Weights of Piping Materials

Weights to be used for design purposed only e.g. estimating loads on supports and platforms

Weights of flanges are based on the heaviest of Tube Turn; Taylor Forge; Ladish and VOGT.

Weights of valves are based on the heaviest of CRANE; PACIFIC; O.I.C; Chapaman; R.P. &Co. and VOGT

For weights of Pipe See ANSI B36.10 and DIN 2448

Weights of Piping material

Flow coefficient (Cv or Kv) value

Flow coefficient normally expressed as Cv or Kv depending on the countries. It is used to determine the appropriate sizing of the valve as well as evaluating the flow kinetic energy in regards with process and piping integrity

Cv is volume (in US gallons) of water at 60°F that will flow per minute through a valve with a pressure drop of 1 psi across the valve.

Kv is the same definition of flow passing through valve with in accordance with pressure drop. However flow is expressed in units of cubic meters per hour, and the pressure in bar

Some flow coefficient data taken from various On/off valve manufacturers’ sources are follow

Disclaimer: information below is indicative only since manufacturer reserve the right to amend it without notice

a. Butterfly valve (Triple offset)

Butterfly triple offset flow coefficient

b. Gate valve
Gate valve
c. Globe valve

Globe valve

d. Ball valve floating type for Reduce and Full bore

Ball valve (Reduce and Full Bore)

 

Sizing example

Process engineer requested to design a system to load 50% sodium hydroxide into a carbon steel tank in his plant. Sodium hydroxide is considered a hazardous material, hence not recommended to move 50% sodium hydroxide at velocities over 6 ft/sec in carbon steel piping. The supply pump at the plant can generate a flow of up to 250 gpm. The recommended maximum pressure drop across the valves in the system is 3 psi. Specific gravity of the sodium hydroxide solution is 1.52. Please specify a control valve for this service.

Step 1: Find Cv

Fmax  =250 GPM
Gt      =1.52
ΔP     =3 psi

Cv example

Cv value is 178

Step 2: Find literature of Cv value (at various opening of ball valve) versus Valve sizes.

Example below

Size (NPT) C@10% Valve Opening C@25%

VO

C@50%

VO

C@75%

VO

C@100%

VO

1″ 0,33 0,75 3 5 10
1-¼” 0,53 1,2 4,8 8 16
1-½” 0,83 1,88 7,5 12,5 25
2″ 1,33 3 12 20 40
2-½” 2,10 4,73 18,9 31,5 63
3″ 3,33 7,5 30 50 100
4″ 5,33 12 48 80 160
5″ 8,33 18,75 75 125 250
6″ 13,33 30 120 200 400

At 50% or more opening, in order to meet C178, then valve sizes should be 5″ or 6″ ball valve.

Step 3: Check piping minimum diameter.

What diameter pipe would correspond to a flow of 6 ft/sec?

A = πr² = π(d/2)²

v = 6 ft/sec

Fmax = 250 gpm = 0.557 ft³/sec

Since Fmax = Av = π(d/2)² · v

Then

calc diameter

A pipe with diameter larger than 4.1 inches shall not exceed the 6 ft/sec requirement.

Answer: Combination between step 3 and 2 is valve and piping size should be 5″ inch.

 

Seat leakage problem

Leakage problem

Its a condition where service medium passing through the supposedly sealing area exceeding its tolerable leakage criteria. This is caused by Seat(s)’ sealing area is not in full contact with obturator’s sealing area when the valve expected to be in close position.

One of predominant failure mode contribute to seat leakage is:

Scratches or indentations on seat(s) and or obturator

Simply caused by “hard” substance entrapped between Seat(s) and obturator being forced moved along valve movement either for both linear motion or quarter turn valve. Size of this damaging  substance varies from hair size to larger volume.

Sample of various scratches are but not limited to:

Method to assess and repair scratch failure mode:

STOP (See – Touch – Observe – Polish)

See; whenever possible see the valve while still installed. In order to predetermined scope either major or minor. Check whether miss-alignment or other abnormalities occurred. Even though not quite common, performing X-ray is recommended. How to perform good X-ray is simply by notifying wall thickness to the radiography operator

X-ray

Touch;

Roughly examine flow rate: Have you ever feel your own plumbing or hoses when your tap valve opened? The principal is the same, when there is passing flow it will induce vibration through the piping. Examination mostly on leakage rate (if its < 60 bubbles per min one may not feel the vibration) and also the sensitivity of the hand

Roughly examine temperature difference: If this subjected valve is process boundaries between relatively warm and relatively colder medium, then there is a good chance that one can feel the difference and determine whether its leaking or not. Obturator in most occasion due to its thickness is acting as a good insulator between warmer upstream medium and cooler downstream.

Please be cautious before touching any valve. Do check with operator of its temperature or start touching the valve from sensing its hand-wheel or spindle.

Surface roughness sensing upon valve dismantling is conducted; everybody already have the tool thumb. After obturator and seat being cleaned, rub the sealing surface area with your tip of the thumb.  If you feel the line, then it is considered as scratch and will contribute to (built up) leakage.

Observe;

Visually check the sealing contact evidence by mating the obturator against the Seat. This method usually called “check with blue marking”. Apply pigment blue marking on Seat and or obturator and then press both parts against each other for several seconds. Pull up one of the component (whichever is lighter), there will be line-like remarks remain as indication of sealing area. If the line is continuous it is indicating that the sealing area is perfect, however if there is any slight cut then it is indication of leakage path. Check below image and observe the white circle line

Polish;

Normally if scratches is so small up to 0,5 x 0,5 mm deep x width, it can be fixed by means of polishing or lapping. If it is deeper and or wider extra preparation usually required e.g. welding repair. Compound used is normally micron sized diamond compound and method used is 8 shape stroke polishing either by hand or by lapping machine.