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How PM&I Can Help Prevent Delays

Plate and Frame Heat Exchanger:

Gasket and Plate Maintenance

1. Plate Cleaning

A: Gross Fouling

Gross fouling is fouling by seaweed, wood chips, fibers, mussels, barnacles and other substantial fouling

Gross Fouling Cleaning Techniques:

a) Soft brush and running water

b) High pressure hose

c) Back flushing of the unopened heat exchanger can sometimes be sufficiently effective.

Note:

Be careful not to damage gaskets. Under no circumstances should hydrochloric acid be used with stainless steel plates. Water of more than 300 ppm Cl may not be used for the preparation of cleaning solutions. It is very important that carrying bars and support columns in aluminum are protected against chemicals.

B: Biological Growth – Slime

Biological growth is from bacteria, nematodes and protozoa.

Biological Growth Cleaning Techniques:

a) Soft brush and running water

b) High pressure hose.

c) Chemical cleaning using alkaline cleaning agents:
- sodium hydroxide
- sodium carbonate
- Cleaning effect can be considerably increased by the addition of small quantities of hypochlorite or agents for the formation of complexes and surfactants.

Note:

Be careful not to damage gaskets. Concentration max of 4%. Temperature max of 80 degrees C. Under no circumstances should hydrochloric acid be used with stainless steel plates. Water of more than 300 ppm Cl may not be used for the preparation of cleaning solutions. It is very important that carrying bars and support columns in aluminum are protected against chemicals.

C: Incrustation – Scaling

Incrustation is caused by calcium carbonate, calcium sulphate and silicates.

Incrustation Cleaning Techniques:

a) Soft brush and running water

b) High pressure hose.

c) Chemical cleaning on opened unit by using:
- Nitric acid
- Citric acid
- Sulfamic acid
- Phosphoric acid
- Complexing agents (EDTA, NTA)
- Sodium polyphosphates

Note:

Be careful not to damage gaskets. Concentration max of 4%. Temperature max of 60 degrees C. Under no circumstances should hydrochloric acid be used with stainless steel plates. Water of more than 300 ppm Cl may not be used for the preparation of cleaning solutions. It is very important that carrying bars and support columns in aluminum are protected against chemicals.

D: Sediment

Sediment is caused by corrosion products, metal oxides, silt, alumina, diatomic organisms and their excrement of various colors.

Sediment Cleaning Techniques:

a) Soft brush and running water

b) High pressure hose.

c) Chemical cleaning on opened unit by using:
- Nitric acid
- Citric acid
- Sulfamic acid
- Phosphoric acid
- Complexing agents (EDTA, NTA)
- Sodium polyphosphates

Note:

Be careful not to damage gaskets. Concentration max of 4%. Temperature max of 60 degrees C. Under no circumstances should hydrochloric acid be used with stainless steel plates. Water of more than 300 ppm Cl may not be used for the preparation of cleaning solutions. It is very important that carrying bars and support columns in aluminum are protected against chemicals.

E: Oil Residues, asphalt and fats

Oil residues, asphalt and fats are a byproduct of the heat exchange process that includes oil, asphalt and fat.

Oil, Asphalt and Fat Cleaning Techniques:

a) Hydrocarbon-based deposits may be removed by using a soft brush and a PARAFFINIC or NAPHTA-BASED solvent (e.g. KEROSINE)

Note: Gaskets in natural, butyl and EPDM rubber swell in these media. Contact time should be limited to 0.5 hour.

The following solvents should not be used:

- Ketones (acetone, methyletylketone, methuylisobutylketone)
- Esters (Ethylacetate, Butylacetate)
- Halogenated hydrocarbons (Chloro-thene, Carbon tetrachloride, Frenons)
- Aromatics (Benzene, Toluene)

b) Dry with a cloth or rinse with water.


Be careful not to damage gaskets. Concentration max of 4%. Temperature max of 60 degrees C. Under no circumstances should hydrochloric acid be used with stainless steel plates. Water of more than 300 ppm Cl may not be used for the preparation of cleaning solutions. It is very important that carrying bars and support columns in aluminum are protected against chemicals.

2. Regasketing

There are two types of glue to be used in regasketing plates.

A. EPDM, NBR (rubber based)

- Single component rubber based solvent adhesive.

- Normally used for repair work in an uncured condition

- Can be used for operating temperatures below 95 degrees C

- For operation temperatures above 95 degrees C and oil coolers / heaters the glued joints should be cured at 120 degrees C for one hour.

- Future removal of the gasket can usually be carried out without heating of the cement joint.

- Storage life at room temperature is about two years. This period can be extended after checking the glue.


B. Viton and Silicon

- A two component, cold curing epoxy glue which gives a strong joint for higher temperatures.

- Future removal of gaskets usually requires heating or freezing of the joint.

- The shelf life is limited to approximately 1 year when stored at room temperature but can be prolonged when kept in a refrigerator.

C. Clip in gasket (glue free)

- The clip in gasket is attached to the plate by two gasket prongs which slip under the edge of the plate to hold the gasket securely in alignment in the gasket groove.

- The prongs are situated at regular intervals around the periphery of the plate.

- When the plate heat exchanger is then assembled and tightened, the gasket provides a tight seal around the plate.

3. Fault Detection

A. Leakage between plate pack and frame

- Mark the area where the leakage seems to be and open the heat exchanger.

- Investigate the gasket condition of the end plate and the connection if applicable. Look for dislocation, foreign objects, scars and other damage to the gasket surfaces.

- Check the surface of the pressure plate for unevenness, foreign objects etc., that might spoil the joint between the gasket and the adjacent surface.

- Check the plate itself for cracks and holes.
 


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