Terry G. Clevenger
Director of Marketing for Industrial NDT Company, Inc.
Level II inspector in the major nondestructive testing disciplines
Summary: The following article is a part of the National Board Technical Series. This article was originally published in the July 1991 National Board BULLETIN. (6 printed pages)
To say that pressure vessels and piping systems have received an extraordinary amount of attention in recent years is a gross understatement. Even storage tanks at atmospheric pressure have been more heavily scrutinized by the Occupational Safety and Health Administration (OSHA), the Environmental Protection Association (EPA), and industry in general.
The planning or process engineer is faced with a multitude of adverbs when considering the best approach to a vessel, piping, or system inspection program; why inspect, where to inspect on which vessels, how to inspect and when?
This paper attempts to organize the planning process for an inspection program into four (4) basic phases, and discusses each phase at length. Topics include categorizing or prioritizing vessels, assigning inspection techniques and scopes to various categories, implementing inspections, documentation formats, engineering evaluation, and applications of the program to future purchases of new systems.
Let us first establish some common denominators for planning and implementing a vessel, tankage and piping inspection program. The objective of the program can be to establish a QA/QC (Quality Assurance/Quality Control) system which ensures that all pressure vessels, tanks, and piping systems are scrutinized on a regular, timely and cost-efficient basis. This objective will clearly enhance the concept of a mill life extension effort. The purpose of such a program is to reduce the risks of personnel injuries, property or production losses, or environmental damage which could result from an unexpected catastrophic failure of a system. The benefits, aside from reducing the risk factor, are enhanced predictability in maintenance, repair and replacement functions as well as assurance that QA/QC standards are applied toward new systems. Again, these benefits are aimed at enhancing mill life extension decisions.
With these common goals in mind, all vessels, tankage, and piping systems will generically be referred to as "systems." Planning or organizing the thought process of a systems inspection program (SIP) can then proceed as follows:
- Phase I - Feasibility study to determine the appropriate course of action
- Phase II - Implementation of the systems inspection program (SIP)
- Phase III - Engineering evaluation of data gathered during implementation
- Phase IV - Application of SIP to future purchases
Phase I - Feasibility Study
The obvious purpose of the feasibility study is to determine the appropriate course of action for the SIP.
Our first step is to perform a comprehensive inventory of the targeted systems. As an example, each pressure vessel and storage tank within the facility will be physically located and inventoried by name, location and responsible department.
During the inventory process, the technician will perform a limited visual survey of each system. Results of the survey can be recorded in the form of a field drawing. When possible, the field drawing will include information such as size, coating material, accessibility, location of weld seams, location of openings or penetrations, alterations, surface conditions, and other pertinent information.
The comprehensive inventory is essential in subsequent planning of inspection time frames, costs, support activities, etc. The final product of the inventory process should be individual field drawings accompanied by data unique to each system and a plan view of how the systems can be "grouped" for inspection.
Classifying or categorizing each system is the next step. Input from facility management is beneficial to ensure that systems are evaluated objectively and in accordance with company goals of production, safety, and environmental impact. Obviously, a pressure vessel situated outside a plant cafeteria will be classified and inspected differently than a warm water storage tank in the middle of a field!
While classification guidelines will vary, some of the considerations in determining classification standards are:
- Systems affecting personnel safety
- Systems regulated by federal, state, or local agencies, the insurer, or by in-house requirements
- Systems critical to production or those affecting plant reliability or availability
Staying with our example of pressure vessels and storage tanks, the following classification categories could be applied:
Category P-1 - ASME code unfired pressure vessels which meet any of the following criteria:
- Failure poses safety risk to personnel
- Failure jeopardizes other critical components
- Vessel contains hazardous or toxic contents
Category P-2 - All pressure vessels serving as heat exchangers or ASME code stamped National Board registered vessels which do not meet the risk criteria of P-1 vessels. Additionally, any vessels whose operating and service conditions are different from their original design and construction.
Category P-3 - All remaining pressure vessels not classified as P-1 or P-2 systems.
Category S-1 - All vented storage or process tanks whose rupture or leakage could pose significant risk of injury to personnel, environmental pollution, or loss of production.
Category S-2 - All remaining vented storage tanks whose rupture poses little or no risk to personnel or continued operation because of remote or protected location, low temperature, or mild contents.
Determining a Course of Action
With the inventory and classification system completed, the owner's representatives will need to make two decisions: first, determine the inspection scope of work desired for each category of system; and secondly, determine the timetable or milestone schedule to complete the inspections.
It is helpful to consider a scope of work matrix to consistently organize the inspection format for similar types of systems. The matrix can offer varying degrees of inspection thoroughness depending on the owner's need.
The maximum scope of work would be utilized when the test component is suspected of having varied potential defects, is an extremely critical component, and has no prior history of inspection. The average scope would be applied to components which have targeted areas of concern and are of a less criticality. The minimum inspection scope is utilized on components of less criticality which have been inspected previously and/or only require spot-checking of certain areas.
The desired time frame for completion of the program will dictate manpower loading, degree of support costs, and other factors. Obviously, the size of the facility and the number of systems to be examined weigh heavily in this decision. Time frames can be as little as six weeks to as much as several years depending on the factors we have discussed.
With inventory, classification, scope of work and time frame established, the feasibility study is completed. Costs of the program can now be calculated and implementation can begin.
Phase II - Implementation of the SIP
The tasks in this phase are to establish a documentation/report format, gather the baseline inspection information, and compile a QA/QC package for each system.
The agreed-upon documentation format should suit the needs of the owner and can be in hard copy form or maintained on a computerized database. As a minimum, the documentation format should contain the following elements:
- Baseline Data - includes all pertinent system data such as location, size, temperature, pressure, manufacturer, design criteria, material specification, etc.
- Maintenance Records - all information regarding repairs, modifications, or special requirements of the system
- Nondestructive Testing - all technical reports documenting NDT results should be compiled and displayed, when possible, on system drawings.
Electronic files (computerized documentation) is ideal for the SIP as it allows for features such as easy access and supplementation to reports, establishment of a "tickler file" to remind the engineer of upcoming actions, and storage of large amounts of information in a relatively small area.
The documentation system should automatically incorporate the system classification criteria already established, as well as the inspection procedures and methods chosen for that particular system. This allows for easy recall when planning future inspections and assures consistency in the QC effort.
Gathering Inspection Information
Once the documentation format has been established, the process of gathering baseline information on each system begins. The methods and sources for obtaining this information are
- System General Information - including engineering or maintenance files, drawing files, original equipment manufacturer's (OEM) records, contractor files, etc.
System Condition - determining the current condition of the system through nondestructive test methods including visual, magnetic particle, dye penetrant, ultrasonic, radiographic, and other appropriate disciplines. Each system is inspected per the guidelines established in the scope of work matrix with any additions or deletions to the scope clearly documented.
Compiling a QA/QC Package
The Phase II activities are concluded with the assembly of a QA/QC package on each targeted system. To recap what constitutes this package, the engineer will have at his/her disposal an organized documentation format consisting of:
- A classified listing of all systems
- Historical information on each system
- Targeted inspection procedures/methods
- Inspection results from all examinations
Once a comprehensive package is available, we are ready to make use of the information as a routine planning tool for preventive/predictive maintenance, repair or replacement activities.
Phase III-Engineering Evaluation
To this point we have organized and compiled a tremendous amount of valuable information and documented it into a useable format for review. The information is practically worthless, however, without a concerted effort to evaluate each system as to its current performance/condition and take corrective actions where necessary.
Competent engineering personnel should be utilized for this effort from in-house staff, insurer authorized inspectors, or outside engineering consulting firms. At least three areas of evaluation should be considered by these individuals:
- Systems which require immediate remedial measures to comply with the mandated level of compliance
- Systems which will require future maintenance or less critical action
- Determining reinspection guidelines including frequency and extent based on initial baseline findings. These reinspection guidelines would typically be inserted back into the QA/QC package for each system and result in the "tickler file" previously mentioned.
Phase IV - QA/QC for Future Systems
To effectively close the loop on the SIP, we should consider applying the same scrutiny to future systems. Indeed, during the examination (Phase II), situations will probably be found where "design thickness was not suitable" or "workmanship on the welding was poor." These situations lead us to consider how we can assure that future purchases meet the desired quality levels. Topics for this consideration can be, but are not limited to:
- Design Conformity
- Fabrication Surveillance
- Installation Surveillance
- Material Conformity
- Weld and Welder Qualification
- Baseline Inspection
By implementing and documenting a SIP, it becomes increasingly clear which areas of a future system purchase need to be better controlled. Naturally, all information gathered during a new installation is documented in the same manner as "on line" systems, and becomes an automatic member of the program.
An attempt has been made to organize the thought process of planning and implementing an inspection program for pressure vessels, tanks, and piping systems. Programs will vary from one facility to another, but the basic ingredients are still similar.
Because it can be a monumental task, the engineer should consider performing the program in phases and even concentrating the effort on individual sections of larger facilities to keep the program manageable. When thought out and implemented, however, the program allows for regular, timely and cost-efficient monitoring of critical systems.
Editor's note: Some ASME Boiler and Pressure Vessel Code requirements may have changed because of advances in material technology and/or actual experience. The reader is cautioned to refer to the latest edition of the ASME Boiler and Pressure Vessel Code for current requirements.