Hello,
I am working in a fertilizer company capacity 2800MT/Day. We have 2 STG each capacity 32MW. In the condenser of STG, we use diaphragm seal capillary tube level transmitter. There are 2 Diaphragm type capillary tube level transmitter (Yokogawa Brand) one used for control action and other one used for Emergency shutdown action. Both LT have same Nozzle elevation (Calibration Range: -8.20kpa to 0.65kpa). In recent time we observed that the Control LT showing more value (15% more) than the LG and ESD LT (we make confirm that LG and ESD LT showing correct reading). Then we flush the HP and LP side of the transmitter and make zero adjustment (Auto Lower PT) and line up. But the reading remaining same. Then we open the diaphragm seal from impulse line. We did not find any physical damage on it and clean the diaphragm, again lineup but no improvement. Then we adjust the same value (looking from other Transmitter) by using Yokogawa transmitter zero adjustment screw. Then after sometimes the value of this transmitter again reach the previous value. My question is:
1) What is the exact maintenance procedure if we fount this type of problem?

 

You need to contact your supplier, and read the maintenance literature. Sealed capillary systems are not meant to be flushed.

 

Seal is not flushed...only flushed by vent plug of diaphragm seal.

 

Then we open the diaphragm seal from impulse line.

The remote diaphragm seal is usually a welded assembly to the capillary.

You removed the capillary with its diaphragm from the transmitter body?

Or you removed the remote diaphragm from its seal on the capillary?

Did you pull a hard vacuum and backfill when re-installing the diaphragm seal?

 

1) You removed the capillary with its diaphragm from the transmitter body?
Answer: No, we just open the flushing connection ring from the process line flange and flush from vent plug..
2) Or you removed the remote diaphragm from its seal on the capillary?

Did you pull a hard vacuum and backfill when re-installing the diaphragm seal?
Answer: we did not touch this part.

 

Your IMG-202404821_0 appears to show the flush ring mounted on the back of a flanged diaphram seal.

 

>Then we adjust the same value (looking from other Transmitter) by using Yokogawa transmitter zero adjustment screw

Which model DP transmitter are you working with the has a zero adjustment screw?

 

Yokogawa
Model: EJA118E-JMSCJ-914EB-WA18C1SW40-BA23/KU22 +
M20 X 1.5 f Blind Plug MOC SS + 2 Nos Valves for Flushing
and Calibration 1/4” NPT MOC SS 316 with connector

 

Don't forget the transmitters only report a pressure differential. If the fluid is subject to temperature or composition gradients, or unexpected flow patterns that alter the reported pressure, you can only estimate the actual fluid level.

 

Zero point adjustment instructions yokogawa EJA118E

https://web-material3.yokogawa.com/IM01C22T01-01EN_008.pdf

Note that the zero adjust needs to be enabled, (18) External Switch mode, page 2-17

 

Please read the User manual mounting instructions (chapter 4) : make sure all precautions have been taken. Sorry but I disagree with Dave : according to IMG-202404821_0 the flushing ring is mounted on the correct side of the diaphragm seal.
No air should be introduced in the capillaries (i.e. the capillaries should never be disconnected from the diaphragm seals or from the DP transmitter)
An example of LRV and URV calculation is shown on Smart Level Setup Feature

 

Don't forget the transmitters only report a pressure differential. If the fluid is subject to temperature or composition gradients, or unexpected flow patterns that alter the reported pressure, you can only estimate the actual fluid level.

NO..There is nothing like that...Condenser has 2 LT.. One is working fine without any errors...so the process condition is ok

 

Zero point adjustment instructions yokogawa EJA118E

https://web-material3.yokogawa.com/IM01C22T01-01EN_008.pdf

Note that the zero adjust needs to be enabled, (18) External Switch mode, page 2-17

Its done according to the instruction manual

 

Please read the User manual mounting instructions (chapter 4) : make sure all precautions have been taken. Sorry but I disagree with Dave : according to IMG-202404821_0 the flushing ring is mounted on the correct side of the diaphragm seal.
No air should be introduced in the capillaries (i.e. the capillaries should never be disconnected from the diaphragm seals or from the DP transmitter)
An example of LRV and URV calculation is shown on Smart Level Setup Feature

all precautions have been taken according to the instruction manual..2 days ago we replaced the LT with new one and now working fine. But i am confused about the older LT. There are no visible damage in the diaphragm of the LT and did the maintenance work according to the instruction manual but did not recover...

 

The DP transmitter itself is a pretty rugged beast, and can take significant overpressures, which is unlikely in the service that it's used for.

There must be something wrong in one of the capillary tubes to cause the 15% offset.

Are the capillaries and seals all-welded construction or are connections screw-threaded?

 

Screw threaded connection of capillary tube in the transmitter high low side.

 

There's the possibility of a leak in the threaded fitting that allows fill fluid to leak or air to enter capillary.

 

I have heard of leaking capillaries being repaired with the requisite vacuum evacuation and backfill by a reputable remote seal 'house'.