管道、壓力容器HIC抗氫致開裂性能評價的試驗方法

抗氫致開裂性能檢測方法主要依據(jù)NACE協(xié)會的TM0284標準進行試驗檢測，隱石檢測腐蝕實驗室從試驗方法的發(fā)展歷史和新版(2016版)標準兩個方面做一個簡介。

1、發(fā)展歷史

氫致開裂最早被描述于一篇1949年發(fā)表的關(guān)于探討酸性服役壓力容器的裂紋和鼓泡的文章，在管線方面的報道最早在1958年。不過直到二十世紀七十年代，發(fā)生了幾次比較嚴重的管線失效，如1972年英國石油公司的海上管線的失效，德國一酸性服役的管線失效及阿美石油公司的三起酸性氣體輸送管線失效，最終促使人們?nèi)パ芯繖z測管線抗氫致開裂性能的試驗方法。先驅(qū)是英國石油公司，基于他們海上失效的案例，制定了一個介質(zhì)為合成海水溶液的檢測方法。

由于BP試驗流程不是很明確，試驗控制不充分，導致試驗結(jié)果差異較大，重復性差。促使成立了T-1F-20工作組，由該工作組研究制定標準化的檢測方法。從各相關(guān)方收集到的9種試驗方法中最終選擇了一個，經(jīng)過一系列的試驗室內(nèi)部和試驗室間的測試比較，于1980年發(fā)表了推薦性標準化試驗流程，經(jīng)過多次的修訂，標準NACE TM0284最終形成于1984年，1987年進行了很小的修訂。

1984年一場災難性氨吸收裝置的失效促使煉化行業(yè)重視了硫化氫引起的失效，進行了大范圍的檢查，于2147個容器中發(fā)現(xiàn)25%的受檢對象有裂紋。于是在1990年NACE TM0284修訂中增加了壓力容器、電阻焊管、薄壁和小直徑管線。另外增加了溶液A，即將NACE TM0177中的A溶液(最早用于應力腐蝕檢測)引入進來。1996、2003年進行了很小的修訂，如試樣不允許展平等。2011年又增加了酸性服役環(huán)境下的相關(guān)附件的檢測，最新版本為2016版，將在第二部分重點講述。

從名稱的轉(zhuǎn)變看對該損傷認識的提高：早期氫致開裂被稱為階梯狀裂紋(Stepwise Cracking)損傷,由日本學者最先提出，可見其是以裂紋的形貌特點來命名這種損傷，隨著逐步深入的研究，發(fā)現(xiàn)這種損傷起源于氫進入材料基體，在氫陷阱處聚集形成氫分子，局部壓力增大，形成了裂紋，因此，學術(shù)界開始使用了氫致開裂(Hydrogen Induced Cracking)來命名這種損傷，NACE標準從1990版開始采用。

最大裂紋率值規(guī)定的來源：一些產(chǎn)品標準中(如API 5L、NACE MR0175、ISO-15156)，要求CLR≤15%、CTR≤5%、CSR≤2%，這些值是通過大量全尺寸試驗(Full Scale Tests)和試驗室試驗(Laboratory Tests)結(jié)果的比較作為基礎，從而確定的。即考慮全尺寸試驗無裂紋下，試驗室試驗會檢出裂紋。(參考文獻-Review of the HIC test requirements for line pipe over the years 1975 to 2000)

2、新版(2016版)標準簡介

本部分以修訂章節(jié)為線進行介紹。

2.1 1.3 In Fitness-for-Purpose testing, the test environment and partial pressures of gases appropriate to the intended application are selected. 對于適用性試驗，要選擇目標實際環(huán)境和實際氣體分壓。注：即相當于模擬實際生產(chǎn)工況。

2.2 1.5 For additional information, the presence or absence of HIC in the exposed specimens may be evaluated by automated ultrasonic testing prior to metallographic sectioning and examination. A procedure is provided in Appendix A (nonmandatory). 金相分析前使用超聲探傷檢查HIC裂紋作為附加信息列于本標準中。試驗流程見附錄A(非強制性)。注：從此前生產(chǎn)檢測過程的遇到的情況來看，只有道達爾和泰國石油明確了超聲探傷試驗方法，而其他公司雖也有超聲探傷要求，但沒有具體試驗流程?，F(xiàn)標準中列出，則今后客戶或監(jiān)制就可以據(jù)此提出意見，目前我們還需解決一些問題。

2.3 NOTE: In Fitness-for-Purpose HIC testing, a homogeneous test solution is required to facilitate pH control. In large test vessels, this may be achieved by continuous stirring of the test solution throughout the test. For Fitness-for-Purpose tests where buffering is less strong, stirring of the solution may also limit an increase in pH local to the corroding steel surface. 在HIC適用性試驗中，需要一個均質(zhì)的溶液來方便控制酸堿度，在大試驗容器中試驗可通過攪拌來實現(xiàn)。由于適用性試驗所用溶液的酸堿度緩沖能力低，同樣需要對溶液進行攪拌來防止鋼鐵腐蝕表面局部酸堿度的升高。注：酸堿度作為一個重要影響因素，在試驗過程必須得以很好的控制，此處給出了如何控制的方法之-試驗過程攪拌溶液，使溶液處于均質(zhì)的狀態(tài)下。

2.4 4.3.4 Small-diameter, thin-wall ERW and seamless pipe test specimens shall have all mill scale removed from the internal and external surfaces. Each test specimen shall be either machined and/or ground (wet or dry) to an equivalent 320 grit paper finish, or grit blasted to a uniform near-white metal finish in accordance with NACE No. 2/SSPC(4)-SP 109 or ISO 8501-1, Grade Sa 2?. For machining, the last two passes shall be such that a maximum of 0.05 mm (0.002 in) of material is removed. 或噴砂，使其達到近白亮金屬表面，參照標準NACE No. 2/SSPC(4)-SP 109 or ISO 8501-1,級別Sa 2?。注：即增加了小尺寸管試樣表面處理要求，給出了具體的參照標準。

If Test Solution A or B is used, the ratio of the volume of test solution to the total surface area of the test specimens shall be a minimum of 3 mL/cm2. If Test Solution C is used, the ratio of the volume of test solution to the total surface area of the test specimens shall be a minimum of 5 mL/cm2. As long as the specified ratio of volume of test solution to test specimen surface area is maintained, as many test specimens as will fit in the test vessel fully submerged and without touching may be exposed at one time. 如果使用溶液C，溶液體積與試樣面積比最低為5毫升每平方厘米。

2.6 NOTE: For Test Solution C, a ratio of the volume of test solution to the total surface area of the test specimens higher than 5 mL/cm2 should be used for tests at pH levels below to reduce the frequency of re-adjustment of pH to the target pH (see

Paragraph 8.3.1). The use of an alternate test solution with greater pH stability may also be appropriate (see Paragraph 8.1.5). 注：本條解釋了的要求的原因，即溶液C在酸堿度低于時，通過增加溶液體積與試樣面積比來減少試驗過程中調(diào)節(jié)酸堿度的頻次。

2.7 8.1.5 If Test Solution C is used, the oxygen concentration in the test solution shall be maintained below 50 ppb. The laboratory shall have a demonstrated and documented procedure for solution deaeration validating that the methodology adopted achieves the required concentration of oxygen. The test solution shall consist of 5.0 wt% NaCl and 0.40 wt% CH3COONa in distilled or deionized water (i.e. 50.0 g of NaCl and 0 g of CH3COONa dissolved in 946 g of distilled or deionized water). The initial pH shall be adjusted to the target pH ± pH units by addition of HCl or NaOH before saturation with the H2S/CO2 gas mixture for the test to be valid. All reagents added to the test solution shall be measured to ± 1.0% of the quantities specified. 如果使用溶液C，則溶液中含氧量要維持在50個ppb以下，實驗室需證明所采取的措施能達到這個要求。溶液C的成分為5%氯化鈉、的醋酸鈉來組成。起始酸堿度可以通過添加氫氧化鈉或鹽酸來調(diào)至目標值，控制在± 范圍內(nèi)。

2.8 NOTE: The oxygen concentration in the test vessel may be monitored directly or in a separate test carried out using the same apparatus and procedure, but with an oxygen concentration monitor, to demonstrate that the methodology adopted achieves the required concentration of oxygen. 氧濃度可氧濃度檢測器來進行測量，可在試驗容器上直接進行測量，或在相同的裝置和流程下單獨試驗測量，以證明除氧方法有效。

2.9 NOTE: For tests requiring greater pH stability, NACE TM0177 Solution B (0.47 N total acetate) adjusted to the selected test pH value by addition of HCl or NaOH may be more appropriate. Where this solution is selected, it shall be reported as "NACE TM0177 Solution B" quoting the adjusted test pH. An alternate solution with strong buffering capacity proposed by the Iron and Steel Institute of Japan (ISIJ) high-strength line pipe (HLP) research committee, including high CH3COOH /CH3COONa (0.93 N total acetate), may also be appropriate. Where this solution is selected, it shall be reported as "HLP

solution pH x.x". 注：本部分推薦了倆個緩沖能力更強、酸堿度更穩(wěn)定的溶液，即NACE TM0177中的B溶液和日本用于高強鋼試驗中的溶液。此處可能有一個小錯誤，可能應該是。

2.10 8.2.4 If Test Solution C is used; after purging, the H2S/CO2 gas mixture shall be bubbled through the test solution. The rate of bubbling should be 200 mL/min per liter of test solution for at least one hour; thereafter, a constant flow of test gas shall be maintained at a sufficient flow rate to ensure that the test solution remains saturated with the test gas for the duration of the test. The concentration of H2S in the test solution shall be measured by iodometric titration at the start (after saturation) and at the end of the test, and shall be of the minimum value as calculated from Equation (1), dependent on the mole fraction of H2S in the test gas. An acceptable iodometric titration procedure is detailed in Appendix D (nonmandatory). 注：本部分增加了溶液C的控制，類似，但硫化氫濃度要根據(jù)實際情況進行滴定溶液的選擇。

2.11 If Test Solution C is used, the test duration shall be in accordance with Table, dependent on the partial pressure of H2S in the test gas.

NOTE: The test parameters given in Table for HIC tests in Solution C have been chosen in accordance with literature data to ensure HIC cracking of susceptible steels. Test durations shorter than those given in Table for HIC tests in Solution C may not lead to HIC cracking in steels susceptible to HIC under the selected test conditions of Table.

NOTE: The test durations given in Table are also appropriate for Fitness-for-Purpose testing in alternate test solutions. 注：如果使用溶液C，試驗的周期將根據(jù)硫化氫的濃度來確定，這部分要求已通過敏感性材料試驗得以確定。

2.12 A1.2 The procedure is not applicable to curved specimens or to small fittings tested as complete components. 超聲探傷不適用于弧形和小試件試樣。

2.13 A1.3 The procedure provides a method for determining the Crack Area Ratio (CAR). 超聲探傷需要報出裂紋面積比。注：裂紋面積比為超聲檢出的傷面積除以受檢面積。

2.14 D8 Calculate the H2S concentration (mg/L) using Equation (D1):

H2S concentration (mg/L) =(A ? B) x 17.04/C

硫化氫濃度計算公式如上。注：此處有修改，紅色字體部分老版為，其實際上是將硫化氫分子量進行了修正，由36改為38.。

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References

3.1 History of NACE TM0284 Development;

3.2 Review of the HIC Test Requirements for Line Pipe Over The Years 1975 to 2000;

3.3 NACE TM0284-2016;

3.4 NACE TM0284-2011.

2.9 NOTE: For tests requiring greater pH stability, NACE TM0177 Solution B (0.47 N total acetate) adjusted to the selected test pH value by addition of HCl or NaOH may be more appropriate. Where this solution is selected, it shall be reported as "NACE TM0177 Solution B" quoting the adjusted test pH. An alternate solution with strong buffering capacity proposed by the Iron and Steel Institute of Japan (ISIJ) high-strength line pipe (HLP) research committee, including high CH3COOH /CH3COONa (0.93 N total acetate), may also be appropriate. Where this solution is selected, it shall be reported as "HLP

solution pH x.x". 注：本部分推薦了倆個緩沖能力更強、酸堿度更穩(wěn)定的溶液，即NACE TM0177中的B溶液和日本用于高強鋼試驗中的溶液。