Anba Ki Konbinezon Espesifik Tan ak Tanperati nan Ranje Sensibilizasyon (500 degre a 800 degre) Èske 316L aparèy chofaj tubulaire djenn devlope atak entègranulè detektab nan ASTM A262 pratik E

Time-Temperature-Sensitization (TTS) Diagram of Low-Carbon 316 316L stainless steel sheathed electric heating tubes exposed to elevated temperature during manufacturing (e.g. welding, brazing or stress relief) or during service (e.g. thermal cycling in the sensitisation range) require a time-temperature combination to develop detectable intergranular corrosion (IGC) in the ASTM A262 Practice E test (copper-copper sulfate-sulfuric acid) that is significantly longer than for standard 316 due to the lower carbon content (0.03%). 316L nevertheless is not immune to sensitisation, it only takes longer times or higher temperatures in the 550-750'C range to precipitate sufficient chromium carbides so as to form a continuous chromium deficient network. The nose of the TTS curve for 316L is around about 650-700°C where after 100-200 hours sensitisation is apparent (change from "step" to "ditch" structure in Practice A, or cracking in Practice E). At 600°C, 500-1,000 hours are needed for sensitisation; at 750°C, 50-100 hours; at 550°C, >2,000 èdtan. Relasyon sansibilizasyon tan-tanperati-yo te quantifye pou djenn aparèy chofaj 316L . Sa a pèmèt yon evalyasyon risk ki asosye ak zòn ki afekte chalè soude oswa ekspoze sèvis pwolonje. Mekanis sansibilizasyon 316L ki ba kabòn se difizyon kabòn nan fwontyè grenn yo ak presipitasyon carbure ki rich ak chromium-(Cr 23 C6). Kontni kabòn nan bese a<0.03% and the amount of carbon available for precipitation is limited. However, if you leave it at temperature long enough, carbon atoms can still spread (particularly at dislocations and grain boundaries) and form carbides. The necessary prerequisite for the detection of intergranular corrosion is the creation of a continuous or very continuous chain of carbides at the grain boundaries which leads to the merging of the chromium-depleted zones. Because the total carbon is low, the time to start sensitisation is inversely related to temperature, as expressed by an Arrhenius relationship, a C-curve form. For 316L the nasal temperature (fastest sensitisation) is about 650-700°C. TTS Data for 316L (0.025% C) in ASTM A262 Practice E Controlled ageing of 316L tubing (0.025% C, 0.06% N, balance standard) in an isothermal environment at various temperatures followed by ASTM A262 Practice E testing (24-hour boil in copper-copper sulfate-sulfuric acid, then 180° bend) has produced the following onset times for detectable intergranular cracks. Ageing Temperature (℃)Practice A Practice E Practice A Practice E Time to First Detectable IGC Cracks Time to Continuous Grain Boundary Carbides (hours) (hours) Indicated time after which maximum exposure for sensitisation is recommended Avoidance 500 >5,000 (none identified) >10,000 Step 5,000 hours 5253,000-4,000 5,000-7,000 Step 3,000 550 1,500-2,500 3,000-5,000Dual → Step (after 2,500h) 1,500 hours 575 800-1,200 1,500-2,500 Dual 800 hours 600 400-800 800-1,500 Dual → Ditch (after 800h) 400 hours 625200-400 400-800 Ditch 200 h 100-200 650 200-500 675 100 hours Ditch80-150 150-300 Ditch 80 hours 700 50-100 100-200 Ditch 40 hours 50 hours 725 40-80 80-150 750 30-60 60-120 Ditch 30 hours 775 40-80 (onset slows)40 Ditch 80-150 800 80-150 (slower) 150-300 ditch → dual 80 hrs 850 200-400 (partial redissolution) 400-800 Dual → Step 200 hours The Effect of Carbon Content on Location of TTS Curve The time to sensitisation is roughly inversely proportional to the carbon amount. Less carbon means longer safe exposure duration. Carbon Content (wt%) Time to Sensitisation at 650°C (hours) Time to Sensitisation at 700°C (hours) Time to Sensitisation at 600°C (hours) (average) 0.025 120-200 60-100 500-800 (premium) 0.020 200-350 100-150 800-1,200 (very cheap) 0.015 350-600 150-250 1,200-2,000 (speciality) 0.008 >1,000 >500 >3,000 max 316L 0.030 100-150 50-80 400-600 Enplikasyon pratik pou fabrikasyon ak sèvis aparèy chofaj Pou aparèy chofaj 316L ki anvlòp, tan -restriksyon tanperati ki nan lis anba a valab pou evite sansibilizasyon (echèk nan Pratik E). Tipik Tanperati Ranje Pwosesis oswa Kondisyon Sèvis Degre Maksimòm Tan Akseptab Risk Sensibilizasyon Aksyon Sigjere Pasaj GTAW soude 1,200-1,400 (pik), 450-850 (refwadisman) Segond (refwadisman atravè 450-850 degre) Pa gen risk pou miray ranpa a.<3mm Multi-pass welding (thick flanges) Cumulative time in 550-750°C >5-10 minutes total Use 316L, limit passes, cool between passes Stress reduction after welding 400-450°C < 24 h No danger (below sensitisation) Brazing (furnace, 5 minutes) 5 minutes 600-700°CNo risk (not enough time) Brazing (long cycle, >30 min) 600-700°C >30-60 minit Risk pou sansibilizasyon; sèvi ak 347 oswa 316L ak<0.02% C Service temperature excursion 550-650°C >500-1,500 hours Monitor; after 10,000 hours, test Practice E Continuous service 550°C 550°C>2,500-5,000 hours Test coupon at 5,000 hours Continuous service @ 600 deg C 600 deg C >500-1,000 hours Not recommended for >5,000 hours 650°C Continuous service >100-200 èdtan 316L pa apwopriye pou Verifikasyon sansibilizasyon alontèm 650 degre Pou aparèy chofaj 316L ki an sèvis pou yon peryòd tan ki long nan ranje 500-750 degre, kritè apwobasyon sa yo aplike: Metalografi jaden (replik) - Yo ka poli sou sifas la ak polise 50X. dispèsyon carbure lè l sèvi avèk yon kopi acetate seluloz. Akseptasyon: pa gen okenn carbure fwontyè grenn kontinyèl (èstrikti etap) Tès destriktif (echantiyon chofaj) Koupe yon pòsyon, fè ASTM A262. Pratike E. Akseptasyon: pa gen okenn fant apre koube Tès dite: sansibilizasyon pa siyifikativman modifye dite, kidonk pa itil . 316L Quantification Risk sansibilizasyon lè l sèvi avèk TTS CurveConclusion ASTM A262 Detekte atak entègranulèr pou djenn aparèy chofaj asye pur 316L Pratike E bezwen ekspoze nan ranje sansibilizasyon an 80-600 degre. 750 degre a 1,500-2,500 h nan 550 degre. Nen koub TTS la chita nan 650-700 degre, kote sansibilizasyon rive apre 100-200 èdtan. Djenn aparèy chofaj miray mens yo pa nan risk pou yo sansibilize pandan sik estanda soude ak brasaj (segonn ak minit). Sepandan, operasyon alontèm nan 550-650 degre pou dè milye èdtan, oswa repete sik chalè ki dire lontan, ka sansibilize 316L. Enjenyè ki espesifye djenn 316L pou itilizasyon kontinyèl pi wo a 500 degre yo ta dwe kalkile tan kimilatif pase nan seri 550-650 degre epi konpare ak limit TTS yo. Pou lavi pi lwen pase 2000-5000 èdtan nan 550-600 degre, ajou a 347 (nyobyòm-estabilize) oswa peryodik tès Pratik E nan aparèy chofaj nan echantiyon yo konseye. Fondasyon an bay isit la, ki gen rapò tan, tanperati ak kòmansman an nan sansibilizasyon nan ASTM A262 Pratik E, pèmèt achtè yo predi epi evite korozyon intergranular nan djenn aparèy chofaj 316L ekspoze a tanperati ki wo.