Grit blasting is a method of abrasive blast cleaning used to prepare substrates for a wide variety of purposes. These range from general cleaning, vehicle restoration, preparation of a substrate for subsequent painting, coating or lining, through to preparing large scale components and plant for Non-Destructive Testing / Evaluation (NDT / NDE).
This guide has been compiled to aid in making an informed decision about whether or not grit blasting is appropriate for your application – and if we can help.
At KUE Group we specialise in dry grit blasting and wet abrasive blasting for NDT / NDE surface preparation for the power generation industry, as well as other heavy industrial applications. Grit blasting is an extremely effective method of preparing plant, tanks,vessels, pipework and components for NDT / NDE and for creating a surface suitable to receive a protective coating or lining. We are one of the UK’s leading suppliers of contract surface preparation services, with mobile blasting units, a fleet of bespoke vehicles containing all equipment to carry out a stand alone service on any site within the UK and Europe.
Our services are also available within our fully equipped in-house facility in Bradford where two large blast booths receive items from small components through to large items up to 4m in diameter x 12m in length.
By the end of this guide, you will understand what grit blasting is and what it is used for, as well as several alternative surface preparation methods. Full contact details and asummary of our services are included in a later section of this guide. If you have any questions in the meantime, please don’t hesitate to call +44 (0) 1274 721188 or send an email to [email protected]
Grit blasting is the operation of forcibly propelling a stream of abrasive materialunder high pressure against a surface to clean or modify its surface properties. Theabrasive material is contained either in a stream of compressed air (dry blasting) orwater (wet blasting). Here at KUE Group we use a wide variety of abrasivesdependent on the client’s specification and surface finish required and / or thesubsequent activity. Commonly used abrasives are Garnet, Chilled Iron Grit, SteelGrit, Aluminium Oxide, Glass Beads and Crushed Glass all of which remove oldcoatings, mill scale, rust, heat scale and contaminants from the substrate, preparingit for subsequent coating, lining, welding, NDT / NDE.
The abrasive and pressure are selected to prepare a surface to meet your demandsdepending on your application.
There are a number of grit blasting methods. Abrasive can be propelled by compressed airalone, the addition of water enables wet blasting or mechanically such as in a wheelabratormachine. This ensures that there is a wide range of applications for which grit blasting is asolution.
1. Surface Preparation for Non-Destructive Testing / Evaluation (NDT / NDE)
Grit blasting is used to prepare a surface in readiness for Non-Destructive Testing /Evaluation (NDT / NDE). Its purpose is to provide a clean surface, free from mill scale, rust, heat scale and contaminants to enable the NDT / NDE professional to evaluate thesubstrate.
2. Surface Preparation for Coating and Lining
Coatings and Linings act as a protective layer to protect the underlying surface from either corrosion, erosion or both. Application of a coating or lining to a correctly prepared surface will enhance the performance and life expectancy of both the coating / lining and crucially the plant, equipment or item it is applied to. Grit blasting removes old coatings, mill scale and other surface contaminants as well as leaving a surface anchor profile that aids adhesion of the subsequent coating or lining.
3. Surface Cleaning
Grit blasting can be used to clean a surface by removing residues, contaminants and scale, therefore improving and increasing efficiency of a never-ending range of plant and equipment.
In order to carry out industrial blast cleaning / grit blasting the following is required;
- A source of high volume, high pressure clean compressed air.
- A blast pot, this is a pressurised, tank like container filled with abrasive blast media,used to allow an adjustable amount of abrasive blast media into the blast line.
- An abrasive blast media.
- A blast hose, deadman handle and venturi design blast nozzle to deliver the abrasivemedia stream to the substrate.
Health and Safety is of paramount importance when undertaking grit blasting operationsand PPE is the last line of defence for the blast operative. As a minimum a blast operativeis provided with a blast helmet providing impact protection and a source of cleanbreathing air. Blasting overalls providing enhanced protection from the abrasive mediaricochet. Blasting gauntlets to protect the hands and forearms and safety footwear.
There is a wide range of abrasive blasting media available in the marketplace today, eachwith its own beneficial uses and benefits and drawbacks of use. The table below provides an overview of those commonly or uncommonly used.
BS EN ISO 8501-1:2007 is a visual assessment of surface cleanliness that specifies a seriesof rust grades and preparation grades of steel surfaces. The various grades are defined bywritten descriptions together with photographs and are summarised below.
- A) Steel surface largely covered with adhering mill scale but little, if any, rust.
- B) Steel surface which has begun to rust and from which the mill scale has begun torust.
- C) Steel surface on which the mill scale has rusted away or from which it can bescraped, but with slight pitting visible under normal vision.
- D) Steel surface on which the mill scale has rusted away and on which general pitting isvisible under normal vision.
The required type of finish depends upon the application as follows:
- Sa1: Light blast cleaning – When viewed without magnification, the surface shall be freefrom visible oil, grease and dirt, and from poorly adhering mill scale, rust, paint coatingsand foreign matter.
- Sa2: Thorough blast cleaning – When viewed without magnification, the surface shall befree from visible oil, grease and dirt, and from most of the mill scale, rust, paintcoatings and foreign matter. Any residual contamination shall be firmly adhering.
- Sa2½: Very thorough blast cleaning – When viewed without magnification, the surfaceshall be free from visible oil, grease and dirt, and from mill scale, rust, paint coatingsand foreign matter. Any remaining traces of contamination shall show only as slightstains in the form of spots or stripes.
- Sa3: Blast cleaning to visually clean steel – When viewed without magnification, thesurface shall be free from visible oil, grease and dirt, and from mill scale, rust, paintcoatings and foreign matter. It shall have a uniform metallic colour.
As with any methodology, grit blasting is better suited to some applications than others. Here is a quick guide to how grit blasting compares to alternative methods.
✔ Grit blasting is fast, efficient, and effective. Within the industry, it is recognised as having the best ratio of time taken to required surface cleanliness. For end users and clients, this means reduced downtime and, consequently, improved productivity. Therefore, in terms of ROI, grit blasting is an excellent choice.
✔ The availability of differing abrasive blasting media options mean that grit blasting can be optimised for the duty of use. From expendable single use Garnet for general NDT / NDE and coating / lining use to Aluminium Oxide and Glass Beads which are both recyclable and used in the surface preparation of critical turbine components and non-ferrous items.
✔ The abrasive media is often inexpensive, and in many cases features the added capacity for either recycling or reuse. This often makes it a cost-friendly approach to surface preparation.
✔ Grit blasting can be carried out both in-house or on-site as required. As such there is a solution for all your surface preparation needs.
✔ UHP Water Jetting involves firing water at a surface at pressures up to 60,000 psi. It can be effective at reducing salt/chloride levels from the substrate.
✔ UHP jetting is also optimised for assisting in the removal of thicker coatings. In these cases, more than one methodology may have to be employed.
✖ There are always logistical concerns when working with water. The need for the residual water to drain and debris to be filtered has to be taken into consideration. This includes the safe disposal of any hazardous material.
✖ UHP Water Jetting produces high noise levels at the work face requiring specialist hearing protection. Coupled with ultra-high working pressures, increased levels of PPE are required. In addition, specialist training is required to be a UHP Water Jetting Operative.
✖ UHP Water Jetting equipment is both expensive to hire or purchase and has historic reliability issues
✔ Shot blasting is often confused with grit blasting, but they are actually used for very different purposes. Shot Blasting involves firing small, smooth spherical particles, usually steel to clean iron, steel, forgings and provide a smooth surface finish, also used in peening to alter an items mechanical properties, increasing resistance to fatigue for critical parts used in aerospace, automotive, ship building and rail industries.
✔ Manual or tool cleaning is considered to be the best option for small localised areas.
✖ Manual or tool-based cleaning is also time-consuming, which translates to increased downtime and higher staffing costs. As a general rule, these approaches take 75% longer than grit blasting.
In this section we answer a few of the questions we receive most frequently about grit blasting:
How Much Will It Cost?
This depends on the type of grit blasting that is required, the size of the project, and how the work is to be carried out. As this varies from small one-off projects to preparing large or complex surface areas within OGC and Power Generation Sites, individual quotes are prepared. KUE Group provides detailed quotes for free via our online form.
How Quickly Can You Do It?
KUE Group endeavour to complete your requested scope of work within the shortest time frame possible. We have immediate access to our fully trained workforce and own plantand equipment ensuring your needs are met wherever possible. Precise details of timescales can be provided when the project details are outlined.
Will You Damage My Plant?
The simple, short and honest answer is no, KUE Group have been at the forefront of surface preparation for over 46 years with an exemplary record.
How Quickly Do I Have To Coat A Surface After Grit Blasting?
The generally accepted industry standard is 4 hours after completing the blasting process with the caveat that ‘all surfaces to be coated should be clean, dry and free from contamination’. Substrate temperature should be at least 3°C above the dew point and always above 0°C. Application at ambient air temperatures below 5°C is not recommended. The maximum air and substrate temperature for application is 50°C providing conditions allow satisfactory application and film formation. If the air and substrate temperatures exceed 50°C and coatings are applied under these conditions, paint film defects such as dry spray, bubbling and pinholing etc, can occur within the coating.
Incorporating leading coating specialists Lithgow Saekaphen Ltd, KUE Group can advise onthe best procedure for your project or include a protective coating or lining service.
For more information on coatings, please browse our selection of free guides.
Grit blasting is offered as a service by many multi-disciplined companies within the UK asan ‘add-on’ to the main core business. KUE Group ARE Surface Preparation specialists it’swhat we do, pure and simple.
If you work within the power generation, oil, gas or chemical sectors or indeed anyindustry where surface preparation, coatings or linings are required then KUE Group canbe a key business partner. Here’s why:
KUE Group has over 46 years’ experience of surface preparation and corrosion protection. This means that we were leading the development of grit blasting boiler pressure partsand turbine components well before it became the industry standard. Experience leads toa safer, more reliable, and more accurate project approach. It also means confidence andpeace of mind for our clients.
After 46 years, we have seen a lot. However, there is always a new challenge on thehorizon, and if KUE Group can help you with it we will.
KUE Group have a commitment to maintaining a safe, healthy, environmentally sound and productive work place on all sites where our personnel are employed and this has beendemonstrated by the award of OHSAS 18001, ISO 14001, ISO 9001 and high scoring Achilles UVDB B2 Verification in recent years.
Details of our accreditations include:
Thank you for downloading this guide. We hope you have found it useful and it hasanswered some of your questions about grit blasting. If you’d like to find out more ordiscuss a project, please get in touch by phone or email.
Tel:+44 (0) 1274 721188
Email: [email protected]