Api580 chapter 10

10 Assessing Probability of Failure (POF) 失效概率评估

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Contents 10 Assessing Probability of Failure 10.1 Introduction to Probability Analysis 10.2 Units of Measure in the POF Analysis 10.3 Types of Probability Analysis 10.4 Determination of POF

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10.1 Introduction to Probability Analysis 概率分析介绍 The probability analysis in an RBI program is performed to estimate the probability of a specific adverse consequence resulting from a loss of containment that occurs due to a damage mechanism(s).

RBI 程序的概率分析是评估一个特点的因一或多个损伤机理, 造成受压设备溶液 流失的逆向结果.

The probability that a specific consequence will occur is the product of the POF and the probability of the scenario under consideration assuming that the failure has occurred. This section provides guidance only on determining the POF. Guidance on determining the probability of specific consequences is provided in Section 12. 将发生的特定结果的概率依故障概率与发生故障后正在审议的方案中 的概率 Key words: Probability of specific consequence, POF, probability of the scenario.

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The probability of specific consequence

POF

The probability of the scenario under consideration

The probability that a specific consequence will occur is the product of the POF and the probability of the scenario under consideration API 580 Charlie Chong/ Fion Zhang

The probability of specific consequence

POF

http://www.wermac.org/others/ndt_pressure_testing.html

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The probability of the scenario under consideration

The probability of specific consequence

POF

The probability of the scenario under consideration API 580 Charlie Chong/ Fion Zhang

The probability of specific consequence

POF

The probability of the scenario under consideration API 580 Charlie Chong/ Fion Zhang

There could be many scenario

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Guidance on determining the probability of specific consequences is provided in Section 12.

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The POF analysis should address all damage mechanisms to which the equipment being studied is or can be susceptible. Further, it should address the situation where equipment is or can be susceptible to multiple damage mechanisms (e.g. thinning and creep). The analysis should be credible 可信, repeatable 能重复 and documented 必须记录. It should be noted that damage mechanisms are not the only causes of loss of containment. Other causes of loss of containment could include but are not limited to: 但应注意的是, 损伤机 理并不是唯一导致溶液流失的原因, 其他原因有 a) b) c) d) e) f) g)

seismic activity, 地震活动 weather extremes, 极端天气 overpressure due to pressure-relief device failure, 过压,由于减压装置故障 operator error, 操作失误 inadvertent substitution of materials of construction, 施工材料无意取代 design error, 设计错误 sabotage. 破坏活动

These and other causes of loss of containment may have an impact on the POF and may be (but typically are not) included in the POF analysis for RBI. API 580 Charlie Chong/ Fion Zhang

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seismic activity

有一定影响但通常不包括在RBI分析

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weather extremes

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overpressure (under pressure) due to pressure-relief device failure,

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operator error

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operator error

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design error

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sabotage

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sabotage

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sabotage

http://en.wikipedia.org/wiki/Military_use_of_children

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10.2 Units of Measure in the POF Analysis 故障概率分析,的计量单位 POF is typically expressed in terms of frequency. Frequency is expressed as a number of events occurring during a specific time frame. For probability analysis, the time frame is typically expressed as a fixed interval (e.g. one year) and the frequency is expressed as events per interval (e.g. 0.0002 failures per year). The time frame may also be expressed as an occasion (e.g. one run length) and the frequency would be events per occasion (e.g. 0.03 failures per run).

Time Frame 期限 : (1) fixed interval 固定时间间隔 (2) Occasion 时机 (per run etc.) 故障概率 (POF) 一般上是以频率表示,频率是在特定的时间范围内发生的事件的 数次.

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For a qualitative analysis, the POF may be categorized (e.g. high, medium and low, or one through five). However, even in this case, it is appropriate to associate an event frequency with each probability category to provide guidance to the individuals who are responsible for determining the probability.

If this is done, the change from one category to the next could be one or more orders of magnitude or other appropriate demarcations that will provide adequate discrimination. 个别类别(高低等)的相应特定概率(数次)关联, 有助于, 有效, 可信的故障频率计量的分配与变动.

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http://www.skybrary.aero/index.php/Risk_Assessment

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Two examples of this are listed in Table 1 and Table 2.

Table 1—Three Levels of POF

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Table 2—Six Levels of POF

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10.3 Types of Probability Analysis 概率分析的类型 10.3.1 General 概要 The following paragraphs discuss different approaches to the determination of probability. For the purposes of the discussion, these approaches have been categorized as “qualitative” or “quantitative.” However, it should be recognized that “qualitative” and “quantitative” are the end points of a continuum rather than distinctive approaches (see Figure 3). Most probability assessments use a blend of qualitative and quantitative approaches. 大多数概率评估使用混合, 定 性和定量方法 The methodology used for the assessment should be structured such that a sensitivity analysis or other approach may be used to assure that realistic, though conservative, probability values are obtained (see 12.4). 用于评估的方法,应该灵活操作; 灵敏度分析或其它的方法也可以并用, 以确保获 得真实的, 尽管保守的概率值.

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10.3.2 Qualitative POF Analysis 故障概率定性分析 A qualitative method involves identification of the units, systems or equipment, the materials of construction and the corrosive components of the processes.

On the basis of knowledge of the operating history, future inspection and maintenance plans and possible materials deterioration, POF can be assessed separately for each unit, system, equipment grouping or individual equipment item. Engineering judgment is the basis for this assessment. A POF category can then be assigned for each unit, system, grouping or equipment item.

Depending on the methodology employed, the categories may be described with words (such as high, medium, or low) or may have numerical descriptors (such as 0.1 to 0.01 times per year). 定性分析考虑包括识别单元,系统或设备,建 材和腐蚀. 工程判断是评估依据. 计量单位可以为描述性如, 高/中/低 或数值描述 如 0.1~0.01次数/年

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10.3.3 Quantitative POF Analysis 故障概率定量分析 There are several approaches to a quantitative probability analysis. One example is to take a probabilistic approach where specific failure data or expert solicitations are used to calculate a POF. These failure data may be obtained on the specific equipment item in question or on similar equipment items. This probability may be expressed as a distribution rather than a single deterministic value.概率方法计算方法, 故障数据可在特定有问题的设备项目或类似设备项目获 得. 得到的概率可以为一个分布来表示, 而不是一个单一的确定性概率值

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Another approach is used when inaccurate or insufficient failure data exists on the specific item of interest. In this case, general industry, company or manufacturer failure data are used. A methodology should be applied to assess the applicability of these general data. As appropriate, these failure data should be adjusted and made specific to the equipment being analyzed by increasing or decreasing the predicted failure frequencies based on equipment specific information. In this way, general failure data are used to generate an adjusted failure frequency that is applied to equipment for a specific application. Such modifications to general values may be made for each equipment item to account for the potential deterioration that may occur in the particular service and the type and effectiveness of inspection and/or monitoring performed. Knowledgeable personnel should make these modifications on a case-bycase basis. 当不准确或不足的故障数据时, 另一种方法是使用一般行业,公司或制造商的故 障数据.在适当情况下, 这些故障数据应按照正在分析的具体的设备进行调整. 这 数据调整工作应当是由有相关知识的人员进行.

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故障概率定量分析有两种数据来源;  明确的设备故障数据 概率方法计算; 故障数据可在特定有问题的设备项目或类似设备项目获得. 分析到的概率可以一个分布来表示, 而不是单一的确定性概率值  一般行业,公司或制造商的故障数据 当不准确或不足的故障数据时, 另一种方法是使用一般行业,公司或制造 商的故障数据.在适当情况下, 这些故障数据应按照正在分析的具体的设 备进行调整. 这数据调整工作应当是由有相关知识的人员进行.

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10.4 Determination of POF 确定故障概率 10.4.1 General 总则 Regardless of whether a more qualitative or a quantitative analysis is used, the POF is determined by two main considerations: 无论是是定性或定量分 析, 故障概率的确定的两个因素是 a) damage mechanisms and rates of the equipment item’s material of construction, resulting from its operating environment (internal and external); 运作环境(内/外)所导致的损伤机理与腐蚀率 b) effectiveness of the inspection program to identify and monitor the damage mechanisms so that the equipment can be repaired or replaced prior to failure. 检查程序对损伤机理的识别和监控的有效性.使设备在在失效前能够进行修理 或更换.

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Failure occurred Probability of Failure POF

Damage Tolerance Limit Planned Inspection

Mitigation Deterioration Rate Time Unacceptable inspection interval

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Analyzing the effect of in-service deterioration and inspection on the POF involves the following steps. 在分析在(1) 职恶化和 (2) 检查对POF的影响包 括以下步骤 a) Identify active and credible damage mechanisms that are reasonably expected to occur during the time period being considered (considering normal and upset conditions). 识别在考虑时间段, 合理预期可能产生的可信 损伤机理 b) Determine the deterioration susceptibility and rate. For example, a fatigue crack is driven by cyclic stress; corrosion damage is driven by the temperature, concentration of corrosive, corrosion current, etc. A damage accumulation rule may be available to mathematically model this process.

Rather than a given value of the magnitude of the damage mechanism driving forces, a statistical distribution of these forces may be available (see API 579-1/ASME FF2-1). 确定的恶化易感性和速率. 这可以通过损伤累 积规则运用数学模拟过程计算数据. 除了确实值, 也能以统计分布体现数据.

API 579-1/ASME FF2-1为例子.

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c) Using a consistent approach, quantify the effectiveness of the past inspection, maintenance and process monitoring program and a proposed future inspection, maintenance and process monitoring program. It is usually necessary to evaluate the POF considering several alternative future inspection and maintenance strategies, possibly including a “no inspection or maintenance” strategy.使用一致的方法, 量化的过去的策略效 力(检验/ 维护/ 工艺控制) 与未来预期成效. 评价POF也应考虑几种可供选择 的未来的检查和维护策略, 可能包括- “不检查或维修”战略 d) Determine the probability that with the current condition, continued deterioration at the predicted/expected rate will exceed the damage tolerance of the equipment and result in a failure. The failure mode (e.g. small leak, large leak, equipment rupture) should also be determined based on the damage mechanism. It may be desirable in some cases to determine the probability of more than one failure mode and combine the risks. 确定在当前的情况下, 持续恶化将超过设备的损伤容限, 并导致失效的 概率. 相应失效模式也应根据损伤机制确定. 在某些情况, 可能会有多个失效 模式, 并结合有关风险来分析.

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Failure occurred Probability of Failure POF

Damage Tolerance Limit Planned Inspection

Extended Interval

Mitigation Deterioration Rate Time Interval sufficient to detect pitting & SCC

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Extended inspection interval failure mode: Crack open if failure occurred leading to different failure scenarios thus consequences

10.4.2 Determine the Deterioration Susceptibility and Rate 确定退化敏感性和速率 Combinations of process conditions and materials of construction for each equipment item should be evaluated to identify active and credible damage mechanisms. One method of determining these mechanisms and susceptibility is to group components that have the same material of construction and are exposed to the same internal and external environment. Inspection results from one item in the group can be related to the other equipment in the group. 每个设备的工艺条件和材料组合应进行评估, 以确定活跃和可信的损伤机制. 设备 拥有共同工艺条件和材料组合可以归类为一组, 从改组的一个设备检验结构同时 能运用在其他在组里的设备.

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For many damage mechanisms, the rate of damage progression is generally understood and can be estimated for process plant equipment. Deterioration rate can be expressed in terms of corrosion rate for thinning or susceptibility for mechanisms where the deterioration rate is unknown or immeasurable (such as stress corrosion cracking). Susceptibility is often designated as high, medium or low based on the environmental conditions and material of construction combination. Fabrication variables and repair history are also important. 设施设备的许多损伤机制, 损伤进展的速度一般都能探知和可可靠地估计. 劣化率 可以腐蚀速率表示 (mm/yr) 或未知或无法估量的劣化率 (如应力腐蚀开裂等), 以 高,中或低定位.

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The deterioration rate in specific process equipment is often not known with certainty. The ability to state the rate of deterioration precisely is affected by equipment complexity, type of damage mechanism, process and metallurgical variations, inaccessibility for inspection, limitations of inspection and test methods and the inspector’s expertise. 在特定的工艺设 备恶化率往往不能真确的确知. 不确知的因素有      

equipment complexity,设备的复杂性 type of damage mechanism,损伤机理类型 process and metallurgical variations, 工艺和冶金的变化 inaccessibility for inspection,难以进行检查 limitations of inspection and test methods and 检查和测试方法的局限性 the inspector’s expertise 检查员的专业知识

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equipment complexity,设备的复杂性

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type of damage mechanism, 损伤机理类型

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process and metallurgical variations, 工艺和冶金的变化

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inaccessibility for inspection,难以进 行检查

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inaccessibility for inspection,难以进 行检查

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limitations of inspection and test methods and 检查和 测试方法的局限性

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the inspector’s expertise 检查 员的专业知识

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Sources of deterioration rate information include (also see Section 8): 恶化率信息的来源包括 a) b) c) d) e)

published data and unpublished company data, 公布和未公布的公司数据 laboratory testing, 实验室测试 in-situ testing and in-service monitoring, 现场测试和在线监测 experience with similar equipment, 与同类设备的经验 previous inspection data. 以前的检测数据

The best information will come from operating experiences where the conditions that led to the observed deterioration rate could realistically be expected to occur in the equipment under consideration. Other sources of information could include databases of plant experience or reliance on expert opinion. The latter method is often used since plant databases, where they exist, sometimes do not contain sufficiently detailed information. 最好的信息将来自运行经验, 其它信息来源可能包括厂里的经验数据库或依赖 专家意见补充厂里数据库的不足处.

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恶化率信息的来源包括     

公布和未公布的公司数据 实验室测试 现场测试和在线监测 与同类设备的经验 以前的检测数据

公司数据:  厂自运行经验  厂数据资料库  专家意见补充

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Damage rates will often vary as the mechanism progresses. In some cases, the mechanism is self-limiting (i.e. after progressing to a certain point), and damage will nearly arrest. In other cases, damage will occur in a slow, stable manner until it reaches a point where failure occurs. In some cases, damage by one mechanism may progress to a point at which a different mechanism takes over to control the rate of further damage (e.g. pitting that gives rise to stress corrosion cracking).腐蚀率是多变化的, 有的时候加速, 自限, 或从一种损伤机理改 变为另种损伤机理,比如点蚀导致环境应力开裂等.

The following parameters should be considered in the determination of damage rates: 确定损伤率的应要考虑参数 a) fluid stream composition, including electrolytes and ions in solution; 流体流 组成, 包括在溶液电解质和离子 b) the temperature, humidity and corrosiveness of the atmosphere or soil; 温度, 湿度和大气中或土壤的腐蚀性 c) process temperature; 工艺温度 d) the flow velocity;流速 e) the amount of dissolved oxygen; 溶解氧气量

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the phase of the fluid (liquid, vapor, or gas); 流体相 (液体,气体或蒸发体) the pH of the solution; 溶液的pH值 the contaminants in the flow stream; 流体中的污染物 the process operating phase (operation, shutdown, wash, etc.); 操作阶段 (操作中/关断时/清理,等) j) the mechanical properties of the metal (hardness, cold work, grain size, etc.); 材料机械性能 (硬度, 冷作, 晶体大小 等) k) the metallurgical properties and corrosion resistance of the alloy; 冶金性能和合金的耐腐蚀性 l) the weld properties: heat treatment, hardness, residual stresses, sensitization, inclusions, etc.; 焊接性: 热处理/硬度/残余应力/敏化/夹杂物等 f) g) h) i)

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m) the component geometry (crevices, local turbulence, etc.); 组件几何 n) the coating and lining condition (no holiday); 涂层和衬垫条件 (无孔) o) the relative size of anodic and cathodic regions; 阳极和阴极区域的相对大小 p) the solubility of corrosion products;腐蚀产物的溶解度 q) the addition of corrosion inhibitors (type, quantity, and distribution); 加入缓蚀剂 (种类/数量以及分布) r) process control and stability. 工艺控制和稳定性

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10.4.3 Determine Failure Mode 确定故障模式 POF analysis is used to evaluate the failure mode (e.g. small hole, crack, catastrophic rupture) and the probability that each failure mode will occur. It is important to link the damage mechanism to the most likely resulting failure mode. For example: a) pitting generally leads to small-hole-sized leaks; 点蚀通常会导致小的孔大小的泄漏 b) stress corrosion cracking can develop into small, through wall cracks or, in some cases, catastrophic rupture;应力腐蚀开裂可发展成小的, 通过墙体裂 缝或者, 在某些情况下, 灾难性破裂 c) metallurgical deterioration and mechanical damage can lead to failure modes that vary from small holes to ruptures; 冶金变质和机械损伤可导致失效模式从小孔至破裂 d) general thinning from corrosion often leads to larger leaks or rupture; 广义腐蚀减薄往往会导致大泄漏或破裂 e) localized corrosion can lead to small to medium-sized leaks. 局部腐蚀可导致小到中等规模的泄漏

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Failure mode primarily affects the magnitude of the consequences.

For this and other reasons, the probability and consequence analyses should be worked interactively. 失效模式主要影响失 效后果的严重性

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a) pitting generally leads to small-holesized leaks; 点蚀通常会导致小的孔大小的泄漏

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a) pitting generally leads to small-holesized leaks; 点蚀通常会导致小的孔大小的泄漏

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a) pitting generally leads to small-holesized leaks; 点蚀通常会导致小的孔大小的泄漏

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b) stress corrosion cracking can develop into small, through wall cracks or, in some cases, catastrophic rupture;应力腐蚀开裂可发展成小的, 通过墙体裂缝或者, 在某些情况下, 灾难性破裂

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b) stress corrosion cracking can develop into small, through wall cracks or, in some cases, catastrophic rupture;应力腐蚀开裂可发展成小的, 通过墙体裂缝或者, 在某些情况下, 灾难性破裂

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b) stress corrosion cracking can develop into small, through wall cracks or, in some cases, catastrophic rupture;应力腐蚀开裂可发展成小的, 通过墙体裂缝或者, 在某些情况下, 灾难性破裂

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c) metallurgical deterioration and mechanical damage can lead to failure modes that vary from small holes to ruptures; 冶金变质和机械损伤可导致失效模式 从小孔至破裂

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c) metallurgical deterioration and mechanical damage can lead to failure modes that vary from small holes to ruptures; 冶金变质和机械损伤可导致失效模式 从小孔至破裂

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d) general thinning from corrosion often leads to larger leaks or rupture;广义 腐蚀减薄往往会导致大泄漏 或破裂

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d) general thinning from corrosion often leads to larger leaks or rupture;广义 腐蚀减薄往往会导致大泄漏 或破裂 API 580 Charlie Chong/ Fion Zhang

d) general thinning from corrosion often leads to larger leaks or rupture;广义 腐蚀减薄往往会导致大泄漏 或破裂 API 580 Charlie Chong/ Fion Zhang

d) general thinning from corrosion often leads to larger leaks or rupture;广义 腐蚀减薄往往会导致大泄漏 或破裂

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e) localized corrosion can lead to small to medium-sized leaks.局部腐蚀可导致小到中等规 模的泄漏

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10.4.4 Quantify Effectiveness of Past Inspection Program 量化过去的检验程序的有效性 the combination of nondestructive examination (NDE) methods such as visual, UT, radiographic etc., frequency and coverage/location of inspections] vary in their effectiveness for locating, characterizing and sizing deterioration, and thus for determining deterioration rates. After the likely damage mechanisms have been identified, the inspection program should be evaluated to determine the effectiveness in finding the identified mechanisms.可能的损伤机理已经确定后, 应 当评估该检验程序在找到所确定的机制的有效性.

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Limitations in the effectiveness of an inspection program could be due to the following items. 检查程序的有效性的限制 a) Lack of coverage of an area subject to deterioration. 缺乏覆盖受到恶化的区域 b) Inherent limitations of some inspection methods to detect and quantify certain types of deterioration. 一些检查方法固有对某些类型的恶化的局限性 c) Selection of inappropriate inspection methods, techniques and tools. 选择不恰当的检查方法 d) Application of methods and tools by inadequately trained inspection personnel. 训练不足的检验人员 e) Inadequate inspection and examination procedures. 不充分的检查和审查程序

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f) Deterioration rate under some extremes of conditions is so high that failure can occur within a very short time. Even though no deterioration is found during an inspection, failure could still occur as a result of a change or upset in conditions. For example, if a very aggressive acid is carried over from a corrosion resistant part of a system into a downstream vessel that is made of carbon steel, rapid corrosion could result in failure in a few hours or days. Similarly, if an aqueous chloride solution is carried into a stainless steel vessel, chloride stress corrosion cracking could occur very rapidly (depending on the temperature). 极端高劣化率, 导致故障可能发生在很短的时间内(例如: 操作更改或工艺颠 覆状况)

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API 580 Charlie Chong/ Fion Zhang

API 580 Charlie Chong/ Fion Zhang

If multiple inspections have been performed, it is important to recognize that the most recent inspection may best reflect current operating conditions. If operating conditions have changed, deterioration rates based on inspection data from the previous operating conditions may not be valid. Determination of inspection effectiveness should consider the following: 检查效果应考虑以下 equipment type; 设备类型 active and credible damage mechanism(s); 积极的和可信的损伤机制 rate of deterioration or susceptibility; 速率或易感性率 NDE methods, coverage and frequency (i.e. ability to detect the specific deterioration); 探伤方法,覆盖范围和频率(对具体的恶化检测能力) e) accessibility to expected deterioration areas. 预期恶化的地区与可达性

a) b) c) d)

The effectiveness of future inspections can be optimized by utilization of NDE methods better suited for the active/credible damage mechanisms, adjusting the inspection coverage, adjusting the inspection frequency or some combination thereof. 未来的检验方法应按照需要优化来达到最佳效果

API 580 Charlie Chong/ Fion Zhang

10.4.5 Calculate the POF by Deterioration Type 由变质类型计算POF By combining the (1) expected damage mechanism, (2) rate or susceptibility, (3) process monitoring, (4) inspection data and (5) inspection effectiveness, a POF can now be determined for each deterioration type and failure mode. The POF may be determined for future time periods or conditions as well as current.

It is important for users to validate that the method used to calculate the POF is in fact thorough and adequate for the users’ needs. 通过结合 (1) 预期的破坏机理, (2) 速率或易感性, (3) 过程监控, (4) 检验数据和 (5) 检验成效, 每个损伤类型和失效模式的失效概率能于确定(包括当前或未来时 间段). 注意事项: 用户需要确认所用的概率方法是否彻底和适当.

API 580 Charlie Chong/ Fion Zhang

API 580 Charlie Chong/ Fion Zhang