2 replies to this topic

[simadri]

Hello Experts,

 

We are facing to find out reason for support failure of raw water storage tank outlet line. Please find the attached sketch in Microsoft word  to understand the system.

 

There are two nos. of raw water storage tank (Dimension: Height 18 m X Dia 37.5 m).

Both the storage tanks outlet lines are connected to 4 nos. of pumps (2 working + 2 standby) as per the attached sketch.

 

As shown in attached sketch, at time of the event, only one pump was operational from both the storage tanks at a time. This means all isolation and on-off valves on both the tank outlets were in open condition. Surprisingly per DCS history, at time of the event, tank 002 has 87% level and tank 003 has 53% level. I have no idea why the level of both the tanks are not same (level balancing because both tanks outlets are in open condition).

 

I do not have concrete information how the support failed. However, I got this info from DCS history; the outlet on-off valve of tank 003 closed, then opened and then closed in a time interval of 2 minutes. And in next minute somebody detected leak because of taper joint failure (check the sketch) and stopped the pump.

 

The line has shifted from Tank 003 towards tank 002. It is shifted a bit from support. And one support failed (attached image) in the direction towards tank 002. 

 

Can you help me with possible reasons for support failure?Is there a possibility of water hammer?

 

Thanks

 

Attached Files

•  Raw Water Pumping.docx   165.52KB   10 downloads
•  20170307_083308.jpg   70.89KB   0 downloads

[Dazzler]

Hello Simadri

 

A few thoughts.

• If you have a piping designer or someone that understands pipe stress analysis, good to get them to inspect.
• Level difference could be due to heavy silt or solids build up in one tank more than the other, covering level sensor or restricting outlet.  Alos, obviously level transmitter basic calibration.
• Auto valves opening or shutting too fast can cause pulsations or water hammer.
• Are tanks still level since construction or possibly structurally sinking different to each other and creating new stress on pipes and supports.
• Perhaps some different types of supports are needed in some areas.

 

Do let us know in your post how it turns out so we can learn also.

 

Thanks

Dazzler

[simadri]

Hello Dazzler,

Thank you for sharing your valuable thoughts.

With primary investigation we came to know that tank 002 outlet manual isolation valve was in closed condition during the event. We also looked from pipe stress point of view. It looks good.  Till the time, it seems that water hammer is the reason for the failure.