Refinery and petrochemical plant inspection groups have evolved into the organizations that exist today as a result of varying needs over time. Consequently, as it is with most organizational evolutionary processes, there always will be things that an inspection group will do well and areas where improvements will be desirable. That’s why it is so important to frequently review inspection organizations and their functions– doing so can help you achieve the maximum benefit from your inspection program.
Before any organizational review begins, one must first clearly define what is expected from that organization. An inspection organization has the primary function of providing the plant owner/operator with accurate and timely assessments of the current condition and future serviceability of process equipment in the plant. The owner/user should be aware of the limitations of the inspections and examinations conducted and the serviceability risks involved under present and future process conditions. The inspection organization also must satisfy jurisdictional and regulatory requirements, monitor the effects of process changes on equipment and determine that repairs, alterations and reratings meet the minimum plant requirements.
Many plant inspection organizations are organized, staffed and tasked to just comply with various jurisdictional and other regulatory requirements–which prevents them from capturing the benefits of proactive inspection programs. Inspections, though, are supposed to provide the necessary data to operate a process plant in the most cost-effective manner possible. This rarely happens when inspections are used primarily to meet regulatory requirements.
The types and extent of inspections based on regulatory requirements are sometimes more excessive than inspections based on good engineering practice. Regulatory authorities generally allow relaxation of strict and often capricious inspection requirements where it can be demonstrated that a plant has and is utilizing a well-engineered inspection program. Furthermore, a comprehensive inspection program that includes a thorough engineering analysis of the inspection results will meet all the intended goals of regulatory requirements.
The following tasks are necessary for an effective and comprehensive inspection program:
The inspection organization
Numerous (and diverse) inspection organizations exist at various plants.Some are very proactive and effective, while others add little or no value to the operations. The more effective organizations have a senior inspector (usually an engineer), certified inspectors,Non-Destructive Examination (NDE) examiners (either in-house or contract personnel) and ready access to and a good working relationship with in-house or outside subject matter experts.
In North America, inspectors should be certified to the API or National Board Inspection Codes (NBIC) as these are recognized as best practices. NDE examiners are most often certified per ASNT SNT-TC-1A (usually level 2) and often have a Welding Inspector Certification. Subject area experts include equipment engineers and designers, corrosion engineers, welding engineers, metallurgist or material engineers,NDE specialists and structural engineers. These subject area experts are usually in a different organization than the inspectors. The more effective inspection organizations report to the plant manager, a reliability group or the director of operations. Inspection organizations reporting to maintenance or engineering departments tend to be less effective. Most jurisdictions don’t require inspectors to be certified to one of the inspection codes or that the plant adopt an inspection code. Nevertheless, effective process plant inspection organizations almost always adhere closely to API inspection codes, in both spirit and detail, including inspector certification–even when not required to do so by the jurisdiction. The NBIC is less detailed than API regarding piping, vessels and storage tank inspection requirements, but, since API Codes don’t address boilers,NBIC would apply in such cases.
When developing an effective inspection organization, it is essential to gain (and earn) the respect of management, engineering, maintenance and operations. This can only be accomplished through good leadership, clear and welldefined goals and working with other plant organizations on a continuous and cooperative basis. It also is desirable for a plant with several units to have an individual inspector assigned to each unit. Continuity of knowledge about plant equipment can’t be over-emphasized–having the same inspector performing inspections over many years for the same equipment is beneficial.
Equipment to be inspected
Jurisdictional and other regulatory requirements and inspection codes usually identify the equipment that requires inspection. This includes some, but not all, of a plant’s process equipment, and may or may not include utility equipment. Prudent mechanical integrity practices usually necessitate that additional equipment also deserves inspections. If all equipment not required to be inspected by a governmental authority is not included in the inspection plans, it is a strong indicator that an inspection program is, at least, somewhat ineffective.
Remembering that effective inspections support the continued availability of process operations, one should ask what equipment is necessary for effective process operations and include essential equipment in the inspection program. Equipment whose failures may adversely affect other equipment also should be considered for inclusion in the inspection plans.An example would be a cooler tube failure that might result in severe corrosion throughout a cooling water system.Other items to be considered in whether or not equipment should be included in inspection programs are health, safety and environmental issues.
Determine minimum equipment requirements
The minimum required mechanical and process design bases must be defined for both new equipment and in-service equipment.Unless the operating unit has detailed engineering analysis indicating another design basis is more appropriate, the plant should comply with the current minimum requirements of the ASME Construction Codes as the basis for new equipments and the API Inspection Codes or API storage tank standards, including Fitness-for-Service (API RP 579) calculations as appropriate, for in-service equipment. The requirements of state and federal regulations are more applicable when they are more stringent than the ASME or API codes or standards. Generally recognized and accepted good engineering practices should be used to validate the design of equipment not meeting the design criteria of the ASME Codes or API standards, (e.g. horizontal tanks or vessels with design pressure less than 15 psig).
Consideration must be given to effects on equipment due to changes in service conditions since the original design assumptions. Refineries are now using heavier crudes of different acidity sulfur and cyanide contents than those assumed during the initial materials of construction selection. Production cycles, process volumes and fluid velocities also have probably changed since the plant was constructed. Intervals between plant shutdowns generally seem to have increased over the years, as well. All of these post-construction changes tend to result in increased equipment corrosion, erosion and fatigue. A basic question to ask during inspection planning is: "Based on mechanical integrity concerns,would we build equipment differently today due to the process changes that have occurred since construction?" If the answer is "yes," it indicates where and what kind of damage is most likely to occur.
Changes to the ASME Codes or API standards may have been made since in-service equipment was originally constructed, too. Subject matter experts should review the original and current design practices and determine if there are mechanical integrity concerns arising from obsolete design practices.As an example, prior to the 1980s, fracture toughness at ambient and low temperatures of carbon steels were not adequately addressed in the ASME and API Codes and standards for pressure vessels, piping and tanks. Consequently, many heavy-wall carbon steel vessels are being operated at temperatures under pressure where there is a significant probability of brittle fracture.
Based on industry experience, from 5% to 10% of the equipment delivered to plants has significant design or construction deficiencies, even though they were "built to Code." Some of these deficiencies are due to manufacturing errors, but most are caused by not considering all of the loads imposed on the equipment. Inspectors typically use as the equipment’s minimum thickness for retirement or repairs, the nominal thickness less corrosion allowance, or the minimum thickness calculated by thickness data storage software programs based only on internal pressure considerations or some arbitrary thickness (common for piping). If, however, loads other than internal or external pressure are the governing factor in determining minimum thickness and were not considered in the original design, such approaches may compromise mechanical integrity.
Even when the equipment has been designed, constructed and installed to the best current practices, there may be additional loads that develop over time due to structural settling, operating conditions or maintenance practices that can impose excessive loads on nozzles and other attachments. For these reasons, inspectors and appropriate subject matter experts, after appropriate engineering analysis, should concur on the minimum mechanical and process requirements for serviceability.
During the past 30 years,much of the material used for process equipment construction has come from offshore sources. A significant amount of this material is equal to the quality of material obtained from domestic suppliers. Some offshore material, though, particularly piping components, is of lesser quality than required by new construction codes and in a few cases is actually "counterfeit material." The potential problems that might result from use of substandard materials must be considered in inspection planning.
Once the minimum equipment serviceability requirements have been established, it is then necessary to determine those mechanical,wear, chemical and thermal mechanisms that can damage or degrade the equipment–and the likelihood of them occurring. Inspectors should consult with the appropriate subject matter experts, process engineers, maintenance personnel and operators to determine those damage mechanisms that are most likely to happen and where they might occur on the equipment. Experienced corrosion and materials engineers are essential for this appraisal.
Process Flow Diagrams (PFD), P&IDs,Management of Change (MOC) documents, equipment files, historical records, root cause failure investigations, industry experiences and reports of damage to similar equipment at other locations are invaluable for these assessments. Possible damage for both the process side and nonprocess side must be considered. Possible equipment damage due to shutdowns, startups, abnormal operating conditions, maintenance procedures (including cleaning) and long-term out of service must be considered along with normal service conditions.
This damage mechanism assessment is identical to that required for Risk Based Inspection (RBI).An RBI program considers both the damage mechanisms and the consequences that might result should failures (leakage) occur to calculate risk. The equipment that has the greatest risk and where these risks can be lowered by inspection is given priority for inspection.
RBI analyses are very beneficial for plants with good inspection organizations, but they have considerably less or no value for plants with ineffective inspection organizations. In the latter case, it is better to postpone RBI until the inspection organization efficiency improves, so that RBI can be a useful planning tool.
Examination, testing & monitoring methods selection
Once the damage mechanisms have been identified and the desirability of detection and monitoring these mechanisms have been established, the inspection organization must determine the best methods for damage mechanisms detection, quantification and monitoring. Subject area experts such as non-destructive examination specialists and materials engineers should be consulted for this stage of the inspection process.
Several damage mechanisms are quite difficult– if not impossible–to detect and monitor by NDE methods, especially in the early stages of development. Damage may also occur at places on the equipment that are difficult or impossible to inspect or examine by NDE methods. Some forms of damage can only be detected and monitored by metallographic techniques or destructive testing.
Ideally, designers would design equipment constructed of materials that would not suffer difficult-to-detect damage mechanisms, that has all locations accessible for inspection or is capable of being inspected by common NDE methods. It would be helpful if equipment designers had more input from inspectors and subject area experts concerning equipment inspections.
Process fluids can be analyzed for corrosion products or wear particles where these damage mechanism are possibly active. Various corrosion probes, corrosion coupons and other process chemistry monitoring instruments, such as pH meters, are useful indicators of corrosive process conditions. Water treatment service companies usually monitor cooling waters and boiler waters for control of corrosion. The results of these tests should be provided to the inspector, but quite frequently they aren’t.
All parties involved in the inspection processes should be aware of the various limitations and strengths inherent in inspection, monitoring and examinations methods. Many inspection organizations put considerable effort into NDE methods that are useless for the most probable damage mechanisms. These organizations probably put even more effort into the use of inspection practices that are only suitable for damage mechanisms that are highly unlikely to occur.
It’s unlikely that any plant has the tools and in-house skills necessary to conduct valid NDE examinations for all the damage mechanisms possible at its site. Outside contractors are necessary for NDE examinations that plant inspectors are not qualified to perform. Contractors only get paid when they do the examinations or tests, and many are quite willing to conduct examinations, even if their NDE methods are worthless. Using inappropriate NDE methods for heat exchanger tubes is fairly common. A more common problem with contractors is that the technician conducting the test or examination is not qualified. Inspectors with assistance from NDE specialists should carefully review the suitability of NDE methods selected and qualifications of the technicians conducting the examinations.
Develop inspection plans
Inspection planning is a continuous process that involves the collective knowledge of inspection, subject matter experts, maintenance and operations. Once the inspector knows what damage mechanisms may occur and how to detect and monitor the extent of damage, planning for inspection is required. Usually, assistance is required from maintenance and/or operations to prepare the equipment for inspection, provide scaffolding and other means for the inspector to examine difficult- to-reach locations and provide other assistance so that the equipment can be safely inspected. NDE contractors, especially those using special NDE techniques, often must be scheduled in advance. Inspections and examinations that can be performed while the equipment is in service should be completed prior to shutdowns.
No matter how extensive shutdown planning is, the possibility exists that something will be found during shutdown inspections that requires additional examinations and repairs. Contingency planning for such occurrences should be part of the shutdown plans.
Perhaps the highest equipment life cycle costs are the expenses of preparing equipment for intrusive inspections; the actual inspection and examination expenses are usually much less, especially for large storage tanks and vessels.When tank or vessel entry is required, it is prudent to do additional inspections and examinations if some future intrusive entry can be avoided.
Conduct the inspections, tests & examinations
Inspections, tests and examinations are usually started at the first opportunity, even if the inspection planning stage has not been completed. Consideration should be given to measuring base-lined thickness and using appropriate surface flaw detection techniques prior to placing the equipment into operation. Obtaining these results prior to service provides the most reliable methods to detect and confirm excessive corrosion, erosion or stress cracking at the next inspection or examinations.
During shutdowns, schedules usually allow little time for inspectors to conduct additional examinations beyond what was originally planned or to evaluate the inspection and examination results.Non-intrusive examination methods should be used while the equipment is in service whenever practical. Sometimes, equipment has to be opened up for cleaning or repairs prior to a planned inspection. It is often advisable to conduct intrusive inspections at such times, especially if intrusive inspections can be avoided during a scheduled shutdown.
Inspectors and examiners should always receive the budget and support necessary to conduct inspections and examinations of highrisk equipment. It should be recognized that during shutdowns and other maintenance activities, suitable inspections are of equal importance to equipment repairs, cleaning and other maintenance. The time and actions necessary for appropriate equipment inspection should be defined by the inspection organization and not by maintenance or operations.
Evaluate inspection, test and examination results
Perhaps the most neglected action in the inspection process is failure to adequately review the inspection results.Too often, plants depend on the guidance provided by inspection-thickness-data computer programs to judge the suitability of equipment for continued service. As discussed previously, these programs only provide a limited assessment of mechanical integrity,but even more troubling, they fail to adequately highlight many significant problem areas. All inspection data and results should be examined and reviewed by inspectors and appropriate subject matter experts.
A suitable engineering analysis of the inspection results determines the equipment’s present and future mechanical integrity. The analysis should quantify degradation trends, locations and rates. When degradation is a concern, the analysis also should develop a plan to better define those service conditions that are causing the damage and how to monitor future degradation.
During shutdowns, the time and effort required to inspect equipment frequently does not allow time for detailed analysis of most equipment. Equipment considered to be critical or where extensive damage was found should receive at least a Fitness-for-Service, Level 1 (API 579) assessment prior to preparing it for start-up.During the shutdown planning phase, specialized NDE firms, equipment assessment engineers and outside subject area experts should be put on notice that their services might be required during the shutdown. The evaluation must not only determine the equipment’s present and future status, but also directly and indirectly measure the engineering, operating and maintenance practices that affect suitable equipment integrity.
Reports and documents Reports should always be written and filed in the equipment files.When significant damage is noted that might affect the continued equipment operations, the owner/operator should be immediately notified verbally. The reports should be in a form that accurately and unequivocally conveys an equipment condition to operations, but in sufficient detail for a through analysis by subject matter experts in the future. The owner/operator must have a clear understanding from the reports and plant inspection practices of what was and what was not inspected, examined or tested.Where appropriate, the reports should indicate those damage mechanisms that could have been missed by special inspection and examination techniques used. Furthermore, it often is necessary to brief operations on the limitations of inspection and examinations techniques used.
An equipment file should exist for each vessel, tank and piping circuit. These files should include all of the design, construction, installation, maintenance, testing, inspection, engineering assessments, operating history and other records that could possibly be required by subject area experts or inspectors. Equipment files should be current and kept in a known location with all of the documents and records assessable on short notice.A paper copy should be kept of all records and documents as electronic files might not be readily assessable several years into the future.
When critical documents such as design calculations are not available and obtainable, they should be created through reengineering. Some records, such as mill test reports and prior inspection history, cannot be reengineered; thus, it is essential that these documents be obtained and filed right after the tasks are completed or the documentation is compiled.
Those reporting inspection and evaluation results and conclusions should be sensitive to cases where human error may have resulted in equipment degradation. Facts and valid engineering conclusions must always be included in the reports.Unless inspection is part of a root cause failure investigating team, no conclusions should be drawn indicating or insinuating who was at fault for the damage found.
Any planned or unplanned changes in the process–including what are expected to be "corrective actions"–could have some influence, either positive or negative, on damage mechanisms. Changes that may affect equipment include fluid velocities, process stream compositions, temperatures, pressures, equipment alterations, modifications in structural supports and changes in materials of construction.
Inspectors need to be aware that changes in temperature may result in changes in both internal and external corrosion rates. Typically, such changes affect the corrosion or erosion rates, but, in some cases, they may cause a different type of corrosion other than general corrosion or other damage. Moreover, corrosive attack might show up at different locations in the equipment than where it did in the past. Inspectors should consult with subject matter experts to determine how these changes might distress the equipment. Inspection plans may require modification to monitor such changes.
The inspector should be provided information on various corrosion monitoring programs being conducted by corrosion engineers, water treatment contractors and shift operators. The results of monitoring programs need to be considered in inspection planning.
Maintain effective communications
An inspection organization should have continuous, accurate, timely and effective communications with all parties who can influence or have knowledge concerning equipment integrity. Most organizations outline various communication avenues in management system documents, organization charts and other procedural documents.
Successful inspection programs also seem to have intangible communication aspects that are rarely delineated in procedural documentation. Essentially, these intangible aspects involve the interpersonal relationships that exist among various plant organizations and how individuals approach their responsibilities. In ideal cases, operating and maintenance personnel inform the unit’s inspector of all events that could affect plant integrity, often by very informal means. Then, there is the other extreme–where the inspector is told very little since "it is the inspector’s job to figure out what is going on."
All operations outside of the "normal"operating envelope should involve a mechanical review. There are many monitoring programs to help organizations enforce this. Even if the inspection organization is not a participant in these events,the details and conclusions of a mechanical review should be communicated to the inspectors.
The importance of effective communications becomes evident when it is recognized that the inspector, based on what is known, develops and implements a plan to determine what is unknown.The less an inspector knows, the more likely he is to develop plans that miss some equipment degradation or that result in expensive and unnecessary inspections.
The inspection process, including all its elements, must be evergreen in nature. As things change and new events occur, they must be accounted for and included in inspection planning, execution, evaluation and reporting. Effective inspection groups continuously look for new ways to inspect and monitor equipment and are knowledgeable about events pertaining to their equipment that occur throughout the industry. Gathered information must be maintained and used for the life of the equipment, even though it may be 30 years old, or may only be applicable many years in the future.
When unusual events occur or inspection results indicate that current inspection plans are inadequate, the plans should be modified accordingly. After each inspection (and evaluation), the inspection plan should be reviewed, updated as necessary and implemented.
Inspection is not a task conducted by a single group within a facility. It involves many people with various jobs and responsibilities, working together to determine the present and future status of process equipment. The inspection organization not only inspects equipment, it also gathers and assimilates the necessary information to perform a valid inspection. MT