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July 9 - July 14, 2018

How many areas should be tested for possible chloride contamination during fabrication of an offshore production platform, and why?

Selected Answers

From Yan Lin, Yu of DNVGL on August 6, 2018:
If you want to evaluate the salt contamination level for a very large area, I do not recommend doing it based upon 1000 sq ft areas. First,  select the rust spots for testing. Those dark spots have a high possibility of excessive salt content. In case the dark spots are over the salt limit, you need be  careful to test all color- changed areas. I don't think testing clean areas is the most efficient way to detect polluted areas.

From David Zuskin of Indepedent on July 31, 2018:
I address ships, Navy and commercial, where surface contamination is almost always chloride contamination. "Chemically clean" steel does not want to rust. I have observed steel hulls where areas were abrasive blasted thoroughly (removing Capastic from anode shields) and test areas water-jetted thoroughly. The areas observed remained "white metal" for two months in high humidity and rain (but no water running down off  a contaminated surface onto the reference areas and no rain actually depositing on these surfaces). Chloride contamination is mostly visual; chloride- contaminated steel that has been abrasive blasted or water-jetted but not thoroughly enough to remove all chloride contamination will "turn" or "flash rust" rapidly under most conditions. In a tank, sometimes relative humidity can be driven so low (with DH) that the chloride contamination is still present but not easily seen. For this reason I support not dehumidifying a tank until the abrasive blasting is complete. Dehumidification (DH) should be installed during the final cleaning of the tank for inspection/coating application. Blasters can be instructed to "polish" areas that have turned black (looking like mill scale). The blaster shoots the spots "white" and then dwells on the surface again (because if you do not, these areas will again "flash" before the contractor can get the tank/space clean.)

From Mika Mack of MAPPA TESTLAB INC. on July 24, 2018:
Visually go over the entire structure and map potential "problem areas," and then go from that point outward and Sp-0716's test frequency would be exact.

From Regis Doucette of Durable Solutions on July 19, 2018:
I would promote the use of NACE SP-0716, which has a variable approach or formula based upon conditions. In a nutshell, this standard front loads some extra tests in the first section and then relaxes that rate of testing. However, if there is a failure where the desired threshold of contamination is crossed, then that higher frequency is done again. This higher rate of testing, which is 5 tests for the first 1000 sq ft, followed by 2 tests for the subsequent 1,000 sq ft, and then 1 test per 1,000 sq ft, protects the project from suddenly reverting back to allowing contaminated surfaces. So, in a 100,000 sq ft project with 1 failure midway, the number of tests would grow from 105 tests to 110 tests. My final comment is that the industry should focus also on sulfate contamination during that testing because it is also widely prevalent and corrosion-causing. The rate described above has been found in engineering books for years and was developed by NACE and private industry as well. The UFGS predates SP-0716 and allows that front-loaded value to be 3 tests instead of 5 tests as currently written.

From SubbiahRajendran surendran of L&T oman on July 18, 2018:
For external coatings work, test one area per 100 square meters with a minimum of two per structure. For internal coatings jobs, test one area per 10 square meters with a minimum of two per structure.

From Christophe Le cloarec of GEPI on July 18, 2018:
Test one area per 100 square meters.

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Tagged categories: Chlorides; Offshore; Oil and Gas; Salt exposure; Site/field testing; Surface Preparation; Testing + Evaluation

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