Thursday, July 28, 2011

Re-posted comments

Comments for SP0169 Re-ballot July 2011

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 that isolates a metallic structure from the surrounding electrolyte.

Why did we remove the last statement? The first part is not a true definition of a coating used with CP. I would suggest leaving it in.
6.1.1 [Last sentence] A commonly used benchmark for demonstrating effective external corrosion control is 0.025 mm per year (1 mil per year) or less.

This statement is still an issue because there is not a reasonable way to measure this on a pipeline. Coupons can be measured, but not pipelines. Why do we need this?

Delete this sentence.

6.2.1.1 Criteria that have been documented through empirical evidence to accurately indicate corrosion control effectiveness on specific piping systems may be used on those piping systems or others with the same characteristics.

Remove the word “accurately”. How do we define accurately? The sentence works just fine without it. The same for 6.2.5.1, 6.2.6.1, and 6.2.7.1 statements.

6.2.1.3.1.1 Measuring or calculating the voltage drop(s) to establish whether a –850 mV potential across the structure-to-electrolyte boundary has been achieved, or;

This statement needs to be changed to read “…to establish whether a -850 mV potential or more negative potential across the structure-to-electrolyte …”
Reasoning for change: We do not want to restrict the potential to just -850 mV. There is no way to hold the potential at a certain level. The question is do we restrict the upper limit of the polarized potential?

6.2.1.4.7 When operating pressure and conditions are conducive to high pH stress corrosion cracking, polarized potentials in the cracking range relative to the temperature indicated in Figure 1 should be avoided.

One of the issues with this statement and the table is that it does not take into consideration that SCC on pipelines almost always, if not always, develops under disbonded and CP shielding pipeline coatings. How are we to measure the polarized potential of the pipe in this case? I do not doubt that the information given is correct for the potential ranges and temperatures given, but there is just no way to determine this in the field under disbonded CP shielding coatings. Most the studies and research are performed on uncoated steel pieces, not under disbonded coatings.

I would suggest that we leave this information as a precaution without the table. There needs to be a separate SP0 for SCC that explains all the information. The pH levels are critical as well as the stress level and whether the stress is residual or applied. This is an important issue, but not sure this is the way to cover it.

Suggested replacement statement:

6.2.1.4.7 When operating pressure and conditions are conducive to high pH stress corrosion cracking, polarized potentials and temperatures in the cracking range should be avoided. Pipelines that have or have the potential for disbonded CP shielding coatings should be monitored for SCC through the use of ILI with Electro Magnetic Acoustical Transducer (EMAT) technology or ECDA methods to determine if SCC exists. Certain types of EMAT technology will also detect disbonded coating as well as SCC. Existing disbonded coatings and potentially CP shielding coatings should be removed and where practical replaced with a non-shielding coating system.

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