Leakage from seals and gaskets in heat exchangers is a well-known problem within most process industries. One of the main reasons is that the operating environment for gaskets within heat exchangers could be defined as quite extreme, consisting of high temperatures, steep temperature gradients, high pressures, and perpetually fluctuating conditions. Also, the typical start-up and shut-down stress present extra challenges for the system, with traditional seals and gaskets being especially vulnerable to failure.
In addition, unlike pipes that use flanges, heat exchangers have bolted joints. The difference lies in the temperatures that will act on these joints. At a typical flange, we will find two temperatures, the fluid temperature inside the pipe/flange, and the one outside of the flange which is also related to the ambient temperature of the external environment.
In contrast, on a heat exchanger, we will often find more than 3-4 significantly different temperatures interacting on the same bolted joint at different points. The effect is that the rate of expansion and contraction throughout the bolted joint will not be uniform. In addition, the nuts and bolts used are often made of a different material to the rest of the metal parts, adding a different expansion and contraction speed to the equation.
Very often we get questions regarding how best to seal Shell and Tube heat exchangers that are facing leakage problems. Customers ask us due to our expertise in using alternatives to existing gasket technology and conventional materials.
We have found that typical heat exchangers have a high tendency to leak at the channel cover joint, the tubesheet to channel cover joint and the shell to tubesheet joint, based on the above explanations.
The shell to cover joint and the floating head joint are less critical to leakage because they are only exposed, similar to flanges, to two temperatures. With that said, these two joints can also lead to very expensive maintenance when leaking, as the heat exchanger will require to be taken out of service.
Pipeotech has found that our patented sealing solution, DeltaV-Seal can be adjusted to fit both small and large heat exchangers providing a 100% leakproof seal. This article focuses on large heat exchangers.
There are several large diameter gaskets in a typical heat exchanger setup:
Channel Cover Gasket,
Tubesheet to Channel Cover Gasket / Shell to Tubesheet Gasket
Shell to Cover Gasket
Floating Head Gasket
As heat exchangers are often built to customer specifications there are no established standardized sizes however typical variations range from 24”(610mm) to 65”(1651mm).
Examples of typical heat exchanger gasket shapes are illustrated above in figure A to F however many other shapes are possible. Pipeotech can easily adapt our DeltaV-Seal technology to every conceivable size and type of heat exchanger gasket including sealing of inlet and outlet flanges and also in applications where several heat exchangers are stacked together.
The DeltaV-Seal Advantage
DeltaV-Seal is always made out of 100% metal, with the sealing alloy always matching the material of the connecting surface. This provides some important and distinct advantages that can ensure a permanent leak-proof seal for heat exchanger applications such as:
Prevention of all galvanic corrosion – a major source of leakage
Mitigation of temperature fluctuation stresses - the DeltaV-seal will contract and expand at a similar rate as the flanges forming a static and permanent bond throughout any changes in temperature.
Compatibility with the media (process fluid) is ensured
The physical design of DeltaV-Seal is just as important when it comes to heat exchanger applications. This is not a flat gasket, the geometric shape of DeltaV-Seal contains several special sealing ‘ridges’ which partially deform on contact with the flange to create the perfect enduring leak-proof seal.
The mechanical stability and the tightness created by using DeltaV-Seal greatly out-perform ALL incumbent gasket solutions and can be relied on to maintain a perfect seal over time.
With standard circular gasket sizes, the number of sealing ridges on each side of the DeltaV-Seal is normally three. In the case of heat exchangers, the number of ridges can change to account for factors such as pressure class, flange type, and bolt seating forces.
Custom sizes and designs can be engineered after consultation and dialog with end-customers.
The typical values we would need to create a new custom design for heat exchangers are:
Shell and Tube pressures (design, test, and operation)
Shell and Tube temperatures (max, test, and operation)
Shell and Tube media
Number of bolts
Bolt circle diameter
Bolt hole size
A technical drawing of the matching flanges
The surface roughness of the matching flanges
Material specification of flanges.
We also need an overview drawing of the system to be able to fully understand your application.
By using DeltaV-Seal™ technology within heat exchangers, the extreme variations of operating conditions can be handled and sealed for good – no more leaks!
Contact Pipeotech today, we will look into your application.