Chair: David Kroon Vice-Chair: Chuck Lawrence

Transcription

1 CONFERENCE CALL MINUTES TASK GROUP 284 CATHODIC PROTECTION, GALVANIC ANODE FOR INTERNAL SUBMERGED SURFACES OF STEEL WATER STORAGE TANKS: REVIEW OF NACE SP ASSIGNMENT: To review and update NACE Standard SP , Galvanic Anode Cathodic Protection of Internal Submerged Surfaces of Steel Water Storage Tanks, as required. JULY 22, 2015 Chair: David Kroon Vice-Chair: Chuck Lawrence 1.0 Chair Kroon called the teleconference meeting to order at 11:05 am, once sufficient attendees were on line. He indicated that this teleconference had been called in lieu of a meeting at CTW2015. He said that in discussions with Vice-chair Lawrence, NACE liaison Southard and others it was determined that the business of the meeting, solely responding to the ballot comments of Antony Semerad, could be easily handled in a conference call. This would save on travel time and expense for those who did not have other meetings they needed to attend. 2.0 The attendees introduced themselves, nine attendees were present. An attendance roster is attached to the end of these minutes. 3.0 Chair Kroon asked for a motion to approve the minutes of the Corrosion2015 meeting. Motion was approved unanimously. 4.0 Chair Kroon said that the first five comments by Mr. Semerad had been addressed at Corrosion2015 and this meeting would be concerned with the remaining nineteen comments. 4.1 The meeting proceeded to review the affirmative and negative comments that had been received: Semerad Comment 6: Page 4, Section 4: Design of Galvanic Anode Cathodic Protection System, Subsection g It is recommended to add one additional item after subsection g to read as follows: h) Galvanic Anode Attachment Configuration; i.e. protruding through the walls, mounted at the floor, or suspended from the roof. Some consideration was given to inserting this suggestion into paragraph 4.3.3, but ultimately the committee decided to add the following into paragraph 4.2.1, between the former items (c) and (d):

2 (d) Galvanic anode attachment configuration (i.e. protruding through walls, mounted internally, or suspended from roof); Semerad Comment 7: Page 4, Section 4: Design of Galvanic Anode Cathodic Protection System, Subsection m It is recommended to add one additional item after subsection m to read as follows: h) Minimum, maximum, and normal fluid levels anticipated for tank operation NOTE: In order to calculate water-wet surface area for minimum, maximum, and normal fluid levels, the designer must know this information. The committee agreed that this is important information and added the following as (i): (i) Minimum, maximum, and normal fluid levels anticipated during tank operation; and the duration of exposure at each of these levels Semerad Comment 8: Page 5, Section 4: Design of Galvanic Anode Cathodic Protection System, Subsection 4.2.1g It is recommended to add one additional item after subsection g to read as follows: h) Anticipated length of exposure at Minimum, Maximum, and Normal fluid levels during the tank operation NOTE: Length of exposure of the water-wet areas needs to be known in order to properly size the galvanic anode CP system. See also the Reviewer s comment in previous Paragraph 7. The committee felt that this should be incorporated with Mr. Semerad s Comment 7. (see above) Semerad Comment 9: Page 6, Section 4: Design of Galvanic Anode Cathodic Protection System, Table 1 Typical Galvanic Materials and Characteristics, Last Row & Notes It is recommended to add one additional cautionary note (D) regarding the use of Zinc (Low Fe) anodes in elevated temperature water, which should read as follows: (D) With increasing service temperature the effectiveness of Zinc Galvanic Anodes may significantly diminish. Depending on the water composition Zinc may completely reverse its polarity in the

3 temperature range between 60 and 82oC (140 and 180oF). Thus, caution is required when selecting Zinc anodes for elevated temperature immersion service. Note: There are numerous references (including NACE publications) dealing with this anomaly. Readers of this standard should be made aware of it. In addition, in elevated temperature applications (i.e., below the water boiling point), the Reviewer successfully used Aluminum-alloy based (offshore type material) anodes. They deliver less driving voltage (and, thus, lower CP potential), than the Magnesium alloy based anodes. Less coating disbondment was observed at such temperatures, when Aluminum-alloy based anodes were used. This was even more noticeable in elevated temperature seawater, oilfield brines, and brackish waters. The Reviewer is not sure, why the Aluminum-alloy based anodes are omitted from the Table 1 on Page 4. Is it the opinion of the TG 284 committee that Aluminum-alloy based anodes are not suitable for elevated temperature fresh, potable waters? Perhaps it should be explained to the standard reader why the Aluminum-alloy based anodes are excluded from the subject table. The committee agrees that a cautionary note regarding zinc is worthwhile. The following note has been added to the table in paragraph 4.3.2: (D) Cautionary Note: With increasing service temperature the effectiveness of some zinc galvanic anodes may significantly diminish. Depending on the water composition zinc may completely reverse its polarity in the temperature range between 60 and 82 C (140 and 180 F). Caution is required when selecting zinc anodes for elevated temperature immersion service. Consult the anode manufacturer for such usages. The committee felt that the waters for which Mr. Semerad proposed the use of aluminum anodes were not the waters covered by the main body of the Standard, but rather waters that are covered by the Appendix. The following was added as paragraph A.5.6: A.5.6 Anode Selection: Under certain conditions of water chemistry and/or elevated temperature the list of anode materials may be expanded to include other anode materials such as aluminum and zinc alloys other than ASTM B418 Type II At this point Doug Gilroy noted that paragraph calls out the CP system driving potential as the difference between the open-circuit potential of the minimum polarized potential of the tank. He questioned, shouldn t it be the closed-circuit potential? There was general consensus that he was correct. Doug moved that open-circuit be

4 changed to closed-circuit in paragraph This was seconded by Jim Chmilar, and approved unanimously Semerad Comment 10: Page 6, Section 4: Design of Galvanic Anode Cathodic Protection System, Subsection It is recommended to add one additional sentence after subsection to read as follows: Galvanic anodes suspended from the tank roof should never utilize their electrical connection cable (also called pigtail ) as the galvanic anode carrier. Properly sized steel cable, steel rod, sucker rod, kernmantle plastic rope, etc. shall be used for the anode weight support and attachment. NOTE: The reviewer saw many cases when the anode separated from the pigtail (electrical connection cable), when pigtail was used to support the anode weight. The committee agrees with Mr. Semerad s concern and added a new paragraph , which reads: Anodes with lead wires should have a separate structural support Semerad Comment 11: Page 7, Section 4: Design of Galvanic Anode Cathodic Protection System, Subsection It is recommended to add one additional sentence after subsection to read as follows: Mass or volume of each galvanic anode should be measured and recorded before installation. Galvanic anode volume can be determined by measuring fluid volume displacement in calibrated plastic or steel cylinders. NOTE: The Reviewer recommends the following for your consideration and inclusion in this standard. The actual consumption rate galvanic anodes (in Kg/y) could be then calculated using the following equations: or where:

5 GAMi, GAMr. Mass of new and consumed galvanic anodes (in Kg), respectively GAVi, GAVr. Volume of new and consumed galvanic anodes (in m3), respectively ρ. Density of Galvanic Anodes (in Kg/m3) Actual Service Life Length of exposure of Galvanic Anodes in service (days) Furthermore, Current Output of galvanic anodes (in Amps) can be then back-calculated by dividing the calculated Actual Consumption Rate by the Nominal Consumption Rate of the particular galvanic anode material (shown in Table 1 on Page 6). This method and calculations (by using the measured mass or volume) is more accurate than when measured dimensions of the consumed anode are used. Most of the galvanic anodes materials are consumed by deep irregular pitting, which makes accurate measurements of metal loss difficult. The Reviewer used this method extensively in the past to back-calculate the actual current output, and actual current density for the particular tank. However, by measuring the remaining mass or remaining volume of the consumed anode (after a high pressure wash), and comparing it to the initial mass and volume, much improved accuracy is obtained. Prediction of requirements for future replacements of Galvanic Anodes is also more accurate when this approach is used. The committee did not believe this recommendation was useful, and would be very unlikely to be followed in practice. No change was made to the document in response to this comment Semerad Comment 12: Page 8, Section 5: Installation of Galvanic Anode Cathodic Protection System, Sub-section This could be an alternative location for the additional comments that the Reviewer made earlier in Paragraph 9 above. Galvanic anodes suspended from the tank roof should never utilize their electrical connection cable (also called pigtail ) as their carrier. Properly sized steel cable, steel rod, sucker rod, kernmantle plastic rope, etc. shall be used as the sole weight support of suspended anodes. Appendix

6 A-7, the use of zinc reference electrodes is mentioned. Although this is true that zinc is sometimes used, the use of zinc as a reference electrode is dangerous as the zinc potential drifts in the positive direction with time giving a false indication of increasing levels of C.P. Suggest that this be considered in future revisions of this SP. This comment was previously addressed Semerad Comment 13: Page 9 Section 6: Criteria for Cathodic Protection, Sub-section It is recommended to add additional sub-section to read as follows: Circuit resistance of individual anodes should be measured at periodic intervals and trended. Increasing circuit resistance could be an early warning signal of anode depletion and could be effectively used for prediction and/or scheduling of anode inspection or replacement. This recommendation was felt to be impractical and unnecessary. No change to the Standard was made Semerad Comment 14: Page 11 Section 7: Operation and Maintenance, Sub-section It is recommended to expand the Sub-section to read as follows (see the underlined, non-italic text) below: Galvanic anodes should also be examined to determine consumption. The anodes showing an advanced stage of consumption should be dismounted and pressure washed with water to remove loose corrosion product and deposits. Volume and/or mass of the cleaned anodes should be measured to facilitate calculation of the remaining life. When galvanic anode remaining life is less than the time to the next inspection, anodes should be scheduled for replacement. The committee s opinion is this is not needed, and no change to the document was made Semerad Comment 15: Page 11 Section 7: Operation and Maintenance, Sub-section , 2nd Sentence It is recommended to expand the Sub-section nd Sentence, to read as follows (see the underlined, non-italic text) below: This information includes both the chemical and electrical characteristics at normal and extreme temperatures encountered in tank service, as well as information about the variations in these characteristics that occur throughout the year.

7 The committee agrees and modified the paragraph as follows: Complete information about the water stored in the tank should be recorded. This information includes both the chemical, and electrical, and temperature characteristics, as well as information about the variations in these characteristics that occur throughout the year. If different sources of water that have substantially different resistances resistivities are used, the frequency of maintenance testing may need to be adjusted so that tests are performed at each time a change in water chemistry occurs. Basic to determining the changes in chemistry would be the resistivity of the water, which can be reflected by the total dissolved solids in the water Semerad Comment 16: Page 11 Section 7: Operation and Maintenance, Sub-section It is recommended to expand the Sub-section , to read as follows (see the underlined, non-italic text) below: Operational information about frequency and duration of draining, cleaning, and filling should be recorded The committee agrees and made the modification Semerad Comment 17: Page 11 Section 7: Operation and Maintenance, Sub-section It is recommended to add a new Sub-section , to read as follows (see the underlined, non-italic text) below: Operational information about frequency and duration of minimum, maximum, and normal operating temperatures The committee does not believe this paragraph is needed. This information is called for in both and Semerad Comment 18: Page 12 Section 7: Operation and Maintenance, Sub-section (a) It is recommended to expand the existing Sub-section (a), to read as follows (see the underlined, non-italic text) below: (a) The number and configuration (including the attachment, location, suspension details) of galvanic anodes; The committee believes this can be better addressed by modifying the paragraph as follows: (a) The number and configuration of galvanic anodes, preferably on scaled as-built drawings;

8 Semerad Comment 19: Page 12 Section 7: Operation and Maintenance, Sub-section (b) It is recommended to expand the existing Sub-section (b), to read as follows (see the underlined, non-italic text) below: (b) Galvanic anode dimensions, volume, mass, and typical composition; It is the committee s opinion that volume and mass are not standard units by which anodes are obtained. They also feel that the term typical is unnecessary. The paragraph as amended reads: (b) Galvanic anode dimensions, weight and typical composition; Semerad Comment 20: Page 12 Section 7: Operation and Maintenance, Sub-section (a) It is recommended to expand the existing Sub-section (a) Tabulation of annual measurements of galvanic anode output voltage and current and tank-to-water potentials, to read as follows (see the underlined, non-italic text) below: (a) Tabulation of annual measurements of galvanic anode driving voltage, current output, tank-to-water potentials, and circuit resistance. The committee believes this change is unnecessary Semerad Comment 21: Page 13 Appendix A Tanks and Vessels Containing Other Waters (Nonmandatory), Sub-section A-3, Second Bullet It is recommended to expand the existing 2nd bullet (o Conductivity) to read as follows (see the underlined, non-italic text) below: o Conductivity vs. anticipated service temperatures The committee believes that this has been adequately covered by modifications to the main paragraph, as follows: The designer shall satisfy himself that evaluate whether the application of CP is suitable to the particular tank and service conditions in question. The designer s considerations should include, but not be limited to: Semerad Comment 22: Page 13 Appendix A Tanks and Vessels Containing Other Waters (Nonmandatory), Sub-section A-3, Second Bullet It is recommended to expand the existing 2nd bullet (o Temperature) to read as follows (see the underlined, non-italic text) below:

9 o Temperature(s) anticipated in service; i.e. minimum, maximum, and normal Operating Temperatures The committee believes that this has been adequately covered by modifications to the main paragraph, as follows: The designer shall satisfy himself that evaluate whether the application of CP is suitable to the particular tank and service conditions in question. The designer s considerations should include, but not be limited to: Semerad Comment 23: Page 14 Appendix A Tanks and Vessels Containing Other Waters (Nonmandatory), Sub-section A-3, 6th Bullet It is recommended to expand the existing 6th bullet ( Settlement of solids or sludges) to read as follows (see the underlined, non-italic text) below: Settlement of solids or sludges including anticipated accumulation in service; i.e. minimum, maximum, and normal sludge accumulation in the tank The committee believes that this has been adequately covered by modifications to the main paragraph, as follows: The designer shall satisfy himself that evaluate whether the application of CP is suitable to the particular tank and service conditions in question. The designer s considerations should include, but not be limited to: Semerad Comment 24:. Page 14 Appendix A Tanks and Vessels Containing Other Waters (Nonmandatory), Sub-section A-3, 7th Bullet It is recommended to add new 7th bullet as follows (see the underlined, non-italic text) below: Minimum, maximum, and normal anticipated fluid levels during operation of the tank The committee believes that this has been adequately covered by modifications to the main paragraph, as follows: The designer shall satisfy himself that evaluate whether the application of CP is suitable to the particular tank and service conditions in question. The designer s considerations should include, but not be limited to: 4.2 The above being the last of Mr. Semerad s comments Chair Kroon indicated that the work of this conference call was complete. 4.3 Chair Kroon will prepare letters to the Commenters advising the of the Committee s decisions. 5.0 Adjournment

10 5.1 Chair Kroon announced the next meeting of the combined committees to be held at Corrosion2016, March 6-10, 2015 in Vancouver, BC. 5.2 There being no further business the meeting was adjourned at 1:00 pm. Attendees Jim Chmilar Laurie Grainawi Charles Lawrence Laszlo Forgo Stu Greenberger Dick Newell Douglas Gilroy David Kroon Rick Southard