Types of Pipeline Corrosion and Erosion

In our last blog we looked at the need for ultrasonic testing when it comes to monitoring the corrosion and erosion of pipelines and tanks. In this, we explore the types of corrosion and erosion that can occur and how best to maintain and monitor them.

What kinds of corrosion and erosion occur in pipelines and tanks?

Uniform Corrosion  

Uniform corrosion or general corrosion is the most common form of corrosion, and is caused by several individual electrochemical processes that occur consistently over the whole of the surface considered. The problems caused by this type of corrosion are:

• Loss of metal thickness
• Loss of weight per unit

Pitting Corrosion

This form of corrosion is particularly menacing. The attack is in the form of highly localised holes that can penetrate inwards extremely rapidly, while the rest of the surface remains intact. A component can be perforated in a few days with no appreciable loss in weight on the structure as a whole.

When looking at pitting and the way in which it works, it is most aggressive in solutions containing chloride, bromide or hypochlorite ions, opposed to Iodides and fluorides which are significantly less harmful. Stainless steels are particularly sensitive to pitting corrosion, but other metals, such as passive iron, chromium, cobalt, aluminium, copper and their alloys are also prone to this form of damage.

Erosion-corrosion

This is caused by the flowing movement between a corrosive fluid and a metal surface. This process leads to the formation of groove valleys, wavy surfaces and holes. Each form of this type of corrosion will have a directional appearance on the metal surface that will mimic that of the fluid. Most metals and alloys can be affected, particularly soft materials (e.g. copper, lead, etc.) or those whose corrosion resistance depends on the existence of a surface film (aluminium, stainless steels).

This form of pipeline corrosion will be particularly worse in two-phase liquids (containing suspended solid particles or gas bubbles), the impact of the particles can damage or even eliminate the protective layers or passive films that are normally stable in the absence of particles, and the local corrosion rate is then markedly accelerated. This phenomenon is called abrasion-corrosion.

So how do you control pipeline corrosion?

The first step would be to have employees or contractors trained in corrosion control. When pipeline operators assess risk, corrosion control must be an integral part of their evaluation. Corrosion control is an ongoing, dynamic process. There are a few key aspects that you need to keep in mind in this process:

• Quality design and installation of equipment
• Use of proper technologies
• Ongoing maintenance and monitoring by trained professionals.
• Controlling the pressure, flow, temperature, and filter/control the make-up of fluids.

The benefits of an effective maintenance and monitoring programme

When looking at the benefits of an effective pipeline corrosion maintenance and monitoring program it must be kept in perspective that the oil, gas and chemical industries lose billions of dollars every year through unexpected shutdowns on pipelines or plants, and in reduced productivity. 

Corrosion testing can be an operator’s best insurance against preventable corrosion related problems. Effective corrosion control can extend the useful life of all pipelines and tanks. The increased risk of pipeline/tank failures far outweigh the costs associated with installing, monitoring, and maintaining corrosion control systems. Preventing pipelines from deteriorating and failing will save money, preserve the environment, and protect public and workforce safety.

How does the CorDEX UT5000 help to overcome these issues?

The UT5000 is the perfect solution to the problems associated with corrosion detection on an operating petrochemical facility. With its certified, intrinsically safe design it allows you to work in hazardous areas drastically reducing downtime and internal administration when applying for hot work permits. The UT5000 allows you to get on site, and get the job completed safer, faster and better.

If you’d like more information on the CorDEX UT5000 Thickness Gauge, CorDEX CONNECT™ software, or any of our other products, please contact us on +44 (0) 1642 454373.