Materials Performance

DEC 2014

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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Page 12 of 100

10 DECEMBER 2014 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 53, NO. 12 Continued f rom page 9 Continued on page 12 THE BLOG could be the cause of the crack initiation in the weld joints? A: You will need a metallurgical failure analysis by a frm with a scanning electron microscope and an energ y dispersive x-ray analysis for chemical analysis of the crack surfaces. It sounds as though the problem might be SAGBO (stress-accelerated grain bound- ary oxidation), or relaxation cracking. Tis will be an intergranular crack. Tis can happen to UNS NO8810 and some other high-temperature alloys at your operating temperatures. A: Tis is one of the widely experi- enced phenomenon on reformers in refneries, gas plants, and fertilizer plants due to limitations of the material design. Creep is the main reason for this problem. A number of technical forums across the globe have discussed and published articles to assess this damage and predict the tube life. Detailed micro- structural analysis is one of the require- ments to assess the material condition to determine future plans. Seal welding of vent holes Q: We have provided vent holes on saddle plates per ASME B31.3. We have used these plates at support locations as a protection shield to pipe. Now we would like to close the vent hole by seal welding after completion of saddle welding with the pipe and carrying out postweld heat treatment (PW HT). Permanent closing of the vent hole is required to avoid corrosion in offshore conditions. The service is crude oil with hydrogen sulf ide (H 2 S). Is seal welding acceptable for these service conditions? A: One option for sealing vent holes without welding is to tap the vent holes and install threaded plugs. Some users install grease zerks and pump heav y grease into the space between the reinforcing pads and pipe before replac- ing the zerks with plugs. Tis operation may be more desirable when the vent holes are in reinforcing pads for nozzle penetrations, as threaded plugs could be removed for insertion of a pressure gauge to check for slow leaks through the nozzle to pipe weld. Te grease is generally considered to ofer protection should a threaded plug leak. Presumably the sequence you propose is 1) complete saddle welding to pipe, 2) PW HT pipe with saddle attached, and 3) seal weld the vent hole. The seal welds and their heat-affected zones should not be exposed to sour f luids. Seal welding the vent holes prior to PW HT could cause excessive pressure when air trapped in the space between the pad and pipe is heated to 1,100 °F (598 °C) during PW HT. A: You are correct in the case of saddles applied over pipe only and as wear pads. If the pad covers a weld such as at a branch connection, ASME YOU KNOW IT WHEN YOU SEE IT NO FLASH RUST = A CLEAN SURFACE HoldTight®102 is the standard of performance for preventing fash rust. ◗ NO SALT. Removes all contaminants ◗ NO RUST. Leaves a rust-free surface for 48 hours or more—often 3 to 5 days ◗ NO DETECTABLE RESIDUE. There is nothing left on the surface that might interfere with your coating. Among rust preventers and salt removers, HoldTight®102 is the most widely used, reliable, time-proven, lab- tested, feld-tested, recommended and approved by coating companies. Call, email or visit our website today to see why HoldTight®102 is the best option for lowcost, easy-to-achieve, and easy-to-measure contaminant-free surface preparation. Contact us today! International +1 713 266 9339 1 800 319 8802 (Toll Free in N. America)

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