August 2019

Maintenance and Reliability

Asset life assessment: A strategic reliability tool for the process industries

Asset life assessment (ALA) has become a strategic tool for process plants (e.g., petrochemical, chemical, and oil and gas) to determine the extent of degradation and the ability of assets to bear static and dynamic loads while sustaining the desired production processes.

Pyne, T., Reliability and Asset Strategy Specialist

Asset life assessment (ALA) has become a strategic tool for process plants (e.g., petrochemical, chemical, and oil and gas) to determine the extent of degradation and the ability of assets to bear static and dynamic loads while sustaining the desired production processes. ALA is also commonly referred to as remaining life assessment (RLA), with a slight variation from ALA in the coverage of assets and the depth of analysis features in the testing techniques applied.

A balance exists between an ever-increasing demand for plant reliability and availability, and the continuous degradation and aging of machinery influencing direct and indirect costs in every stage of a production process. Due to the presence of inappropriate and obsolete designs, as well as national and international safety and environmental regulations, it has become mandatory to assess and ascertain the current and future health of assets throughout the entire production line. Over the last decades, life assessment of machinery has become a crucial task for industry.

Literature concerning ALA/RLA is mainly concentrated on the reports and case studies of consulting firms and original equipment manufacturer (OEM) maintenance and asset-disposal guidelines. The scholarly articles/cases focus mainly on RLA using specific diagnostic techniques. In this article, the relevant tasks, coverage and merits of life assessment are collated with an isolated viewpoint on ALA/RLA to justify the concept of life assessment, and to appreciate this vital task as a unique asset management activity, unlike prevailing exclusive reliability, diagnostic techniques and proactive approaches.

Assessment tools and literature

The task of life assessment is multi-disciplinary. The level and depth of study vary depending on the unavoidable facts of accelerated degradation of plants and environmental regulations stipulated by government. However, this task demands serious attention, as it can not only establish a decision-making platform for running hazard-prone plants, but can also add value when organizations plan to acquire an old plant. A concise and well-defined structure of life assessment establishes a solid foundation and enables the organization to effectively conduct life assessment of its assets.

FIG. 1. An ALA process model.
FIG. 1. An ALA process model.

Today, numerous health assessment techniques are being used in various forms, based on the needs during normal running and/or post-breakdowns/planned shutdowns that require special tools to test integrity. Due to the development and availability of diagnostic technology, new assets are equipped with monitoring instrumentation systems to asses health and performance degradation parameters. Similar setups are deployed to inspect and test material integrity or dynamic stability. However, from the reliability and risk viewpoints of equipment that are already on the verge of reaching design life, any isolated, specific parameter assessment will not ensure a viable base for replacement or repair decisions.

In the comprehensive ALA process, the remaining life of assets is determined by a thorough examination of the extent of degradation in a planned and systematic manner and with the use of various tools, depending on the level and depth of assessment. The assessment may be of qualitative or quantitative nature, using the data sets available in an enterprise resources planning (ERP) system, reports, interviews, manuals, drawings, condition-based maintenance (CBM) databases, etc. The process involves the use of in-house and external expertise, as demanded by the nature of risks, and requires a risk mitigation strategy outlining the actionable parameters with quantitative presentation on the scope of execution, duration and likely costs of mitigation.

Some firms use both RLA and ALA approaches, but a visible demarcation is possible regarding the need for more laboratory tests in any research and development (R&D) setup that an RLA process endures. Literature on RLA is limited, but the life estimation methodologies tabulated while assessing the remaining life of electronic product are worth noting.1 Asset life planning, also referred to as a life assessment approach, applies after the life assessment is completed. At this stage, the risk mitigation plan with time-bound execution, including the necessary budget, is made available.

FIG. 2. A typical process flow chart.
FIG. 2. A typical process flow chart.

An asset’s current condition assessment, both qualitative and quantitative, is carried out based on failure modes and degradation mechanisms. They require data on mean time between failure (MTBF), mean time to repair (MTTR), root cause analysis (RCA), test and inspection, failure rates, bad actors, etc. They also normally require formulae and engineering tools. The qualitative assessment includes asset age, operational performance, health parameters, duty cycles, major overhauls, upgrades, etc. Mathematical calculations of risk are involved in quantitative analysis, rather than subjective decisions as in qualitative analysis—often, both are complementary.2

Reliability analysis provides a high-level picture of equipment reliability and availability, using various technology application packages that assist an industry’s specific points of concentration of unreliable sources, so further corrective actions may be taken in design, operation and maintenance strategies. Reliability testing, such as highly accelerated life testing (HALT) and highly accelerated stress screening (HASS), are applied during asset and spares manufacturing stages, and possibly in a laboratory. These assessments are highly desirable before the asset is shipped to the operation site. HALT is to understand the failures caused by accelerated tests within a short time during the design process, and HASS inspects the manufactured components before shipment.3 In running plants, the tools can be used to simulate the present state of operational and maintenance effectiveness.

Condition monitoring and nondestructive inspections are viewed as diagnostic tools concentrated mainly on the current health of equipment based on live data. The tools may occasionally form the basis for ultimate future life estimation, but are inadequate to quantify remaining life.

The life assessment conforming to the API 579 standard, “Fitness for service (FFS),” is mainly intended to evaluate the mechanical integrity of equipment such as pressure vessels, pipelines, welded structures, etc., and of a quantitative nature based on an evaluation of the damage mechanism and fracture process in varying degrees of required evaluation.4

LIFE ASSESSMENT PROCESS

The process should identify and include equipment, units and plants that require assessment, as well as the resources required, depending on the economic and technical viability checks by an in-house unit level team that determines the scope, depth and level of assessment. A centralized expert team, appointed exclusively for this task, should be available to examine the resources, data needs and obligations for consultants, and to frame a post-assessment quality check.

Any life assessment schedule and execution tasks must fit the current ongoing plant management structure. FIG. 1 illustrates a typical ALA process in any business operation. The process flow chart in FIG. 2 reflects the sequence of activities that this task must follow.

ALA levels

Depending on the scope, purpose and level of expertise available within the organization and the depth of study required, life assessment can be categorized into three levels. The exercise can be conducted either using an in-house team or by external qualified and experienced firms.

No distinctive criteria exists by which the various levels can be demarcated. An overlap between levels is always possible, as the outcome of assessment for each level may incidentally fall within another level boundary. Note that there is some uncertainty in achieving the desired assessment results for a level.

Level 1 includes design and fabrication documents, basic inspection and maintenance history, if available. In addition, plant engineers may carry out simple, visual non-destructive testing/non-destructive examination (NDT/NDE) techniques—such as magnetic particle testing, dye penetrant testing and ultrasonic testing for pipelines, structures, ducts, etc.—that provide a foundation for any further advanced analysis. The basic calculations (as per API 579) are carried out. At the assessor’s discretion, risk-based inspection (RBI), reliability-centered maintenance (RCM), reliability-instrumented systems (RIS) and root cause analysis (RCA) records and trends, spare parts and vendors’ support documents can be reviewed.

This basic level provides an understanding of the basic condition of the assets. This level requires approximately 1 mos, depending on the plant size and the number of persons involved in the assessment exercise.

Level 2 is deeper than Level 1 in terms of analyzing assets, with a more elaborate focus on:

  • Inspection and maintenance strategy/history
  • Failure history and associated investigations
  • Obsolescence and availability of spare parts and technical support
  • Records of the reliability initiatives, if any (e.g., RCM, RBI)
  • Operation practices and the extent of adherence to design operating condition
  • Competency of people handling the assets.

For some assets, the basic calculations may also require adherence to API 579. Advanced NDT/ NDE techniques, such as ultrasonic flaw detection, metallographic testing, thermal imaging and radiographic testing, may be used. Consequently, a Level 2 assessment requires more resources (capacity, level of expertise and inspection tools) than what is normally available inside the plant; therefore, it requires more interfacing with the external resources.

The duration of this level of assessment may extend from 3 mos–5 mos for each plant, depending on the availability of expertise, resources, depth of assessment, equipment coverage, etc.

FIG. 3. Assessment efforts and investment.
FIG. 3. Assessment efforts and investment.

A Level 2 assessment involves a deeper understanding of the assets’ condition due to the higher-order findings of health parameters than those expected in Level 1, and it builds a platform on which certain equipment may require a Level 3 assessment for ALA.

Level 3 assessments are more advanced and demand higher technological and engineering analysis inputs. Complex and critical equipment that qualify for a Level 3 assessment include those with significant uncertainty in the available data that represent equipment current health conditions and a prediction of future health assessment. At this level of study, Level 2 outcomes are used to screen a few most critical assets that require further analysis. On certain occasions, this level may be directly utilized as a direct diagnostic assessment tool, without passing through the steps of previous levels. Only select, critical equipment expected to face threatening failures are eligible for this classification.

Extensive engineering analyses using modern advanced software may be required for equipment qualified for Level 3. Comprehensive calculations for some parts/components may be required, based on API 579.

The related work here is detailed, demanding and costly, requiring an experienced team (firms with adequate laboratory facilities) to conduct the assessments. The optimized allocation of resources and investment for the various levels may be better understood in FIG. 3.

The scope typically covers less than 10% of the total plant assets, and the assessment may extend for 1 yr per plant, or longer, depending on other factors, as mentioned in Level 2. The confidence level is much higher in this level of assessment.

Takeaway

ASA benefits include:

  • Reliability and safety levels of plant machinery are known, based on qualitative and quantitive data
  • Decision-making in scrapping/disposing of existing aging assets is easy and cost-effective
  • Research scope widens on damage mechanism and structural integrity under various environmental conditions.

ASA has become a strategic tool for economic decisions while acquiring an old plant and revamping existing old assets. ALA is also useful for fresh risk assessment to determine equipment criticality in deciding maintenance strategies and to comply with the statutory government norms on sustainability and environment. A well-defined approach with suitable levels of expertise and tools will go a long way for a profitable business. HP

LITERATURE CITED

  1. Mathew S., et al., “A methodology for assessing the remaining life of electronic products,” International Journal of Performability Engineering, October 2006.
  2. Paik, J. K. and R. E. Melchers, Condition Assessment of Aged Structure, Woodhead Publishing Ltd. and CRC Press, Cambridge, England, ISBN: 978-1-84569-334-3, 2008.
  3. Huston, D., Structural Sensing, Health Monitoring and Performance Evaluation, CRC Press, Cambridge, England, 2011.
  4. American Petroleum Institute (API) standard, “Fitness for Service,” API RP 579-1.

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