Heat exchanger . How to dry after hydrostatic test? 3

[Adrian Gzz93]

How can I dry a stainless steel heat exchanger after hydrostatic testing?

Note:The customer does not allow me to use hot air.

I am currently purging with nitrogen for 3 hours, I check the dew point is below 0° and that it is pressurized to 1.5kg/cm.
But when the exchanger arrives with the customer and they open the valve, water is still coming out.

 

[MJCronin]

Is there some reason why the "customer" does not want you to use hot air ? .....Are you simply out of time ?

Hot dry air is commonly used and most HXs will take a day or two to dry out .... This cannot be rushed ...... A nitrogen pad is commonly applied after the hot air operation

Does he simply want to make things more difficult for you, or do you simply do as you are told without asking any reason ?

Can you provide any drawings of your heat exchanger ?

Are you behind schedule ?

MJCronin
Sr. Process Engineer

 

[Compositepro]

Using hot dry dry air or nitrogen relies on the process of evaporation to work. Evaporation only works if the dry gas flow contacts the liquid surface. A draft across the liquid surface is required. Otherwise, drying can take days, weeks, or years. This is particularly the case where the liquid pocket may have some significant depth, such as a crevice or a low point.

If you use a vacuum sufficient to make the water boil at room temperature, all of the liquid water will be removed. The removal rate will be limited by the rate of heat transfer to the water.

 

[EdStainless]

Unless the HX is sealed after drying and kept under a positive pressure of dry nitrogen it will always have water in it on arrival.
A couple of weeks of getting warm during the day and cool at night will cause condensation to form.
W3e used to use heated nitrogen. If there was no unusual reason we would heat to about 400F, and try to get the entire HX to about 250F.
I know of someone that rinses with alcohol and then purges with warm nitrogen.
You can use warm air if you have good enough dehumidification.
A 3 hour purge will likely remove about 2/3 of the water, the rest will take another 60 hours at least.

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P.E. Metallurgy, consulting work welcomed

 

[r6155]

Why not a pneumatic test instead of a hydraulic one?

Regards

 

[MJCronin]

r6155 ..

This is another topic

Pneumatic testing is dangerous, especially for larger volumes and higher testing pressures

This has been discussed many, many times on this forum

(... and BTW, its "hydrostatic" testing, not "hydraulic")



MJCronin
Sr. Process Engineer

 

[r6155]

@ MJCronin
I know exactly what the pneumatic test is and is allowed. See UG-100.
It may be a solution for this case.

Regards

 

[LittleInch]

First off how well can you drain it?

Can you lift it and move it to get as much free water to drain out of the flanges first.

Dewpoint just below zero when dewpoint of nitrogen as it comes out of the cylinder is probably -70 if it's come from a liquid nitrogen source or possibly a lot higher if its a nitrogen gas RO plant, but still indicates it's picking up a lot of water from somewhere.

Did you seal it and add a load of desiccant in the breather pipe? If not then you don't stand a chance.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[r6155]

@ MJCronin
(... and BTW, its "hydrostatic" testing, not "hydraulic")
----------------------------------------------------------
In PD 5500 5.8.3 Hydraulic testing

In ASME VIII Div1 UG-99 STANDARD HYDROSTATIC TEST

In EN13445-3 HYDROSTATIC and HYDRAULIC.

Regards

 

[Adrian Gzz93]

The heat exchanger weighs 128,000 lbs. and is made of stainless steel.

Dimensions: 390" long and 60" in diameter.

Water is pooling in the floating head.
It is very difficult to move the equipment because of the weight and capabilities of my shop cranes.

 

[btrueblood]

One of the most beneficial drying/purging schemes I've ever tested is cycling between warm vacuum and dry nitrogen backfill/purging. 2-3 cycles and you should have water levels at less than 1 ppm.

 

[EdStainless]

... after all residual liquid is gone.

You need to be able to tilt it enough to get the pool out.

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P.E. Metallurgy, consulting work welcomed

 

[georgeverghese]

Use a vacuum pump and keep the tube side (floating head side) under vacuum for a day or two under as low a pressure as you can go ? That should get that trapped pool of water to evaporate. Vacuum pressure on floating head side should be below sat pressure at the ambient temp.
Also check if there are drain notches at the low point of all cross flow baffles in the shellside of the HX, else water may be trapped under the tube bundle on shellside also. Obviously, the HX should be oriented such that these drain notches are at the lowest point of the HX for these to allow free draining toward the shelllside drain location.

 

[LittleInch]

Can you access the end plate?

Might take a while but temporarily plug all those tubes at the top of the bottom set of tubes and blow the liquid out?

Gradually plug 90% of them so only the bottom few are left until you get no more water out. Then unplug and do your drying.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[r6155]

There should be a hole of approx. d = 6 mm in each pass partition plate for drainage. Also this hole is necessary to vent air during filling with water for hydrostatic pressure test.
Is this hole in this heat exchanger?

Regards

 

[GD2]

Adrian,

Did you control the Chloride content while doing the hydrotest?

GDD
Canada