Risk Based Inspection (RBI) of Aboveground Storage Tanks to Improve Asset Integrity
Authors: Al-Mitin Abdul Wahab , Sardesai Vinayak , Al-Harbi Bader , Murthy Srinivasa Hari , Hannan Abdul Sattar Abdul 
Published: March 2015

Kuwait Oil Company (KOC) has 85 crude oil aboveground storage tanks in its Tankfarms for the storage of crude oil prior to export. These tanks have storage capacities ranging from 162,000 to 597,500 bbl. (US). Hydrocarbons leaks / spillages resulting from tank failures, if any, could be very expensive and could pose serious fire hazards apart from major environmental issues. Therefore, in order to carry out a comprehensive assessment of the tanks to prevent any impending failure, KOC decided to adopt Risk Based Inspection (RBI) approach to evaluate the risks associated. With the aging tankfarm facilities and the changes in oil production processes, it became even more important to ensure the reliability of to ensure the reliability of tankfarm facilities from the viewpoint of "just in time maintenance" and regulatory requirements. The outcome of the evaluation enabled formulation of inspection strategies to mitigate these risks for improving asset integrity.

A qualitative RBI methodology was established and the procedure was developed in-house based on the guidelines in international standards (API, NFPA). The procedure was then used to perform the RBI study of each individual tank in KOC Tankfarms. A workbook was developed to carry out the risk assessment of the tanks as per API RP 581 and the RBI assessment results were presented in a risk matrix.

For carrying out the risk assessment, the tank is divided into three sections viz. the Bottom Plate, the Shell and the Roof and each section is subjected to risk assessment separately. Relevant damage mechanisms are considered for each of the sections.

The RBI analysis includes the information on original design, operation & maintenance, damage mechanisms, timing the failure of individual evaluated components, condition inspections, process condition, NFPA (National Fire Protection Association) rating for service fluid and current operating conditions. RBI study recommendations include the suggested improvements to the inspection program and maintenance schedules to enhance the asset life-cycle.

This paper describes the entire Tank RBI process adopted at KOC, some interesting findings of the RBI study and the recommended Asset Management Strategy for the Tankfarms.

1. Introduction

1.1 Brief of KOC Facilities

Crude oil from oil wells is transported to the Gathering Centre (GC) via a number of flowlines. The Gathering Centre processes fluids to separate gas, water and salt associated with oil before pumping to the Tankfarms. The crude oil processed at various Gathering Centers of Kuwait Oil Company is transported through the transit pipelines to the Tankfarms.

Over 85 tanks in the Tankfarms receive crude oil with a minimum API of 30.5 from the incoming transit pipelines via a Central Mixing Manifold. The tanks are equipped with automatic level gauges, Motor Operated Valves, firefighting facilities and manual oily water disposal system.

The crude oil is stored at these Tankfarms prior to export. KOC sets the production targets on the basis of continuous market demand.