Valves

PIPING ENGINEERING CELL

VALVES T. N. GOPINATH

INTRODUCTION Estimates reveal that a substantial portion, approximately 8-10%, of the total capital expenditure of the chemical process industry is used for the procurement of valves. In terms of the number of units also, valves exceed any other piping component. Hence, proper

thought should be given for the selection of valves. The first step in the selection is to determine exactly what function the valve is expected to perform after it has been installed. Valves are installed on equipment/piping to perform any one of the following functions;

Functions of Valves

Isolation

Regulation

The design of the valves are done in such a way as to perform any of the above functions. The type of valves used can be classified in the following categories.

Non-Return

Special Purpose

2.2

Needle Valves

2.3

Butterfly Valves

2.4

Diaphragm Valves

2.5

Piston Valves

1.0 ISOLATION

2.6

Pinch Valves

1.1

Gate Valves

1.2

Ball Valves

1.3

Plug Valves

1.4

Piston Valves

4.0 SPECIAL PURPOSE

1.5

Diaphragm Valves

4.1

Multi-port Valves

1.6

Butterfly Valves

4.2

Flush Bottom Valves

1.7

Pinch Valves

3.0 NON-RETURN 3.1

2.0 REGULATION 2.1

Globe Valves 4.6

Valves

Check Valves

4.3

Float Valves

4.4

Foot Valves

4.5

Line Blind Valves

Knife Gate Valves

PIPING ENGINEERING CELL The above classification is based on functions. The valves could also be classified based on the type of construction. Valve manufacturers offer endless varieties of constructions. Based on the operation, valves can be broadly classified as operated valves and selfoperated valves. Mainly the check valves are self-operated and all other types come under operated valves. The valves can further be classified based on the end connections. End connection means the arrangement of attachment of the valves to the equipment or to the piping. The types of end connections are:

4.0

Gun metal

5.0

Carbon Steel

6.0

Stainless Steel 7.0

Alloy Carbon Steel

8.0

Poly Propylene, UHMW-PE, UHMW-HDPE etc.

9.0

Special Alloys

10.0 Fluoro polymer/Elastomer lined metals Glass

1.0

Screwed ends

2.0

Socket weld ends

3.0

Flanged ends

4.0

Butt weld ends

5.0

Socketted ends

TERMS USED FOR VALVES SPECIFICATION 1. Pressure - Temperature Ratings Pressure - Temperature Rating is the maximum allowable sustained non-shock pressure at the corresponding tabulated temperature. These are listed in ANSI B 16.34 and ANSI B 16.5.

6.0

Wafer type ends

2. Class

7.0

Buttress ends

The valves could also be classified based on the materials of construction. There can be any number of combinations possible with the materials of construction. It is for the piping engineer to select the same in consultation with the process engineer to suit the process fluid. The environment in which the valves are installed is also to be considered for selection of materials of construction. However, the most commonly available materials are: 1.0

Cast Iron

2.0

Ductile Iron

3.0

Bronze

Valves

The valve is specified by the pressure rating of the body of the valves. The American standard specifies the following classes. 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9

Class Class Class Class Class Class Class Class Class

150# 300# 400# 600# 900# 1500# 2500# 800# 4500#

3. Trim The trim is comprised of Stem, Seat Surfaces, Back Seat Bushing and other small internal parts that normally contact the surface fluid. The table below indicates trim of common types of valves. API 600

PIPING ENGINEERING CELL specifies Trim numbers in table 3 of the standard. It specifies the types of material, which can be used for the

parts with its typical specification and grade.

Trim Parts on common Valves Gate

Globe

Swing Check

Lift Check

Stem Seat Ring Wedge Ring Bushing

Stem Seat Ring Disc nut Bushing

Seat Ring Disc holder Side plug Holder pin Disc nut pin

Disc guide Seat ring

4. Wetted Parts All parts, which come in contact with the service fluid, are called the wetted parts. 5. Wire Drawing This term is used to indicate the premature erosion of the valve seat caused by excessive velocity between seat and seat disc. An erosion pattern is left as if a wire had been drawn between the seat surfaces. Excessive velocity can occur when the valve is not closed tightly. A WOG (Water-Oil-Gas, relatively cool liquids) disc is the best defense against wiredrawing because its resiliency makes it easier to close tightly. Discs of harder material are to be closed carefully to prevent wire drawing. In LPG Service, the wire drawing effect causes a threat of anti-refrigeration. The ice formation on the wedge will obstruct movement thereby increasing the leak through seat further. 6. Straight - Through Flow This refers to the valve in which the closing element is retracted entirely so that there is no restriction of flow.

Valves

7. Quarter - Turn Valves This refers to the valve where the entire operation of valve is achieved by 90 degrees turn of the closing element. 8. Pressure Drop Pressure drop is the loss of pressure through resistance across the valve while flows and is expressed in terms of equivalent length in pipe diameters. Type of Valve

Position

Gate

Fully open “ “ “ “

Globe Angle globe Swing check Plug – Rectangular Plug Port Ball – Regular port Ball – Full port

Equivalent length in pipe dia (L/D) 13 340 145 50 18

“

40

“

8

9. Upstream Pressure This is the pressure of the fluid that enters the valve. This is sometimes referred to as inlet or supply pressure.

PIPING ENGINEERING CELL 10. Downstream Pressure This is the pressure of the fluid that is discharged from the valve. This is sometimes referred to as outlet or reduced pressure. 11. LDAR Signifies “Leak Detection And Repair” to ensure that the fugitive emissions standards of EPA are met. Fugitive emissions are the minute amount of process media that escape into the atmosphere though gland packing along valve stem. 12. LAER Signifies “Lowest Achievable Emission Rate”. It is the minimum rate of fugitive emission, which is achieved by deploying proper sealing arrangement.

13. LEAKAGE CLASS Leakage class

Maximum seat leakage

Class I

A modification of any class II, III or IV valve where design intent is the same as the basic class, but by agreement between user and supplier. No test is required. 0.5% of rated valve capacity 0.1% of rated valve capacity

Class II Class III Class IV

0.01% of rated valve capacity

Class V

5 x 104 ml per minute water per inch of orifice diameter per psi differential

Class VI

as per below

Valves

table

Size, NB

ml. per min.

Bubble per minute

1 1.5 2 2.5 3 4 6 8

0.15 0.30 0.45 0.60 0.90 1.70 4.00 6.35

1 2 3 4 6 11 27 45

Valves

f

f

f

350

f

350 c c c f 350 c f 350 e c

f

350 f 300

300

300 f 750

T r im 5 o r 5 A

a H B is B r in e ll h a r d n e s s n u m b e r s y m b o l p e r A S T M E 1 0 ( fo rm e r ly B H N ) b B o d y a n d g a te s e a ts 2 5 0 H B m in im u m , w ith 5 0 H B m in im u m d iffe re n tia l b e tw e e n b o d y a n d g a te s e a ts . c M a n u fa c tu r e 's s ta n d a r d s h a r d n e s s d D iffe r e n tia l h a r d n e s s b e tw e e n b o d y a n d g a te s e a t s u r fa c e s n o t r e q u ir e d . e c a s e h a r d e n e d b y n itrid in g to th ic k n e s s o f 0 .0 0 5 - in c h ( 0 .1 3 m illim e te r s ) m in im u m .

13 14

12

9 10 11

8A

8

7

d

d

350 d 350 f 250 f 175

750

b c c

F6 304 F 310 H a rd F 6 H a rd fa c e d H a rd fa c e d F6 and C u -N i F6 and H a rd F 6 F6 and H a rd fa c e d F6 and H a rd fa c e d M onel 316 M onel H a rd fa c e d 316 and H a rd fa c e d A llo y 2 0 A llo y 2 0 and H a rd fa c e d

1 2 3 4 5 5A 6

13 C r 1 8 - 8 C r- N i 2 5 - 2 0 C r- N i H a rd 1 3 C r h C o C r- A l N i- C r 13 C r C u -N i 13 C r H a rd 1 3 C r 13 C r h C o C r- A l 13 C r N i- C r N i- C u a llo y 1 8 - 8 C r- N i N i- C u a llo y T r im 5 o r 5 A 1 8 - 8 C r- N i T r im 5 o r 5 A 1 9 - 2 9 C r- N i 1 9 - 2 9 C r- N i

M a te r ia l ( H B , m in im u m ) T y p e

a

T r im N o.

S eat h a rd n e s s

f g h i

S e e T rim 5 o r 5 A

- - -- A W S A 5 .9 E R 3 1 6 ----S e e T rim 5 o r 5 A A W S A 5 .9 E R 3 1 6 S e e T rim 5 o r 5 A A W S A 5 .9 E R 3 2 0 A W S A 5 .9 E R 3 2 0

H a r d n e s s d iffe r e n tia l b e tw e e n b o d y g a te s e a ts s h a ll b e a s p e r th e m a n u fa c tu r e r's s ta n d a r d . M a n u fa c tu r e r 's s ta n d a r d , w ith in 3 0 N i m in im u m T h is c la s s ific a tio n in c lu d e s s u c h tr a d e m a r k e d m a te r ia ls s u c h a s s te llite 6 , S to o d y 6 , a n d W a lle x 6 . M a n u fa c tu re r 's s ta n d a r d h a r d fa c in g , w ith 2 5 p e r c e n t F e m a x im u m .

A S T M A 3 5 1 (C N 7 M ) A S T M A 3 5 1 (C N 7 M ) -----

---A S T M A 3 5 1 (C F 8 M ) --------A S T M A 3 5 1 (C F 8 M )

A S T M A 2 1 7 (C A 1 5 )

E R 410

E R 410

E R C o C r- A

E R 410 E R 308 E R 310

A W S A 5 .9 E R 4 1 0 A W S A 5 .1 3 E R C o C r- A A W S A 5 .9 E R 4 1 0

A W S A 5 .9

A S T M A 2 1 7 (C A 1 5 ) A S T M A 2 1 7 (C A 1 5 )

A W S A 5 .9

A W S A 5 .1 3

A W S A 5 .9 A W S A 5 .9 A W S A 5 .9

W e ld e d

A S T M A 2 1 7 (C A 1 5 )

A S T M A 2 1 7 (C A 1 5 ) A S T M A 3 5 1 (C F 8 )

C ast

T a b le 3 - N o m in a l S e a tin g S u rfa c e M a te ria ls

N o m in a l T r im

T R IM :

PIPING ENGINEERING CELL

PIPING ENGINEERING CELL

RECOMMENDATION FOR VALVES CHEMICAL/BULK DRUG PLANT

Valves

PIPING ENGINEERING CELL 3.

4.

Condensate

Utilities like Water, Air, LSHS

½” – 1 ½”

2” – 12” ½” – 1 ½”

2” – 12”

a)

C.S. Body SS a) C.S. Body ball PTFE 13% Cr. seat 800# SW Trim 800# Ball SW Globe valve b) C.S. Body 13% Cr. Trim 800# SW Globe SAME AS LP STEAM a) C.S. Body SS a) C.S. Body a) Ball PTFE 13% Cr. Seat 800# Trim 800# Scrd. Ball SW Globe b) G.M. Body b) G.M. Body Bronze trim Bronze Scrd Gate to Trim Scrd IS 778 b) Globe to IS 778

a)

b)

CI Body 13% Cr disc 125# wafer type Butterfly Gear Operator above 6” NB CI Body 13% Cr or 18% Cr trim 125# Flgd Gate to IS 14846

5)

Hot Oil / Heating

Valves

½” – 1 ½”

a) CI Body 13% Cr disc 125# wafer type Butterfly Gear Operator above 6” NB

a)

b) CI Body 13% or 18% Cr trim 125# Flgd Globe

b) CI Body 13% or 18% Cr tri 125# flgd swing check to IS 5312

CS Body 13% Cr trim 150# Flgd Gate d) Cast Iron Body 13% Cr plug 125 # Fldg Lub. Plug Valve

c) CS Body 13% Cr trim 150# flgd Globe

a)

a)

c)

C.S. Body

C.S. Body 13% Cr. Trim 800# Lift check With SW Ends G.M. Body Bronze Trim Scrd check to IS 778 CS Body 13% Cr. trim water type check

-------

CS. Body

c) CS Body 13 % Cr trim 150# flgd swing check

-------

a)

C.S.

Bronze body not Recommen ded in acidic atmosphere

Recommen dation for Air CS Body Ball or Gate for Isolation

PIPING ENGINEERING CELL Fluid

2” – 12”

Stellited trim Graphoil pkg 800# SW Globe b) C.S. Body 13% trim 800# SW Piston with suitable sealing rings

Stellited trim Graphoil pkg 800# SW Globe b) CS. Body 13% trim 800# SW Piston with suitable sealing rings

a)

a) CS Body stellited trim graphoil pkg 300# (Min) Flgd Gate with 125 – 250 AARH Flgd finish

CS Body stellited trim Graphoil pkg 300# (Min) Flgd Gate with 125 – 250 AARH Flgd Finish

b) CS Body 13% Cr trim Graphoil pkg 300 # (Min) Flgd Piston with Suitable sealing ring and 125 – 250 AARH Flgd finish

b) CS Body 13% Cr trim Graphoil pkg 300 # (Min) Flgd Piston with Suitable sealing ring and 125 – 250 AARH Flgd finish Globe Valve with CS Body Monel / Hastalloy C trim a) C.S. Body 13% Cr. trim 150# Flgd Globe

6)

Chlorine (Dry)

½” – 12”

Ball valve with CS body Monel/ Hastalloy C ball & stem

7)

Solvent/ Process (Carbon Steel)

½” – 12”

a)

Solvent/ Process

½” – 12”

a)

Valves

C.S. Body SS Ball 150 Flgd full port Ball valve with PTFE/ GFT seats b) CS Body 13% Cr plug 150# Flgd sleeved plug seats

SS Body SS

a) SS body SS

Body stellited trim 800# SW lift check

CS Body stellited trim 300# (Min) Flgd swing check with 125 – 250 AARH Flgd Finish

Check (Lift / Swing ) valve CS Monel / Hastalloy C trim a) C.S. Body 13% Cr. trim Flgd Lift check ½” to 1 ½” and Flgd swing check 2” & above

SS Body SS

PIPING ENGINEERING CELL (Stainless Steel)

Solvent/ Process (Highly Corrosive)

Valves

½” – 12”

ball 150 # Fldg full port ball valve with PTFE / GFT seats b) SS Body SS Plug 150# Flgd sleeved plug a) Ductile Iron body & plug lined with fluoropoymer plug valve b) Ball valve with suitable plastic body and ball

trim 150# Flgd Globe

trim 150# Flgd swing check

a)

____

Ductile Iron body lined with fluoro polymer ball check valve b) ---do---

Suitability with Temperature to be checked

PIPING ENGINEERING CELL 1.0 ISOLATION VALVES The isolation valves used in the Process Industry are: 1.1 Gate Valves 1.2

Ball Valves

1.3

Plug Valves

1.4

Piston Valves

1.5

Diaphragm Valves

1.6

Butterfly Valves 1.7

1 7 1 6 1 2 1 1

Pinch Valves

Of these, the Butterfly, Diaphragm and Piston Valves can be used for regulating the flow as well. Similarly, the Globe Valve design could be modified to use it for positive shut-off purposes. The present trend in industry is to go for quarter turn valves for this duty due to ease of operation. The types of valves in this category are the Ball valves, Plug valves and Butterfly valves. Ball and Plug valves are also can be used for flow control with shaped port of the closing element. More over the design of quarter turn valves are inherently better suited for emission control applications. The linear stem movement of the gate and globe valve tends to open the path of emissions release and in its dynamic mode, emissions can be “dragged” along the stem.

1.1.4 1.1.5

Stem Gland

1.1.6

Seat ring

1.1.7

Yoke

1.1.8

Packing

1.1.9

Gland Flange

1.1.10

Valve Port

1.1.11

Yoke Bush

1.1.12

Lantern

1.1.13

Back Seat Bushing

1.1. GATE VALVES

1.1.14

Gland eyebolts & nuts

A typical Gate valve will have the following parts, which could be identified. 1.1.1 Body

1.1.15

Bonnet bolts & nuts

1.1.2 1.1.3

Valves

1.1.16

Hand Wheel

1.1.17

Hand Wheel nut

1.1.18

Bonnet Gasket

Bonnet Wedge

PIPING ENGINEERING CELL 1.1.1 Body The body is the part which gets attached to the vessel or piping. The classification of the body could be done depending on the end connections as indicated earlier. Body could also be specified based on the material of construction of the same. This could be cast, forged or fabricated. The wall thickness and end to end/face to face dimensions of the body shall be as per the Regulatory code to which it is designed. The end flanges shall be integrally cast or forged with the body. It can also be attached by welding, if so specified. The end connection shall suit the rating specified. The flanged connection shall be to ANSI B 16.5 or any of the flange standards. The buttwelding end connection shall be to ANSI B 16.25 or any other end preparation required. The socket weld/screw connection shall be to ANSI B 16.11 or any other equivalent standards. The body can have auxiliary connection such as drains, by-pass connections, etc. 1.1.2 Bonnet The bonnet is classified based on the attachment of the same to the body. The type of connection normally adopted are Bolted, Bellow sealed, Screwed-on, Welded, Union, Pressure sealed etc. The bolted connection shall be flanged, male and female, tongue and groove or ring type joint. In low pressure rating valves, it may be flat faced. The bonnet gasket is selected to suit bodybonnet connection. It can be corrugated flat solid metal, flat metal jacketed, asbestos filled, metal ring joint, spiral wound asbestos filled or flat ring compressed asbestos in case of low pressure rating, Teflon or Teflon filled for corrosive applications. The bellow sealed bonnets can be bolted or welded on to the body. These are selected for very critical

Valves

services like the nuclear, very high temperature and lethal services. The screwed-on bonnet/union bonnet is used for very low priority application and small size valves. When valves are used for Cryogenic Service extended bonnet design is used to take care of large insulation thickness. When used for very high temperature bonnet attached with fins are also used. 1.1.3 Wedge This is the part, which facilitates the service by its movement up and down. The types of wedges are classified as; • Solid Plain Wedge •

Solid Flexible Wedge

•

Split Wedge

When solid disc is wedged into the rigid body seat and the valve undergoes temperature changes, the wedge gets jammed in the seat. Hence the flexible wedge and split wedge design is developed to overcome this difficulty. Normally the solid plain wedge is referred as solid wedge and the split wedge is referred as flexible wedge. The design slightly alters with the manufacturers though the basis remains the same. The flexible wedge design is followed for valve sizes 50 NB and above. Valves 40 NB and below are available in solid wedge design only. Flexible wedge design is superior as it will not get jammed during high temperature operations. The wedge material should be at least of the same quality as that of the body. In case of integral seat rings the wedge circumference is deposited with superior quality material. In smaller valves, the whole wedge will be manufactured out of superior material.

PIPING ENGINEERING CELL

1.1.4 Stem The stem connects the hand wheel and the wedge for operations. The design can have rising stem and nonrising stem. The stem is operated rotating the stem nut by hand wheel mounted at the top of the yoke. In the rising stem design, the stem moves up along with the wedge to open. This is called the OS & Y (Outside Screw and Yoke) type of design. In case of non-rising stem the wedge moves up and down and the stem is stationary. This is called the inside screw non rising stem design. Normally, bar stock or forging are used for the construction of stem. 1.1.5 Gland, Gland flange, Packing and Lantern There are two types of gland designs possible, Single piece and Two piece. In two-piece design, there will be gland flange and a follower. The follower will have a spherical end, which facilitates proper aligning of follower and loading on the packing. In Single piece, the gland and follower will be integral. This design is used mostly in low-pressure valves. Normally gland follower will be of superior material than the gland flange. Gland flanges are made of carbon steel only. The glands are bolted to the bonnet with gland eyebolts in lowpressure valves. The regulatory codes specify that the stuffing box should accommodate minimum six packing rings for class 150 valves. As regards higher rating valves, it should have lantern ring with five packing rings above and two packing rings below lantern. Lantern is not provided for class 150 valves. Lantern is provided for higher rating if required. When lantern is provided, the stuffing box shall be provided with two plugged holes. The

Valves

material of lantern shall have corrosion resistance equal to that of the body. Normally, the packing is of braided asbestos with suitable corrosion inhibitor. When special packing such as 'Graphoil' is used, the number of packing rings required will be more. To accommodate more packing rings, the length of gland is also modified. This design is called the 'Deep Gland' design. This is used for the high temperature services. But this cannot satisfy the EPA’s fugitive emission standard of