In this interactive webinar we discussed alternatives to welding. Through the use of testing reports, practical demonstrations and case study examples, the speakers illustrated how composite repairs can be used to:
- Repair corroded pipework and pipelines in compliance with ISO and ASME standards
- Repair tank wall corrosion without using hot work
- Install wear pads for piping which do not corrode or disbond
Click the video below to see the recording summary. The content of this webinar, including the Q&A, has been transcribed below the video.
First of all, let’s look at the problems which metallic assets can experience. External and internal erosive forces and corrosive substances can lead to pitting and thin-wall defects. If not addressed soon enough, they are likely to go through-wall. We also see issues with localised damage on large structures, such as storage tanks and even boat hulls. Finally we will look at more innovative uses for non-metallic solutions, addressing the issues of pipe support erosion and corrosion.
In order to define this problem more easily, we can separate it into two types of defects. Type A defects are where the steel has started thinning due to corrosion or erosion. This type is not expected to produce a through-wall defect within the lifetime of the repair system, and only requires structural reinforcement.
Contrasting to this, Type B defects are either through-wall, with a thickness less than 1mm remaining, or expected to become through wall. This type of defect requires sealing as well as structural reinforcement. In order to fix these defects, there are a few ways of completing a repair.
Let’s look at some repair methods, such as cut and weld. Apart from all the typical metallurgical issues associated with hot work, there is of course downtime. We also know that welding requires a high level of expertise.
When methods alternative to welding are being used such as clamps, there is a question of longevity. Even when we accept the repair to be “temporary”, we want it to last close to the lifetime of the asset and not require ongoing maintenance.
If this is a new topic for you, you might be asking what a composite repair is. Composite repairs are basically repair systems made up of a thermoset resin used in conjunction with glass or carbon fiber reinforcement. This reinforcement can be a mixture of the two materials or made of something else entirely.
The advantages it offers are simple:
- No heat or hot work
- No shutdown – these repairs can be completed online, provided that you can stop any leak
- It is a cost-effective repair when compared with its counterparts
Composite repairs can be defined by the following features:
- Strong mechanical adhesion: The resins generally have good adhesion to a variety of substrates, giving an inter-locking finish which holds the repair in place.
- Low tendency to creep: Corrosion that begins outside the repair area does not easily travel underneath the composite system.
- High HDT values: The resins don’t soften until higher temperatures, meaning application at elevated temperatures is possible, even when high pressures and forces are involved.
- High Heat Resistance: The resins which Belzona offer can see a service temperature of up to 150C (320F), and some other resins can potentially go even higher.
- Extremely durable: As well as possessing heat resistance, the resins also have good mechanical strength – including impact, compressive and tensile resistances.
The first, and most common method, is to apply it as a wrap. This is where the material is wrapped around the entire circumference of the pipe.
If the asset’s diameter is large enough, such as a storage tank, a wrap may no longer be practical! If this is the case then a patch can be applied.
Finally, most recently, composite pads have been introduced where a prefabricated pad is bonded to the substrate using a paste grade epoxy material.
When it comes to applying the composite repair system, it can be done in accordance with the recognised engineering standards. ISO 24817 standard gives requirements and recommendations for the qualification and design, installation, testing and inspection of composite pipe repairs. ASME standard also covers similar aspects.
For any composite repair to adhere to these standards, it must meet two main requirements.
- The composite repair itself should be pre-qualified against these industry recognized standards
- The solution must be mathematically engineered and applied by factory trained personnel.
NB: Although not a requirement, we also recommend to have inspection protocols in place to check the system for continuity.
By creating a mathematically engineered repair, we obtain two critical variables. These are the thickness and axial extent.
With these, we can apply a system which is designed specifically for the asset. This will also tell us if the repair is possible to complete and give a measureable variables to inspect once the wrap is complete.
Those of you more familiar with these standards will be aware there are various annexes detailing the test regimes for materials to be used in accordance with these standards. Not all of these tests are essential for a repair system to be qualified and considered compliant, however these additional tests provide crucial design information for the system.
Annex E testing is one of the optional tests, however it is an important test in the compliance process as it gives data relating to the long-term performance of a composite system. All of these tests, when combined together, give a much clearer picture of how the system will perform in-service, and helps to create more accurate designs.
Let’s look at the example of an Annex E test. Belzona completed the testing with their compliant wrap system on both grit blasted and manually prepared substrates. These test spools were designed and wrapped at Belzona Harrogate then sent to an external test facility.
It was calculated that the spool on its own would yield at around 600 bar, so the test pressure was set to be slightly above in order to guarantee a failure in the system. The pressure was ramped and it was the spool cap weld that failed at 800 bar and no damage was seen on the repair at all.
In addition to testing carried out for the ISO and ASME standards, Belzona and its distributors work with universities and major asset owners on various tests. The most recent test assessing performance of the system has been carried out at the end of last year by the University of Miskolc, in cooperation with Belzona Distributors in Hungary and Croatia, H+K and ISEA. The initial test included testing a 20mm thick wrap for over 100,000 cycles at 94 bar, completed without any damage to the wrap. The composite wrap was then tested to destruction with a maximum pressure recorded as 340 bar.
So, how do we use this to create a design? The first step is information collection. We first need basic information about the asset, such as:
- Wall Thickness
And a few other details. This information is then input into a design system, which is based on equations given in the ISO/ASME standards.
After running the calculations, you obtain 2 main outputs, plus a method statement written by the composite repair supplier. We get the design thickness, which tells an applicator how many layers to apply and the axial extent, which tells them what length of repair is required. These values are largely dependent on the forces which will be acting on the repair, such as the pressure inside the pipe and any mechanical loads which are present, such as bending moments or torsional loading.
A product is only as good as the people who apply it, so the design must be carried out by trained personnel. As part of the ISO/ASME standard, all people working with the system must be trained on proper application techniques. The courses on offer at Belzona currently are:
- Installer; where attendees learn how to apply the composite system correctly, and within the design parameters
- Supervisor; which teaches attendees about hold points and inspection techniques, to ensure the application follows the set method. All supervisors must have also completed the installer training previously.
- Designer; which teaches attendees how to create a design, both through manual calculations and with the use of software.
As mentioned before, inspection plays a big part in ensuring the applications are successful. There are many methods available to asset owners when it comes to inspection of composite wraps, and the steel they are repairing, including:
- Gamma Ray
One system which has been tested with Belzona is the DRS or Dynamic Response Spectroscopy unit. This unit makes the steel vibrate at its natural frequency, and the resultant sound waves can be used to calculate the remaining thickness of the steel. It ignores the composite system entirely, and as you can see on the slide, gives a map of the substrate which is easily readable.
Up until now we have covered the theory behind composite repairs. Let us now look at this know-how in action. Here we are looking at a problem encountered at a sewage treatment plant. Carbon steel pipe elbows have been suffering from external corrosion. Both pipes required repairs and protection from future corrosion. In this case a 6-layer composite repair system was designed and applied. The customer reported to be very pleased with the ease of application and more importantly the reduced downtime. As the pipework was back in service within 24 hours.
In our second case study we see a cooling water pipe which supplies a steam turbine had burst. This meant that water was leaking out at an alarming rate – up 15,000 gallons per minute!
The shear volume of water meant the soil surrounding the pipe was being eroded away, causing the road above to crack and become damaged due to the movement underneath.
At the time when the customer contacted Belzona, they had already tried 2 other types of repairs which had been unsuccessful.
In order to create a good repair, they first widened the rupture so that all the water could be pumped out. The hole was covered with a steel plate and bonded in place with Belzona 1212, due to this material’s fast curing ability.
Once this had cured, the Belzona SuperWrap II system was applied over the top, sealing in the plate and creating a complete repair. This entire job was completed all within the same day, meaning that downtime was kept to an absolute minimum for the customer.
Not all wraps are applied to pipes. When feasible, larger areas can also be repaired with a composite wrap. Here, a petrochemical plant was experiencing thin-wall and through-wall defects on a 70 foot tall absorber tower. Belzona SuperWrap II was used to restore the lost wall integrity to a compromised 30 foot area.
Remember, when a wrap is deemed impractical, a composite patch can be a way to go. Here, a boat hull was experiencing loss of steel, leading to thin-walling. The asset owner was looking for a solution to reinstate metal loss and provide lasting protection from erosion and corrosion. A composite patch was applied to restore integrity overcoated with a ceramic s metal epoxy, which offers excellent erosion-corrosion resistance.
Our final case study demonstrates the idea behind another different composite repair technique. An oil pipeline crossing the desert from the oil fields to a marine terminal was suffering corrosion in the support areas due to constant thermal expansion and contraction. Over 300 metal pads were bonded with a Belzona paste grade material. Nowadays, this application is possible with a composite pad, offering a completely non-metallic solution that can be created on-site, reducing both installation and lead times.
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