Wednesday, August 3, 2011

NITROGEN PADDING FROM ASHORE-- CAPT AJIT VADAKAYIL


This is in reponse to a query from capt allen brink vide my blog MY COUSIN VINNY - VADAKAYIL -- dated 28th jan 2011

A lot of chemical tankers have burst their cargo tanks while purging/ drying / padding their tanks, with high pressure shore nitrogen.

US chemical terminals are the worst culprits -- as they lack elementary commonsense.  I have yet to see a US terminal understand vapor return calculations-- and i have dealt with almost all of them.

While purging an empty tank with shore nitrogen , make sure that the volume into the tank does NOT exceed the PV valve vent capacity which is 125% of your cargo load capacity usually.

First of all Nitrogen cannot be delivered by liquid shore cargo hose--as per USCG rules. Unless they are pigging--or blowing the line.

You must remember that YOUR manifold valve is with you, to prevent excessive overload--nobody is stopping you from throttling this valve, to suit your system. Use it as a reducing valve.

Padding loaded tanks must be done by shore vapor hose which complies with USCG 46 CFR 39.20-1(f) ( 1/2/3 ).

The bursting pressure of such a hose with a one inch hole at 12 o clock position--  is 25 psi where 1 Atmosphere = 14.69 psi. Its MAWP is +5 psi/ -2 psi.

It may acceptable to keep tankdome one inch open while inerting an empty ship's tank with shore nitrogen , high pressure supplied by liquid cargo hose. -- if this is agreed in writing at the pre-load meeting. ( nobody will sign this sheet , as it is wrong ) . Keep you sailors away on the windward side.

NITROGEN IS LIGHTER THAN AIR.

Here are some actual emails-- glean from it and be safe--

----

From: XXX MASTER

Date: Thu, 17 Mar XXX 18:17 +0000 Msg: A03153-43187

Subject: Re: FEEDBACK ON XXX TRAINING DVD

To: XXX Ship Management XX
Cc:  XXX
Cc:  XXX Ship Management XX
Cc: MARINE XXX Ship Management
Cc: Technical XX Ship Management
gentlemen,
i must expound further--
1) keeping a tankdome open with FULL 98% ( or even 1% ) loaded chemicals
is a crime all over the world -- whether it be for PADDING carcinogenic
benzene or inflammable gasoline or polymerising styrene. 
READ ABOVE SENTENCE THRICE.
this ship then becomes history as far as the terminal is concerned.
the master gets blacklisted personally, and is removed from ship in
disgrace, before cargo can be resumed . 
more serious it will affect the company's fortunes and the " risk
profile " of other innocent ships of the company.
padding is a LOW PRESSURE LOW VOLUME operation done via the vapor line--
NOT the liquid line.
2) keeping a tankdome open as shown in the karko dvd video is allowed
only for PURGING an EMPTY tank -- in case ship is using high volume/
high pressure shore nitrogen to purge the tank --

this is just to prevent tank rupture -- as some terminals shove in 10
bars of nitrogen into the tank via liquid drop at HIGH VOLUME  (which
cannot be handled by the small orifice PV valve) to save on "berth
occupying time".

so despite the PV cone lifting at 2000 mm aq ( 0.2 bars ) the huge
volume high pressure nitrogen ingress in tank will still burst the tank
-- as the residual pressure will be greater than the 0.45 bars approx
required to burst the tank. the PV orifice is of very low diameter.
the tank bulkhead corrugations will start getting flattened out at 0.35
bars .
the HIGH VOLUME nitrogen ingress into tank can be reduced by throttling
the ships liquid manifold valve.

comments:
a)capuccino effect is used by the singapore bunker mafia , to make the
chief engineer sign for 10% excess bunkers. it takes 24 hours for this
entrapped air to escape.
b)capuccino effect causes SEVERE SURFACE FOAMING on some chemicals --
even simple cargoes like veg oils . quality of chemical cargo gets
affected.
c)on ship we do NOT get impressed by zooming and tantalising video
graphics -- we are all mature professional adults on board, addicted to
professional facts NOT visual fiction . my own son is a Cornelluniversity ,

ME in computer graphics man -- what he can conjure will make even adults drool --
brgds
capt ajit vadakayil
master
XXX
##############

A03153  Fri, 18 Mar XXX 10:00
From: XXX MASTER
To  : XXX TECH2                          Sent    3/18/ XXX 7:16 AM
Cc  : XXX MARINE                        Sent    3/18/XXX 7:16 AM
Cc  : XXX SQE                               Sent    3/18/XXX 7:16 AM     

Date: Friday, March 18, XXX 7:17 AM Msg: A03153-43243
Path: \MASTER\SentBox@@@@@@@@\0ajit out
Sub : Fw: FEEDBACK ON XXX TRAINING DVD
gentlemen,
here it is!
XXX   is NOT receptive to suggestions --
the ships management had decided via a shipboard management meeting --
that these two substandard videos will NOT be shown to our crew.
1) NITROGEN: which shows nitrogen being bubbled up through cargo in a
loaded tank to PAD -- inlet from from cargo drop -- outlet from tank
dome.
the fact he says DEG or diethylene glycol ( a HYGROSCOPIC syrup ) --
rings a bell-- mafia shippers know for sure that there is inherent
moisture inside this cargo. there are using this method to dry up the
liquid cargo, before shipbaord samples are drawn.
they should be doing this HYGROSCOPIC GYMNASTICS in shore tank-- not
ships tank.
2) ANCHOR: where all are we gonna put red flags ? thinking that it may
get "sheared off" .
a hundred red flags can be visualised in my mind's eye already. i can
start off with the bridge telegraph--
i close this subject right here!
brgds
capt ajit vadakayil
master
##############-----------------------------------------------------

From: XXX - XXX Ship Management XX
Date: Thu, 17 Mar XXX 16:50 +0000 Msg: AMOS-306905411
Subject: FEEDBACK ON XXX TRAINING DVD
To: XXX
Cc: MARINE XXX Ship Management
Cc: Technical XXX Ship Management
Dear XXX,
Recently we purchased training DVD for our Fleet on the subject of
Anchoring and Nitrogen on Chemical Tankers.

The following feedback was received from a Master in our fleet.
We have high regard for the opinion of this Master because, he has

an impeccable service record with us and has over 28 years of

command experience in tankers including over twenty years

command experience on chemical tankers with several leading operators.
His observations are:
Anchoring Movie:
The way the anchor cable dances under the seawater, ignoring the laws of
gravity and surface tension of the water is  hilarious. A underwater
video camera will tell totally a different story from the graphics
churned out by a computer graphics technicians delusional imagination .
The use of red flag on the anchor cable at the forecastle , to indicate
if the anchor brake slips to the wheelhouse ,is done only by river barge
operators. Ocean going ships put the bow stopper after anchoring. Anchor
brake friction cannot hold a ULCC yawing due to swell.
Nitrogen Movie:
It is ridiculous to see nitrogen being bubbled up through the cargo drop
to pad the 98% full cargo tanks. When a tank has to be padded , the tank
is purged with nitrogen before loading. Then after completion of loading
the oxygen content is reduced to the required percentage by padding
nitrogen using the vapor line, not liquid line. Bubbling up nitrogen in
a tank having 98% cargo , with tank dome open, will cause overflow, due
to cappucino effect. Such things are never done at sea on chemical
tankers. Cappucino effect causes the Bill of Lading figure to be wrong.
Padding a polymerising tank is never done as most of the inhibitors are
oxygen dependant.
Please revert with your response regarding above, and your plans for
making necessary revisions to the DVD.
With best regards
XXX Ship Management (XXX) Pte. Ltd.
(For and on behalf of Owners as Agents only)
XXX
XXX General Manager



CAPT AJIT VADAKAYIL
( 29 YEARS IN COMMAND )


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4 comments:

  1. Sir, can you please explain the N2 Padding system onboard chemical tankers?

    ReplyDelete
  2. hi ajit,

    in the olden days ships had a nitrogen bottle bank ( say 40 bottles of 250 bars each ) to pad the tank after loading. 250 bars pressure is reduced to 0.2 bars before you inject it into the tank.

    this means you have to fill up the tank to about 97% at least to prevent wastage.

    in modern chemical tankers we have a nitrogen plant.

    the membrane separates the nitrogen from oxygen when you run air through it.

    I HAVE PUT A PICTURE OF A NITROGEN PLANT PIPELINES --IN THE POST ABOVE.

    when you run the air with membranes in parallel, the nitrogen strength is 95%--and the flow is fast--and high volume flow.

    when you run the air with membranes in series the nitrogen strength is 99.9% --and the flow is SLOW-- and low volume flow.

    nitrogen goes into the tank and displaces the oxygen in the tank--either by dilution or displacement method.

    the nitrogen enters the tank from top of the cargo surface.

    it is as simple as that!

    capt ajit vadakayil
    ..

    ReplyDelete
  3. Captain Thnx for sending such a text however a point need to be cleared which you had mentioned in article ''PV valve vent capacity which is 125% of your cargo load capacity usually'' but as you know cargo load capacity changes depends on cargo to be loaded.. Thus considering inerting empty tank - fitted PV valve setting is 0.2 mmWg - by N2, can you simply explain how to caculate flow rate ? (Karco animation refers that PV flow rate is 880cbm/hrs, but I don't know whether it's true or not..=

    ReplyDelete
    Replies
    1. hi cs,

      for nitrogen shipboard operations use P&A manual and Vapor return manual calculations and graphs.

      for nitrogen padding from ashore , do NOT rely on ship's PV valve alone-- as you may rupture the tank.

      punch into google search-
      VAPOR RETURN SYSTEM CHEMICAL TANKERS VADAKAYIL

      KARCO videos are all bullshit.

      they wanted to use shore nitrogen and bubble it upwards through the cargo via the bottom cargo loading drop/ bellmouth .

      never try to learn chemical tanker work from a ANIMATION AND GRAPHICS VIDEO PRODUCER.

      i had told them to change their bullsh#t video 3 years ago.

      capt ajit vadakayil
      ..

      Delete