Materials Performance

NOV 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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21 NACE INTERNATIONAL: VOL. 53, NO. 11 MATERIALS PERFORMANCE NOVEMBER 2014 Information on corrosion control and prevention —Kathy Riggs Larsen Examples of internal corrosion and corrosion products found in sprinkler pipes for dry and pre-action fre protection systems. Photos courtesy of South-Tek Systems. will always be some degree of constant, acceptable supervisory gas leakage in a f ire protection system, the contents of high-pressure cylinders are continually consumed and there is a risk that the gas supply will be depleted, which could potentially lead to the sprink ler system being activated if the low-pressure alarm is not acknowledged. The nitrogen generator for f ire protec- tion systems was developed to provide a safe alternative to high-pressure nitrogen gas cylinders and provide an inf inite sup- ply of nitrogen, which eliminates the potential for a supervisory gas run-out. The nitrogen generator draws on decades-old gas molecule separation technolog y, and similar systems have been used in the power industry for the inhibition of corrosion in laid-up or moth- balled boiler tubes. The nitrogen generating system is engineered to supply >98% nitrogen supervisory gas to dry and pre-action sys- tems by mechanically separating nitro- gen from the compressed air feed. It runs on electricity and is comprised of an inte- gral air compressor and air dryer to pro- vide ultra clean, dry feed air to the mech- anism that separates the nitrogen from the air. The nitrogen generator uses either membrane or pressure swing adsorption (PSA) technolog y to mechanically sepa- rate the nitrogen from the air stream, and the technolog y used in a specif ic generat- ing system is primarily based on the total volume capacity of the sprink ler system to be protected. The membrane technolog y utilizes a f iltration process featuring thousands of polymer f ibers, each with a diameter of approximately the size of a human hair. Clean, pure compressed air passes through the membrane, and nitrogen is separated out of the air stream as a result of partial pressure differences between the external and internal membrane sur- faces. PSA employs a carbon molecular sieve (CMS) adsorbent to extract the oxy- gen from the feed air. The oxygen diffuses into the pores of the CMS under pressure, while the nitrogen molecules pass through. Bodemann comments that the membrane technolog y has a service life of up to ~13 years, while the PSA technolog y can provide between 18 to 25 years of service life. The nitrogen gas produced is stored at a low pressure (~80 psi [552 k Pa]) in a receiver tank and enters the building's f ire protection system through the sprin- k ler system's supervisory air mainte- nance device. One generating system is capable of providing supervisory nitrogen to dry and pre-action sprink ler systems with a total sprink ler capacity of up to 20,000 gal (75,700 L). Downstream from the nitrogen generator, a patent-pending pneumatic automatic purge system installed on the sprink ler piping expels a low-volume amount of supervisory gas from each f ire protection zone, which introduces fresh nitrogen into the system and displaces and/or dilutes any residual oxygen. The nitrogen purity can also be monitored at the point where the gas is purged. An integrated leak-detection sys- tem provides notif ication of signif icant leaks, so the nitrogen generating system doesn't operate excessively to maintain supervisory pressure. The nitrogen gas generating system for f ire protection systems has been installed in hundreds of facilities ranging from parking structures to mission- critical facilities. Contact Scott Bodemann, South-Tek Systems—e-mail: Reference 1 O.J. Van Der Schijff, S.C Bodemann, "Corro- sion of Piping in Dr y and Preaction Fire Sprinkler Systems: Interim Results of Long Term Corrosion Testing under Compressed Air and Nitrogen Supervision," CORROSION 2013, paper no. 2846 (Houston, TX: NACE International, 2013).

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