Piping Systems" the deadline for voting has been extended to January 11, 2010. NACE has not received the 50% response from the STG voters necessary to close this TG 020 Ballot.

Please respond to the ballot if you have not. I have attached my negative response below.

COMMENTS ON SPO497 REVISION

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Third Paragraph - Second Sentence

It includes methods for voltage drop considerations when pipe-to-electrolyte potential measurements are made and provides guidance to prevent minimize incorrect data from being collected and used.

Change “prevent” to “minimize”. This document can not prevent someone from taking incorrect data, but if followed, can minimize the problem.

Definitions

Coating: A liquid, liquefiable, or mastic composition that, after application to a surface, is converted into a solid protective, decorative, or functional adherent film.

Definition needs to be changed to below since pipeline coatings are much more than the proposed definition.

Coating: (1) A liquid, liquefiable, or mastic composition that, after application to a surface, is converted into a solid protective, decorative, or functional adherent film; (2) (in a more general sense) a thin layer of solid material on a surface that provides improved protective, decorative, or functional properties. For the purposes of this standard, “Coating” is defined as an electrically insulating material applied to the surface of a metallic structure that provides an adherent film which protects a metallic structure from the surrounding electrolyte.

Section 4: Instrumentation and Measurement Guidelines

4.1 Valid cCathodic protection electrical measurements require proper selection and use of instruments. Pipe-to-electrolyte potential, voltage drop, potential difference, and similar measurements require instruments that have appropriate voltage ranges. The user should must know the capabilities and limitations of the equipment, follow the manufacturer’s instruction manual, and be skilled in the use of electrical instruments.

Change second sentence to read –

The user should must know or be directed by someone who knows the capabilities and limitations of the equipment, follow the manufacturer’s instruction manual, and be skilled in the use of electrical instruments.

Reason: Someone just starting in CP work will need to be under the direction of someone who is experienced in the use of these instruments.

4.3.1 To measure pipe-to-electrolyte potentials accurately, a digital voltmeter must have a high input impedance (high internal resistance, for an analog instrument) compared with the total resistance of the measurement circuit.

To what “accuracy” do we make these measurements? Delete the word “accurately” unless the level of accuracy is defined.

4.3.1.1 An input impedance of 10 MΩ or more should be sufficient for a digital meter. An instrument with a lower input impedance may produce valid data if circuit contact errors are considered. One means of making accurate measurements is to use a potentiometer circuit in an analog meter.

Delete the second and third sentence. The first sentence is all that is needed. The rest is confusing and would need much more detail.

4.3.2 Some analog-to-digital converters used in digital and data logging instruments operate so fast that the instrument may indicate only a portion of the input waveform and thus provide incorrect voltage indications.

Why include such meters if they are incorrect? Delete this sentence and all other references to these type meters or add more definition to clarify which instruments are not acceptable.

4.3.3 Parallax errors on an analog instrument can be minimized by viewing the needle perpendicular to the face of the instrument on the centerline projected from the needle point.

Define “Parallax”.

4.3.4 The accuracy of potential measurements should be verified by using an instrument having two or more input impedances (internal resistance, for analog instruments) and comparing potential values measured using different input impedances. If the measured values are virtually the same, the accuracy is acceptable. Corrections need to be made if measured values are not virtually identical. Digital voltmeters that have a constant input impedance do not indicate a measurement error by changing voltage ranges. An alternative is to use a meter with a potentiometer circuit.

In 4.3.1.1 indicates if a digital meter of 10 MΩ of impedance or more is used, then this should not be a problem for digital meters. Why complicate the matter. 4.4 tells how to check for the accuracy of the meter.

Information like this if needed should be placed in Appendix.

5.5 A pipe-to-electrolyte potential is measured using a DC voltmeter having an appropriate input impedance (or internal resistance, for an analog instrument), voltage range(s), test leads, and a stable reference electrode, such as a saturated copper/copper sulfate (CSE), silver/silver chloride (Ag/AgCl), or saturated potassium chloride (KCl) calomel reference electrode (SCE). The CSE is usually used for measurements when the electrolyte is soil or fresh water and less often for salt water. When a CSE is used in a high-chloride environment, the stability (lack of contamination) of the CSE must be determined before the readings may be considered valid. The Ag/AgCl reference electrode is usually used in seawater environments. The saturated KCl calomel electrode is used more often for laboratory work. However, more rugged, polymer body, gel- filled saturated KCl calomel electrodes are available, though modifications may be necessary to increase contact area with the environment.

Where is the reference for zinc? Some still use zinc for reference electrodes and we teach it in the CP classes. We should have guidance in this document for zinc also.

5.7 Valid The pipe-to-electrolyte potential measurement of a buried pipe should be are made with the reference electrode placed close to the metal/electrolyte interface of the pipe. The common practice, however, is to place the reference electrode as close to the pipe as practicable, which is usually at the surface of the earth above the centerline of the pipe. (See Figure 1[a].) This measurement includes a combination of the voltage drops associated with the:

Change last sentence:

This measurement includes, but is not limited to, a combination of voltage drops associated with the:

Reasoning: There could be other possible voltage drops that may affect these potential readings such as contact resistant of reference electrode contact to the electrolyte, etc.

5.8 The pipe-to-electrolyte potential measurement as described above is a resultant of the:

(a) Voltage drop created by current flowing through the electrical resistances of the items listed in Paragraph 5.7; and

(b) For coated pipe, the influence of coating holidays, depending on their location, number, and size.

Remove part “b”. We have already mentioned that coating has an affect on the reading. The holidays in the coating are part of the circuit, but there are many others that also affect it. Do we list all of them? If needed make a separate section or add it to the 7.1.4 section. Make one statement:

5.8 The pipe-to-electrolyte potential measurement as described above is a result of the voltage drop created by current flowing through the electrical resistances of the items listed in Paragraph 5.7.

5.9 (d) Parallel coated pipelines, electrically connected and polarized to different potentials;

Restate:

(d) Parallel pipelines (coated or bare) and other metal structures, electrically connected and polarized to different potentials;

Reasoning; All metal structures connected to the circuit will affect the potentials.

(i) Unknown, inaccessible, or direct connected galvanic anodes;

Restate;

(i) Galvanic anodes, known or unknown, connected to the pipe;

Reasoning; Galvanic anodes are going to affect the potentials whether they are known or not and whether they are inaccessible or direct connected.

5.10 Voltage drops other than those across the pipe metal/electrolyte interface shall be considered for valid interpretation of pipe-to-electrolyte voltage measurements made to satisfy a criterion. Measurement errors should must be minimized to ensure reliable pipe-to-electrolyte potential measurements.

Reword or remove the last sentence. The first sentence should be sufficient since we say the voltage drops shall be considered.

5.12 When voltage drops have been evaluated at a test location and the pipe-to-electrolyte potential found to be satisfactory, the ―on‖ pipe-to-electrolyte potential value may be used for monitoring until significant environmental, structural, or cathodic protection system parameters change.
5.12.1 Significant environmental, structural, or cathodic protection system parameter changes may include:
(a) Replacement or addition of piping;
(b) Addition, relocation, or deterioration of cathodic protection systems;
(c) Failure of electrical isolating devices;
(d) Effectiveness of coatings; and
(e) Influence of foreign structures (bonded or not).

Do we need to further define significant?

Section 6: Causes of Measurement Errors ????????

Are these really errors? Change to:

Causes of Measurement Inaccuracies

6.1 Factors that contribute to faulty inaccurate potential measurements include:

Add:

‘’’’’’’ potential measurements include, but are not limited too:

6.1.2 (e) Reference electrode placed in the potential gradient of an anode;

When we take potentials on a cathodically protected pipeline are we not always in a potential gradient of an anode? If not, we will not be protected.

(e) Reference electrode placed in the potential gradient of too close to a galvanic or impressed current anode;

(f) Reference electrode positioned in the potential gradient of a metallic structure other than the one with the potential being measured;

Again this is a statement that can not be measured or defined easily. How can we prevent this when in a ROW with multiple pipelines and CP systems? Either explain and define this better or leave it out!

(g) Electrolyte between pipe and disbonded coating causing error due to electrode placement in electrolyte on opposite side of coating;

This does not cause an error in the potential as related to the cathodic protection at that location.

Suggested change:

(g) Electrolyte between pipe and disbonded coating causing error due to electrode placement in electrolyte on opposite side of coating; can be shielded by certain coatings from the cathodic protection current and if shielded will not be in the same circuit as the electrolyte external to the disbondment and will not have the same potential as the surrounding electrolyte;

6.1.6 Instrument having an analog-to-digital converter operating at such a fast speed that the voltage spikes produced by current interruption are indicated instead of the actual “on” and “off” values.

How is any one going to know this? When did we get equipment that can actually measure the “actual” ON and Instant Off potentials?

6.1.8 Cathodic protection current-carrying conductor used as a test lead for a pipe potential measurement.

Please be more descriptive. All wires we use to measure potentials have carry current or we could not make voltage measurements. Suggestion:

6.1.8 Cathodic protection current-carrying conductor, such as the negative lead of the rectifier, used as a test lead for a pipe potential measurement.

Or make a list of such current carrying conductors.

6.1.9.1 Electromagnetic interference or induction resulting from AC power lines or radio frequency transmitters inducing test lead or instrument errors. This condition is often indicated by a fuzzy, fluctuating, or blurred pointer movement on an analog instrument or erratic displays on digital voltmeters. A DC voltmeter must have sufficient AC rejection capability, which can be determined by referring to the manufacturer’s specification.

Is “Fuzzy” a technical word to be used in this document? If so, define it!

What is “sufficient” AC rejection? Terms like these need to be defined or acceptable limits placed on them.

6.2.1 Soil moisture—If the surface soil is so dry that the electrical contact of the reference electrode with the electrolyte is impaired, the soil around the electrode may be moistened with water until the contact is adequate.

How do we know when “contact is adequate”? Once again this must be defined or better explained.

6.2.4 Concrete or asphalt paved areas— All readings shall be taken with reference electrodes that are in contact with the electrolyte. Readings shall not be taken through concrete or asphalt. Soil contact may be established through at-grade openings or by drilling a small hole through the concrete or asphalt., or by contacting a seam of soil between concrete and asphalt.

Remove “, or by contacting a seam of soil between the concrete or asphalt.” How wide should this seam be? Soil may only be in a surface crack that does not extend completely through the concrete or asphalt and there is not a way too determine this.

7.1.1 Measurement Circuit— The voltage drop other than across the pipe metal/electrolyte interface in the measurement circuit is the sum of the individual voltage drops caused by the meter current flow through individual resistances that include:

Change to “voltage drops caused by the meter current flow through individual resistances that include, but are not limited to:

Reason: The “current” in this circuit is not from the meter, but from the CP system.

Add: voltage drops caused by the current flow through individual resistances that include, but are not limited to:

A measurement error occurs if the analog meter internal resistance or the digital meter internal impedance is not several orders of magnitude higher than the sum of the other resistances in the measurement circuit.

Should this not be 7.1.2 or if it is a part of 7.1.1 then it should be 7.1.1.1? Suggest replacing “error” with “inaccuracy”.

7.1.2 Pipe—Current flowing within the pipe wall creates a voltage drop. This voltage drop and the direction of the current shall be considered when the reference electrode is not near the pipe connection and significant current is conducted by the pipe. Consideration is needed because an error in the pipe-to-electrolyte potential measurement will occur if the pipe current causes a significant voltage drop. Current directed to the pipe connection from the reference electrode causes the measured potential to be more negative by the amount of the pipe current voltage drop (see Figure 2[a]). Conversely, the potential is less negative by that amount if the pipe current direction is from the pipe connection to the reference electrode (see Figure 2[b]).

The use of the word “significant” in sentence 2 and 3 needs to be defined or deleted. Replace “error” with “inaccuracy” in the third sentence.

(b) A voltage drop caused by large voltage gradients in the electrolyte that occur near operating anodes (sometimes termed “raised earth” effect).

Remove (sometimes termed “raised earth” effect) or define it.

7.1.4 Coatings—Most coatings provide protection to the pipe by reducing the pipe surface contact with the environment. Due to the relative ionic impermeability of coatings, they resist current flow. While the insulating ability of coatings reduces the current required for cathodic protection, coatings are not impervious to current flowing through them. Current flow through the coating causes a voltage drop that is greater than when the pipe is bare, under the same environmental conditions.

7.2 Specialized equipment that uses various techniques to measure the impressed current waveform and to calculate a pipe-to-electrolyte potential free of voltage drop is available. This equipment may minimize problems resulting from spiking effects, drifting of interrupters, and current from other DC sources.

Do these instruments actually give a potential “free” of voltage drop or just minimize the affect? There are too many variables in taking potentials to say any method would truly eliminate all voltage drops.

Restate: Specialized equipment that uses various techniques to measure the impressed current waveform and to calculate a pipe-to-electrolyte potential free to help minimize the of voltage drop is available.

8.2.2 Test Method 1 measures the pipe-to-electrolyte potential as the sum of the polarized potential and any voltage drops in the circuit. These voltage drops include those through the electrolyte and pipeline coating from current sources such as impressed current, galvanic anodes, and telluric effects.

Restate first sentence: Test Method 1 is the “ON” potential which is a sum of the native potential, polarization caused by the CP and voltage drops in this circuit.

Restate second sentence: These voltage drops include, but are not limited to those through the electrolyte and pipeline coating from current sources such as impressed current, galvanic anodes, and telluric effects.

8.4.1 Voltmeter with adequate input impedance. Commonly used digital instruments have a nominal impedance of at least 10 MΩ. An analog instrument with an internal resistance of 100 kΩ/V may be adequate in certain circumstances in which the circuit resistance is low. A potentiometer circuit may be necessary in other instances.

Restate the second sentence:

Commonly used digital instruments should (or shall) have an nominal impedance of at least 10 MΩ.

Reasoning: It has been established that there is a need for the digital meters to have at least this much impedance.

8.5.1 Before the test, verify that cathodic protection equipment has been installed and is operating properly. Time should be allowed to pass for the pipeline potentials to reach polarized values.

Restate the second sentence and additions:

If the CP system is newly installed, allow sufficient time for the pipeline to polarize to stable potentials before recording the potentials. If the CP system current output has been recently adjusted, time should be allowed for the changes in polarization, before recording potentials. Polarization should be established on existing CP systems, therefore no time should be allowed to pass before recording potentials.

Reasoning: Each of these situations must be understood by those taking potentials.

8.5.2 (d) Known location of an ineffective coating when the pipeline is coated;

Define ineffective coating. Is this coating that has disbonded, deteriorated, or just does not stop CP current.

8.5.2 (e) Location of a known or suspected corrosive environment.

Delete this statement. What environments are not corrosive or suspected to be? We can not take potentials at all corrosive or suspected corrosive environments.

8.6.1 The significance of voltage drops can be considered by several methods, including:

Restate:

The significance of voltage drops can be considered by several methods, including, but not limited too:

Reasoning these are not all the possible ways to consider voltage drops.

8.6.1.1 Comparing historical levels of cathodic protection with physical evidence from the pipeline to determine whether corrosion has occurred.
8.6.1.2 Comparing soil corrosiveness with physical evidence from the pipeline to determine whether corrosion has occurred.

Add:

8.6.1.3 Measuring or calculating the voltage drop(s).

8.6.2 Physical evidence of corrosion is determined by evaluating items such as:
(a) Leak history data;
(b) Buried pipeline inspection report data regarding locations of coating failures, localized conditions of more corrosive electrolyte, or substandard cathodic protection levels have been experienced; and
(c) Verification of in-line inspection tool metal loss indications by follow-up excavation of anomalies and inspection of the pipe external surface.

Add:

(d) Proper evaluation of external corrosion, if found, to ensure the corrosion that has occurred was not caused by disbonded CP shielding coatings, other shielding materials or corrosion that existed before adequate CP was applied.

9.32.2 To avoid significant depolarization of the pipe, the off period should be limited to the time necessary to make an accurate potential measurement. The off period is typically less than 3 seconds.

If the typical “Off period” is given, why not the typical “on period”?

9.32.3 The magnitude and duration of a voltage spike caused by current interruption can vary, but the duration is typically within 0.5 second. After the current is interrupted, the time elapsed until the measurement is recorded should be long enough to avoid errors caused by voltage spiking. On-site measurements with appropriate instruments may be necessary to determine the duration and magnitude of the spiking.

Is this the so called “instant off” potential? If so, there are many folks who use a faster cycle than 0.5 second for CIS. How do we actually measure “instant”? What about all the other variables mentioned above in section 8.6? Seems as if this is a very difficult procedure with many variables that must be properly addressed and not just mentioned.


9.32.4 Current sources that can affect the accuracy of this test method include the following:

Restate:

Current sources that can affect the accuracy of this test method include, but are not limited too, the following:

(a) Unknown, inaccessible, or direct connected galvanic anodes;

Restate:

(a) Unknown, inaccessible, or direct connected galvanic anodes or unknown impressed current systems;

(h) Parallel coated pipelines, electrically connected and polarized to different potentials;

Restate:

(h) Parallel coated pipelines (bare or coated), electrically connected and polarized to different potentials;

9.54.1 Voltmeter with adequate input impedance. Commonly used digital instruments have a nominal impedance of at least 10 MΩ. An analog instrument with an internal resistance of 100 kΩ/V may be adequate in certain circumstances in which the circuit resistance is low. A potentiometer circuit may be necessary in other instances.

Restate as above in 8.4.1.

9.54.3 Sufficient current interrupters to disengage influential cathodic protection current sources simultaneously.

Define “influential” and “simultaneously” as related to this statement. These surveys are difficult enough to perform to get somewhat accurate data without using these type words. Please define or restate.

9.65.1 Before the test, verify that cathodic protection equipment has been installed and is operating properly. Time should be allowed for the pipeline potentials to reach polarized values.

Restate as in 8.5.1.

9.65.2 Install and place in operation necessary interrupter equipment in all significant DC sources protecting the pipe at the test site, and place in operation with a synchronized or known off and on cycle. The off cycle should be kept as short as possible but still long enough to read a polarized pipe-to-electrolyte potential after any spike as shown in Figure 3(a) has collapsed.

Again this is vague in the description of what is expected. Nice words, but do they really give the user the guidance they need to perform these tests? The problem of course is that we do not know how long any of this should truly be since each situation is different. Suggest we are at least consistent with what we do and provide more specific values of times at which to set the on/off readings.

(d) Known location of an ineffective coating when the pipeline is coated; and

See statement as in 8.5.2 (d) above.

(e) Location of a known or suspected corrosive environment.

Delete as in 8.5.2 above.


9.65.5.1 If spiking may be present, use an appropriate instrument, such as an oscilloscope or high-speed recording device, to verify that the measured values are not influenced by a voltage spike.

How do you know if spiking is present unless you use one of these instruments? Either require use of these meters or delete the statement. Does not the spiking change along the pipeline? The accuracy of these instruments needs to be given. Why not just require meters that using a time cycle to determine what the potential is at that particular time and record this value. At least it is consistent!

10.2 Other current sources that can affect the accuracy of this test method include the following:

Restate as in section 8 and 9.

Current sources that can affect the accuracy of this test method include, but are not limited too, the following:


(a) Unknown, inaccessible, or direct connected galvanic anodes;

(a) Unknown, inaccessible, or direct connected galvanic anodes or unknown impressed current systems;

(h) Parallel coated pipelines, electrically connected and polarized to different potentials;

Restate:

(h) Parallel coated pipelines (bare or coated), electrically connected and polarized to different potentials;

10.2.2.310.3.2.2 The magnitude and duration of a voltage spike caused by current interruption can vary, but the duration is typically within 0.5 second. After the current is interrupted, the time elapsed until the measurement is recorded should be long enough to avoid errors caused by voltage spiking. On-site measurements with appropriate instruments may be necessary to determine the duration and magnitude of the spiking.

Restate as in section 9.2.3

Is this the so called “instant off” potential? If so, there are many folks who use a faster cycle than 0.5 second for CIS. How do we actually measure “instant”? What about all the other variables mentioned above in section 8.6? Seems as if this is a very difficult procedure with many variables that must be properly addressed and not just mentioned.

(b) This method is advantageous when corrosion potentials may be low (for example, 500 mV
or less negative) or the current required to meet a polarized potential criterion would be considered excessive.

Restate:

(b) This method is advantageous when the “ON” corrosion potentials may be more positive than -850 mV low (for example, 500 mV or less negative) or the current required to meet a polarized potential criterion would be considered excessive.

10.23.4.1 Voltmeter with adequate input impedance. Commonly used digital instruments have a nominal impedance of at least 10 MΩ. An analog instrument with an internal resistance of 100 Ω/V may be adequate in certain circumstances in which the circuit resistance is low. A potentiometer circuit may be necessary in other instances.

Restate as in 8.4. 1

10.23.4.3 Sufficient current interrupters to interrupt influential cathodic protection current sources simultaneously.

10.3.3.2 As shown below contradicts the statement above when we say that we can just interrupt the “influential” CP current sources.

(c) Test results are difficult or impossible to analyze when direct connected galvanic anodes or
foreign impressed current devices are present and cannot be interrupted, or when stray currents are present.

These statements need to be resolved and restated.

10.23.5.1 Before the test, verify that cathodic protection equipment has been installed and is operating properly. Time be allowed for the pipeline potentials to reach polarized values.

Restate as shown in 8.5.1 above.

10.23.5.2 Install and place in operation necessary interrupter equipment in all significant DC sources protecting the pipe at the test site, and place in operation with a synchronized or known off and on cycle. The off cycle should be kept as short as possible but still long enough to read a polarized pipe-to-electrolyte potential after any spike as shown in Figure 3(a) has collapsed.

Again this is vague in the description of what is expected. Nice words, but do they really give the user the guidance they need to perform these tests? The problem of course is that we do not know how long any of this should truly be since each situation is different. Suggest we are at least consistent with what we do and provide more specific values of times at which to set the on/off readings.

(d) Known location of an ineffective coating when the pipeline is coated; and

See statement as in 8.5.2 (d) above.

(e) Location of a known or suspected corrosive environment.

Delete as in 8.5.2 above.

10.23.5.5.1 If spiking may be present, use an appropriate instrument, such as an oscilloscope or high-speed recording device, to verify that the measured values are not influenced by a voltage spike.

How do you know if spiking is present unless you use one of these instruments? Either require use of these meters or delete the statement. Does not the spiking change along the pipeline? The accuracy of these instruments needs to be given. Why not just require meters that using a time cycle to determine what the potential is at that particular time and record this value. At least it is consistent!

10.23.5.6 Measure and record the pipe-to-electrolyte on and instant off potentials and their polarities with respect to the reference electrode.

Is this the so called “instant off” potential? If so, there are many folks who use a faster cycle than 0.5 second for CIS. How do we actually measure “instant”? What about all the other variables mentioned above in section 8.6? Seems as if this is a very difficult procedure with many variables that must be properly addressed and not just mentioned.

10.23.5.6.1 The instant off pipe-to-electrolyte potential is the baseline potential from which the polarization decay is calculated.

Is this the so called “instant off” potential? If so, there are many folks who use a faster cycle than 0.5 second for CIS. How do we actually measure “instant”? What about all the other variables mentioned above in section 8.6? Seems as if this is a very difficult procedure with many variables that must be properly addressed and not just mentioned.

10.2.5.7.310.3.5.7.2 When extended polarization decay time periods are anticipated, it may be desirable to use recording voltmeters to determine when adequate polarization decay or a corrosion potential has been attained.

Add 10.3.5.7.2.1

Ensure there are no interference problems with foreign CP systems and other DC power sources that will affect the depolarizing pipeline during the time the CP is off.

Make the same adjustments and comments in Test Method 3B as mentioned above in Test Method 3A.

Thank you very much for your very hard work and effort to make this document better. I hope my comments and suggestions help.

Richard Norsworthy
214-912-9072
richnors@flash.net

1 comment:

Anonymous said...

It seems funny to me after reading thru most of the negative comments I have not really seen many changes that were made in the "New" revision.

One more thing I just dont understand. "Why" it is not important for the Members voting for this "not" to be required to leave comments why they are voting for it.

Unless.. most of the members voting for this are either vendors or contractors that would profit from this change.

Would you not think maybe NACE needs to do a study of leak history. Should we not look at the causes before we just go out and change the recommemded practies?

I can tell you the guys in the white trucks in the field know there is something wrong with this picture.