Antisurge Control Valves Description

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Nuovo Pignone

Nuovo Pignone ANTI-SURGE CONTROL VALVES

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Nuovo Pignone INDEX

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INTRODUCTION . . . REQUIRED CHARACTERISTICS . NUOVO PIGNONE ANTISURGE VALVE BODY . . . . . BONNET . . . . BOLTS. . . . . BONNET-BODY SEAL . . BALANCING . . . . TRIM . . . . . ACTUATORS . . . . STEM PACKING . . . CONTROL DYNAMICS. . . ACCESSORIES . . . QUALITY ASSURANCE . . 14.1 Acceptance control and Functional 14.1.1 Dimensional check . 14.1.2 Pneumatic actuator test 14.1.3 Valve functional test . 14.1.4 Plug-seat leackage test 14.1.5 Stem packings leakage test 14.1.6 Test of accessories . 14.2 Valve identification . . 14.3 Final certification . .

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INTRODUCTION

Any gas centrifugal compressor has a by-pass circuit for anti-surge and recirculation. It has the task to keep the whole compressor in a stable operating zone, ensuring, whichever will be compression ratio, a flow greater than that corresponding to surge limit. In this circuit it is installed a control valve of a primary importance, whose principal purpose is to avoid serious damages to compression machine. 2

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When the forces, necessary to close the valve are too high and double effect pneumatic actuators with counter-spring cannot be used, it is preferable to use valves with external balancing. This happens frequently for rating ANSI 900÷2500. When required rating is larger than ANSI 2500, forged body Z valves are preferred.

REQUIRED CHARACTERISTICS

Basic requirement of anti surge control valves are: • Flow capacity properly calculated for the effective operating conditions. A flow capacity margin of  10-20% is usually employed for valve Cv selection. • A very high Rangeability (150:1), in order to allow a smooth control of the flow, even when high pressure drops and low flows are present. • Gas speed limitation in the outlet of the valve (0.3 Mach), controlling the sound pressure level and the vibrations to acceptable values (typically 85dB(A)). • Fast opening times (0.5 - 2 seconds). Closing times (10÷20 seconds) depending on valve size. • High reliability even in heavy service conditions, expansion ratio larger than 10 (ratio between downstream and upstream pressure) with inlet pressure varying between 50 and 700 bar. 3

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BODY

Bodies and flanges for ratings less than calss 2500 are generally casted and designed according to ANSI B16.34 and ANSI B16.5. In some cases, Finite Element Method has been used to verify the stress levels with allowable stress criteria defined by ASME VIII Div. 2. Fig. 5 shows the equivalent stress obtained by FEM for a 16” ANSI 600 cast valve body. For ratings greater than ANSI 2500, bodies are forged and dimensioned according to ANSI B 16.34 or ASME sect VIII, flanges are in conformity with API 6A code. Weldings connecting the flanges to the body are controlled by RT examination (acceptability criteria according to ANSI B16.34 appendix B). Casted bodies ANSI 900-1500-2500 are controlled in critical zones by RT controls, forged bodies are controlled by standard ultrasonic waves. Different controls are performed upon request. All bodies are hydro tested with a pressure 1.5 times the rating pressure at 20°C. Standard body materials are: • ASTM A 216 Grade WCB (when non corrosive fluids are used; temperature varying from –20°C up to 420°C) • ASTM A 352 Grade LCB (when non corrosive fluids are used; temperature varying from –45°C up to 300°C; according to NACE MR0175) • ASTM A 352 Grade LC1 (when non corrosive fluids are used; temperature varying from –100°C up to 300°C; according to NACE MR0175) • ASTM A 890 Grade 5a (when corrosive fluids are used; temperature varying from –50°C up to 420°C; according to NACE MR0175 and OFFSHORE) • ASTM A 351 Grade CF8M (when corrosive fluids are used; temperature varying from –200°C up to 590°C; according to NACE MR0175 and OFFSHORE)

STANDARDS

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In line valves with external balancing: type 1000/BDE (fig.2). Standard sizes: 1”÷12” rating ANSI 2500. Forged body Z configuration valves with external balancing: type BDE/Z (fig.3). Standard sizes: 2” 9  / 16 , 3” 1 / 16 , 4” 1 / 16 , 5” 1 / 8 7” 1 / 16 rating API6A 10000-15000. Angle valves: type 1400 (fig.4).

Nuovo Pignone Valves are designed and produced according to ANSI B16.34 and ASME VIII standards. Since 2001 Nuovo Pignone valves are PED and ATEX certified. Nuovo Pignone valves are also certified by ISO 15-848-1 and ISO 15-848-2 fugitive emission standard with various endurance and temperature levels. Tightness class B is available with high pressures valves. Positive experiences on severe sour service (up to 17% H2S) have been carried out. High pressure valves are fully in accordance with to API 6A.

NUOVO PIGNONE ANTISURGE VALVE

Since 1968 Nuovo Pignone has been producing this type of valves. Experience, collected in all these years, has allowed us to follow constantly up the technological development of this service, by optimising all the technical aspect that are able to fully satisfy all the requirements. In particular the entire production is divided in the following valve lines: • In line valves: type UNIVERSALVALVE (fig.1). Standard sizes: 1”÷24” rating ANSI 150÷1500.

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BONNET

All bonnets are:

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Nuovo Pignone Internal Balancing (Fig. 6) is obtained by means of a

forged hydro tested at a pressure of 1.5 times the Rating pressure at 20°C • final ultrasonic test different types of controls may be performed upon request. Standard bonnet materials are: • ASTM A 105 (when non corrosive fluids are used; temperature varying from –20°C up to 420°C) • ASTM A 350 Grade LF2 (when non corrosive fluids are used; temperature varying from –45°C up to 300°C; according to NACE MR0175) • ASTM A 350 Grade LF3 (when non corrosive fluids are used; temperature varying from –100°C up to 300°C; according to NACE MR0175) • ASTM A 182 Grade F5a (when corrosive fluids are used; temperature varying from –50°C up to 420°C; according to NACE MR0175 and OFFSHORE) • ASTM A 182 Grade F316 (when corrosive fluids are used; temperature varying from –200°C up to 590°C; according to NACE MR0175 and OFFSHORE) • •

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plug with holes and a seal between plug ant cage guide This seal is usualli made by Garlock type rings (PTFE support plus O-ring). This system, installed on valves type UNIVERSALVALVE (Fig. 1), does not perform a perfect balancing, because the stem remains still unbalanced. O-ring material is normally Viton GF, for low temperatures (less than 20°C) Silicon is used instead. External balancing (Fig. 7) is obtained by means of a Stem-Plug, having the same diameter in the upper and lower part. In this way, a perfect balancing can be obtained on the moving parts. This system is necessary when the force necessary to close the valve is very high and double effect actuators cannot be used (Fig. 2). External balancing is used also for valve ratings higher than ANSI 2500 (Fig. 3). because this allows to have a better guide for the moving parts. Material for StemPlug is, normally, 17-4PH coated by Chrome Carbide Layer obtained by “Detonation Jet” Technique (thickness 0.2 mm; hardness 1000 HV). Guiding bushings are in Teflon – Graphite enriched of DU type. 10

Two trim configurations can be selected: • Multi-hole cage trim • VECO trim Multi-hole cage trim (Fig. 8) is composed by a cylinder fixed between the body and the bonnet. On its external surface drilled holes are properly distributed in such a way that the desired valve characteristic is obtained. VECO trim (Fig. 9) is composed by a number of  drilled and co-axial cylinders. Holes distribution is linked to the type of desired regulation characteristic. By moving from internal to the external of these cylinder, the dimension of the holes diameter increase, but the number of such holes remains constant. This is to limit the speed of the fluid during the expansion, thus reducing the noise. In fact, by leaving the same dimensions of the valve and the same operating conditions, a VECO trim produces a noise which is about 25dB(A) less than that produced by the same valve with a simple multi-hole cage. The number of  cylinders to be used depends on the pressures ratio across the valve. In Figure 13 it is reported the noise reduction as a function of the relative pressure drop with different number of cylinders. Standard trim materials are: • Plug: 17–4 PH H900 (40 HRC) • Cage 17–4 PH H1150 (30 HRC) • Stem : 17–4 PH H900 (40 HRC) • Cylinders: 17–4 PH H1150 (30 HRC ) The trim is a quick change type and the sealing between cage and body is obtained by means of  GARLOCK™ rings with Teflon support and Viton or Silicon O-Ring depending by the temperature.

BOLTS

Bolts connecting bonnet and body are sized according to ASME VIII Div.1. Standard materials are: • ASTM A 193 Gr. B7 (for all carbon steel bodies; temperature varying from –20°C to 420°C) • ASTM A 320 Gr. L7 (for all carbon steel bodies; temperature varying from –100°C to 300°C) • ASTM A 320 Gr. B8 (for all stainless steels and Duplex steel bodies; temperature varying from – 200°C to 590°C) 8

BONNET-BODY SEALING

Sealing between Bonnet and Body is obtained by means of the following gaskets: TYPE MATERIAL USE Planar and Inox 304 type + rectangular Laminar ANSI 150÷600 section Graphite Planar and Inox 304 type rectangular ANSI 900÷2500 soft annealed section Inox 304 type ANSI 2500 and Ring Joint soft annealed API 10000 Table 1 9

TRIM

BALANCING

In order to reduce the force necessary to operate the valve, a pressure balancing of the moving parts is frquently necessary. It can be obtained by means of: • Internal balancing • External balancing

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Moving parts guide is obtained by means of Teflon bushings Graphite enriched of type “DU”. Fig. 14 shows the characteristic properly designed for anti-surge service that allows to obtain a Rangeability of 150:1. Both IV or V ANSI B 16-104 seat tightness class can be obtained. 11

At high pressures (ratings greater than 2500) a special packing made of a set of alternated density V-rings is employed. In this case the initial energizing load is given by means of sets of Belleville springs. For the applications where low fugitive emissions are required a special packing, qualified by TÜV according to TALUFT standard (see attachment 1), is used. This packing is made of one or two sets of V-rings, the load is guaranteed by sets of Belleville springs and in the gland two O-rings with PTFE sliding supports are inserted.

ACTUATORS

Actuators for anti-surge valves have the following characteristics: • Pneumatic actuators • Simple or double effect actuators • On air failure open • Actuators without manual override In Table 5 max stroke, standard spring ranges, force rate, and max air supply pressure are reported for all available single effect pneumatic actuators.

12.2

Graphoil packing is used when the temperature of the fluid is greater than 230°C. It is made of two sets of  packing rings of rectangular section. Each packing is made of one upper ring and one lower ring that operate as containers and have a grater density than that of the central rings. These central rings provide the sealing action. In case of double packing ring set Belleville springs provide the initial energizing load.

Figure 12 shows a diaphragm pneumatic actuator with

a simple effect, direct acting (on air failure open) with manual override. The yoke is casted and the standard materials are the following: • ASTM A 216 Gr. WCB • ASTM A 352 Gr. LCB • ASTM A 352 Gr. LC1 Shell material is FE430B UNI7070, the stem material is stainless steel type 304. Membranes are made of  Neoprene + Rayon, Dutral, or Silicon rubber, depending on the operating temperature. Bolts and nuts can be galvanized carbon steel or stainless steel. Figure 13 shows a simple effect pneumatic piston type actuator with rolling membrane, direct action (on air failure opens) with manual override. Materials are the same of those for the diaphragm actuator except for the material of the shells that is cast Aluminium. Figure 14 shows a double effect pneumatic actuator with direct action. Sometimes, in order to operate the pneumatic actuator, process gas is used and an additional pressure reducing regulator if fitted to the valve. 12

12.3

Fugitive emission packing

Fugitive emission compliant packings are available in our production. Actually, Nuovo Pignone Valves are able to control emissions for sour services up to 17% of  H2S and 500 bar of operating pressure contemporarily. According to the level of emission required and to the operating conditions requested, different solutions may be provided; it is also possible to control the status of  packing and during valve operation. This design is patented and successfully applied since 2001. 13

Control dynamics

In the past, Anti surge valves were requested to open in emergency, with a time of 2 seconds or less, in order to guarantee the safety of the machine in case the system was getting closer to the surge line of the operating map. This represented for the process a cause of  continuous emergency stops and a loss of productivity. Nowadays, antisurge valves have been called to be a part of compressor system. During normal activity, this component shall ensure a stable operation of the machine on every occurrence, without any possible loss of time. On this purpose, the response of the valve shall be validated by dynamic test during production and setting phase. In order to do this, a variety of  checks have been implemented into Nuovo Pignone production system, in order to obtain an effective set of  valve parameters. Calibration of valve response, lead to

Stem Packing

Sealing between stem and bonnet is guaranteed by the following packing systems: • Teflon packing: Single or Double • Graphoil packing: Single or Double • High pressure packing • Low emission packing 12.1

Graphoil packing

Teflon Packing

Teflon packing is done by one or two sets of “V-ring” packings and by a spring. Sealing is guaranteed by rings deformation due to fluid pressure. At low pressure the spring provides to the packing the deformation needed to avoid leakage.

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minimization of overshoots during steps

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reduction of stroke time during normal control

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increase of response to wavy signals.

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Nuovo Pignone

Paragraph 15.1.6 reports the checks described above.

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15.1.5

A check is performed on al accessories included in specifications, in order to verify whether or not they comply with the same specifications in addition to the correct assembling and wiring. a) Positioners: when supplied by Nuovo Pignone, the OEM performs all the QA test and certification. Positioners sent by the final customer to Nuovo Pignone are directly mounted on the valve for the final global functional test. b) Handwheel: The correct functioning of the handwheel is verified by performing at least two complete opening and closing stroke. c) Limit Switches: The correct positioning of limit switches is checked. The position at which end stroke is detected is included in the 10% of the total valve stroke.

ACCESSORIES

Protection class of the accessories normally mounted on the valves are shown in table 5. 15

QUALITY ASSURANCE

15.1

Final and functional tests

All valves according to their type, dimension and specific features are subjected to the following checks and tests. 15.1.1

Dimensional and Visual check

According the applicable technical specifications (gauge facing, feed, actuator type, etc…) 15.1.2

15.1.6

Valve functional test

Valves, with their actuators assembled and complete with all accessories, are subjected to testing. This test consists in verifying full stroke opening and closing time, hysteresis, linearity, and dead band of the valve in response to the input signal. The values and tolerance permitted for these tests, depend on the valve type, the valve constructive design and characteristics. The allowable positioning errors for valves with pneumatic positioners and PTFE packing, are reported table 2. Hysteresis 1.5% Linearity 1.5% Dead band 0.5% Table 2

For valves having graphoil packing and/or having internally or externally balanced trim, the allowable values, at ambient temperature, may exceed those listed in table 3 by no more than 40%. 15.1.4

Dynamic tests

Full opening by automatic control in response to the control signal step from 20 to 4mA. Partial opening to 80% by automatic control in response to the control signal step from 20 to 4mA. Closure by automatic control in response to the control signal step from 4 to 20mA. Opening dead time. Max. stroke overshoot in response to signal step of  25% in opening and closing directions. Valve movement in response to the control signal continuous changing from 4 to 20 and 20 to 4mA. Full stroke time = 5 minutes. Max. control signal changing in order to move the valve in opening and closing direction, starting at 10%, 50% and 90% of stroke. Max. control signal changing in order to initiate to open/close the valve. The frequency response (gain/phase Bode diagram) of the assembly composed by the positioner, the actuator and the valve position transmitter, for 10% amplitude signal at 50% of valve stroke. - Gain versus frequency (max freq. = 2Hz) - Gain at phi = -120°

Pneumatic actuator functional test

The test consists in pressurising the cylinder with air at 1.2 times the maximum normal supply pressure and verifying the absence of leakage with soap water for at least one minute. A pressure drop non exceeding 0.6 psig during the testing time is allowed. 15.1.3

Test of accessories

- Gain at phi = -180° Full opening by through solenoid valve deenergizing.

Plug – seat leakage test

The test consists in pressurising the upstream side of  the closed valve by air, for class IV and VI, or by water for class V according to ANSI B16.104. In the following table the correlation between the type of seat and leakage class is reported: Standard metal – seat Class IV Improved metal – seat Class V Seat with resilient insert Class VI

15.2

Valve identification

All the valves are supplied with a metal identification plate fastened to the yoke and containing the following data: a) Nuovo Pignone – Bari – Italy b) Supply c) Type d) Serial Number e) Body size

Table 3

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f) g) h) i)  j) k)

Seat size Rating and type of connections Body material Trim material Plug symbol (form and set number) Plug type (equal percentage, linear, ON-OFF, Anti-surge). l) Range of pneumatic or electric control signal. m) Air supply pressure n) Actuator type (air to open, air to close) o) Valve tag number Plate and index indicating valve stem position are also standard. 15.3

Final standard certification supplied by Nuovo  Pignone

Nuovo Pignone issues a copy of the chemical analysis and mechanical tests concerning body and bonnet. A final test certificate, with all the measured data relevant to each valve is also issued. This certificate is considered as a conformity declaration for the materials of the other pressure parts. In Attachment 2 a typical “Quality control plan” for anti surge valves is reported.

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Fig.1 In line valve UNIVERSALVALVE

Fig.2 In line valve with external balancing 1000/DBE

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Fig.3 Z valve with external balancing 1000/DBE/Z

Fig.4 Angle valve type 1400

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Fig 5 Finite element structural calculation of a 16” ANSI 600 cast body.

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Fig.6 Internal plug pressure balancing

Fig.7 External plug and stem pressure balancing

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Fig. 8 Single stage multi-hole cage trim

Fig.9 Multi stage VECO trim 12

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Cage+4 Cylinders Cage+3 Cylinders Cage+2 Cylinders Cage+1 Cylinder

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   ]    )    A    (    B20    d    [   n   o    i    t 15   c   u    d   e   r    l 10   e   v   e    l   e 5   s    i   o    N

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

X = (P1 - P2) / P1

Fig. 10

ANTISURGE VALVE FLOW CHARACTERISTIC 100

90

80

70

60

   %    V 50    C 40

30

20

10

0 0

10

20

30

40

50

Stroke %

Fig. 11

13

60

70

80

90

100

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Fig.12 Diaphragm pneumatic actuator with hand wheel

Fig.13 Pneumatic Piston actuator with hand wheel

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ACT. TYPE

MAX STROKE

SPRING RANGE

(mm)

Diaph. 11

25

Diaph. 13

40

Diaph. 18

60

Diaph. 18L

80

Diaph. 24

100

Piston φ 450 Piston φ 550

170

FORCE RATE N/kPa (kgf/psig)

(psig) 3÷15 6÷30 15÷30 3÷15 6÷30 15÷30 3÷15 6÷30 15÷30 3÷15 6÷30 15÷30 3÷15 6÷30 15÷30

220

MAX AIR SUPPLY PRESSURE (psig)

47 (33)

40

67 (47)

40

131 (92)

40

131 (92)

40

188 (132)

40

159 (112) 238 (167)

100 100

Table 4 Single effect actuators TYPE • Pneumatic positioner

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Electro-pneumatic positioner and smart positioner

SPEC.

----------------Cenelec NEMA 7-9; NEMA 7-9;

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Solenoid valves

Limit switches mechanical lever type

Proximity Limit switches magnetical type

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PROTECTION

IP 54; IP 65 Exd II CT6 – IP54 Exd II CT6 – IP65 Ex ia II CT6 – IP67 cl.I ; Div.I ;Gr. B-C-D; IP54 cl.I ; Div.I ;Gr. B-C-D; IP65 cl.I ; Div.I, II, III ;Gr. A-G ; IP54 cl.I ; Div.I, II,III ;Gr. A-G; IP65

NEMA 3-7-9;

Exd II CT5 – IP65 Exia II CT5 – IP65 EEx lm II T5 - T6 – IP67 cl.I ; Div.I - II; Gr. B-C-D;

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Exd II CT6 – IP67

NEMA 7-9;

cl.I ; Gr. B-C-D; cl.II ;Gr. E-G;

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Exd II CT6 – IP67

NEMA 7-9;

cl.I ; Gr. B-C-D; cl.II ; Gr. E-G;

Table 5

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Fig. 14 Double effect piston actuator

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Fig.15

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