Introduction:
Corrosion management is a key concern for all oil & gas assets. This is mainly due to the nature of fluids produced and injected throughout the assets lifecycle, regardless of the age of asset types and the level of corrosive agents present in the flow stream, be it CO2, H2S, water, or chloride. The limited remaining quantity of significant oil and gas reserves are concentrated in challenging locations, such as deep-water offshore, deserts, remote arctic locations, and difficult-to-manage reservoirs. Corrosion is a huge cost in these aggressive environments and in the transportation of the resources through pipelines, tankers and ships. I There are many methods to prevent corrosion such as using drying agents, coating or barrier products or a layer of backfill. However, the surface must be prepared and cleaned before applying rust inhibitor coatings. An effective method of surface preparation for large industrial machinery is through sandblasting, more specifically wet blasting. According to NACE, the annual cost of corrosion to the oil and gas industry exceeding $60 billion. It is therefore imperative to protect the assets from corrosion due to the excessive cost of replacement or failure in these difficult-to-access locations.
Types of Corrosion in the Oil and Gas industry:
There are four main types of corrosion that disrupt the pipes and tanks in the oil and gas industry.
1. Atmospheric Corrosion
Atmospheric corrosion is the degradation of materials caused by air and the pollutants contained in the air through an electrochemical process due to rain, dew or humidity in the atmosphere.
2. Aqueous Corrosion
Aqueous corrosion is the deterioration of the material and its vital structural properties due to a wet environment (e.g. submerged pipes). The higher the acidity level of the water, the greater is the impact of corrosion.
3. Soil Corrosion
Soil with high moisture content, high acidity, high dissolved salts, and high electrical conductivity is very corrosive and represents a geologic hazard that affects buried metals and concrete that is in direct contact with soil or bedrock.
Types of Corrosion in the Oil and Gas Industry
There are many different types of corrosion but only main types are listed below in the interest of brevity.
1. General Attack Corrosion
This is the most common form of corrosion created by an electrical or electrochemical reaction that breaks down the surface of an exposed metal, causing it to weaken until it fails.
2. Localized Corrosion
Corrosion that is localized can be of three types:
Corrosion that arises from a small hole and breaches the metal causing failure is called Pitting corrosion.
In stagnant crevices, such as underneath gaskets and clamps, Crevice Corrosion can be caused by acidity or oxygen depletion.
When water breaks through flaws in the coating it may eventually spreads and causes weakness in the structure through Filiform corrosion.
3. Galvanic Corrosion
Galvanic corrosion occurs when two dissimilar metals are immersed in a conductive solution and are electrically connected. One metal (the cathode) is protected, whilst the other (the anode) is corroded at an accelerated pace.
4. Environmental Cracking
This type of corrosion is the result of a number of conditions in the environment, such as temperature, chemicals, and stress. There are four kinds of environmental cracking:
- Stress Corrosion Cracking (SCC)
- Corrosion fatigue
- Hydrogen-induced cracking
- Liquid metal embrittlement
Corrosion can wreck disastrous results in the oil and gas industry from oil spills, fires, large scale environmental disasters, downtime in the plant, leaks, pressure drops, wasted energy, clogging of rust particles in piping accessories, dryers and filters etc.
Different Maintenance solutions used to remove corrosion
Given the typical size of the area required to be covered, manual methods such as sanding, scraping are not suitable in the oil and gas industry.
The following are the main methods for removing rust from pipes and tanks:
1. Cleaning
Solvents and emulsions are used to clean the steel surface to remove oil, grease, dust, lubricants and similar organic matter, but it cannot remove rust, oxide scale, welding flux, etc. on the steel surface.
2. Pickling
Chemical treatments for anticorrosion in pipelines use chemical pickling which can remove oxide scale, rust, and old coatings. It can also be used as a means of reprocessing after sandblasting and rust removal. Although chemical cleaning can achieve a certain degree of cleanliness and roughness on the surface, its anchor lines are shallow and easily pollute the surrounding environment.
3. Manual Derusting tools
Tools such as wire brushes, bristle brushes, can remove loose oxide scale, rust, welding slag, etc. Hand tools can reach up to the Sa2 level of surface cleanliness
4. Power Tools
Rotary files, Flap discs are power tools used to remove rust and they can reach the Sa3 level of surface cleanliness. It must be noted that improper usage can also cause more damage due to the stress and pressure of the grinding. The metal must be periodically allowed to cool to prevent overheating. If the steel surface has solid oxide scale, the rust removal tools are not effective and the anchor pattern depth required for anti-corrosion construction cannot be reached.
5. Bristle Blasting
The process utilizes a dynamically tuned rotary wire bristle tool whose tips are both hardened and sharpened. Upon impacting the corroded surface, bristle tips immediately retract, thereby causing a repetition of craters that mimic indentations which are commonly associated with grit blast media.
6. Dry Sand blasting
In dry sandblasting, abrasive media such as steel shot, steel grit, garnet, aluminium oxide etc. is propelled onto the surface. The violent impact and friction of the abrasive remove oxides, rust and dirt to achieve the required uniform roughness. Sandblasting therefore not only removes the corrosion layer but also provides a good surface profile for the protective coating to adhere.
7. Wet Abrasive Sandblasting
Wet abrasive sandblasting also known as dustless blasting or vapour blasting adds an additional element of water to the abrasive media and compressed air used in sandblasting. When the abrasive media such as garnet is saturated and is laden with moisture, it provides a forceful impact. The significant advantage of wet sandblasting is that it is virtually dustless as the water particles suppress the dust.
When it comes to aluminium, corrosion must be removed from pits. In the case of pitting on a critical structure, the pit hole must be blended so that there are no sharp corners. The final blended area must be saucer-shaped with the major axis oriented to limit its effect on structural integrity. On non-critical structures, the edges do not need to be blended.
Advantages of the Sandblasting Process to remove corrosion
Even though many different tools and equipment have been developed for surface cleaning and restoration, the sandblasting process has emerged as the most common and widely used method to maintain aging, corrosion-prone infrastructure. The success of the sand blasting process can be explained by its inherent ability to provide multiple benefits simultaneously. These are deemed necessary for the reapplication and successful adhesion of protective coatings:
- Removal of foreign aggregate substances from the surface
- Exposure of an essentially contamination-free, fresh surface (i.e. exposure of base metal/substrate material)
- Creation of a surface morphology or anchor profile that is receptive to application of protective coatings
Within the sandblasting process, wet abrasive blasting provides even more benefits than dry sandblasting.
- Unlike dry sandblasting, wet blasting or vapour blasting is virtually dust less and 95% of the dust is suppressed.
- Wet abrasive blasting does not require the use of a specialised sandblasting booth or the construction of containment barriers and can be performed anywhere in the open. It can also be done in high pedestrian traffic areas.
- Wet sandblasting provides a nice feathered finish
- Unlike dry blasting, there is no heat and resultant warping of thin substrates
- It is truly portable and compact and can be used on offshore rigs and on pipes and equipment in remote areas
The Quantum Blast Solution
RapidBlast™ Wet Abrasive Blasting Equipment
Quantum Blast manufactures wet abrasive blasting equipment under the RapidBlast™ range. The equipment is extremely versatile to suit a wide range of applications on different surfaces. Built tough and durable, the equipment is virtually maintenance free.
The equipment is designed, developed and manufactured in Australia and supported by a strong team of technical experts.
Elcometer™ Dry Abrasive Blasting Equipment
Quantum Blast Australia also is the exclusive distributor for the world renowned Elcometer™ dry blast pots. Elcometer™ pots are engineered and manufactured in the United Kingdom. Compared to the competition, they work harder, last longer and perform better through optimising the volume, speed and pressure of air to the nozzle. Faster blast coverage reduces operator labour time and reduce abrasive usage saves money and clean up time.
For more details, call the sales team on 1300 822 569 or email sales@quantumblast.com.au
You can also visit our website at www.quantumblast.com.au to learn more about us and our products and services.
Summary:
Extending the life of aging assets that are often degraded by corrosion is a major challenge that every operator is currently facing. Installed and running over several kilometres, pipelines carrying oil & gas are subjected to extreme weather, dirt, dust, and rain. Without any proper coating and absence of periodic maintenance, the chances of critical failure of these pipelines increase due to mass built-up and internal scaling.
Simple steps such as blasting of inner walls of pipes allows a smooth flow of liquids and gas through pipes, thus increasing their efficiency and operability. Even a slight increase in the pipes’ operability means growth in financial figures and company’s profitability. It is widely recognized within the oil and gas industry that effective management of corrosion will contribute towards the maintenance of asset integrity and achieve optimization of mitigation, monitoring, and inspection costs.
