Quick Estimation of Frictional Loss in Water Network - Spreadsheet Available

Recent post "Quick Estimation of Frictional Loss in Water Network" has presented frictional loss estimation using Hazen-William equation. Ankur has recently programed it in Excel spreadsheet. You may download with by clicking this link. Any comments, please drop a notes...




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Quick Estimation of Frictional Loss in Water Network

Firewater, service, portable and drinking water network is common network present in most Oil & gas, Refinery and Industry plant. Water balancing in this network is important and critical in maintaining a constant supply to all users. Correct frictional loss estimation within network is the key activity in providing a well balance of water supply. Hazen-William formula is one the method widely accepted and used in industry in estimating frictional loss.

Hazen-William frictional loss is a function of fluid velocity, hydraulic radius and a constant subject to fluid condition and type of pipe. Equation as follow :

C Change with Pipe Material

Hazen-William friction loss coefficient (C) subject to condition and type of pipe. It possibly range from 60 to 150. The following summary listed the Hazen-William friction loss coefficient (C) for different type of material 

(source : Handbook of Chemical Engineering Calculation)

Another set of Hazen-William friction loss coefficient also listed in NFPA 15-2007.

(source : NFPA 15-2007)

From above figures, the C factor is almost decrease with surface roughness.

C Decrease With Service Life

One shall take note that Hazen-William friction loss coefficient will decrease with service life. From King & Crocker "Piping Handbook", C = 120 when the pipe is new and decrease to C=90 after 20 years. From "Handbook of Chemical Engineering Calculation", C factor for a new Cast-iron pipe (30 inches) is 130, decrease to 120 after 5 years, decrease to 115 after 10 years, decrease to 100 after 20 years, decrease to 90 after 30 years, decrease to 80 after 40 years and decrease to 75 after 50 years.

An excel spreadsheet prepared by Ankur is under reviewed. Find out in "Quick Estimation of Frictional Loss in Water Network - Spreadsheet Available".

Related Topic

• Some Recommendation for Process Critical Line
• Process Critical Line
• Control Valve Cavitation Damage and Solutions
• Problems and Measures for Condensate Recycle Control Valve
• FAQ Related to Control Valves
• Useful Documents Related to Control Valve

Consider Rated flow or Required Relieving Flow ?

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Pressure Relief Device (PRV) inlet line lose shall be limited to 3% of set pressure while the outlet built-up back pressure shall be limited to 10% for a conventional PRV and 30 for balanced PSV (without affecting it flow).

Excessive PRV inlet loss can result rapid opening and closing of the valve which normally called chattering. Chattering will result in lowered capacity and damage to the seating surfaces. The inlet line loss here is referring to non-recoverable entrance losses (turbulent dissipation) and frictional line lose.

The impact of excessive built-up back pressure on discharge piping discussed in "Several Impact of Backpressure on Conventional PRV".

One of the question raised is that should the rated flow or required relieving flow to be considered for inlet line loss and discharge built-up backpressure estimation ? Should the flowing fluid phase affecting this requirement ?

Flowing phase & PRV type
The flowing fluid phase would affect the PRV type. Example, pop action spring loaded PRV is good for compressible vapor or gas service and modulating type PRV is good for incompressible liquid service.

Flowrate to be considered for Discharge line
As per API Std 521, section 7.2.1, table 12, the flowrate to be considered for tail pipe, lateral & main header subject to PSV type (refer table below).


Above is inline with API RP 520 PII - Ed 5 Aug 2003, section 5.3.

"...The rated capacity of a conventional spring loaded, balanced spring loaded or pop action pilot-operated pressure relief valve should typically be used to size the atmospheric vent piping or the discharge line from the pressure-relief valve to the relief header. Common relief header piping in closed discharge systems should be sized using the protected system's required relieving capacity.

For a modulating pilot-operated pressure-relief valve, the discharge piping can be sized using the required relieving capacity of the system that the valve is protecting..."

Flowrate to be considered for Inlet line
Following API Std 521, section 7.2.1, table 12, the inlet line loss for Modulating type PSV may consider required relieving flow. However, API RP 520 PII - Ed 5 Aug 2003, section 4.2.2. stated :

"When a pressure-relief valve is installed on a line directly connected to a vessel, the total non-recoverable pressure loss between the protected equipment and the pressure-relief valve should not exceed 3 percent of the set pressure of the valve except as permitted in 4.2.3 for pilot-operated pressure relief valves. When a pressure-relief valve is installed on a process line, the 3 percent limit should be applied to the sum of the loss in the normally non-fowing pressure-relief valve inlet pipe and the incremental pressure loss in the process line caused by the flow through the pressure-relief valve. The pressure loss should be calculated using the rated capacity of the pressure-relief valve."

API RP 520 PII - Ed 5 Aug 2003 has not clarified if required relieving flow can be used for modulating type PSV.

2-cents opinion
Modulating type PSV is intended to work to modulate the flow passing the PSV. Those theoretically, on the required relieving flow should be passing the PSV. In taking conservative approach and in compliance with API recommendation, rated flow is recommended for modulating type PSV inlet line loss estimation.

Related Post

• Several Impact of Backpressure on Conventional PRV
• Useful Documents Related to Pressure Relief Valve (PRV) - Part 3
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• Discussion on ISENTROPIC and ISENTHALPIC process via Relief Valve
• Use of conventional type PSV with back pressure exceeded 10% set pressure

Plate heat exchanger - Remove some plates...will the pressure drop across the exchanger increase or decrease ?

Plate heat exchanger - Remove some plates...will the pressure drop across the exchanger increase or decrease ?

In a Plate heat exchangers, there are number of plates for the 'hot' fluid and given number of plates for the 'cold' fluid. The cold fluid flows through the cold layers in a parallel type arrangement, same for the hot fluid. The hot fluid layers are typically laid counter-current to the cold layers. By removing plates, you will effectively be reducing the free flow area. This will increase the velocity, which is proportional to the square root of the pressure drop, it is anticipated an increase in pressure drop.

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Generalised model to predict pressure drop and capacity of countercurrent gas/liquid packed column

How to calculate pressure drop and capacity of countercurrent gas/liquid packed column ?

J. Stichlmajr et al has published an article may answer above question :

<< Generalised model to predict pressure drop and capacity of countercurrent gas/liquid packed column >>, Gas Separation 8 Purification 1989 Vol 3 March

A generalized model has been developed for the prediction of pressure drop and flooding in packed columns in which gas and liquid flow countercurrently. The model has been validated for a wide variety of packings, both random and structured. A single mathematical expression is used to describe all flow regimes: dry gas, irrigated gas flow below the load point, loading region, and flooding. The approach to the model development is fundamental in character and is an improvement over models published.

The model can be used with

- Structured packing : Montz, Gempack, Sulzer

- Random packing (ceramic) : Raschig, Pall, Reflux, Hiflow, Berl Saddles, Intalox Saddles, Torus Saddles

- Random packing (metal) : Raschig, Pall, Bialecki, Nutter, Cascade Mini, Super Saddles

- Random packing (plastic) : Pall, NSW, Leva

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