SCOPE

This design guidline covers the guidelines for the preparation of flow diagrams for crude oil and gas onshore installations including GOSPs, oil refineries and related processing facilities.

The main types of diagrams covered are Process Flow Diagrams and Utility Flow Diagrams.

Also covered are Distribution Headers, Interconnecting Pipework and Equipment Auxiliary Flowsheets.

The provisions laid down in this specification shall be complied with in full and any exceptions must be authorised in writing by the Owner.

In the event of any conflict between this specification and any of the applicable codes and standards, the Vendor/Contractor shall inform the Owner in writing and receive written clarification before proceeding with the work.

This General Engineering Specification will form part of the Purchase Order/Contract.

DEFINITIONS

Design Pressure

The design pressure is the pressure to which process systems and equipment are designed to withstand the maximum pressure which can occur under the full range of operating conditions including emergency situations.

Design Temperature

The design temperature shall be determined from the maximum operating temperature under the full range of operating conditions, including emergency situations, or normal operating temperature plus 50^oF (28^oC) whichever is the higher.

GENERAL

Layout

The layouts of the Process Flow Diagram (PFD)  shall be typically as shown in the examples in below Figures.

The drawings shall be presented on Metric Standard Size A1 paper.

All flowsheets shall incorporate the following information in the title block:-

Owner Name and Logo, Location, Owner's Contract Number, Vendor's/Contractor's Contract Number and Drawing Number with revision.

The drawing shall include a revision block, showing the revision number (O, A, B, C, etc), date of issue, approval signatures (as required by the Purchase Order/Contract).

All flowsheets shall have a single line border.

Quality

The quality of the originals and reproducibles shall be such that the drawings are legible when reduced to Metric Size A3.

Therefore care must be taken to select suitable font sizes for the original drawing and lines are to be of sufficient density so as to remain clear after copying.

Revisions

Maintain for all revisions a Project Master Copy of the PFD with all the latest information included. This is the Master for all personnel working on the Contract.

The original drawings are approved and signed by the Project and Process Engineers and Other Specialist Engineers as appropriate.

Revisions to PFD from Rev A onwards shall be shown by encircling the revised portion of the drawing. For definition of issue revision, numerals and letters.

Equipment or data for which information is not available at the time of issue shall be marked clearly with a "hold" designation. This is to ensure that detailed design does not proceed until the relevant information is obtained for the item.

Holds must only be used when absolutely necessary where applicable to both PFD. Normally all holds are to be resolved prior to the issue of Rev B and are not permitted for Rev C.

PROCESS FLOW DIAGRAMS (PFDs)

Scope of PFDs

This section covers Process Unit PFDs and is also applicable for Utility Flow Diagrams.

When Process Unit PFDs are not provided by a Licensor, the Process Engineer (s) assigned to the Project is responsible for preparing the first draft of PFDs.

The first draft shall be prepared considering the drawing layout and arrangement so that sufficient space can be allowed for future development.

For complex utility systems (eg steam and associated water systems) a separate utility flow diagram is prepared showing the flows, pressures and temperatures.

 Issues (example ot revision)

Rev 'O' PFD

(a) The first issue containing basic information for Engineering Sections to review and develop. It is suitable for initial plot plan development;

(b) The preparation of basic PFD layouts showing the process data and all main equipment;

(c) Ensure that the PFDs indicate the type of equipment which is being purchased (e.g. type of compressor).

Rev 'A' PFD

(a) The second issue is distributed to all engineering groups and also to the Owner for approval;

(b) Review comments and changes by Specialist Engineers are added to the Master copy by the Process Engineer;

(c) From this issue onwards all changes will be listed on a change List which shall be distributed together with revised PFD;

(d) Holds will be indicated and listed.

Rev 'B' PFD

The third issue containing Owner's comments, results of the formal Engineering Review, and some Vendor data.

Rev 'C' PFD

This issue contains remaining Vendor data. No "Holds" are permitted for this "Final" issue, which incorporates the concluding comments of internal reviews including comments on model review, should a model view be part of the project development, if applicable.

Operating and Design Conditions

The operating conditions for pressure and temperature for the main process streams are shown in bubbles and boxes on the PFD. Significant operating temperatures and pressures in the plant are marked on the drawing and also included in the material balance.

Material Balance

Material Balance(s) shall be included showing process details for feed, products and significant internal process streams. These figures are shown in a table on the PFD, or separately, dependant on requirements for information and content and differing cases.

A Material Balance shall be provided for each relevant process defining case.

An example of typical stream data provided on the Process Flow Diagram may include the following, in the preferred metric or imperial units:

• Mole fraction of each major component and contaminant;
• Temperature^oF (^oC);
• Pressure psig (kPag);
• Flow lbmole/h (kgmole/h);
• Mass Flow lb/h (kg/h);
• Liquid Volume Flow bblpd USgph (m³/h);
• Vapour Volume Flow MMscfd (Nm³/h);
• Mass Density lb/f³(kg/m³);
• Viscosity cP.

Consumptions of utilities used directly in the process, eg stripping steam, process water, injected air, etc. Otherwise, no utility quantities are to be shown.

For Utility Flow Diagrams (UFDs) a second sheet for the material balances may be used where there are a large number of design cases and also for steam balances.

Piping

The following piping information shall be shown on the PFDs:

(a) the main process and product routes shall be shown in heavy lines;

(b) secondary process routes and key utilities shall be shown in standard weight lines;

(c) the direction of the flow is shown on each line by an arrow;

(d) lines where there is normally no flow during operation are marked NNF;

(e) a descriptor is added for the origin or destination of each stream entering or leaving the PFD.

Do not show the following:

(a) line sizes or line numbers;

(b) isolation and bypass valving;

(c) slopes.

Equipment

The following equipment information shall be included on the PFDs:

Process Duties

Process duties of equipment are shown for:

(a) pumps - design capacity in USgpm (m³/h) and design ΔP in psi (kPa);

(b) compressors - design capacity MMscfd (Nm³/h) and design ΔP in psi (kPa);

(c) heat exchangers - duty for each operation Btu/h (kW/h) and design;

(d) fired heaters - heat absorbed for each operation Btu/h (kW/h) and design.

One symbol shall be used where there are multiple numbers of items of equipment required for a given service for pumping, heat exchange or furnace duty. The symbol shall be qualified with A, B, C, D, etc to represent the number of units to be installed.

Equipment Data

The following information shall be included on the Process Flow Diagram for equipment:

(a) all major equipment items;

(b) equipment item numbers and service alongside equipment; include only letters A, B, etc after the item number for equipment and note any common sparing;

(c) sizes of vessels - tan/tan length and diameter;

(d) elevations of equipment above grade;

(e) any notes for layout.

Do not show the following:

(a) spare pumps, compressors or other spare equipment;

(b) vessel internals details such as trays, demisters, etc.;

(c) type of drive for pumps and compressors;

(d) individual exchanger shells but include relevant A, B, C, D etc for estimated number of units/shells.

Instrumentation

The followinginstrument information shall be included on the PFDs:

(a) all process control loops;

(b) main utility control loops where these are important for process reasons;

(c) all control valves;

(d) main panel indicators and recorders.

Do not show the following on the PFD:

(a) details of complex control loops, a summary of function is sufficient;

(b) local indicating only instruments;

(c) local instrument panel instruments;

(d) safety valves;

(e) control valve bypasses.

Instruments function by sensing changes in the variables they monitor.

The four basic instrument groups are:

• Flow (F)
• Level (L)
• Pressure (P)
• Temperature (T)

The types of instruments used to sense, control and monitor these variables are:

• Controller (C)
• Indicator (I)
• Gauge (G)
• Alarm (A)
• Recorder (R)

By learning these nine terms, you will be able to understand most of the instrument symbols found on a
mechanical flow diagram.

OTHER PIPING AND INSTRUMENT DIAGRAMS

Utility Piping & Instrument Diagrams

Utility P&IDs and Utility Line Lists are prepared by the responsible Engineer as required by the Project Executive Plan.

Provided a process package is available for the Utility systems they shall be worked on in parallel with the process package. Issue times for Utility P&IDs should be broadly similar to those for Process Unit P&IDs.

The utility flow diagram shows the piping, valves, and instrumentation for the basic plant utilities. Utilities are services that are essential to the proper function of the plant. These utilities correspond to some of the same utilities used in a typical house, such as water, gas, and sewer drains.

Some of the common plant utilities are:

• steam
• condensate
• fuel oil
• utility air
• instrument air
• cooling water
• drainage systems
• flare system

Auxiliary P&IDs

These P&IDs are prepared to show auxiliary equipment associated with major items of rotating equipment. The Mechanical Equipment Engineer carries most of the responsibility for the content of this type of P&ID, since it covers equipment requisitioned by the Mechanical Group.

Because the details of equipment auxiliaries differ depending on the Vendor/Contractor selected, this type of drawing is prepared when the Vendor's/Contractor's drawings for the equipment are available.

6.3Distribution Header Diagrams

Distribution Header Diagrams show the plant piping header systems, and are prepared once the requirements have been shown on the P&IDs, and plot plans have been established.

Offsites Flow Diagrams

Offsites Flow Diagrams show the plant and piping on the offsite areas of the project, and are prepared once the layout of the offsite areas have been defined in sufficient detail.

Offsite flowsheets shall be drawn on a geographical basis with North clearly indicated.

They shall show the same information as required for the P&IDs.

Interconnecting Pipework Diagrams

Interconnecting piping diagrams are used to define the process, utility and offsite lines connecting the various areas of the project. These are usually lines which will be on interconnecting racks or sleepers.

These lines are shown geographically.

They shall show the same information as required for the P&IDs.

Existing lines into which these lines are tied are shown in dotted form.

These drawings are particularly important for the definition of tie-in points to existing lines on the site.

VENDOR/CONTRACTOR FLOWSHEETS

Vendor/Contractor Process Flow Diagrams

For packaged units the Vendor/Contractor shall produce a PFD for the piping, instruments and equipment in his supply.

Vendor/Contractor Piping & Instrument Diagrams

These P&IDs are prepared by a Vendor/Contractor of a Package Unit to show the equipment within the package.

The Vendor/Contractor shall provide the P&IDs to the standards set out in this specification.

The P&ID shall show all important information for the Contractor/Vendor interfaces, including the process and utility piping to and from the Vendor's/Contractor's package.

INFORMATION SHOWN ON FLOW DIAGRAMS

Check List of Information shown on PFDs

The following check list is applicable to most PFDs and covers the main requirements to define the process intent for design purposes. The listing is general and may require adjustments depending on the complexity of the process scheme and the Owner's identified preferences:

(a) design intent fully defined;

(b) all cases fully identified, i.e. summer/winter/early production, etc.;

(c) major equipment items identified; equipment number, equipment title, equipment duty;

(d) major process lines stream to relate to the corresponding heat and mass balance table;

(e) major control loops and valve shown for flow, pressure and temperature;

(f) notes to identify special process considerations;

(g) reference drawings to identify additional process drawings which include special related process and utility documentation;

(h) equipment, instrument and piping symbols as agreed by Owner;

(i) drawing number, title block, revision number, notes and presentation all as per Owner's agreement.

FLOW PLAN ARRANGEMENT

The flow plan should be arranged in a logical order of flow.

The main flow through the unit should be obvious by even a brief examination of the flow plan.

• Use the following checklist as an aid when developing a flow diagram.

• Avoid crossing lines where possible.

• Space equipment on the sketch to avoid overcrowding.

• Use notes with symbols where necessary for clarity.

• Use arrows to show flow direction.

• Show equipment numbers when it is necessary to identify equipment.

• Show control systems on the sketch. The control scheme is frequently the most important part of a flow plan sketch.

• Show important valves, orifice flanges, and control valves.

• Show flow directions through exchangers with arrows.

• Do not run lines diagonally across the drawing.

• Label feed lines entering the unit from the field where the line enters the unit. Label product lines leaving the unit by name.

• Do not draw lines any closer together than necessary.