ISO 12944-4: Surface Preparation Standards

ISO 12944-4: Surface Preparation Standards

Preparing Steel Surfaces for Corrosion Protection Coating

In our previous article in this series discussing ISO 12944, the standard providing guidance for the corrosion protection of steel structures by protective paint systems, we looked at what the standard says about steel structure design and corrosion. In this article, we examine the main points of Part 4 of ISO 12944 which lays out instructions covering surface preparation for different types of surface.

What Is Surface Preparation?

Surface preparation is the first-stage treatment of a steel substrate which must be undertaken before applying a protective coating. Correct surface preparation is essential to the success of the corrosion protection coating being applied.

The objectives of surface preparation are to:

  • Remove deleterious matter
  • Produce a surface that enables paint to adhere to the steel
  • Minimise the contaminants that initiate corrosion

Mill scale must be removed from new hot rolled steel (in accordance with ISO 8501-1) in order to produce a surface profile that is appropriate for the coating system to be applied (which will be defined in the painting specification).

When surface preparation is carried out, health and safety regulations must be observed, and the surfaces that are to be prepared must be accessible and adequately illuminated. Burrs, sharp edges, and weld spatter should normally be removed around weld details and steel edges; this is generally carried out during the fabrication stage of new steel structures. More details on preparation grades can be found in ISO 8501-3, which define acceptance criteria based on a given specification requirement.

Factors that affect surface preparation

There are many factors that affect the surface preparation strategy and method chosen. These include:

  • Whether it is an existing or new structure (and age)
  • The structure’s location
  • The quality of the previous surface prior to preparation
  • The performance of the coating system
  • The type of corrosive environment
  • The coating system that is likely to be used

The preparation grade necessary to provide the required surface cleanliness and the surface profile (roughness) should also be considered.

Types of surfaces covered by ISO 12944-4

The standard covers surfaces of steel structures consisting of carbon or low-alloy steel of the following types:

  • Uncoated surfaces, consisting of bare steel (which are assessed in accordance with ISO 8501-1)
  • Metal coated surfaces, which include hot-dip-galvanised surfaces, zinc electroplated surfaces, sherardized surfaces, and thermally sprayed surfaces
  • Surfaces painted with prefabrication primer (in accordance with EN 10238)

The standard is mainly concerned with the protection of carbon steel new-build structures or extensive maintenance projects to be cleaned back to bare metal.

Surface preparation methods

The method used to prepare the surface for its corrosion protection coating should remove as much oil, grease, dirt, salts, and other contaminants as possible before further surface preparation is performed. Once known contaminants have been removed, testing may be required to detect less visible contaminants such as soluble salts (as per ISO 8502-6).

Any corroded material that exists should be removed by manual or mechanical techniques, though no sound metal should be removed unnecessarily. When preparing surfaces, the two types of surface preparation are:

  • Primary – which takes the whole surface to bare steel
  • Secondary – which leaves the sound parts of any coatings as they are

Methods that might be used to prepare surfaces for their protective coating include (but are not limited to):

·         Water, solvent, and chemical cleaning

A water jet may be used if the contaminants to be removed include water soluble materials and loose rust or paint coatings.

If detergents are used in the cleaning process, then the surface should be rinsed with clean, fresh water after cleaning.

·         Steam cleaning

Steam cleaning removes oil and grease, though again the surface should then be rinsed with clean, fresh water if detergent is added to the steam. Further testing may be carried out to determine the presence of oil and grease in accordance with ISO 8502-7.

Other methods to remove oil and grease include emulsion cleaning, alkaline cleaning, and organic solvent cleaning.

·         Chemical conversion cleaning

For hot-dip-galvanized surfaces, electroplated-zinc coatings, and sherardized surfaces, cleaning may be carried out by chemical conversion. Such treatments can only be used if the manufacturer of the paint system to be applied approves this type of cleaning.

·         Stripping

Solvent-borne pastes or alkaline pastes may be used to strip paint coatings, though this is usually used only on small areas and then followed by other appropriate cleaning.

·         Mechanical cleaning

Mechanical cleaning methods include cleaning with power tools, blast cleaning (of various types), and flame cleaning. Blast cleaning may be used to remove contaminants, to smooth or roughen the surface metallic coatings, or to remove a surface layer. ISO 8503-3 details these methods.

What if the surface preparation doesn’t achieve its aim?

The requirements of surface preparation are based on a range of preparation grades that are laid out in ISO 12944-4. If the required preparation grade is not achieved – or if the surface condition has changed before the coating system is applied – then further surface preparation must be carried out.

Who can carry out surface preparation work?

The standard is specific in describing who can carry out surface preparation work, saying that:

‘Personnel carrying out surface preparation work shall have suitable equipment and sufficient technical knowledge of the processes involved to enable them to carry out the work in accordance with the required specification.’

After the surface has been prepared, it must be assessed as fit for the coating system to be used. There are separate standards that regulate testing and how testing must be carried out – ISO 8501 and ISO 8502.

The Institute of Corrosion Coating and Inspection Training Courses – presented by Argyll Ruane and Corrodere – will help ensure your painters and inspectors work to the latest industry standards and benefit from new technology and innovative approaches. For more information, contact us today.

In our next ISO 12944 article, we look at laboratory performance test methods and the changes that were made to these in the latest revision of the standard.

In the meantime, if you have any questions, please feel free to get in touch with ICorr or download our guide ‘Surface Preparation Methods’.

Survey Drones can now go beyond line of sight

Survey Drones can now go beyond line of sight

The use of drones for aerial inspection and survey is increasing, and their usefulness is set to increase with a demonstration by AmeyVTOL of a drone inspection carried out beyond the visual line of sight.

AmeyVTOL is a joint venture between Amey and aerial robotics specialist VTOL Technologies. AmeyVTOL’s drone, known as The Flying Wing, has a flight range of up to 100 km, and sensors that enable it to capture and send data in real time.

During the demonstration, The Flying Wing autonomously surveyed an area out of the sight of the pilot up to 2km away.

According to Amey, the success of the trial opens up the use of drones for inspections of long linear infrastructure such as roads, railways and overhead power lines, saving time and cost, and improving the safety of staff.  The demonstration project was part of a government-sponsored Rail First of a Kind (FOAK) programme promoted by Innovate UK through the Small Business Research Initiative.

It is reported that AmeyVTOL will now be offering this survey capability to other infrastructure owners and operators.

Corrosion to Covid-19: one start-up company’s effort to support UK front line workers

Corrosion to Covid-19: one start-up company’s effort to support UK front line workers

Hexigone Inhibitors, a Sustaining Member Company, who usually manufacture chromate-free corrosion inhibitors, are now using their large mixing vessels to produce hand sanitiser to help protect staff on the front line. The sanitiser, which meets the standard set by the World Health Organisation, is already in use in local organisations.

The UK Government’s innovation agency, Innovate UK, linked-up Hexigone with pharmaceutical giant, Glaxosmithkline, who subsequently donated 8,000 litres of isopropanol to ramp-up production.

For the sanitiser to be effective, it must contain at least 60% alcohol. The batches made by Hexigone are 75% – precisely made to the WHO recommended formulation – ensuring that the coronavirus and other microbial pathogens are killed. Other ingredients include water to dilute, glycerol to moisturise, hydrogen peroxide to kill any fungal spores, and finally, lemongrass essential oil to scent
the sanitiser.

Effects of graphene on the corrosion of epoxy zinc-containing coatings

A recent report described the effect of graphene on the corrosion of zinc particles in waterborne epoxy zinc-containing coatings.  In the study, graphene/ waterborne epoxy zinc-containing coatings with different graphene contents were prepared, and their corrosion resistance properties were investigated by electrochemical impedance spectroscopy (EIS), immersion testing and neutral salt spray.

The results showed that addition of 0.6 wt% graphene into the coating could remarkably improve its cathodic protection and barrier performance compared to the coating without graphene.

In addition, the effects of graphene on the corrosion evolution of zinc particles in the coating were studied by the field-emission scanning electron microscopy (FE-SEM) coupled with energy dispersive spectroscopy (EDS), which showed that the zinc particles near the interface between a steel substrate and the coating corroded first after the corrosive media diffused into the coating.  The zinc particles then continued to be corroded from the interface to upper part of the coating as they provided cathodic protection to the substrate due to the electrical connection of graphene.  X-ray diffraction (XRD) patterns confirmed the corrosion products of the zinc particles were mainly consisted of Zn5(OH)8Cl2.H2O.

The study was published in Progress in Organic Coatings, Volume 140, March 2020.

Passive Fire Protection – The Financial Cost of Getting It Wrong

Passive Fire Protection – The Financial Cost of Getting It Wrong

There is change afoot in the world of passive fire protection (PFP), especially in the protection of structures in high-risk industries such as oil and gas. Unlike in many other sectors, it is the industry itself that is leading the way in more stringent competencies in application and inspection of PFP to ensure quality installations.

What are the forces that are driving this change? In this article, the first in a six-part series we’ll be publishing over the coming weeks, we look at the financial cost of getting passive fire protection application wrong.

What is passive fire protection?

PFP systems reduce the rate at which temperature rises on the protected structure. They do this primarily through heat absorption, reflection and insulation. They are passive because they don’t require external activation to work, such as water deluge, which is why they are considered more reliable, provided they are installed correctly.

In high-risk facilities such as offshore oil and gas installations, the most common form of PFP is epoxy intumescent coatings. These protect structural steel from extreme heat and provide full corrosion protection. They work by swelling and producing a carbonaceous char when heated, which insulates the steel substrate.

How are PFP coatings applied?

Epoxy intumescent coatings are usually applied by spray application using dedicated spray pumps. They must be applied onto properly prepared surfaces, and surface preparation and priming are critical to their adhesion and, in consequence, longevity. Epoxy PFP systems are frequently reinforced with a fibre mesh system, the primary purpose of which is to reinforce the char formed in a fire situation. On occasion they might be reinforced with a wire mesh, but in some systems there is no reinforcement. Typically, the thickness of an epoxy intumescent coating is between 3mm and 20mm.

The significant advantage of epoxy PFP coatings is their toughness and durability, meaning that they can be applied to steel before it is erected. In modular construction they have the ability to withstand the steel deformation when modules are loaded for transportation to their installation site and during the offloading and installation process.

PFP is failing – but why?

The international standards for PFP have been improved tremendously over the last few decades, especially in response to headline disasters like Piper Alpha and more recent incidents. However, in recent years the industry has witnessed a marked increase in the failure of PFP before the plant is commissioned. The reason for this appears to be changing market dynamics. Let us explain.

There used to be only very few manufacturers that produced epoxy PFP intumescent coatings. It was a highly specialised field, and consequently the margins were high. These manufacturers would provide free-of-charge on-site technical service personnel to help ensure correct application of PFP.

Over the years an increasing number of manufacturers have entered the epoxy intumescent market, chasing the same market opportunity. Consequently, margins have been reduced and a level of commoditisation has taken place. Additionally, the drive in the oil and gas industry to reduce project costs has exerted considerable pressure in all areas of construction and supply. The result has been an inability for manufacturers to offer the same level of on-site technical services that was previously provided free of charge, and instead fabricators and contractors are charged for these services. There is no doubt that this has resulted in a reduction in available competency to ensure quality installations.

A further factor is the tendency to treat epoxy intumescent coatings like paint and even to call them ‘paint’. Whilst they are similar, especially the epoxy types, there are significant differences requiring specific skills and understanding for quality PFP installations.

Shortage of early-stage technical competency is a false economy

PFP is an expensive necessity, and from a financial point of view keeping a lid on those costs is important. However, the cost of correcting poorly applied PFP is colossal. When a PFP system is incorrectly installed or fails, the impact can include:

  • Risk to the project schedule and potential delay of production due to lack of authority to operate whilst corrective action is taken
  • The high cost of access, including scaffolding, to carry out remedial work, particularly in the offshore environment
  • Impact on other trades whilst areas are ‘quarantined’ for corrective PFP work to be carried out
  • The sheer difficulty of removing and reinstating in an on-site environment

Experience from a leading coatings manufacturer shows that:

Offshore maintenance is 15 to 20 times more expensive than performing work at a yard, and corrosion accounts for 60% of offshore maintenance costs. Further, 85% of coating failures appear within 1 to 3 years, with 95% of failures occurring because of:

  • Incorrect specification choice
  • Poor surface preparation
  • Poor application
  • Climatic conditions

To put this into perspective, PFP that is commissioned at an implementation cost of, say, $10 million for a facility in an isolated area of the world (the best fields are usually isolated, right?) and is poorly implemented could cost $150 million to $200 million in rectification costs.

From a purely financial viewpoint, it’s clear that if you spend money upfront you save hugely on project overrun costs, let alone the project complexity of re-work.

How the industry is evolving

The industry is calling for improved competency in the application and inspection of PFP. It simply cannot continue to burn cash on rectification requirements that could and should be avoided. Whilst development, testing and certification for use of PFP materials is regulated, the application and inspection of PFP is not regulated in the same way.

Currently, owner operators specify that inspectors should be paint level 2 qualified as a minimum. What this means is that someone who has good knowledge of paint, but no knowledge or experience of PFP, can go onto a site and inspect PFP. As manufacturers continue to bring new and improved products to the market, with additional features and benefits, this issue is magnified.

In response to this and other issues, PFPNet was established around four years ago to tackle what was becoming a significant loss of skill in the industry across a broad range of PFP topics. With an objective to improve knowledge and understanding, and increase competency across the hydrocarbon passive fire protection industry, PFPNet – whose membership comprises owners, engineers, contractors, manufacturers, and others – has tapped into the skills of its members to tackle key subjects including improving quality of installation.

As PFPNet has evolved and grown with a broad range of membership of companies and individuals who truly understand the business, it has become clear that there is a real desire to develop best practice, navigate regulations, and remove confusion and conflicts.

The result is the evolution of a new PFPNet Competency Framework, which will lay out the knowledge and competency levels expected across all disciplines in the fireproofing of industrial facilities. It is expected that this framework will be mandated by owners and other stakeholders as a requirement for projects and operations.

To stay in the know and be part of the PFP conversation, contact either John Dunk at PFPNet or David Mobbs at ICorr.