To improve efficiency during maintenance, the application of coatings onto live, high temperature equipment is becoming more and more prevalent in the oil & gas industry. The advantages of this approach are clear – shutdowns can cost tens of thousands of dollars every hour, and so ‘hot application’ work plays a clear part in the overall maintenance plan.
Applying coatings at high temperature is very different to ambient temperature application and extra consideration into coating selection is required. Typically, issues such as the below cause major challenges to both applicators and asset owners:
- High VOC flash off - High temperature coatings are typically higher in solvent content (VOC) than ‘ambient temperature’ application coatings. This means that when applied, a large amount of solvent is rapidly released. This poses health concerns to the operator, as well as problems for the porosity of the film due to the creation of pinholes on the surface.
- Poor flow out and spreadability - The high temperature of the substrate causes the coating to cure very quickly, this leads to poor coverage.
- HSE controls when applying - A general concern when working close to high temperature surface. Extra care needs to be taken and proper PPE worn before attempting high temperature applications.
- Difficult to brush - The rapid cure of the paint also causes challenges for a common method of application during maintenance – brushing. The rapidly curing coating can cause brushes to cure hard in minutes, as well as a great reduction in pot life as the hot brush is put back into the can.
Typical online high temperature brush application, Norway
Typical online high temperature brush application, China
Pinholes can form in coatings due to VOC flash off
To illustrate some of these challenges, a benchmarking study was run using a series of coatings typically applied onto high temp steel.
The study includes Intertherm 2205 – a specialist high temperature maintenance coating from AkzoNobel.
Intertherm 2205 is a specialist temperature resistant maintenance coating, designed to resist CUI and cyclic high temperatures up to 205ºC (401ºF), with peaks to 230ºC (446ºF). Based on innovative hot spread epoxy technology, Intertherm 2205 shows excellent application characteristics and can be brush applied to hand prepared, hot steel up to 205ºC (401ºF)
Comparison of application performance:
- Blasted Sa 2½ (SP10) steel
- Steel temperature: 150ºC (302ºF)
- Brush applied
All systems applied as 2 coats:
- 2 x 200µm (4 x 4 mils) for high heat epoxy
- 2 x 100µm (2 x 4 mils) for all other coatings as recommended on TDS.
All coatings are suitable for application by brush at 150ºC (302ºF)according to TDS.
Substrate temperature 144-153ºC (~302ºF)
To view the videos in the benchmarking study please click on each part below:
DFR Variation on hot application
Application performance at 150oC
Significant DFT variation for some of the coatings:
- 1K IMM coating: very difficult to control application thickness as non-volatile part of the coating balled up.
- 1K high heat epoxy: easy to spread, but significant brush marks (some peaks were ~2.5 times higher than target DFT).
- Both epoxy phenolics are relatively easy to spread initially but have a very short wet edge.
Typically, heat resistant coatings are very sensitive to over-application (albeit some more than others): the more paint applied, the more likely it is to crack in service.
Some of the coatings tested contain large amounts of volatile substances:
- Significant bubbling of the coating during application
- Likely to create film defects (pinholes)
- Generation of large clouds of flammable fumes
Intertherm 2205 demonstrated the best application performance at 150ºC:
- Longer wet edge than all coatings
- Good brushability
- Low solvent content = low amount of fumes generated
- Lowest DFT spread of all coatings = easier to control DFT (lower risk of failure due to over-application)
When choosing coatings for online application, it is very important to consider their suitability for the maintenance procedure. A key challenge for applicators and asset owners is that many hot application tolerant coatings are typically designed with new construction end uses in mind, and as such are not optimised for online application with high VOC and poor wet edge retention.
Intertherm 2205 is a specialist maintenance which demonstrates excellent tolerance to hot application up to 205oC (401oF), including on compromised substrates.