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22 SEPTEMBER 2015 COATINGSPROMAG.COM Notes From the Blog Editor's Note: Looking for " in the feld " information about the latest coating appli- cation techniques? We invite you to join the discussion. Te following are excerpts from the NACE Corrosion Network's (NCN) and NACE Coatings Network's email-based discussion groups for corrosion profession- als, with more than 1,000 participants. Te following excerpts have been selected for their potential interest to CoatingsPro readers. Tey have been edited for clarity and length. Authors are kept anonymous for publication. Please be advised that the items are not peer-reviewed, and opinions and sug ges- tions are entirely those of the inquirers and respondents. CoatingsPro and NACE do not guarantee the accuracy of the technical solutions discussed. You' ll enjoy a variety of opinions in this practical information exchange forum. For information on how to subscribe to these free list servers, click on the "Community" link on the NACE Website: www.nace.org. Internal coating for pipeline Q: I have a 16 -in. (406 mm) pipeline that w ill be internally coated w ith phenolic epox y (300 µm, or 11.8 mils). Is it acceptable to do the internal coating before the hydrotest? A: You can per for m hydrotest- ing af ter inter na l coating application. You w i l l want to fol low the NACE R P0291 procedures for decompression of inter na l ly coated pipe. I have been involved in cer tain situations where customers require high-pressure testing (up to 20,000 psi, or 138 MPa) and then rapid decompression. If this is your case, I wou ld a lso recommend r unning a thin-f i lm holiday check af ter your hydrotest procedure. A: Is there a concer n in this case that the coating might plug a pinhole in a g ir th weld? Inter na l ly coating over a g ir th weld can be tr ick y because you are limited to air-cured chemistr ies. Given that situation, if the f i lm has not completely cured pr ior to hydrotesting , there is a possibi lit y of some movement in the coating. We use a sleeve system at the weld that isolates the coating bur n-back ex per ienced dur ing the weld ing process. A: Is the question related to mi l l hydrotest of pipe joints or of the insta l led pipeline? If the latter, you have no option — it w i l l be coated pr ior to insta l lation (don't enter- tain coating application by batch pig g ing ). If the for mer, the coating w i l l have suf f icient streng th to br idge a lea k path in the pipe wa l l and have an ef fect on the outcome of the hydrotest. A lso, why coat and then hydrotest and fai l the pipe — wasting the coating , too? Only hydrotested pipe shou ld be leav ing the pipe mi l l to go to the coating applicator. Dehumidifier placement in a blast system Q: We are having a discussion about placement of dehumid- ifers in a blast system. Te question is: Should the dehumidifcation of blasting air be closer to the blast pot or the compressor? Is it possible for outside air to be sucked into the system through any minor leaks in the hose or couplings through a venturi efect? If so, shouldn't the dehumidifer be positioned as closely as possible to the blast pot to avoid any moisture entering the blast stream? If the venturi efect is not possible, should the dehumidi- fer be located as closely as possible to the compressor? A: Dehumidifers are traditionally set up near the compressor. A suction efect is created by a stream of air going through a venturi (a small pipe with a narrow neck) as the air expands just past the narrow neck. You probably do not have any such confg- urations. A lso, in a regular line, the air pressure inside will be greater than the atmospheric pressure. Tis will make it unlikely that any outside air will be entering the line. A lso, air from the compressors is often used in more than one area. By setting the dehumidifca- tion close to the compressor, the air is dehumidifed for all areas using the air from this compressor. A: In the blasting systems we've worked with, the internal line pressures — even in the turbulent areas — have always been well above atmospheric pressure, preventing inward leakage. A: Unless there is a g reat d istance bet ween the compressor and the actua l blast pot, w ith many hose/pipe mechanica l connections in bet ween, the dr ier shou ld be placed at the compressor; the ventur i ef fect wou ld not seem feasible. T he intent of the dr ier is to remove the moisture f rom the inta ke air into Internal Coating for Pipeline and Dehumidifer Placement