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Cartridge-Based Application of Weld Field Joint
Coatings for Pipelines

FRIDAY, FEBRUARY 3, 2017

By Victor Clemens, MSc., Sulzer Mixpac


 

 

In order to provide a long lifetime for pipelines with minimal maintenance effort, a long-lasting anticorrosive protective coating is essential. The coating is normally applied directly at the pipe manufacturer or at a dedicated coating plant; however, in order to weld the pipelines together in the field, it is necessary to leave approximately 200 millimeters of the pipe ends uncoated. After the required steel surface preparation and welding process (Figure 1), these field joints are unprotected and are now ready to be coated.

Figure 1: Steel preparation of a weld field joint

To achieve maximum flexibility and performance, mostly two-component coatings are used for such field jobs. The application process (Figure 2) is the key to success, as one wants to eliminate the possibility of incorrectly coated areas, which are prone to corrosion, because even the smallest uncovered areas can lead to a failure.

Users expect a fast, flexible, secure, and easy-to-use application of these two-component coatings. A cartridge-based system meets these expectations exactly, as one is able to apply the field joint coatings very quickly with inexpensive equipment, minimal waste, and very little set-up and cleaning time. Furthermore, it can be used irrespective of location and conditions. This outstanding flexibility and reliable performance makes the cartridge-based system a perfect choice to coat weld field joints.

Figure 2: Application of weld field joint coating 

The Challenge

Until now, there have been two main possible application methods for two-component liquid anticorrosive protections for such weld field joints: Manual application or multicomponent high pressure spraying devices.

Manual application is still a common method, but there are many challenges that have to be taken into consideration. Before the coating can be applied, a proper mix is essential. If the coating is metered and mixed manually, there is a chance that it could have an incorrect mix ratio or insufficient mixing due to human error and variability. These types of errors will drastically reduce the functionality of the coatings, as they may not cure properly and meet the desired specifications of the manufacturer.

An additional challenge when applying the material with a brush or a roller is that the required layer thickness may not be achieved in one step — therefore, a second or even third application could be necessary. Furthermore, if the material is metered and mixed manually, there is a potential risk of a contamination of the coating at the job site. Dirt, wind, and rain can influence the functionality of the coating. The last challenge of manual application affects the safety of the user, as they increase their exposure to unmixed hazardous materials.

Challenges of manual application at a glance:

  • Possible off-ratio
  • Possible insufficient mixing
  • Sometimes two or three applications are necessary
  • Long set-up and cleaning time
  • Potential risk of a contamination of the coating
  • User has increased exposure to hazardous materials

The application with a multicomponent high-pressure spraying device also entails various challenges. These rather bulky machines are difficult to transport, and sometimes it is not even possible to move them to the point of application. Also, these machines typically have lengthy set-up and cleaning times, which result in expensive labor costs. Furthermore, during application, high-pressure spraying devices can lead to overspray, which results in unnecessary waste of coating material not to mention a potential risk of anything in the immediate area to be unnecessarily coated. Finally, safety also plays a crucial role for these devices as the tremendous pressures which are used can cause injury and piercing of the skin.

Challenges of an application with a multicomponent high pressure spraying device at a glance:

  • Difficult to transport
  • Long set-up and cleaning time
  • Can lead to overspray
  • Waste of coating within the hose
  • High pressure can cause injury and piercing of the skin
Figure 3: Overview of the cartridge based mixing system  

The Solution

In order to eliminate possible difficulties of the common application methods mentioned above, a new system has been developed: A two-component cartridge-based mixing system (Figure 3).

The plastic cartridge (Figure 4) is pre-filled with the two-component liquid anticorrosive protection. Sealed directly after the filling process by air-venting pistons, the coating is protected from external contamination until it is applied directly at the point of application.

Figure 4: Cartridge with pistons, nose plug and retaining nut  

The main advantage of a cartridge-based system is the high metering accuracy, as the dimensions of the cylinders meet the requirement of the mix ratio exactly. Additionally, the cartridges can be pre-heated up to 55°C. This provides the possibility of decreasing the viscosity of the two components, which allows one to increase the output of the system. Even at colder application temperatures, a pre-heating of the cartridges may be necessary, as a consistent temperature is essential for a reliable process.

In order to provide consistent mixing, a mixer (Figure 5) can be attached to the cartridge.

Figure 5: Static mixer with spray tip  

The mixer head and retaining nut provide a perfect fit to the cartridge and ensure that the two components only meet in the mixer, and not in the cartridge. The mixer element provides a reliable and repeatable mixing quality and the spray tip atomizes the mixed coating, which results in a defined spray cone.

After connecting the pneumatic dispenser to a properly sized air compressor, the system is now ready to use (Figure 6). The dispenser allows one to change the material flow rate and atomization rate of the air separately, and both are infinitely variable—even during the application. On the one hand, this leads to minimal overspray and on the other hand, thicker layers can be achieved with a single coating step too. Additionally, the handling of the dispenser is very user-friendly and only minimal training is required.

Figure 6: Cartridge based application of a weld field joint coating

 
Figure 7 (left): Cartridge outlet after partial usage; Figure 8 (right): 90-degree spray angle for high flexibility

Furthermore, the system provides separate outlets of each component and the option of check valves in the mixer-head which prevents cross contamination (Figure 7). The cartridges can be resealed and used again if not all the coating is used at once. A new mixer just needs to be installed at the next application and use the rest of the coating which is still in the cartridge. This feature minimizes the amount of wasted coating.

Another advantage of the cartridge-based system is its flexibility. Multiple mixer options are available so now coatings can be applied even in narrow and difficult-to-reach areas (Figure 8), which are not easily accessible for a high-pressure spraying devices. The use of a static mixer also opens up new possibilities for fast-setting materials. Coatings with a pot life of 15 seconds have already been successfully sprayed where common application methods would not be feasible.

The last major advantage of the cartridge-based system is the safety of the user, as at no time are they exposed to unmixed, hazardous materials. Additionally, as only low air pressure is required, there is no danger of piercing of the skin.

Summary

The cartridge-based system combines several functionalities: Storage, metering, mixing, and spraying. This results in an interesting possibility for applying two-component liquid anticorrosive protection on weld field joints. First, the cartridge ensures that the coating is applied always in the correct ratio and avoids the risk of contamination of the coating before the application. Additionally, the static mixer, including the spray head, provides reliable and repeatable mixing quality with minimal overspray. Furthermore, the small, light and portable dispenser requires minimal installation time and only uses low pressurized air.

These advantages clearly show that the expectations of the users are met: A fast, flexible, secure and easy to use application. Current manual application and high-pressure spraying devices have their advantages for some scenarios. But especially for the application of weld field joint coatings, the cartridge-based system offers an efficient, flexible and inexpensive approach, and it will play an important role in the future.

Finally, Table 1 gives an overview of the three different application methods.

Table 1: Overview of the different application methods for weld field joint coatings

Feature Manual Application High Pressure Spraying Device Cartridge-Based System
Safety Exposed to unmixed hazardous material Exposed to unmixed hazardous material during the set-up phase No time exposed to unmixed material
High pressure can cause injury and piercing of the skin. Low pressure will not pierce the skin or cause injury
Dosing
Manual dosing can lead to an off-ratio
Can lead to overspray
Minimal overspray
Mixing
Hand mixing with potential errors due to human failure
Properly mixed
Reliable and repeatable mixing quality
Layer thickness Sometimes two or three applications steps necessary
High flexibility
High flexibility
Time
Long set-up time
Long set-up time
Minimal set-up time
Little cleaning time Long cleaning time No cleaning time
Waste
Unused but already mixed coating must be disposed of
Waste within the hose
No waste of coating
Mixer and empty cartridge must be disposed of
Cost
No investment necessary
High investment necessary
Little investment necessary

*Claims or positions expressed by sponsoring authors do not necessarily reflect the views of TPC, PaintSquare or its editors.

ABOUT THE AUTHOR
Victor Clemens, MSc., Sulzer Mixpac

Victor Clemens, Head of Innovation & Technical Services, started his career at Sulzer in Switzerland after obtaining a master of science degree in Industrial Engineering at the Technical University in Vienna. One of his focus areas is the responsibility of application tests for a 2K coating spray system, which made him very adept in this realm for this key future growth area for Sulzer.

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Tagged categories: Coating Application; Field joint coatings; Girth welds; Paint application; Paint application equipment; Pipeline; Spray equipment; Sulzer; Two-component coatings

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