Plug cleaning/pigging of 2" pipeline 10 bar with obstructing valves

[gerhardl]

Problem:
2 inch (DN50mm, PN10) pipeline with knife-gate valves, valves obstructing pigging, damaging pigs in a heat exchanger for sludge (waste water) sterilizing.

Anyone with experience or suggesting of better/best suited type of pig?

Background:
By pigging the line after washing, pigs passing several (many?) valves pigs come out damaged, or also get stucked in the line.

The knife-gate valves are constructed with sidewise guides for the knife (between the two house-halves)restricting the full opening sidewise from 50mm to 45-46mm. Opening else even, knife sidewise and bottom sealing one-piece U-form NBR totally encapsled, (inner steel)as knife/seat sealing , held between the two house halves. U- sealing protuding about 1mm above light opening bottom.

Total building length (along center pipeline) for valve 43mm. Inner sides of valve EKB epoxy coated.

The guides (see above) are thus taking one 'half moon' off the full opening each side of the full circle, and with perpendicular inner side. (Max segment measuremet along circle radius thus 2,5mm).

Claim: With other make 'full opening' constructed knife-gate valves the supplier of the heat exchanger claims there were no problems with this type of heat exchanger construction using pigs.

 

[11echo]

gerhardl ...You ever try "poly pigs" (nerf ball) or "styrofoam pigs" (styrofoam bullet) in this line? They are inexpensive and because they are soft can squeeze through just about any opening (especially the ploy pigs) with no damage too internal coatings. I've even seen a styrofoam pig get pass a butterfly valve! It was in two pieces but the valve was at the storage tank nozzle or end of the line, so not a big deal.

 

[JimCasey]

Or, replace the knife-gate valves with full-port ball valves. The pigs wil pass and the inherent packing leakage of the knife-gates will go away. THe ball valves are also much more compact and will free up a lot of headspace. You'll probably enjoy more floorspace since you can remove all the buckets you have lined up on the floor under the knifegate valves. :-/

The one service where knifegate valves excel is on fibrous slurries such as paper pulp.

 

[gerhardl]

Hello JimCasey,

You wrote

...The one service where knifegate valves excel is on fibrous slurries such as paper pulp...

or, as in this case, waste water 'solids' - sludge to be treated and sterilized.

The problem is not quality and drop-thight sealing of the valves. Correct constructed good-quality knifegate valves will seal drop thight both ways for many years, and also keeping thight at top sealing.

But yes, the description you present, suits regrettably many other cheaper knifegate valve constructions.

I do not believe ball-valves to be the perfect solution in this case, the reason is abrasion on seals and filling/clogging of space between body and seals .

In this case our role is to try help the end-user finding a suitable plug. So far we have checked locally and found reasonably priced plugs that can be compressed 40% (far less required)(and thank you echo11!).

Left is to test if this plug will behave and clean sufficiently for built up (cagulated mass?) on walls to give the calculated planned heat transfer from the heat exchanger. ... Or maybe the whole process should have had different dimensions, layout and equipment to avoid clogging on walls in (too) narrow pipelines.

And I am still looking for especially suited plugs or input from someone with similar experience.

 

[JimCasey]

gerhardl,
Ball valves >can< have the cavity pack with solids, and the seats can wear. The only time the cavity is exposed to the flow is when the ball is in an intermediate position. Likewise the only time the seats are exposed to flow impingement is when the ball is in an intermediate position. Full-Port valves are really not suited for throttling as they have vastly too much capacity for good resolution, so they should really only be operated on-off with little opportunity for the cavity to accumulate solids. ALSO a good tip is for the ball to be installed with the shaft horizontal, and the bottom edge rotates toward the upstream as it opens. ( CCW to open, stem on the right when looking upstream) This will help to lift and dislodge any sediment deposits against the ball/seat interface when the valve is initially being opened, and to flush the sediment in the body cavity. Otherwise the seats should see about the same service the seats see in a knifegate.

Ball valves installed on slurries with the stem vertical can have the ball sitting in a puddle of grit and it adversely effects the service life of the valve.

 

[gerhardl]

Hi JimCasey,


Yes, I see your point.

One of the solutions discussed is changing of valves, either to more 'full port open' knife-gate valves, or to other type (for instance ball valves).

There is still a 'but' for ball valves. The 'sickness' of this particular process is too low heat transfer and too high pressure loss. Different possible causes are at present discussed.

One suspicion is growth on walls, indicating that ball-valve sealings could be suspect to growth of either coagulating material or residues hardening if/when pipeline is dry.

 

[AndrewBRO]

Dear gerhardl,

There is an US company, Goodway who manufactures guns and foam projectiles.

http://www.goodway.com/hosetube_cle...ing_guns/products/155-jetlaunch-jic-2030.aspx

For heat exchangers there are from same company other mechanical or chemical solutions, including cleaning pipes one end with a brush through a flexible shaft and water flow.

http://www.goodway.com/rotary_tube_...tary_tube_cleaners/products/114-ram-4-60.aspx

http://www.goodway.com/liquid-descaler/products/439-scalebreak-1.aspx

If I could know more about the system, I may be able to advise you regarding the best Goodway solution, in case you haven't already solved the problem.

 

[gerhardl]

Thank you all for answers! It is always a help to have different views and input!

To conclude and end the thread, and for your information, last information received:

Very long streches of heat-exchanging tubing.
Not possible to demont for cleaning access from outside.
Inner diameter of tubing 57,2mm!
Selected valve diameter DN50 (50mm max opening)!
Waste water residues (animal and plant type fat) to be pastereurized to 85 deg C.
Temperature causing coagulation and burnt on layer on inside walls.
To obtain clean walls to sufficient heat transfer effect, inner tubing has been decided necessary to be cleaned with steel-brush type pig.

Preliminary conclusion:

a) Obviously one can raise questions if this is the optimum equipment / layout solution for the process. My personal opinion is that there exists better solutions on the market - this is however not the question here.

b) Based on experience with similar solutions we are suggesting to replace the DN 50 mm valves with valves DN 65.

 

[v8landy]

Have you looked at Pigless Pigging???

http://www.whirltech.co.uk

I have used them on a previous project and it realy does work.