2 replies to this topic

[chemtan]

I have a situation where iam connecting flow to existing slop tanks that are externally floating roof type. The tanks are very old (made in 1946) and have no proper datasheet/documentation available, only Safety Instruction Sheet of the tanks are available.

Due to my flow rates, the roof velocity will be 1.6mm/sec (6.1 m/hr). As these are slop tanks, so I'm not sure how much is the existing flow rate into these tanks. I have to verify if:

1. Roof velocity of 6.1 m/hr is adequate for external floating roof tanks?
2. Any rule of thumb value on the roof rise and fall velocities?

The tanks are subject to regular inspection and maintenance and have no mechanical issues with floating roof until now.

Your suggestions will be highly appreciated.

[kkala]

I have a situation where iam connecting flow to existing slop tanks that are externally floating roof type. The tanks are very old (made in 1946) and have no proper datasheet/documentation available, only Safety Instruction Sheet of the tanks are available.
Due to my flow rates, the roof velocity will be 1.6mm/sec (6.1 m/hr). As these are slop tanks, so I'm not sure how much is the existing flow rate into these tanks. I have to verify if:
1. Roof velocity of 6.1 m/hr is adequate for external floating roof tanks?
2. Any rule of thumb value on the roof rise and fall velocities?
The tanks are subject to regular inspection and maintenance and have no mechanical issues with floating roof until now.Your suggestions will be highly appreciated.

To my knowledge, there is no direct restriction on the roof velocity of floating roof tanks, at least we do not consider any in the design of API 650 tanks. But following may affect this parameter indirectly:
1. Ingoing and outgoing pipe lines have liquid velocity limits, as recommended by practices.
2. Floating roof is "sitting" on its legs during last phase of tank emptying or first phase of tank filling, so flow has restrictions similar to cone roof tanks in this case. E.g. cannot exceed capacity of (rim) vents located on the roof, fluid velocity cannot be > 1 m/s if air can contact flowing liquid. But these depend on the policy established for tank emptying or filling.
3. Similarly filling time between HLL and HHLL should be about 20 min (depending on distance, assessed critical conditions, etc), so that operator could react.

Edited by kkala, 19 December 2010 - 03:16 PM.

[chemtan]

Kkala,

thanks for the information. I thought there might be some thumb rules on roof velocity however it seems as if there is no such value.

Between, the 1 m/sec criteria for initial filling of tanks in order to avoid static charge development is mentioned in API 2003 para 4.5.2.