Bell & Gossett HT 50B SM B&G Series U Heat Exchangers Removable Bundle Design User Manual

Page 4

a. Following the procedures previously mentioned for

front head removal, remove the head and replace it with

a companion flange that mates with the shell body

flange. Replace the nuts and bolts/studs.

b. Pressurize the shellside of the heat exchanger with a

cold fluid, preferably water.

c. Observe all tube joints and tube ends for indication of

test fluid leakage.

d. To tighten a leaking tube joint, use a suitable parallel

roller tube expander.

CAUTION: When tightening leaking tube joints:

1. Do not roll tubes beyond the back face of the tubesheet.

Maximum rolling depth should be the tubesheet thickness

minus

2. Do not re-roll tubes that are not leaking since this will

thin the tube wall.
The result of either of the above conditions can lead to

failure of the tube and a leaking bundle.

e. If an emergency repair of a tube is required, use suit-

able tube plugs to seal off both ends of the U-bend

tube. Some loss of performance will result until a new

replacement tube bundle is obtained. Consult your local

ITT Bell & Gossett Representative for proper replace-

ment of the bundle.

CAUTION: Field repair of Diamondback™ double

wall heat exchangers is not recommended. Re-

rolling of the tube joints may result in the closing of the

leak detector flow paths between the two tube walls pre-

venting the heat exchanger from providing a positive

indication of potential cross contamination.

8. Tube bundle removal:

a. During bundle removal, the dead weight of bundle

should never be supported on individual tubes. Rest the

bundle on the tube sheet, support plates, or wood

blocks cut to fit periphery of the bundle.

b. Tube bundles may be raised using slings formed by

bending light plates into a “U” form and attaching lifting

lugs to the ends of the sheets. Baffles can be easily

bent and damaged if dragged over rough surfaces.

CAUTION: When cleaning a tube bundle, tubes

should not be hammered on with any metallic tool

and, in case it is necessary to use scrapers, care should

be exercised that the scraper is not sharp enough to cut

the metal of the tubes.

MAINTENANCE

1. Do not open heads until all pressure is off equipment, the

unit drained of all fluids, and the equipment surfaces

cooled to ambient temperature.

2. Do not blow out heat exchangers with air when operating

fluids are of a flammable or otherwise hazardous nature.

WARNING: Proper precautions must be taken

(special clothing, equipment, etc.) to protect per-

sonnel from injury due to escaping fluids or hot heat

exchanger surfaces.

3. Provide convenient means for frequently cleaning heat

exchangers as suggested below:
a. Circulating hot wash oil or light distillate through tubes

or shell at good velocity will effectually remove sludge

or other similar soft deposits.

b. Soft salt deposits may be washed out by circulating

hot fresh water.

c. Some cleaning compounds on the market, such as

“Oakite” may be used to advantage for removing

sludge or coke, provided hot wash oil or water, as

described above, does not give satisfactory results.

d. If the above methods are ineffective for removal of hard

scale, a mechanical means may be used.

WARNING: Care must be exercised when handling

certain fluids. Follow manufacturers instructions.

Use eye and skin protection. Wear a respirator when

required.

4. Do not attempt to clean tubes by blowing steam through

individual tubes. This overheats the tube and results in

tube expansion strains and sometimes leaking tubes.

5. Frequently and at regular intervals, observe interior and

exterior condition of all tubes and keep them clean. Fre-

quency of cleaning should be according to scale build-up.

CAUTION: Neglect in keeping all tubes clean may

result in complete stoppage of flow through some

tubes with consequent overheating of these tubes, result-

ing in severe expansion strains, leaking tube joints, and

damage to the heat exchanger.

6. Exchangers subject to fouling or scaling should be

cleaned periodically. A light sludge or scale coating on the

tube greatly reduces it effectiveness. A marked increase in

pressure drop and/or reduction in performance usually

indicates cleaning is necessary, if the unit has been

checked for air or vapor binding and this has been found

not to be the cause. Since the difficulty of cleaning

increases rapidly as the scale thickens or deposits

increase, the interval between cleanings should not be

excessive.

7. At times, it may be necessary to locate a ruptured tube or

a leaking joint between the tubes and the tubesheet of a

single wall heat exchanger. The following procedure is

recommended.