In a recent post we highlighted diagnostics to identify wiring corrosion. But what about corrosion in the process piping? I recently received a whitepaper, Solutions for Corrosion Monitoring in Refineries, written by Emerson’s Kjell Wold and Hallgeir Jenssen. They manage the Roxar line of products and services for production optimization and improved decision making for the oil & gas industry through exploration and production.
Downstream, refiners are challenged with corrosion in the process. Some examples include internal corrosion in cooling water systems and side-streams, de-salting units, flare systems in carbon steel and in distillation units.
The whitepaper provides an overview:
…of the differing forms of corrosion, the purposes behind corrosion monitoring and the varying approaches and technologies for addressing corrosion.
Kjell and Hallgeir note the ways various forms of are addressed:
…painting, coating, cladding, cathodic protection and the use of chemicals (corrosion inhibitors)…
Refineries vary by age, construction materials, and processes employed. Temperatures and fluid velocities through the piping can have an impact on the rate of corrosion. Also:
…the quality of the feed (crudes) may affect corrosion in the plant. Different crudes have different corrosion properties, linked to the ‘acid content’ of the crude (TAN number). Acid content is linked to the crude price and lower price crudes often have a higher acid content and therefore are more corrosive to the plant materials. Hence, refineries that buy crude in the spot market (opportunity crudes) often need a proactive corrosion protection strategy related to the blending of crudes, material selection, monitoring and inspection.
…will suffer from uniform corrosion, depending on water content, the efficiency of desalting, the use of corrosion inhibitors, etc. This will be the case in in many of the refineries’ early streams, side streams and cooling water pipes.
…tubes/plates are normally in corrosion resistant alloys, where corrosion attacks more often take place as localized pitting or crevice corrosion.
For high-temperature distillation units:
…’naphthenic corrosion’, which normally initiates as localized corrosion attacks that may later form front lines where a sulfidic film is damaged. Over time, metal loss will appear as a combination of localized corrosion and more uniform distribution at the internal pipe wall.
They highlight several corrosion monitoring technologies including intrusive probes, weight loss coupons, electrical resistance (ER) probes, Linear Polarization Resistance (LPR) probes, ultrasonic sensors and field signature measurements (FSM). It is important to choose the measurement technology according to the application and objectives of corrosion monitoring program. The authors note a trend towards combining more technologies in integrated solutions for a complete monitoring approach.Wired and wireless signals from these sensing devices beyond manual corrosion coupons feed data acquisition and data management systems.
Kjell and Hallgeir shared a case study in which an oil refinery in India illustrating:
…how FSM can monitor and control high temperature corrosion accurately and efficiently, optimize production, and guarantee integrity management. The online systems’ resolution is also within the range of 0.1% of the wall thickness. With crude oils having different corrosive properties, active corrosion monitoring and mitigation is having a key impact on the economics of the refining process and on the safety and maintenance of the plant.
Corrosion is a continuous challenge in refinery operations today – for maintenance and control but also as a potential risk for people and assets if not properly managed. Each refinery must adopt its own monitoring and control strategies to meet its specific needs.
A range of intrusive and non-intrusive methods exist – each with their own benefits and limitations. Yet, often a combination of methods will give the best overall monitoring program for a refinery.
WirelessHart technology is increasingly accepted in the industry, and makes upgrades to on-line monitoring affordable. Many monitoring applications can be combined in the same wireless Hart network, including intrusive corrosion monitoring and non-intrusive UT sensors – all at the same time.
Read the whitepaper for more on the corrosion sensing technologies and how the refinery was able to continuously monitor for internal corrosion. You can also connect and interact with other refining experts in the Refining group in the Emerson Exchange 365 community.