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Atmospheric Storage Tank MI/RBI Programs 

Introduction

With the guidance of OSHA's Process Safety Management (PSM) program, refineries, chemical

and petrochemical facilities are developing more comprehensive and technically advanced

Mechanical Integrity (MI) programs. And within those programs, Atmospheric Storage Tanks

(AST's) continue to be high priority items due to the extensive time and cost associated with

cleaning and inspection. But as operators continue to build best in class management programs,

tanks are emerging as the frontrunners in terms of cost and risk mitigation.

 

Challenge

While tank inspections represent a large cost for facilities, they also present logistical

challenges for operators that coordinate hundreds of tanks across thousands of miles.

Managing these inspections often requires more strategic planning than those vessels seen in a

large, concentrated facility with a full time inspection department. But even in large facilities, the

extensive nature of tank inspections often results in grave deficiencies in the area of

data management. Instead of utilising data to trend corrosion rates or predict failures, large stacks

of documentation are often stored in tank inspection cabinets and only resurrected 15 years later.

 In terms of risk based inspection (RBI), tanks necessitate a different approach than pressure vessels and piping. Tank risk must be assessed differently for the following reasons: 

Consequence of Failure:o Small leaks may go undetected for months

o Leaks are governed by liquid level as opposed to pressure

o Environmental effects are generally mitigated due to liquid state fluids and

containment dikeso Leak detection and secondary containment systems can alter the consequence of

failureo Tank areas are generally much less populated than process areas

o Roof, shell, and floor failure all result in different impacts

Probability of Failure:o Tank failure may not occur until zero wall, as pressure is solely governed by

liquid levelo Multiple tank shells exist that often possess different corrosion allowance values

o Properly assessing corrosion rates on the floor requires more advanced inspection

(MFE) or more advanced modelingo The roof, shell, and floor all pose different damage types and susceptibilities

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For this reason, PinnacleAIS® has developed a unique routine to address the implementation and

management of risk based inspection programs for tanks.

 

The Benefits

Through the course of several hundreds of tank RBI assessments, Pinnacle has demonstrated a

substantial return on investment. While some tanks do in fact assume more aggressive

inspection plans from the assessment, on the whole the cost benefits have been

outstanding. Overall, the benefits can be summarized by the following: 

Inspection Savings: An elongation of internal inspection intervals resulted in an average

of 1,500% Return on Investment (ROI) or an average of $40k savings per tank.

Reduced Tank Downtime: Risk Based Inspection intervals average 24 years between

internal inspections.

Improved Compliance: While this remains particular to the project, many tanks deemed

out of compliance by API 653 were pushed beyond the assessment date.

Below is a summary of the results from a recently completed RBI implementation project in a

facility with 226 tanks: 

RBI plans accelerated the inspection due dates for 33 tanks, deferred the dates of 182

tanks and left 11 tanks unchanged 

The facility had been struggling to bring tank inspections up to date as 46 tanks were out

of compliance per API 653 prior to the assessment After conducting an RBI assessment,

the number of non-compliant tanks was reduced to 26, therefore saving the facility $7

million in budgeted tank inspections in just the first year

After conducting an extensive assessment to understand the status of the tanks, Pinnacle

identified 27 high consequence tanks, two of which were flagged as being out of

compliance. 

Aside from the hard cost savings, PinnacleAIS®'s clients are also left with a comprehensive and

controlled electronic library of all their tank documentation and a validated tank database with

tank design, operating, process, and inspection data. Armed with these tools, PinnacleAIS®'s

clients are able to confidently and efficiently manage their tanks into the future.

 

A Path Forward

While tanks continue to pose significant concerns, risks, and costs to the petrochemical and

chemical industries, implementing a sustainable Risk Based Inspection program within Pinnacle's

approach has proven to be extremely effective in mitigating process inefficiencies, leveraging

historical data, and utilizing modern statistical theory to drive a robust tank MI program going

forward.