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Discussion Forums - The Hendrix Group
HomeHomeDiscussionsDiscussionsOil Refinery Co...Oil Refinery Co...Cracks of Low Finned Admiralty Brass Tubes of Lub Oil CCracks of Low Finned Admiralty Brass Tubes of Lub Oil C
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8/6/2008 9:00 AM
 
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We have come across failures Low finned Admiralty brass tubes conforming to ASTM SB 111 / SB-359 UNS No C 44300 of our Lub Oil Cooler . Damage type is crack . Numerous surface cracks of varying depth are found ( revealed by LPT / DPT ) on the inside surface ( Cooling water side ) of most of the tubes . Cracks are not present in near Tube sheet portion . Cracks are mostly present at zones within Baffles . Material confirmed to be of ASTM SB 111 / SB-359 UNS No C 44300 grade . The material is confirmed to be Inhibited type ( as revealed by the presence of Arsenic ) . Thickness at unenhanced portion (non finned section) = 1.76 mm to 1.77 mm. Required value = 1.65 mm . Enhanced portion (Finned section) = 1.39 mm to 1.41 mm. Hardness Value found is 84-85 HRF . Tube samples passed flattening test . Tube samples passed Mercurous Nitrate Test ( To be performed once more to revalidate test results ) The Cracks appeared similar to stress corrosion cracks . But the fact that the tube passed "Mecurous Nitrate Test " has confused us . Does any one have simi;ar experince with Lob oil cooler tubes of similar MOC ? Can any one share his experience and his failure analysis results ? regards , SHAMIK
 
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8/7/2008 9:00 AM
 
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Shamik Admiralty brass is likely to fail in lube oil cooler (SCC) if lube oil has traces of ammonia (carry over from steam system - turbine or compressor oil cooling). Long years we experienced similar admiralty brass tube failure in lube oil cooler - in ammonia refrigeration and in syn gas turbo-compressor lube oil / seal oil coolers. We retubed the tubes with a better material. Mercurous nitrate test is one way of assurance for this. If stress levels > 800 KSC then in mercurous nitrate brass will fail by sCC. If contaminant (NH3) level is more than expected, SCC (stress corrosion cracks) can develop even at lower than permitted stress levels - than what is required for mercurous nitrate test. From your description, it appears that traces of contaminant in lube oil ( ammonia traces) may be high to develop SCC at < stresses lower than required under mercurous nitrate test for failure or temp of lube oil cooler was higher even with lower stresses. Under both conditions, SCC will develop for admiralty brass in lube oil service Pl check the oil analysis for ammonia traces. Hope this helps C.V.Srinivasan Nishi Engineers Pvt Ltd India August 07, 2008 E-mail: nishi@vsnl.com >We have come across failures Low finned Admiralty brass >tubes conforming to ASTM SB 111 / SB-359 UNS No C 44300 of >our Lub Oil Cooler . > >Damage type is crack . Numerous surface cracks of varying >depth are found ( revealed by LPT / DPT ) on the inside >surface ( Cooling water side ) of most of the tubes . > >Cracks are not present in near Tube sheet portion . Cracks >are mostly present at zones within Baffles . > >Material confirmed to be of ASTM SB 111 / SB-359 UNS No C >44300 grade . The material is confirmed to be Inhibited >type ( as revealed by the presence of Arsenic ) . > >Thickness at unenhanced portion (non finned section) = 1.76 >mm to 1.77 mm. Required value = 1.65 mm . Enhanced portion >(Finned section) = 1.39 mm to 1.41 mm. > >Hardness Value found is 84-85 HRF . >Tube samples passed flattening test . >Tube samples passed Mercurous Nitrate Test ( To be performed >once more to revalidate test results ) > >The Cracks appeared similar to stress corrosion cracks . >But the fact that the tube passed "Mecurous Nitrate Test " >has confused us . > >Does any one have simi;ar experince with Lob oil cooler >tubes of similar MOC ? Can any one share his experience and >his failure analysis results ? > >regards , >SHAMIK
 
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8/20/2008 9:00 AM
 
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Failure of inhibited or uninhibited Admiralty Brass in Lube Oil Coller system is a common phenomenon in Upstream & Downstream Refinery facilities. With due compliments to Mr. Srinivasan U may also check the following to fine tune the conclusion (1) To check occurance of plug /layer type dezincification at crack locations and in general. (2) check pH and inorganic chloride contents of your cooling water passing through alongwith any ammoniacal water. (3) Pl. check wt% "As" to comply with code performance requirement which will render inhibition effect against dezincification. (4) Also pl. chk presence of any high side "Mn" as high level of Mn can promote dezincification (5) Pl. also chk supply condition of C44300 w.r.t. O61 anneal condition. (6) At the baffle section have u identified crack at outside tube-to-baffle crevices ? (7) Also suggest to do one set of micro. regards DM
 
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