Sunday, March 27, 2011

Udate on CORROSION 2011/SP0169



Draft # 3D January 2011

The TG 360 committee meeting on March 15 at CORROSION 2011 presented us with a new version of the document that addressed many of the negatives from the most recent ballot. I like most of the changes made to the document. The committee worked on more changes during the meeting, but hopefully there were no major changes.

Remember this is still in the DRAFT form and has not been approved. The TG-360 will continue to work on the document. Not sure when the new one will be out for viewing and voting.

There will be a new version out to vote when the committee has time to discuss the changes from the comments made at the TG-360 meeting and address the remaining negatives. Hopefully this will be sometime in May/June time frame if not before. I know we are all ready to get this document out the door!

I am not sure when the new version will be ready, but here are some things that I liked about the most recent changes (on the document handed out at the meeting) and some that I would like to see changed or improved.
The underlined areas are the changes from the voted on version.

The (CAPITAL LETTERING AND regular) will be my comments about some of the sections.

6.1.1 This section lists criteria for CP that indicate whether adequate CP of a metallic piping system has been achieved (see also Section 1, Paragraphs 1.2 and 1.4). Adequate cathodic protection can be achieved at various levels of cathodic polarization depending on the environmental conditions. As such, situations may exist where a single criterion for evaluating the effectiveness of CP may not be satisfactory for all conditions or at all locations along a structure. The use of any approach, including a combination of methods or criteria to achieve adequate corrosion control is the responsibility of the user, and should be based on the experience of the user and the unique conditions influencing their piping systems. In determining if adequate corrosion control has been achieved, the conditions and factors listed in Paragraph should be considered regardless of what methods or criteria are used. (I LIKE THIS STATEMENT AND THOSE IN

6.1.2 In selecting the methods or criteria for a specific pipeline, it is the responsibility of the owner to determine whether that level of corrosion control is necessary or sufficient to address the specific conditions. (THIS IS ANOTHER GOOD STATEMENT)

6.1.3 Measurement techniques for evaluating compliance with cathodic protection criteria, and methods for demonstrating that adequate polarization has been achieved are covered in NACE Standard TM0497,“Measurement Techniques Related to Criteria for Cathodic Protection on Underground or SubmergedMetallic Piping Systems.” Fundamental research62 has demonstrated that achieving a polarized potential atleast as negative as -0.850 mV Volt cse or at least 100 mV of cathodic polarization can be expected to reduce the residual general corrosion rate to 1 mil per year (0.025 mm per year) or less.

(I HAVE A PROBLEM WITH LEAVING THIS STATEMENT IN THE CRITERIA SECTION. If the committee will move this to another section or in the Appendix and give some more information of why it is in the document, then I think I would be OK with it. I am not saying it is wrong, but just too many variables involved in getting this data correctly and then trying to apply it to a pipeline. I have made this argument before and have discussed with those who promote it, but they have not convinced me it needs to be in the criteria section.)

6.1.4 In selection of a method or criterion as listed in Paragraph 6.2, it is important that the user includes a means to evaluate the effectiveness of any that method or criterion, whether used separately or in combination. The effectiveness of CP or other external corrosion control measures should be documented. In the absence of such documentation, at least one of the criteria in Paragraph 6.2 shall apply. Criteria that have been documented to successfully control corrosion through empirical evidence on specific piping systems may be used on those piping systems or others with the same characteristics. A minimum of 100 mV of cathodic polarization. Either the formation or the decay of polarization must be measured to satisfy this criterion. A structure-to-electrolyte potential of –850 mV or more negative as measured with respect to a saturated copper/copper sulfate (CSE) reference electrode. This potential may be either a direct measurement of the polarized instant-off potential or a current-applied potential.

Interpretation of a current applied measurement requires consideration of the significance of voltage drops in the earth and metallic paths. Consideration is understood to mean the application of sound engineering practice by either of the following: Measuring or calculating the voltage drop(s) to establish whether a –850 mV potential across the structure-to-electrolyte boundary has been achieved, or Performing a technical evaluation of the system, including data and information, such as the following that are considered necessary and sufficient for the situation: Reviewing the historical performance of the cathodic protection system, such as: type of cathodic protection; consistency with time of the potentials at individual test points along the line, consistency of cathodic protection current over time, number of years with cathodic protection; remedial cathodic protection activities; consistency of CIS over time, and external corrosion related leak history. (Note: Leak history should not be used as the sole means of determining adequate
levels of cathodic protection). When reviewing the historical performance of the cathodic protection system, physical characteristics and results of direct examinations and the environment should also be considered. Determining if there is physical evidence of corrosion, such as: by direct examination to determine evidence of active corrosion, and correlation of direct examination data with other data such as: close-interval surveys, direct current voltage gradient surveys, and in-line inspection results. When direct examinations are used, the number and extent of the examinations performed as well as a comparison of the
environments and their relevance should be considered. Evaluating the physical and electrical characteristics of the pipe and its environment, such as: type of electrolyte, electrolyte resistivity, pH, dissolved oxygen content, moisture content, degree of aeration, differences in pipe metallurgy and installation dates, and variations in coating types and condition. Physical characteristics and operational data, such as: coated or bare, type of coating and possibility to shield cathodic protection, proximity to other lines, especially other lines in the right-of-way, temperature of the pipe, depth of the pipe, proximity to potential stray current sources such as light rail systems, HVAC and HVDC systems, foreign structures with cathodic protection, proximity and electrical
isolation with structures of varying metals where mixed metal potentials may be a concern, locations where concrete weights and anchors may be installed, and changes in operating conditions over time. Construction related information alone may not provide sufficient information to adequately evaluate the effectiveness of cathodic protection, but should be considered during direct examinations and reviewing historical performances. Evaluation of indirect inspection data, such as: above-grade electrical surveys, in-line inspection, and direct assessment. Use of coupons to establish such things as: levels of current density, free corrosion potential, levels of polarization, corrosion rates, and comparisons between coupon and pipe potentials. Other methods that confirm that sufficient polarization has been achieved to control corrosion.

(THIS INFORMATION ADDS GREAT OPPORTUNITY FOR THE END USER TO APPLY SOUND ENGINEERING PRACTICES AS PER EACH PARTICULAR PIPELINE SYSTEM AND ALLOWS FOR USE OF BASICALLY ANY CRITERION THAT PROVIDES THERE IS NO OR VERY LIMITED AND CONTROLLABLE CORROSION. This does not limit the end-user to only two choices, but places the burden on the end user to provide proof that their particular program is working. We must keep in mind that corrosion control is an ongoing battles that involves many phases of control.) When operating pressure and conditions are conducive to high pH stress corrosion cracking, the use of polarized potentials in the cracking range relative to the temperature indicated in Figure 1is not advised.

(THIS AREA JUST NEEDS MORE EXPLAINATION. I AGREE IT IS A VERY IMPORTANT ISSUE AND IS A CONCERN WHEN USING POLARIZED POTENTIAL CRITERION. WE NEED TO MAKE SURE THAT EVERYONE WHO SEES THIS UNDERSTANDS THERE ARE MANY VARIBLES AND CONDITIONS THAT MUST EXIST FOR SCC TO OCCUR. It is always a challenge to place something like this in a standard and give enough information for it to be useful. I would like to hear some other thought on this since I am certainly not the expert on SCC.)

6.4 Alternative Reference Electrodes

6.4.1 Other standard reference electrodes may be substituted for the CSE. Three commonly used portable reference electrodes are listed below. along with tRefer to Table 2 for their voltage equivalents (at 25 °C [77 °F]) to –850 mV referred to a CSE: Saturated KCl calomel reference electrode: –780 mV; and Saturated silver/silver chloride reference electrode used in 25 Ω.cm seawater: –756 mV. Zinc reference electrode; often used as a permanent reference electrode58

6.4.2 In addition to these standard reference electrodes, an alternative metallic element in an electrolyte of fixed concentration may be used in place of the CSE, if the stability of its electrode potential is ensured and if its voltage equivalent referred to a CSE is established.

6.4.3 In situations in which the temperature of the reference electrode is below 15 °C (59 °F) and above 35 °C (95 °F), refer to Table 2.


Examples: –850 mV CSE measured at 100 °F (37.8 °C) would be corrected to –839.5 –838.5 mV (the actual potential is 11.5 mV less negative than the reading), while –850 mV measured at 40 °F (4.4 °C) would be corrected to –868.5 mV (18.5 mV more negative than the reading).

(This is a very confusing table and issue for many. I think is important, but the companies that make the reference cells do not even like the table and do not consider it correct. Not sure how to approach this one, but again we need to keep it simple. There are so many variables when using reference cells that we need a complete Standard on just reference cells! Look at the variables with zinc [+/- 100 mV] and that does not even take into account the other problems with ZRE. Let’s see what happens.)

I personally think the committee is on the right path and hope to be able to support the next revision. Of course others will not. Hopefully, they will comment also so we can continue to learn and share knowledge.

I also want to thank all for the support and kind words at CORROSION 2011. The blog site would not be successful without every ones support and efforts.

Please let me know if I can help in any way!

Richard Norsworthy
Polyguard Products, Inc.
“We Believe in Non-Shielding Pipeline Coatings!” Go to for more information.