Posted on behalf of V.K.Rai
Dy.General Manager( Maint.)


Can you please suggest some modern gadgets for maintenance of Heat Exchangers. Generally for opening of these exchangers even Torque Wrench which we have also fail , then there remains no alternative but to hammer the box spanners which takes days to open.

I will appreciate if you can respond to this question

Regards.

V.K.Rai
Dy.General Manager( Maint.)
raivk@iocl.co.in

Mr. Rai,

Please advise whether the bolts are lubricated with the right lubricant when assembling the exchangers. Three points to consider:
1. The nut faces MUST be lubricated, and the matching faces flat, smooth and clean.
2. The lubricant must be selected keeping the bolt temperature in mind.
3. If in a marine or desert environment, the threads may need additional protection, e.g., by a cap nut to protect the exposed threads.

The opening torque will be higher than the tightening torque, so torque wrenches may not always work.

V.Narayan.

Dear Vee

The 3 points you mentioned are easily achievable but are they really working during the opening those nuts and sufficient to prevent nuts stuck? I have come across nuts stuck on steam turbine bolts during overhaul/turnaround and this caused a delay which lengthened work duration by contractor.

If we use bolt tensioning machine, will we face nut opening difficulties? TQ

We stopped having problems with openning and closing of heat exchangers since we use a "Pneutorque". This tool is strong and work without any impact.
Can be seen following that link :
http://www.torquetools.com/hand_torque5.shtml
You can have it from low torque to very high torque.
Hope this help.
J-Marc

There is a whole range of pneutorque product in the link. Which one is the most versatile product to be owned by a customer?

In particular, I would like to ask:
1) which one can be used for opening & tigthening nuts of steam turbine after operating at 130 bar for say 7 years?
2) which one can be used to just simply open & close a heat exchanger channel heads to prevent leaks after hot operating conditions?

Does your product require special features on the existing eqpt eg bolt tensioning machine requires extended bolts in order to be used. TQ

Hullo Josh,

No solution is guaranteed, but doing the three steps I suggested can go a long way. Bolt tensioning is not easy to retrofit; the existing design must be capable of accomodating its special space requirements. With bolt-tensioning, you MUST fit cap nots, to ensure that you can mount the tensionong head. Bolt tensioning does not solve the inherent rust/salt/dirt/sand kind of problems, but if these are extreme, it might at least manage the dismantling work better. Remember also that tensioned bolts need careful inspection and periodic replacement. This will add to costs.

A number of torquing tools are on the market. But remember that adding more torque is not always the best answer, as it can damage bolts sometimes. The correct procedure is to follow the 3 steps I have listed FIRST, then consider using torquing tools if required. Strong arm methods may appear effective, but must be used with care.

V.Narayan.

Mr. Josh,

For steam turbines with 130 BAr pressure, there are three options - with which I am familiar.

(1) As mentioned by Mr. VEE - usage of hydraulic stu tensioners.

(2) Usage of High Frequency / Medium frequency induction heaters.

(3) Immersion type electric heaters.

Also I beleive now a days good "Antisiege compounds" are available which yeilds good results.

Normally these devices are being supplied by turbine manufacturers along with "Special Tools".

Pneumatic wranches may be used, but we have never used it for final tightening. For pipelines, yes pneumatic wrenches give good results. Also for some heavy duty applications (not steam turbine), "SUPERBOLT" gave good result.

Dear J-Marc

Which pneutorque have you used for opening & tigthening nuts of heat exchanger bolts with operating pressure of 39 bar? Do we need to do hot bolting after using pneutorque? Tq

Josh,
I don't know your application (steam turbine heat exchangers). We use it on Alfa Laval plates heat exchangers. My comments was to mention that strong tool with smooth operation exist adding to the Vee's recommandations you could solve your problem. The best would be to contact Pneutorque dealer. They could better than me tell you the model to best fit your application.
Good luck!
J-Marc

Dear ALL
Thanks I got sufficient details on bolts & nuts.

Another question is how to ensure surface cleanliness after heat exchanger tube cleaning? We use a water jet machine with a spinning nozzle inserted into the tubes. But the cleanliness of the tube surface is rather evaluated in a subjective manner. Sufficient cleanliness is required for proper heat transfer. At same time, some people are concerned about excessive lceaning may reduce the tube wall thickness, thus lead to faster replacement.

Is chemical cleaning advisable for inside and outside the tubes particularly for extractable tube bundles? TQ

We clean hx bundles inside and outside with a water jet machine also. Also we made a soak tube with a mixture of 50% low vacuum gasoil(diesel) amd hvgo. This to elevate the flaspoint of the diesel.
About the replacement of bundles, it depends on what is running in the hx. Hydrocarbons (oil to oil) normally don't give much problems.
The one with water cooling, eventually give problems, especially when people start to throtle the cooling water flow to "increase" temperature.
The worst ones are vacuum overhead condensors, which normally has gases on the shell, and water in the tubes. Since the tubes are not totally submersed in liquid, the top tubes will corrode faster. Our experience with vacuum condensors, if you got leaks in the top row, plug the whole row, because it is going to bite you soon.