Maximizing Value: The Untapped Potential of Non-Intrusive Inspection

Introduction

Conventional wisdom holds that direct entry with internal inspection is the gold standard for endorsing the mechanical integrity of pressure vessels. In many cases, upstream oil and gas operators overlook potential benefits and take on unnecessary operational risk by not considering using non-intrusive inspection (NII). This article provides an overview of a multi-decade-long NII program that started in the early 1980s and progressed to full-scale global implementation. The transformative program over a recent five-year period led to the elimination of over six hundred confined space entries (CSE) and an increase in over US$0.5 billion of operations revenue. Key insights and learnings are provided on the process, program, metrics, and challenges that were overcome to unlock the value by fully leveraging NII. The program included the application of NII across a broad range of onshore and offshore assets, reservoir conditions, pressure vessel types, materials, and worldwide locations.

Program Background

NII was initially used in the early 1980s to assess pressure vessels at field locations in the Western Hemisphere. Technology using automated ultrasonic testing (AUT) systems for corrosion mapping and other ultrasonic inspection techniques was taken directly from the nuclear industry. The NII program described herein employed some of the highest-qualified non-destructive examination (NDE) technicians in the world at that time. Technicians were ASNT qualified and additional requirements for training and qualification developed by either the U.S. Nuclear Regulatory Commission (NRC), Boiling Water Reactor Owner’s Group (BWROG), or Electric Power Research Institute (EPRI). Qualification included the detection and sizing of intergranular stress corrosion cracking [1-4].

Note: Since flaw sizing is critical for determining safe and reliable operation, technicians would sometimes prove up AUT results with EPRI sizing techniques as well. During the proving period, owners would often cut out samples that appeared severely cracked or damaged. They would then cross-section the samples in the laboratory to validate the results. Sometimes over and under-calls were made, even with advanced methods such as AUT. The industry learned from these experiences to improve the techniques and technologies over the last 30+ years.

The initial inspection program included comprehensive NII inspections and follow-up vessel entries with internal inspections to confirm all findings. The vessel types included those across the upstream production spectrum for fluid separation, handling, and gas processing. Pressure vessel materials ranged from bare carbon steel, internally coated carbon steel (epoxy-phenolic, phenolic), various types of clad (e.g., 316 ss/Inconel 625), austenitic stainless steels 304/316, and duplex stainless steels 2205/2507.

Field service conditions ranged from non-corrosive to highly corrosive environments with carbon dioxide partial pressures well above 30 psia and predicted corrosion rates up to 20-100 mils per year [5, 6]. Hydrogen sulfide contents ranged from trace levels to gas compositions of above susceptibility limits for sulfide stress cracking, 0.05 psia H2S [7]. Although alloy and clad vessels were subject to the harshest conditions, numerous bare carbon steel and internally lined vessels were subject to corrosive service. Cathodic protection utilizing sacrificial anodes was frequently part of the internal corrosion protection scheme, especially in internally coated vessels.

Over decades of operation from the 1980s to 2010, additional fields were developed and acquired worldwide across various regulatory jurisdictions. No consistent methodology was practiced or mandated companywide for the endorsement of pressure vessel integrity. Vessel entry and internal visual inspection (IVI) was the method most applied. The practice was influenced by several factors, which will be discussed later. From 2010-2013, there was an increasing recognition of value being delivered by NII at select assets and potential lost opportunities at others. Shortly thereafter, a formal project was sanctioned to develop and expand NII to the extent possible across all global operations.