esd valves

Download ESD Valves

Post on 07-Nov-2014

151 views

Category:

Documents

5 download

Embed Size (px)

DESCRIPTION

VALVE

TRANSCRIPT

ESD VALVE SELECTION GUIDE GENERAL ESD VALVE DEFINITIONESD/ESV valves are the nal defence against process misreactions. These valves have a function which requires much more reliable performance than standard remotely operated on-off valves. Still today ESD valves are ranked often as ordinary shut-off valves in specications. Valves as such may still remain the same but being a part of Safety Instrumented Function (SIF) the performance expectations are much higher. There must be a prove for a reliable long term performance. MTBF (Mean Time Between Failure) number needs to be given to Safety calculations (SIL). ESD / ESV valves are in modern systems connected to Programmable Locig Controller (PLC) and are together with sensors forming a Safety Loop. Whenever sensors identity an upnormal dangerous process situation PLC disconnects the power to ESD valve solenoid and the valve goes to desired fail safe mode by means of spring force (fail close or fail open).

This is the most critical situation for valves. Unless the valve is not frequently tested there is no guarantee that it is available and does the desired safety function. This can cause a major catastrophe.

1.

STANDARDS- IEC 61508 - IEC 61511 - DIN 19250 - ISA SP84.1 - application standards (e.g. furnace)

6.

MATERIALS- coatings - NACE materials

7. 8.

FIRE PROTECTION SAFETY INTEGRITY LEVEL (SIL)- MTBF , DC, PFD, SIL

2.

SPECIFICATIONS- how to identify ESD valve - process duty description - tag number

9. 10.

TOTAL LIFE CYCLE 10 ESD 20 EN Issue 10/2005 APPLICATIONS QUALITY PACKAGE- std. Q-plans - testing procedures - NDE options

3.

VALVES- selection process - typical valves

11.

4.

ACTUATORS- selection process - torque output / safety margins

12.

TERMINOLOGY

5.

ACCESSORIES- Neles ValvGuard - typical ESD connection diagrams

M E T S O AU TO M AT I O N

1. STANDARDSMIL DIN -> IEC 61508

ISA S84.1 IEC 61508 is a globally recognised new safety standard specic to process industry. Very strong guidelines are given there to process operators to test and prove the availability and functional safety of the safety loop including the nal elements and ESD valves. This standard gives practical tools for Safety Design process. As well it is a tool for Auditors to review plants Safety efforts. Very typically Insurance companies would utilize this standard to review if all Safety measures are taken. This can have a great impact to Insurance fees being either lowered or increased.

Compliance to IEC 61508Part 1 of the IEC 61508 demands certain documentation requirements for the development of safety critical devices. As basis documents, the SRS (Safety Requirements Specication) and the V&V Plan (Validation and Verication Plan) were prepared. For the specic requirements of part 2 (system architecture, safe failure fraction, diagnostic, measures against systematic faults and measures to avoid failures during design and development) and part 3 (software), the nally selected measures meet the requirements of SIL 3. Regarding the control of failures, the following results were estimated: 1. Hardware fault tolerance is 0 2. Safe failure fraction of the pneumatic part is > 90 % (low complex component) 3. Safe failure fraction of the electronic part: No hardware/software fault could lead to a dangerous failure in case of a demand. From this point of view the Neles ValvGuard system could be used up to and including SIL 3. For the PFD calculation the nal valve is dominant for the result. The diagnostic coverage of a nal valve could be between 75 % and > 90 % depending on the type of valve. The failure rate, safe failure fraction resp. diagnostic coverage of the nal valve and the automatic test time interval have to be used for the PFD calculation. Depending on this calculation and the required hardware fault tolerance of the application (some applications require a hardware fault tolerance of 1) the max. SIL level is dened. If the PFD calculation does not reach SIL 3 and/or a hardware fault tolerance of 1 is required, a dual redundant conguration has to be used as described in the ValvGuard safety manual.

2. SPECIFICATIONS2.1 How to identify an ESD valve

ESD valves are part of Safety System. The function can be clearly specied in the specication. Quite often specication requires certain safety margins for actuator sizing. Some of above mentioned Safety related standards can be mentioned. 2.2 Duty description

Data sheets describe the valve to be an ESD / ESV or Emergency valve. 2.3 2.4 2.5 2.6 2.7 Tag number is XV or XCV or ZV Jammer or latching devices are specied Volume tanks are specied for emergency function e.g three strokes in cause of supply air failure Strict operating times are specied Strict safety margins in actuator sizing is requested

-2-

E S D VA LV E S E L E C T I O N G U I D E

3. VALVES3.1 Valve series to be considered

Ball Valves150 lbs 150 lbs 300 lbs 300 lbs 150/300/600 lbs 1" 8" 08" 16" 1" 6" 02" 16" 02" 36" X-serie, oating, FB or RB, Bulletin 1X20, 1X21 X-serie, trunnion, FB or RB, Bulletin 1X22 X-serie, oating, FB or RB, Bulletin 1X20, 1X21 X-serie, trunnion, FB or RB, Bulletin 1X22 D-serie, trunnion, FB or RB, Bulletin 1D20

Alternative series Top 5 (1,5" 16"), Bulletin 1T520 Soft seated alternative see bulletins; 1X24 and 1X25.

Buttery valves150/300 lbs, wafer/lug 150/300 lbs, wafer/lug 150 600 lbs, anged 3"- 16" 18"- 48" 4" 64" LW/LG series, Bulletin 2LW20 L1C/L1D series, Bulletin 2L121 L6 series, Bulletin 2L621

Soft seated alternative Wafer-Sphere (3" 60"), Bulletin 2WS21, 2WS22

3.2

Selection process

Application type

Emergency closing or venting, note if selected valve is capable for partial stroke testing (eg. venting vs. buttey) Pressure Shut-off pressure, operating pressure, see temperature relation tables, remember shaft strenght Temperature Soft parts, body material, coatings, seat construction bearings, high temp. extension, low temp./cryogenic Fluid Corrosive, solids, toxic, explosive (O2) Viscosity, errosion, corrosion, solidifying, coke build-up Materials CF8M, WCB, LCC, C5, note temperature, chemical resistancy, NACE Valve type Ball valve reduced bore or full bore, buttery valve, fail open or close, tightness, operating speed, oating or trunnion Actuator type Spring return or double acting, operating speed, handwheel, jammer, seel cylinder, fre box Fire safety API 607, BS6755 Accessories SOV, LS, Booster, QEV, PPS, VT Area clasication EExi, EExd, EExn, FM, CSA, Cenelec Power supply Supply pressure, SV voltage 3.3 Torque tables / safety margins

Preferable method of selecting actuator is to use Nelprof sizing program. Nelprof gives automatically actuator load factor % and Safety margin therefore can be seen. Printout of calculation is the calculation document to be handed to client. Safety margins are typically between 50 100%. Note that actuator oversizing specially at elevated temperatures may lead to shaft strength study. Sample of Nelprof sizing sheet indicating actuator load

Actuator sizing results for rotary valves.To open Torque required to begin opening the valve. Breakaway torque for eccentric valves and friction torque for concentric valves. Calculated with dp Shutoff.

-3-

M E T S O AU TO M AT I O N

Opening LF Opening load factor. Load factor is the required torque divided by the available torque. A value of 62 means that 62% of the torque given by the actuator output torque is needed to open the valve. The opening load factor should be below 50 to allow some safety margin in the selection.

Actuator load factor development via Neles ValvGuard diagnostic

Relative strengths of shaft materials at elevated temperatures450 400 Relative strength (%) 350 300 250 200 150 100 50 0 0 50 100 150 200 250 300 350 400 Temperature (C) 450 50017-4 PH, H1150 XM-19 SS 2324 (Type 329) CA6NM CF8M

550

600

For further torque information use product bulletin. 3.4 Floating vs. trunnion ball valves

Main reason for this consideration is trim / seat surface pressure. Too high surface pressure can cause trim / seat damage within a few strokes. Very expensive coatings can be easily avoided. Floating valves are recommended to be used only for sizes below 8" in ANSI 150 lbs and below 6" in ANSI 300 lbs. ANSI 600 must always be a trunnion design. Always concider the required operating torque (including safety margin) difference between oating and trunnion design. Actuator size can be remarkably smaller with trunnion valves. 3.5 Design standards ANSI 16.34, DIN 3840 ANSI 16.34, DIN 3840

Ball Valves Buttery Valves

-4-

E S D VA LV E S E L E C T I O N G U I D E

4. ACTUATORS4.1 Actuators to be considered B1J, B1JA, B1JAR, or same with "K" or "V" spring. B1J + jammer option (unless Neles ValvGuard is used). B1C (not to be used with ValvGuard) Steel cylinder

Spring return Double acting Material 4.2

Selection process Pneumatic double acting, pneum. spring return, rolling diaphragm spring return or double acting, electric, hydraulic Fail to close, fail to open, fail in place min 3,5 bar, max. 8,5 bar See below for actuators, use QEV's or AOV's to speed operation, also large size SOV is alternative Manual hand operation possibility. Top mounted up to B1J16 . Side mounted for larger sizes. Available as option. Note operating speed. Normal cylinder material aluminium. As an altenative steel cylinders are available Mechanical limits can be adjusted to only partially close or open if desired Firebot or K-mass give total re resistancy.

Actuator type Fail safe function Supply pressure Operating speed Manual hand wheel Hydraulic manual o

Recommended

View more >