Assessment Intervals: Regulations and Challenges

Assessment Intervals Pipeline Safety Blog January 2024

Assessment intervals play a pivotal role in safeguarding against potential risks and failures, ensuring the integrity and reliability of pipelines. 

Understanding assessment intervals is not only a regulatory necessity but a strategic imperative for maintaining effective integrity management programs. In this blog, we will break down the regulatory background of assessment and reassessment intervals, how to determine where your operation fits within the regulations, and the purpose of this important process to maintain safety. 


In pipeline safety, the foundation lies in meticulous technical evaluations which are critical for assuring pipeline integrity. These assessments lay the groundwork for your integrity operation, and the frequency of these assessments plays an important role in all subsequent maintenance and management of the pipeline. This assessment process integrates various data sources, including corrosion surveys, excavations, coating assessments, and corrosion rates, providing a comprehensive understanding of the pipeline’s condition. Tool tolerance and evaluation digs also play a role in ensuring the quality of tool data, contributing to the assessment’s accuracy. 

Balancing reassessment intervals is challenging, as periods that are either too long or too short pose significant risks. Federal statutes have set maximum reassessment intervals – 5 years for hazardous liquid pipelines and 7 years for natural gas transmission pipelines. However, it’s important to keep in mind that these are legal limits and not default intervals. Each operation is different, and there are operational and safety factors that must be considered when determining assessment intervals specific to your organization.  

Further complexity arises as reassessment intervals need to be evaluated for each segment within a pipeline system. While some segments may share similar reassessment intervals, piggable segments may present distinct risks, requiring careful consideration for different intervals. The dynamic nature of reassessment intervals is underscored, emphasizing the ongoing need for re-evaluation based on incidents, pipeline excavations, and emerging information. 

Guidelines and Requirements 

The Pipeline and Hazardous Materials Safety Administration (PHMSA) mandates that operators develop a comprehensive Integrity Management Plan (IMP) to ensure the integrity of all covered segments. This plan is required to incorporate a baseline assessment plan, detailing the methods for assessing integrity based on identified threats, such as internal inspection, pressure testing, direct assessment, or other approved technologies. Additionally, operators must include provisions for remediating conditions discovered during integrity assessments, creating a process for continual evaluation and assessment. The IMP should identify personnel responsible for conducting integrity assessments and those evaluating the results. 

From PHMSA GT IM Fact Sheet 

The Baseline Assessment Plan must: 

  • Identify potential threats to each covered segment 
  • Identify methods to assess integrity based on the threats identified for each covered segment (acceptable methods include internal inspection, pressure testing, direct assessment, or other technology that the operator demonstrates provides an equivalent level of understanding of line integrity) 
  • Identify a schedule for completing the assessments including the risk factors used in determining schedule priorities 
  • If applicable, include a direct assessment plan, appropriate for the threats identified for the covered segments 
  • Include a procedure for ensuring that the baseline assessments are conducted in a manner that minimizes environmental and safety risks 

Cyclic fatigue analysis is mandated for prioritizing both baseline assessments and reassessments. The Baseline Assessment Plan must identify potential threats to each covered segment, outline assessment methods, and establish a schedule with risk factors for completing assessments. The plan must also incorporate procedures ensuring that baseline assessments are conducted in a manner minimizing environmental and safety risks. 

In addition to baseline assessments, operators must conduct risk assessments to identify preventive and mitigative measures for high consequence areas and public safety enhancement. These measures include installing Automatic Shut-Off Valves or Remote-Control Valves, implementing computerized monitoring and leak detection systems, replacing segments with heavier wall pipe, providing additional training, conducting drills with local emergency responders, enhancing inspection and maintenance programs, and fortifying damage prevention programs. Compliance with these regulations is essential for the safe and reliable operation of pipelines. 

From PHMSA GT IM Fact Sheet 

Operators must conduct risk assessments to identify additional preventive and mitigative measures to protect high consequence areas and enhance public safety. Such additional measure include, but are not limited to: 

  • Installing Automatic Shut-Off Valves or Remote Control Valves 
  • Installing computerized monitoring and leak detection systems 
  • Replacing segments with heavier wall pipe 
  • Additional training 
  • Conducting drills with local emergency responders 
  • Implementing additional inspection and maintenance programs 
  • Enhancements to damage prevention programs 

By providing guidance for pipeline operators, PHMSA aims to assist inspectors, operating companies, and the public in navigating the intricate process of evaluating these crucial intervals. The information from PHMSA is designed to minimize inconsistencies and misunderstandings that often cloud the determination of reassessment intervals.  

The guidelines serve as a compass, steering stakeholders through the complexities of pipeline integrity management, offering clarity on the data and information essential for determining reassessment intervals. By understanding and adhering to these guidelines, operators can contribute to a safer pipeline infrastructure and enhance the overall efficacy of integrity management programs.  

Determining Assessment Intervals 

A thorough approach that considers safety factors along with unique aspects of your organization is needed to determine assessment intervals that align regulatory standards. 

The evaluation of reassessment intervals extends beyond a holistic system overview to a granular level, considering the distinct risks and requirements of individual pipeline segments.  

Establishing reassessment intervals for pipeline integrity involves a meticulous four-step process.  

Beginning with the identification of the largest remaining defect, operators must then apply a growth rate while considering tool tolerances and safety factors. Rigorous adherence to conservative assumptions ensures safety and realistic reassessment intervals.  

The methodology varies based on inspection technologies, with in-line inspection tools relying on validated anomaly data and hydrostatic testing calculating defects surviving pressure tests. Learn more about In-Line Inspections and Tools. Defect growth rate determination proves challenging due to non-homogeneous factors, urging caution against an average growth rate. According to PHMSA, non-homogeneous factors can be small variations in environment, stress, cathodic protection, corrosion mechanisms, among other factors.  

For reassessment intervals, estimating the time to failure involves projecting the defect’s growth until the estimated failure pressure aligns with safety standards. Integrated threats and factors like land movement require a case-by-case engineering assessment. It’s important to identify these scenarios, and even more important that these unique cases are documented. Operators should have a process that is flexible enough to adapt to these scenarios.  

Additionally, considerations for crack-like defects and interactive threats, such as corrosion and stress corrosion cracking, demand conservative approaches for accurate reassessment intervals.  

Continuous evaluation, documentation, and adaptation are vital for maintaining the effectiveness of integrity reassessment processes. In summary, the dynamic nature of integrity management necessitates regular re-evaluation of reassessment intervals to ensure pipeline safety and prevent failures. Operators must ensure that their processes and procedures account for dynamic requirements that can change over time, and there should be a process in place to document when these considerations occur.  


Ultimately, the biggest pain point associated with assessment intervals is keeping track of modified schedules and potential changes in CA (consequence area) classification. This is further complicated by changes that only impact one section of the pipeline, causing that section to deviate from the schedule associated with the remainder of the pipeline. 

As areas surrounding the pipeline change and expand, what was previously a Moderate Consequence Area classification could be raised to a High Consequence classification when a new school or subdivision pops up. Changes like this make it important to maintain assessment intervals because there’s a possibility that between the initial assessment and the next scheduled assessment, a lot can change. It is these changes that must be documented as part of your operation’s ongoing assessment rigor.

On any given line, there may be several different consequence areas – all of which require different assessment intervals. 


Assessment intervals are an important factor in upholding the integrity and safety of pipeline systems. As we navigate through the intricate technical evaluations, regulatory nuances, and dynamic considerations, one thing becomes clear: precision in reassessment intervals is not just a regulatory requirement but a strategic imperative for effective integrity management programs. 

To further establish your safety posture, adherence to the regulations put in place by PHMSA is a necessary step. Reassessment intervals are not static; they evolve based on incidents, excavations, and emerging information. Embrace the proactive evolution of reassessment practices to safeguard against potential risks and ensure the resilience of your pipeline infrastructure. 


As part of our efforts to strengthen pipeline safety operations, we work with clients to build customized dashboards to help operators see assessment information at a glance. Users are able to view last completed assessments and next due for assessments that fall under a given consequence area.  

Contact us now for assistance in reviewing your processes for establishing and executing pipeline assessments or reassessments. Together, let’s ensure that your pipeline systems exceed the highest safety standards.