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New Technology for Inspecting Critical In-Plant Piping Systems


Published online July 28, 2011 in Wiley Online Library (www.wileyonlinelibrary.com)

Abstract

Inspection and Fitness-for-Service of Critical In-Plant Piping systems remains an ongoing concern for the chemical industry. Recent failures in the US indicate that there is a present and severe risk in piping systems. Historically un-piggable in-plant piping can now be inspected with advanced smart pigging technology for complete ultrasonic inspection. High-resolution inspection data is analyzed to identify the locations and degree of corrosion and piping deformations. This paper discusses current industry experience with the inspection and assessment of in-plant piping systems using advanced smart pigging technology.

Utilizing more advanced inline inspection and assessment technology helps operators reduce inspection costs associated with difficult-to-inspect pipelines and piping systems; reduce maintenance costs by more accurately pinpointing anomalies and assessing fitness-for-service conditions; and accurately determine the actual conditions for lines previously deemed unpiggable.

Introduction

Inspection and Fitness-for-Service of Critical In-Plant Piping systems remains an ongoing concern for the Chemical industry. The task of inspecting and assessing the condition of in-plant piping systems in a chemical plant represents a potentially insurmountable task and may present any number of areas where the condition is unknown and at risk. Recent failures in facilities in the United States indicate that there is a present and severe risk in piping systems. Many in-plant piping systems have historically been un-piggable due to the size (diameter) and the inherent obstacles such as valves, bends, and diameter changes. These systems can now be inspected with advanced smart pigging technology for complete ultrasonic inspection. High resolution inspection data is analyzed to identify the locations and degree of corrosion and piping deformations. The assessment of corrosion and deformation damage using API 579 Fitness-for-Service methodology [1], dramatically improves the ability of a plant to understand and improve the mechanical integrity of these systems and avoid environmental, safety, and operational risks.
Plant Piping Design and Damage

Process piping within a chemical plant is typically designed to ASME - Process Piping [2] standards. Pipelines and interconnecting piping operated outside the fence is typically designed to ASME - Pipeline Transportation Systems for Liquid Hydrocarbons and Other Liquids [3] or Gas Transmission and Distribution Piping Systems [4] standards. These product distribution, raw material supply, or intermediate transfer lines may also come under the jurisdiction of the Pipeline and Hazardous Materials Safety Administration (PHMSA) [5] which is the primary federal agency responsible for pipeline safety and enforcement. The details of performing an assessment are provided in these documents.

The causes of serious incidents in pipelines are summarized in Table 1. The proportion of incidents resulting from excavation damage has decreased and is no longer the most significant factor in pipeline incidents. Additional causes such as mechanical damage not associated with excavation (vehicle incidents, vandalism, etc.), corrosion, and material failure are also of significance.   

Table 1 ”" Causes of Pipeline Incidents [5]

          Excavation                    22 %          Corrosion                      20 %

          Maintenance Failures    20 %

          Human Error                   7 %

 

                                                                         

Natural Force Damage                4 %

Other Outside Force Damage     1 %

All other Causes                        22 %

Pipelines and piping most often fail because of the development of critical flaws such as cracks, corrosion (including wall-thinning, erosion and pitting), mechanical fatigue, and mechanical damage.  Once initiated, defects in the pipe may continue to grow in service to the point at which a line can either leak or rupture. With a leak, there is no extension of the length of the defect. A rupture will bulge outward prior to failure and then the defect will extend into and the surrounding environment before either propagating or arresting depending upon the material, the pressure, and the physical state (liquid or gas).

Some examples include:
  • A partial wall defect (corrosion, cracking, etc.) eventually fails and becomes a through wall defect.
  • A pipeline may leak when the corrosion or defect reaches the point where the stress carried by the remaining ligament or section of pipe becomes too great.
  • A pipeline may leak when the through-wall defect is small and the pressure is low.

A pipeline may rupture when the through wall defect is large or long and the pressure is high.

Pipeline Inspection and Pigging

Chemical plant piping is typically inspected using conventional ultrasonic technologies to manually locate damage at specified inspection locations and to establish corrosion rate information. These local thickness readings are acceptable as long as the damage mechanism produces broad area corrosion or the ultrasonic inspection happens to hit a spot of localized damage. However, in many instances corrosion is not uniform and a spot reading cannot be used to accurately determine the condition of the piping.

Particularly difficult or costly to inspect with conventional ultrasonic’s and visual inspection are:
  • Localized corrosion
  • Corrosion under insulation or supports
  • Localized internal corrosion
  • Corrosion in jacketed piping
  • Corrosion in buried lines, road crossings, or within casing
  • Piping underwater or through sensitive environmental areas, or otherwise difficult to access areas.

Ultrasonic Inspection Tools

A "Pig" is a term used to describe a tool placed within a pipeline or piping system to clean or to perform an inspection task. Pigs are normally propelled by a product or liquid flow through the line. In-Line Inspection (ILI) is commonly used to describe tools or “smart pigs” designed for the inspection and measurement of pipelines or related piping. The term “pig” originated from the screeching noise and the appearance of the tools when dirty from cleaning a line, “barnyard pig”.

The Quest Integrity Group has designed the InVista™ tool to specifically overcome piping design challenges which generally limit the use of traditional in-line inspection tools. InVistaTM is an intelligent inspection tool, or “smart pig”, capable of rapid ultrasonic inspection of difficult-to-inspect pipelines up to 100 miles (160 km) in length.  The tool is a free-swimming, self-contained, bidirectional tool, providing 100% data coverage for generating highly accurate piping system reliability analysis. Its unique design enables plant operators to inspect traditionally “unpiggable” piping systems with challenging features such as short radius (1.0 diameter) bends, take-offs or tees,  and diameter changes. Figure 1 is a graphical representation image of the InVistaTM tool showing the ease of handling, flexibility, and ability to navigate bends in piping systems.

The current InVista™ tools are capable of inspecting both metal-loss and geometry in a single pass for piping between 3 inch and 14 inch diameter (nominal pipe size (NPS)).  InVista’s compact design allows it to be launched and received with minimal equipment or piping system modifications. The tool can also be launched and received   from a single location if required for the specific application. This technology is a time-proven inspection methodology deriving from Quest Integrity’s fired heater inspection technology servicing the global refining and petrochemical market since 1998.

The InVista™ tools are light weight and manageable by hand without the need of additional lifting equipment which reduces operator costs by eliminating the need for support equipment and related personnel (i.e. crane, logistics).

Figure 1.  Image of an InVista™ Pig within a Bend Section

InVista’s™ physical architecture is constructed of a compact and robust modular design consisting of 2 to 4 separate modules depending upon tool diameter. Within the tool’s specified velocities, the axial data sampling density is set at 0.250 in. intervals.  The wall thickness accuracy is ±0.005 inch and measures thicknesses down to 0.030 inch.  Axial positioning is measured with an odometer system.  Additionally, the tool transmits an external signal which synchronizes with Above Ground Markers (AGM) systems to monitor the tool position during the inspection and establish fixed reference locations in the inspection data for further investigations. These fixed points can also be referenced to GPS locations for underground or aboveground dig locations.

The presence of corrosion or other three-dimensional anomalies in a pipe length disturbs the ultrasonic pulse sequence, and is detected by the receiver and recorded onboard. Time of flight is then used to compute wall thickness as well as diametrical and shape dimensions based on the known acoustic propagation properties of the ultrasonic couplant (fluid medium in the line) and the piping material.  The advanced immersion ultrasonic based pigging technology is specifically designed to simultaneously detect and quantify flaws related to corrosion (i.e. wall thinning, Erosion, Pitting, Mechanical Wear, etc.) in addition to piping deformations (i.e. Denting, Ovality, Bulging, Swelling, etc.).

Key Benefits:

  • High resolution inspection with 100% overlapping axial and circumferential coverage.
  • Differentiates between defects on interior and exterior pipe surfaces.
  • Pinpoints circumferential and longitudinal location of defects.
  • Complete analysis of all inspection data with an API 579 Fitness-for-Service assessment.
  • Lightweight, self-contained, and compact tools are handled easily; no lifting equipment is required to handle the tools.
  • Industry leading tool design for navigating difficult in-plant piping and pipelines and can also negotiate damaged or restricted pipe.
  • Capability to inspect previously un-piggable piping.
  • Tools can be run bi-directional (ability to enter and exit the piping at one location).
  • Efficient inspections that can minimize system shutdown time and in some cases can be performed in-service with liquid products in the line.
  • Ability to perform turnaround inspections and rapid data analysis allowing real-time operating decisions.
The InVista™ inspection system can easily navigate and inspect process plant piping for localized corrosion, corrosion under insulation, localized internal corrosion, as well as locate dents and other dimensional anomalies. Unlike other inspection methodologies, the ultrasonic technology is also specifically suited for  internal corrosion in jacketed piping, inspection of  buried lines,  road crossings, or piping within casing under roads or tank containments, as well as piping located underwater or through sensitive environmental areas, or otherwise difficult to access areas.

Ultrasonic technology directly measures anomalies which in turn provide superior piping integrity assessments.  The high resolution data collected by this inspection tool is viewable in two dimensional (2D) and three-dimensional (3D) formats and covers the entire length of pipe, see Figure 2. The level of detail and accuracy presented by the inspection data allows the data to be further analyzed using LifeQuest™ Pipeline, a powerful graphical data analysis package which provides accurate Fitness-For-Service (FFS) and remnant life assessment data which operators utilize to make real-time operating decisions.

Assessment Methods

Various methods and types of piping inspections including but not limited to ILI tools are utilized by plant operators to gather data about the current condition of their piping. The data obtained is analyzed and acted upon to prevent a future failure of the system and to increase operational efficiencies. Confidence and level of risk of both the present and future operations are highly influenced by the quality of the inspection data and the method used in assessing the piping system.  

The ultimate objective of a Fitness-For-Service (FFS) assessment of piping or other types of equipment is to avoid a leak or rupture in-service. Leaks are generally avoided by applying a safety factor based on the percentage of original wall thickness or an absolute minimum thickness value, both of which consider a future rate of corrosion.  API 579 considers a maximum allowable wall thinning of 80% of original thickness or an absolute value of 0.10 inch. The leak versus rupture condition requires an assessment of the remaining material strength and the stress resulting from the size and shape of the defect.

The API 579 procedure was adopted as a standard by ASME in 2007 as API579-1/ ASME FFS-1 and has been referenced as an acceptable. API579-1/ ASME FFS-1 and has been referenced by ASME B31G-2009 [6] as an acceptable, equivalent, and more advanced assessment method in ASME B31G ”" 2009.     

Fitness-for-Service Assessment Procedures

Fitness-For-Service (FFS) assessment is a multi-disciplinary approach to evaluate structural components to determine, as the name suggests, fitness for continued service. The API 579 Fitness-for-Service standard is used to evaluate several classifications or types of flaws including general metal loss, localized metal loss, pitting corrosion, crack-like flaws, creep, and brittle fracture.

API 579/ASME FFS-1 (FFS) [1] is particularly applicable for pipelines and in-plant piping systems. Piping systems within chemical plants are subjected to a wide range of operating conditions and service environments. These conditions can subject the piping to a variety of damage mechanisms that can be localized either inside or outside of the pipe.  This damage must be evaluated both independently and in conjunction with other adjacent or neighboring damage, defects, or anomalies. The piping may also be subject to different and more severe operating conditions than those specified in the original design.  The typical outcome of an FFS assessment is a “go or no-go” decision on continued safe and compliant operation.  An evaluation of remaining life and/or appropriate inspection intervals may also be part of such an assessment.

LifeQuestTM Pipeline FFS Assessment

Quest Integrity Group has developed and offers customized LifeQuest™ Pipeline  software allowing 2D and 3D visualization of the entire pipeline using data collected by the InVistaTM tool (see Figure 2).  This interactive software enables viewing of the Remaining Strength Factor (RSF) and Reduced Maximum Allowable Operating Pressure (MAOPr) in accordance with an API 579-1  Fitness-For-Service Assessment.

This calculation of RSF is performed every 0.250 inch along the pipeline or piping system or 250,000 times per mile. For consolidation of reporting, the results are typically reported as minimums between girth welds or for each joint of piping. This RSF and MAOPr  profile of the piping system, provides the operator a complete assessment of the condition of the piping sytem along its entire length according to the API 579 FFS, Level 2 standard.

Summary

Combining InVista inspection and the LifeQuest Pipeline engineering assessment enables facility maintenance or reliability engineers to take advantage of a complete API 579 FFS, Level 2 assessment of a pipeline or piping system for continued service. The assessment may provide the faciltity with informantion and confidence to extending the life of the asset. Utilizing more advanced inline inspection and assessment technology helps operators reduce inspection costs associated with difficult-to-inspect pipelines and piping systems; reduce maintenance costs by more accurately pinpointing anomalies and assessing fitness-for-service conditions; and accurately determine the actual conditions for lines previously deemed unpiggable. InVista’s™ direct measurement and engineered asset assessment is the most accurate method to expose pipeline or piping system risks and limit the need for unnecessary remediation and expenditures.

There are additional Process Safety Progress articles covering pipe system inspections [7, 8, and 9]. 

A more detailed article covering the technology described in this article is in an Ammonia Plant Symposium Proceedings [10].


 
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