Replacement Gaskets for Plate Heat Exchangers: Original OEM or Pirate ?

For plate (and frame) heat exchangers, the standard materials are EPDM and Nitrile rubber (NBR). EPDM is used normally for non-fatty/oily applications, and NBR for oil/fat applications. However, there are no rules without exceptions. An "oil" and fatty application may have a low fat content, making the application more suitable for EPDM instead of NBR.

Other rubbers used for PHE's are Hydrogenated Nitrile Rubber (HNBR), Fluorocarbon rubber (FKM), Butyl, Chloroprene Rubber (GR), Chlorsulphonated Polyethylene (CSM), Styrene Rubber (SBR), Natural Rubber (NR) and Silicone Rubber (Q) are less common ones.

All additives matter for the product properties, and not only effect the quality level of the product, they also influence the consistency of the quality level.

Lifetime

Eventually all rubber materials will degrade, loosing their properties, making them unsuitable for further use. It is all a matter of time and the original quality of the product. The lifetime of rubber products is dependent on the environment (chemical types, concentrations) and temperature. Also, temperature changes and pressure changes effect the performance and lifetime of the rubber product.

Chemical Resistance

Each rubber material has its unique resistance towards various chemicals. Polymer used, as well as additives, effect which chemicals each rubber material is suitable for.

High Temperature

At high temperatures the rubber will be attacked faster by the chemicals in use, and the surrounding oxygen. The oxidation process will either make the rubber harder (the most common one) OR make it softer (less common), OR both at the same time. Either way the change in properties will reduce the performance. All rubber materials have a maximum continuous temperature, which should not be exceeded to maintain good performance and to achieve a reasonable lifetime.

Low Temperature

At low temperatures the stiffness increases, and the elasticity decreases. This influences the sealing force of the gaskets. All rubber materials have a certain lowest temperature that have to be exceeded to be able to perform well enough as a gasket.

Fracture models for rubber in FE-applications.

The experimentally determined critical tearing energy is introduced in the figure defining when crack propagation would start according to a fix strain energy release rate, i.e. constant Tc over all crack lengths. 

The rubber material consists of micro cracks with a size of approximately 50µm and according to tests in Chapter 4 the specimens without initiated crack sustained a deformation of 7mm for EPDM. Small crack analyses, see Figure 8, show that T for EPDM reach 0.4 N/mm for a crack of 50µm at critical deformation (70% strain), but at this deformation T should be equal to Tc if the tearing energy criterion is a valid approach for small crack analyses in this rubber. According to the theory of a material parameter Tc constant over all crack lengths, small initial crack lengths would asymptotically reach infinite deformation meeting the critical tearing energy, see Figure 8. Hence, this criterion has a limit of valid application requiring the crack length to be large scale.

 FE-model

The load simulations of the gasket consist of an assembling step when the plates come in contact and compress the gasket in between. Then, a following step simulates the temperature rise in the gasket when the two heat exchanging fluids stream through the plate heat exchanger. The geometry was provided by Alfa Laval, see Figure 10, and is a cut out part of the plate heat exchanger consisting of a piece of a rubber gasket placed between two corrugated plates.

The cut out geometry represents the exterior edge of the plate heat exchanger and the plates are supported by gaskets on both sides. Considering this plate stack symmetry and the relatively stiff stainless plates, the deformation of the plates is negligible, and therefore set as rigid in FE-analyses. Gaskets made of EPDM rubber tend to crack more frequently than NBR gaskets; hence the rubber type used in these FE-simulations was EPDM.

Considerations:

It seems crystal clear that gasket quality is a crucial factor in PHE performance.

Therefore now the question is:  Heat Transfer Specialist should suggest always original PHE Manufacturer gasket as replacement to be sure on operations or not?

As usual it is  a matter of cost/benefit: depends on Application, on process Temperature and Pressure,  if  we are in emergency situation and delivery time is first priority, if quality required is good enough and not critical.

Once upon the time there were PHE Manufacturers selling new units at low profit to get margin on spare parts later on. 

This approach generated interest in spare gaskets in consideration of bunch of dollars in this business available and due to lower investment required to manufacture a gasket mould in comparison with plate die.

In US, United Kingdom, France, Italy and Spain new gasket manufacturers started to compete with two giants Gislaved Gummi and Trelleborg Sealing Solutions.

Multibrand Service Centre created a large turnover including cleaning, regasketing, reconditioning and refurbishing of complete PHE's.

Recently  Chinese Manufacturers came into the picture, with local spare plates and gaskets to replace main PHE brands.

Different manufacturing system (by injection or by compression) were used  in consideration of high volumes.

Thumb rule on gasket price: 

Original gasket                                                                     price level 100

OEM gasket (chemical compound by PHE manufacturer)  price level   60    

Chinese gasket                                                                     price level  30   

One critical issue are Distributors selling Chinese gasket pretending to give original

Of course this is illegal, but it happens and profit of this deal is huge...

My suggestion is to evaluate how critical is application: HVAC Lub oil cooling etc can accept a Pirate Gaskets, but Pharma Food & Dairy for instance required FDA approval

Furthermore after curing Nitrile and EPDM have different elongation and many gaskets manufacturers are using same mould...Look at nail put on table of Service Centre where  worker is pulling the gasket to get right dimension to fit into the plate...

When we are talking about difficult applications like Oil & Gas, Petrochemical, Power no doubt original gasket is a must expecially if location is in the Middle East or Southeast Asia.

Light industry (metal treatment, painting fluid handling) can accept OEM gasket if quality is certified.

At the end of the day  supplying a low cost Gasket Plate Heat Exchanger alternative to manufacturer got as a consequence a general price reduction.

But a damaged gasket can generate a shut down in the plant ...

Heat Transfer Specialist task is to categorize Applications according to critical paths and recommend to Buyer proper solution in each case to reduce CAPEX without jeopardize plant operation and performance.

Credit to Jonas Lindvall and Marcus Minkkinen School of Mechanical Engineering Lund University