外文原稿：Anhydrous Ammonia Pressure Vessels In The Pulp And Paper IndustryThe purpose of this article is to ensure that pulp and paper operating companies, their engineering consultants, and inspection contractors are informed about stress corrosion cracking in anhydrous ammonia service. The information was written by a task group of the TAPPI Engineering Division Nondestructive Testing and Quality Control Subcommittee.Bacteria in some activated sludge effluent treatment systems require supplementary food. In some cases, this food is provided by ammonia and phosphoric acid which are stored on the mill site. Ammonia is commonly stored as anhydrous liquid ammonia in carbon steel vessels at ambient temperature and 16 bar (250 psig) pressure.These vessels can be subject to stress corrosion cracking (SCC).SCC could cause release of ammonia, which is a hazardous chemical. SCC of carbon steel vessels in anhydrous ammonia service is somewhat analogous to that experienced in continuous digesters. For example, the importances of stress relief during fabrication and of in-service inspection are common to both.This article concerns storage in horizontal pressure vessels at ambient temperature, as this type of vessel is used in pulp and paper applications. Large refrigerated storage tanks are used for atmospheric pressure storage in the chemical industry.History of Scc In Ammonia Storage VesselsThe history of SCC in carbon steel ammonia storage vessels was reviewed by Loginow (1) and is also briefly summarized in a NACE Technical Committee Report entitled “Integrity of Equipment in Anhydrous Ammonia Storage and Handling” (2). In the 1950s, liquefied ammonia began to be injected directly into soil for fertilization. Failure of carbon steel storage vessels by SCC began to occur. These failures were unexpected since liquefied ammonia had been used for many years in the refrigeration, chemical, and metal heat treating industries without reported problems.Investigation confirmed SCC to be the cause of cracking. Three recommendations were made in 1962 that still form the basis of modern codes:? Pressure vessels should be fully stress relieved.? Extreme care should be used to eliminate oxygen from ammonia systems.? Ammonia should contain at least 0.2% water to inhibit SCC.Loginow reported that adoption of these recommendations practically eliminated SCC in carbon steel vessels in the agriculture industry. However, in a recent Western Canadian survey SCC was found in 100 of 117 field storage vessels inspected by wet fluorescent magnetic particle testing (WFMT) (3).Despite the above measures SCC continued to occur in road transport tanks constructed from high strength steels, in refrigerated storage vessels and in vessels which had been weld repaired but not subsequently stress relieved. An additional recommendation to limit steel tensile or yield strength was embodied in the U.S. and British ammonia storage codes, respectively (4, 5).? ANSI K61.1—Nominal tensile no greater than 70,000 psi (580 MPa)? U.K. Code—Minimum specified yield strength shall not exceed 350 MPa (51,000 psi).PRACTICAL CONSIDERATIONSThis article is concerned mainly with practical considerations important to pulp and paper mills already possessing anhydrous ammonia storage vessels or planning to fabricate such vessels. In view of the industry’s experience with SCC in continuous digesters the governing objectives should be to control fabrication and inspection to prevent, or at least minimize, in-service problems including over-reaction to relatively minor crack indications. Guidance is available in the published codes and detailed information is available from some ammonia suppliers.FabricationThe two main objectives in fabrication should be to provide the most crack resistant vessel possible at reasonable cost and to ensure that an adequate inspection baseline is available for interpretation of subsequent in-service inspections.ASME Section VIII Division 1 does not require stress relief for anhydrous ammonia storage pressure vessels unless the owner specifies a lethal service designation.The lethal service designation requires radiographic testing (RT) of all butt welded joints plus post weld heat treatment.ANSI K-61.1-1989, “American National Standard Safety Requirements for the Storage and Handling of Anhydrous Ammonia,” adds several requirements:? Fabrication to ASME Section VIII Division 1 Table UW 12 at a joint efficiency less than 80% is not allowed.? Inspection and testing under UG-90(c) (2) (multiple, duplicate pressure vessel fabrication) is not allowed.? Steel used for pressure containing parts shall have a nominal tensile strength no greater than 580MPa (70,000 psi).? The minimum design pressure for ambient temperature storage shall be 16 bar (250 psig).? Post weld heat treatment is mandatory and a furnace of sufficient size to accommodate the entire vessel is recommended. Welded attachments may be made to pads after post weld heat treatment.? Horizontal vessels shall be mounted on saddles which extend over at least one third of the shell’s circumference. Thermal expansion and contraction shall be allowed for and means provided to prevent corrosion between the shell and the saddles.The 1986 British Code “Storage of Anhydrous Ammonia under Pressure in the United Kingdom” requires:? Steel must have specified minimum yield strength less than 350 MPa (51,000 psi).? Weld filler must have minimal strength overmatch compared with the base plate.? 100% magnetic particle inspection of all internal welds in order to provide a record against which all future inspections of the vessel can be assessed.? No welding is permitted after stress relief without subsequent local stress relief.? Concrete saddles are prohibited.? Support must be on continuously welded steel saddles attached before stress relief.Although the British Code does not state that magneti particle inspection should be by WFMT it is generally agreed that WFMT is the most sensitive technique and should be used for inspection of ammonia storage vessels. All inspection should be performed by qualified technicians. SNT-TC-1A Level II is a recommended minimum.One pulp and paper company has added the following requirements for fabrication of such vessels:? Incorporation of a “corrosion allowance” of at least 1.6 mm (1/16 in.) to permit minor defect chasing during in-service inspections and to provide a margin against pitting which may occur if water is allowed to enter an out of service vessel.? All weld toes profiled by grinding prior to wet fluorescent magnetic particle testing (WFMT). All WFMT indications greater than 1.6 mm (1/16 in.) to be removed by grinding before post weld heat treatment.? Shear wave ultrasonic testing (UT) of nozzle-to-shell welds permitted if RT is judged impractical.? WFMT to be repeated after final hydrotest test of the vessel and the report retained by the owner.? Vessel to be dried completely after hydrotest test and nitrogen padded until filled with ammonia.Valves, piping, and fittingsBoth the ANSI and U.K. codes address piping, valves, and fittings. A detailed summary is beyond the scope of this article, but some points are worth noting.? ANSI K61.1 requires all nonrefrigerated ammonia piping to meet the requirements of ANSI/ASME B31.3 “Chemical Plant and Petroleum Refinery Piping.”? The U.K. Code states copper and copper bearing alloys shall not be used.ANSI/ASME B31.3 requires a minimum of 5% of piping welds be radiographically tested. Valves and other apparatus should be rated for ammonia service and should not contain copper or copper alloy components.In one case, a nickel rupture disc corroded to failure at its periphery due to formation of an ammonia solution at a gasketed joint exposed to the weather.In-service inspectionVessel entry Liquid or gaseous ammonia is hazardous and in some jurisdictions release of ammonia vapor to the atmosphere is prohibited by law. Vessels must be properly purged by water and/or steam. Detailed procedures for vessel purging and entry are available from ammonia suppliers (6).Inspection procedures The ANSI standard does not address in-service inspection but does state weld repair or alteration must conform to the current edition of the National Board Inspection Code (NBIC).The 1992 edition of the NBIC includes nonmandatory guidelines for inspection of liquid ammonia vessels (7).These guidelines recommend:? Power buffing or light sandblasting as surface preparation for inspection? All interior welds be examined by WFMT.? Cracks should be removed by grinding without encroaching on the minimum thickness required by ASME Section VIII and the original design.? Weld repairs, regardless of size, should be post weld heat treated wherever possible.Light grinding does increase the sensitivity of WFMT compared to sandblasting or power buffing (8). For example the NBIC mandates grinding as surface preparation for deaerator inspection. The omission of grinding in the guidelines for ammonia vessel in-service inspection may be due to concern that rough grinding may produce residual stress sufficient to initiate SCC in anhydrous ammonia service. If welds have been properly profiled for WFMT on initial fabrication, then grinding for in-service inspection should not be needed.The NBIC guidelines also state that other inspection methods such as acoustic emission or ultrasonics may be used and that fracture mechanics may be used to assess the integrity of vessels where complete removal of cracks is not practical.Normally the only corrosion that occurs in anhydrous ammonia vessels is due to water ingress during out of service periods. Shallow pitting, however, has been found in the bottom of some vessels beneath oily deposits. The source of oil is presumed to be from compressors used to handle the ammonia.In view of concerns over air contamination due to vessel entry and residual stress imparted by grinding nonintrusive inspection, techniques like acoustic emission and UT could be considered by vessel owners. The British Code does not mention nonintrusive inspection of ambient temperature pressure vessels but does state that, if acoustic emission is to be used for spherical storage vessels, a reference base should be taken during initial hydrotesting. Nonintrusive inspection is being used in other industries (9).Vessel refilling Safety procedures should be established for refilling a vessel that has been emptied for inspection. It is also very important to purge the vessel of air to prevent the occurrence of SCC. Detailed instructions are available from ammonia suppliers (10). If a vessel is not to be returned to service immediately after inspection, then care should be taken to dry it and possibly nitrogen-pad it depending on the time it will remain out of service.Inspection frequency Neither the ANSI document nor the NBIC deals with inspection frequency. The British Code recommends the following:? WFMT inspection of 100% of all internal butt welds within the first three years of service? WFMT re-inspection within 2 years if significant defects are found? Subsequent to no significant defects being found, any subsequent inspection should include WFMT of all Tee junctions and 10% of the total length of butt welds? In no case should the subsequent examination interval exceed 6 years.It is apparent from the above that latitude can exist for in-service inspection techniques and frequencies. Each owner should determine inspection frequency in conjunction with the appropriate authority. Some jurisdictions require a 3-year inspection frequency.SUMMARYThe use of carbon steel pressure vessels for storage of anhydrous ammonia in the pulp and paper industry could be a non-event or deteriorate into a cycle of inspection and repair. This article has highlighted major concerns related to SCC. There is a wealth of additional information available on all considerations related to these vessels from the ANSI and British Codes, the NACE document, ammonia suppliers, and the current technical literature. The American Institute of Chemical Engineers (AIChE) holds the annual AIChE Ammonia Safety Symposium aimed at finding ways to safely manufacture, transport, and store ammonia and related chemicals. The proceedings of these symposia are published by AIChE. It is recommended that any owner of such vessels keep aware of current expertise.Reid is materials and corrosion section head with MacMillan Bloedel Research, 4225 Kincaid St., Burnaby, BC, Canada V5G 4P5.Task group members: Craig Reid; R.S. Charlton, Levelton Associates Consulting Engrs.; R.C. Faloon, MQSInspections Inc.; and W. E. Boudreau, Belle Testing Inc.Literature cited1. Loginow,A.W. , Materials Performance 25 (12): 18(1986). 2. NACE Technical Committee report 5A192, Integrity of Equipment in Anhydrous Ammonia Storage and Handling, Houston, NACE Storage Tank, Spokane, 1992.3. Stephens, J. D. and Vidalin, F., 1994 AIChE Ammonia Symposium Notes, American Institute of Chemical Engineers, New York, p. 9. 4. Compressed Gas Association Inc., American National Standard Safety Requirements for the Storage and Handling of Anhydrous Ammonia ANSI K61.1-1989, Arlington, VA, 1989 (CGA Pamphlet G-2.1-1989).5. Storage of Anhydrous Ammonia Under Pressure in the United Kingdom, London, Her Majesty’s Stationery Office, 1986. (Health and Safety Booklet HS/G 30)6. Cominco Fertilizers (U.S.) Inc., Decommissioning an Ammonia Storage Tank, Spokane, 1992.7. The National Board of Boiler and Pressure Vessel Inspectors, National Board Inspection Code: A Manual for Boiler and Pressure Vessel Inspectors, Columbus, OH, 1992, p.197.8. Reid, J. C. and Reid, C., TAPPI 1992 Engineering Conference Proceedings, TAPPI PRESS, Atlanta, Book I, p.163.9. Conley, M. J., Sture, A., and Williams, D., “Ammonia Vessel Integrity Program: A Modern Approach, 1990 AIChE Ammonia Symposium Notes, New York, AIChE, 1990.10. Cominco Fertilizers (U.S.) Inc., “Commissioning an Ammonia Storage Tank”, Spokane, 1992.附錄二 外文翻譯：紙漿和造紙行業(yè)中的無水氨壓力容器本文的目的是為了確保紙漿和紙張經營公司，他們的工程顧問，承建商了解在脫水氨設備中的應力腐蝕開裂現(xiàn)象。這篇資料是由美國紙漿與造紙工業(yè)技術協(xié)會無損檢測工程部和質量控制小組委員會共同編寫。細菌生存在一些活性污泥污水處理系統(tǒng)中需要充足的食物。在某些情況下，這種食品是氨和磷酸的儲存現(xiàn)場。氨通常以無水液氨的形式貯存在室溫和 1.6MPa（250 磅）的壓力的碳鋼容器中。這些容器可能會受到應力腐蝕開裂（SCC） 。應力腐蝕開裂可能導致氨泄露，這是一種危險化學品。用于無水氨設備的碳鋼容器中的 SCC 是有點類似于連續(xù)蒸煮罐的經驗。例如，減少壓力的引入在生產和在役檢查過程都是很常見的。本文關注在常溫下的臥式壓力容器，像這類型容器通常用于紙漿和造紙的應用。大型冷藏儲罐在化工行業(yè)一般是常壓儲存。SCC 在氨儲罐的歷史SCC 在碳鋼氨儲存容器的歷史是由 Loginow（1）審查通過,也是在簡要回顧了 NACE 技術委員會報告題為“完整的設備在無水氨的儲存和處理”(2)。在 20 世紀 50 年代，液氨作為肥料直接注入土壤。碳鋼貯存容器由于應力腐蝕開裂而導致的故障開始出現(xiàn)。這些故障是意外，因為液氨已用于在制冷，化工多年，金屬熱處理行業(yè)沒有報告的問題。調查結果證應力腐蝕是開裂的原因。1962 年提出了三條建議構成了現(xiàn)代條例的基礎：?壓力容器應充分消除應力。?要特別小心是消除氨系統(tǒng)中的氧氣。?氨應該包含至少 0.2％的水，以抑制應力腐蝕開裂。Loginow 報告說，采用這些建議能有效避免應力腐蝕發(fā)生在農業(yè)用碳鋼容器中。然而，最近的加拿大西部的調查顯示通過濕熒光磁粉探傷檢查（WFMT） （3）發(fā)現(xiàn) 117 處農場的儲罐中有 100 處發(fā)生了應力腐蝕開裂。盡管采用了上述措施，SCC 仍然發(fā)生在由高強度鋼建造的公路運輸油罐、冷藏儲存容器以及作了焊接修復卻沒后續(xù)的應力消除的容器。另外一條建議被納入美國和英國的氨儲存條例，以限制鋼材的拉伸或屈服強度。?ANSI K61.1 -名義抗拉強度不超過 70,000 磅（580 兆帕）?英國條例指定的最低屈服強度不超過 350 兆帕（51,000 磅） 。實用的考慮本文主要關注是實際問題對于已擁有無水氨貯存容器的紙漿和造紙廠或計劃制作這類容器的重要性。以連續(xù)蒸發(fā)罐中 SCC 的經驗來看，執(zhí)行目標應該是控制制造和檢驗，以避免或至少減少在運行中的問題，包括過度反應相對輕微裂縫的跡象。從一些氨的供應商提供公開條例和規(guī)范資料可以得到相關的指導。制造制作中的兩個主要目標應是提為抗裂容器供合理的成本，并確保為后續(xù)在役檢驗的解釋有適當?shù)臋z驗基線可用。ASME 第 1 部第 VIII 節(jié)沒有要求無水氨存儲壓力容器要應力消除，除非擁有者指定了一個致命的部件名稱。指定的致命部件需要焊接接頭的焊后熱處理加所有對接射線檢測（RT） 。美國國家標準化組織（ANSI）K – 61.1 - 1989， “美國國家標準無水氨的存儲和處理安全要求”增加了幾個要求：?制造符合 ASME 第一部第 VIII 節(jié) UW12 表的效率不能低于 80％。?基于 UG-90(c)檢查和測試是不允許的。?用于壓力容器部件的鋼材的標稱抗拉強度應當不低于580MPa（70,000 psi） 。?室溫儲罐的最低設計壓力應當為 16bar（250 psig）的。?必須進行焊后熱處理，要求足夠大的熔爐來適應整個容器。附件的焊接點可能要進行熱處理?臥式壓力容器應當安裝在鞍座超過至少有一個殼體的周長三分之一。應允許熱膨脹和收縮和給出以防止殼體和鞍座之間腐蝕的方法。1986 年英國章程“英國常壓無水氨儲存”要求：?鋼材的指定最低屈服強度必須小于 350 兆帕（51,000 磅） 。?焊接填充物的最小強度必須高于于比母材強度。?100％的內部焊縫磁粉探傷，對未來所有的容器檢查提供可以評估的紀錄。?沒有后續(xù)局部應力消除的應力消除后允許無焊接?混凝土鞍座是禁止的。?鋼制鞍座連續(xù)焊接必須在應力釋放之前。雖然英國規(guī)范并沒有規(guī)定磁化粒子檢查應當進行濕熒光磁粉實驗，人們普遍認為，WFMT 是最靈敏的技術，應該用于檢驗氨貯存容器。所有的檢查應該由合格的技術人員來完成。SNT-TC-1A II 級是建議的最低水平。其中紙漿和造紙公司已對這些容器的制造增加了下列要求：?設立“腐蝕裕量”至少 1.6 毫米(1 / 16 英寸)，允許在役檢驗中出現(xiàn)的微小缺陷，并在容器停止服役期間浸水，對可能出現(xiàn)的腐蝕保持一定的裕度， 。?濕熒光磁粉探傷（WFMT）檢驗所有焊接接頭前要進行磨削。在焊后熱處理前，大于 1.6 毫米（1 / 16 英寸）所有 WFMT 跡象要被磨削。?如果射線探傷不符合實際，可以使用橫波超聲波檢測（UT） 。?容器水壓試驗后重復進行 WFMT，由業(yè)主保留的測試報告。?容器水壓試驗后要完全干燥，并且進行充氮保護直至填充氨。閥門，管道及配件ANSI 和英國壓力容器規(guī)范都對管道，閥門和配件進行了論述。詳細摘要已經超出了本文的范圍，但有些要點是值得注意的。?ANSI K61.1 要求所有的非冷卻氨管道要滿足符合 ANSI / ASME B31.3的規(guī)定“化工廠和石油精煉廠管道。 ”?英國壓力容器規(guī)范規(guī)定銅及銅合金軸承不得使用。ANSI / ASME B31.3 要求 5％以上管道焊縫需要 X 線測試。閥門和其他設備應使用標準的的氨部件，并且不能含有銅或銅合金成分。在一個案例中，一個鍍鎳爆破片腐蝕失效原因在于襯墊上的氨溶液的形成在役檢查容器引進。液態(tài)或氣態(tài)氨是危險化學品的，而且某些司法管轄區(qū)的法律禁止氨蒸氣釋放到大氣中。容器必須用水或蒸汽妥善清除。從氨供應商獲取詳細的清洗和引進說明（6） 。檢查程序。 ANSI 標準不涉及在役檢查，但要求焊接修復或改裝，必須符合現(xiàn)行版國家檢測局規(guī)范（NBIC） 。該 NBIC 1992 年版包括液氨儲罐非強制性的檢查指導。這些指導原則建議：?拋光或噴砂表面處理為檢查做準備?所有的內部焊縫進行 WFMT 檢測。?裂縫應磨削處理以符合 ASME 第八節(jié)規(guī)定的最小設計厚度。?焊縫，不論尺寸，都應進行焊后熱處理。輕微磨削相對噴砂處理和電學拋光可以增加 WFMT 靈敏性相（8） 。例如，NBIC 要求磨削作為除氧檢測的表面處理的準備。在氨儲罐的在役檢查指導中磨削的遺漏可能是由于擔心粗磨可能產生的殘余應力以致產生應力腐蝕開裂。如果在初始制造過程中焊縫因 WFMT 產生了合適的變形，那么在在役檢查中磨削就沒有必要了。該 NBIC 準則還規(guī)定，如可能使用聲發(fā)射或超聲波等檢查方法，斷裂力學可用于評估那里的容器完整性裂縫徹底清除是不實際的。通常，腐蝕只發(fā)生在無水氨儲罐，是因為在停止運行期間滲入水。淺點蝕已發(fā)現(xiàn)在有些容器底部的油性沉淀物。油源被假定為從用來處理氨的壓縮機。針對由于容器引進而產生的空氣污染問題和磨削無損檢測產生殘余應力的問題，采用如聲發(fā)射技術和 UT 的技術可以由使用者考慮。英國規(guī)范并沒有提及常溫常壓容器的無損檢測，但指出了，如果聲發(fā)射檢測要用于球形儲存容器，應當在初始水壓試驗采取相應的參考。無損檢測應用于其他行業(yè)。儲罐填充。應該為因檢查而清空的容器填充建立一個安全規(guī)程。這對于凈化容器空氣防止發(fā)生應力腐蝕開裂是非常重要的。從氨供應商獲取詳細說明（10） 。如果容器在檢查后沒有被立刻送回返修，然后應注意干燥，并有可能氮封它取決于停止服役的時間。檢查頻率。無論是 ANSI 文件或 NBIC 沒有處理檢驗頻率。英國規(guī)范建議如下：?在首三年服役期 WFMT100％檢查所有內部的對接焊縫?如果在兩年內發(fā)現(xiàn)重大缺陷進行重新檢查， ?繼無發(fā)現(xiàn)明顯缺陷后，后續(xù)的任何檢查應對所有 T 型接頭和的對接焊縫總長度的 10％進行 WFMT 檢測?在任何情況下后續(xù)檢查的時間間隔超過 6 年。從上述可以很明顯看出在役檢查技術和頻率存在一定范圍。每個使用者應與結合相關部門確定檢查頻率。有些管轄區(qū)需要 3 年的檢查頻率?？偨Y對紙漿和造紙工業(yè)的碳鋼無水氨儲存壓力容器的使用可能是一個非活動或進入檢查和維修的惡性循環(huán)。本文重點關注的是應力腐蝕開裂。從ANSI 和英國規(guī)范，NACE 文件，氨儲罐供應商和現(xiàn)行的技術文獻可以獲取的大量有關注意事項的信息。在美國化學工程師學會（AIChE）舉行的年度合成氨安全研討會旨在發(fā)現(xiàn)在安全生產，運輸和儲存氨及相關化學品的方法。這些專題討論的會議記錄 AIChE 公開發(fā)表。它建議任何此類容器的所有人應及時了解當前的專業(yè)知識。里德材料和麥克米蘭布勒德爾研究，4225 金凱德街，本拿比，BC，加拿大 V5G 4P5 腐蝕科科長。工作組成員：克雷格里德; R.S.查爾頓 Levelton 協(xié)會咨詢工程部。R.C. Faloon 鋼筋混凝土 s 公司和 W. E. Boudreau 檢測公司參考文獻：[1] Loginow，A.W. ，材料性能 25（12）：18（1986） 。[2] NACE 的技術委員會的報告 5A192，無水氨儲存和處理設備的完整性，休斯敦，NACE 的儲罐，斯波坎，1992 年。[3] 斯蒂芬斯，JD 和 Vidalin，F(xiàn)，1994 年 AIChE 氨研討會報告，美國化學工程師協(xié)會，紐約，P，9。[4] 壓縮氣體協(xié)會公司，貯存及無水氨的 ANSI K61.1 - 1989，阿靈頓，弗吉尼亞州，1989 年處理的美國國家標準的安全要求（CGA 手冊的 G - 2.1 - 1989） 。[5] 無水氨在英國倫敦常壓下的儲存，英國政府文書局，1986。 （健康及安全手冊協(xié)/克 30）[6] Cominco 的肥料（美國）公司，退役氨儲罐，斯波坎，1992 年。[7] 全國鍋爐壓力容器督察局和國家局檢查規(guī)范：鍋爐壓力容器檢驗手冊，哥倫布，俄亥俄州，1992，p.197。[8] 里德，JC 與里德，三，1992 年 TAPPI 工程會議論文集，TAPP 出版社，亞特蘭大，第一冊，臨 163。[9] 康利，麻將，Sture，A.和威廉姆斯，博士， “氨壓力容器完整性方案：一種現(xiàn)代方法，1990 年 AIChE 氨研討會報告，紐約，AIChE，1990年。[10] Cominco 的肥料（美國）公司， “調試氨儲罐” ，斯波坎，1992 年。