Table of contents
1. Scope
2. Abbreviation and Definition
3. Design pressure
4. Design Temperture
1. Scope
1.1. This design guide shall be used for the determination of the design pressures and temperatures of equipment and piping in case the Client has no specific rules or their rules have to be supplemented because they do not cover all cases.
1.2. For each job the Engineering Design Basis which forms part of the Project Procedure Manual shall refer to this Engineering Design Guide and shall contain applicable rules in the country of installation and/or additional Client’s requirements.
1.3. The process engineer is responsible for the determination of the design pressures and temperatures.
2. Abbreviation and Definition
2.1. Abbreviations
| Op = | Operating | barg. (kg/cm2g) |
| DP= | Design pressure | barg. (kg/cm2g) |
| BDP= | Design pressure at bottom of equipment | barg. (kg/cm2g) |
| MSP= | Maximum suction pressure | barg. (kg/cm2g) |
| MPP= | Maximum pump pressure | barg. (kg/cm2g) |
| RP= | Set pressure of relief valve | barg. (kg/cm2g) |
| NDH= | Normal differential head of rotating equipment | bar . (kg/cm2) |
| MDH= | Maximum differential head of rotating equipment | bar . (kg/cm2) |
| EDH= | Differential head in equipment | bar . (kg/cm2) |
| SH1= | Static head in equipment at maximum level | bar . (kg/cm2) |
| SH2= | Static head on suction side at maximum level in equipment | bar . (kg/cm2) |
| SH3= | Static head on pump discharge side | bar . (kg/cm2) |
| MBP= | Maximum back pressure at relief valve outlet | barg. (kg/cm2g) |
| OT= | Operating temperature | °C |
| DT= | Design temperature | °C |
| MRT= | Maximum relieving temperature | °C |
2.2 Definitions
2.2.1. Operating pressure and operating temperature are the extreme conditions - maximum or minimum - which are required to sustain the process. These extreme conditions are determined by considering possible changes in yield of feeds. Factor such as control surges, pump shut-off pressures, upset of refrigerant levels, that need to be recognized in the mechanical design, shall not be considered as operating conditions.
Regeneration of catalyst shall be considered as a separate operating condition.
The operating temperature shall be the base for the calculation of the expansion stress range of pipelines and for determining the insulation thickness.
2.2.2. Design pressure and temperature are defined in par. 3. and 4.
The design pressure and temperature shall be used for wall thickness calculations of equipment and piping. The design temperature shall also be used in calculating the reaction exerted on load sensitive equipment such as pumps, compressors, turbines etc. and for determining the paint system.
2.2.3. Maximum suction pressure is the maximum possible pressure at pump level (considering set pressure of safety valve and/or maximum level and maximum density).The maximum suction pressure is the design pressure for piping, up-stream of pump and compressors.
2.2.4. Maximum back pressure at relief valve outlet is the pressure caused by the pressure drop in the relief system during a relief at the controlling case.2.2.5. Maximum relieving temperature is the temperature that occurs during relieving conditions except for fire case.
3. Design Pressure
3.1. The design pressure shall at least be:
3.1.1. Equipment protected by a safety valve: the greater of:
DP = 1.1 x OP
DP = OP + 1.5
DP = 10 X MBP for a conventional safety valve
DP = 2(MBP + 1) - 1 for a balanced seal safety valve.
Discuss the factor of 2 for balanced seal safety valve with Instrument Department before preparing process data sheet. Factor depends on make and type of safety valve.
3.1.2. Equipment protected by a rupture disk or a combination of safety valve and rupture disk: the greater of:
DP = 1.4 x OP
DP = OP + 1.5
Discuss factor of 1.4 with Instrument Department before preparing process data sheet. Factor depends on make and type of rupture disk.
3.1.3. Equipment down-stream of centrifugal pumps or compressors, with a block valve in the outlet line and no protected by safety valve or rupture disk:
a. DP = MPP = RP + EDH + SH2 + NDH
b. DP = MPP = OP + EDH + SH2 + MDH
For elevated equipment the formulae may be reduced by the static head SH3.
3.1.4. As per the applicable rules in country of installation. For the applicable rules see
Appendix A.
3.1.5 .As per Client’s requirements.
These shall be discussed in case they are lower than the above.
3.2. The final design pressure shall be rounded off to 0.5 kg/cm2. For vertical equipment the top pressure is the design pressure and only this pressure shall be rounded off.
This is the nameplate pressure.
3.3. For vertical equipment the design pressure at the bottom shall be stated on the process data sheet by the process engineer.
For a column the bottom pressure shall be.
BPD = DP + EDH + SH1
3.4. Equipment arranged in a train and protected by a safety valve on the last item in the train shall be designed such that the first item can stand at least a pressure equal to the set pressure of the relief valve + total pressure drop in the train. The pressure drop in equipment and piping shall be determined with extra care. In case reactors are forming a part of such trains, the plugging of these reactors shall be considered as well.
3.5. The design pressure for equipment in vacuum service shall be specified based on the operating conditions.
Steaming out shall in general not be considered as an operating condition unless required by the Client.
3.6. At the beginning of a job the maximum differential pump head is not know; take 1.2 x normal differential pump head and order the pumps accordingly.
In case factor of 1.2 or lower cannot be achieved the Process engineer shall be notified.
3.7. Piping
The design pressure shall be determined exactly along the same lines as is stated in the preceding paragraphs.
Special attention shall be payed to the increase or decrease in pressure due to static head or pressure drop.
4. Design Temperature
4.1. The design temperature shall be:
4.1.1. Temperatures below 0°C:
DT = OT - 5°C:
4.1.2. Temperatures above 0°C: The highest temperature of the following:
a. DT = OT + 30°C
b. DT = For equipment with a vapour-liquid equilibrium the temperature belonging to a vapour pressure of 1.1 times the design pressure on top and/or bottom. This rule shall not be applied when the higher temperature can only be reached in case of fire.
4.1.3. As per Client’s requirements. These should be discussed in case they are lower than the above.
4.1.4. As per applicable rules in country of installation. For applicable rules see Appendix A.
4.2. The final temperature shall be upgraded to a multiple of 5°C. For low temperature service no rounding-off is allowed.
4.3. For equipment containing liquified gasses and operating above 0°C, the atmospheric boiling point of the mixture in each equipment when below 0°C shall be stated on the process data sheet. This information is required to enable the Vessel engineering department to select the proper type of carbon steel.
4.4. Design temperatures for heat exchangers in a train and provided with bypasses shall be based on the worst possible operating case (see example).
Example Bypassing of either B or C in a train of three exchangers.
The shell side design temperature of exchanger B shall be based on the inlet temperature of exchanger C.
The shell side design temperature of cooler A shall be based on the maximum possible inlet temperature depending on which up-stream exchanger is bypassed. In case exchanger C is bypassed the turbine side of exchanger B shall be designed for the increased outlet temperature caused by the bypassing.
4.5. Piping
The design temperature shall be determined exactly along the same lines as is stated in the preceding paragraphs.
Appendix A
To Engineering Design Guide BN-EG-UE002
Applicable Rules in the Country of Installation
Table of Contents
Section 0: Scope
Section 1: Applicable Rules in the Netherlands
Section 2: Applicable Rules in Germany
Section 0
Scope
1. This appendix gives a summary of some rules and regulations applicable in various countries and related to the establishment of design pressures and design temperatures.
2. This appendix is intended to be a guide only and may not in any way be considered as a substitute of the official rules and regulations.
3. This appendix shall be read in conjunction with BN-EG-UE002.
Section 1
Applicable rules in the Netherlands as required by the “Diest voor het Stoomwezwn”.
1. Abbreviations and Definitions.
1.1. Abbreviations
MOP = Maximum operating pressure kg/cm2g *
MOT = Maximum operating temperature °C *
Note: Due to the fact that bar g. is not yet legal in the Netherlands the conventional unit of measurement is used.
1.1.1. For other abbreviations see the Engineering Design Guide BN-EG-UE002.
1.2. Definitions
1.2.1. The maximum operating pressure (maximum bedrijfs druk) and maximum operating temperature (maximum bedrijfs temperatuur) are defined in “Toelichting Classificatielijsten” (Explanation Classification lists) issued by the “Diest voor het Stoomwezwn” in July 1970.
According to this “Explanation” the MOP and the MOT are the maximum conditions during the operation of the plant to which a piece of equipment or a line, operating in its intended service for its intended purpose, may be subjected as long as the process can be sustained.
The prevention of a pressure and/or temperature raise in excess of the MOP and/or MOT shall be sufficiently warranted.
Legal classification of equipment and lines will be based on the MOP and MOT.
1.2.2. For other definitions see the Engineering Design Guide BN-EG-UE002.
2. Maximum Operating Pressure and Design Pressure.
2.1. The maximum operating pressure shall be for:
2.1.1. Equipment protected by a safety valve or rupture disk MOP = RP
2.1.2. Equipment down-stream of centrifugal pumps or compressors with a block valve in the outlet line and not protected by a safety valve or rupture disk. MOP = MPP = MSP + MDH in which the maximum suction pressure shall be: MSP = RP + EHD + SH2 For elevated equipment the MOP may be reduced with SH3.
2.2. The design pressure for equipment and piping shall be PD ³ MOP. This design pressure shall be stated on the nameplate.
2.3. NoBo requirements to allow equipment to be arranged in a train and protected by one safety valve as per BN-EG-UE002 paragraph 3.4 are:
2.3.1. An acceptable reason for not installing interjacent safety valves.
2.3.2. No interjacent block-or control valves.
2.3.3. An additional safety valve on or before the first item for cases where the speed of the up-stream pump or compressor can be increased above the design speed.
2.3.4. Reactors in which plugging can occur shall be considered as blocks.
Note: In the past plugging had not to be considered for reactors with radial flow over their full length.
3. Maximum Operating Temperature
3.1. In general the maximum operating temperature for equipment shall be determined in accordance with the definition as per par. 1.2.1.
For an example of how to apply this rule, reference is made to the example given in para. 4.4. of the Engineering Design Guide BN-EG-UE002. The “design temperatures” indicated in the example are the MOT, according to the NoBo rules.
3.2. For equipment with a vapour-liquid equilibrium the maximum operating temperature is the temperature belonging to the vapour pressure equal to the set pressure - RP - of the relief valve or rupture disk. (For a combination of safety valve and rupture disk set pressure of the safety valve shall be used). The maximum operating temperature for subsequent equipment shall be based on above determined temperature.
3.3. The maximum operating temperature for an equipment down-stream of an airfin shall be equal to the outlet temperature of the airfin in case of fan failure provided the process can be sustained.
4. Design Temperature
4.1. The design temperature shall be at least equal to the maximum operating temperature (DT = MOT).
Where a single failure can cause a higher temperature than the MOT this higher temperature shall be the design temperature. This design temperature shall be stated on the nameplate.
4.2. The cold side of a heat exchanger or cooler provided with block valves on both inlet-and outlet requires a thermal relief valve. The design temperature of the cold side shall be the lowest of:
4.2.1. The boilingtemperature of the fluid at the set pressure of the thermal relief valve.
4.2.2. Thedesign temperature on the hot side of the heat exchanger or cooler.
4.2.3. In case steam is the heating medium, the saturated steam temperature at the design pressure of the hot side.
4.3. Piping
4.3.1. Thedesign temperature for piping components shall be determined exactly along the same lines as stated in para. 4.1.
4.3.2. The operating temperatures may not be used in the calculation for the expansion stress range. The design temperatures shall be used instead of the operating temperature.