12. Disposal System Design Review
12.1 New Installations
12.1.1 SABIC shall review and approve all pressure relief system, flare and vapor depressuring designs
that are prepared by others. The detailed mechanical designs for pressure relief systems and flares shall
be provided by the contractor, in accordance with this Section and local regulations.
12.1.2 SABIC requires the information and documents listed in Section 12.3. The information and
documents shall be assembled in a single, complete design package and submitted to SABIC for final
design review. This package shall be issued by the contractor as a technical data book after final approval
by SABIC.
12.2 Existing Installations
Expansion projects generally require that new pressure relief and vapor depressuring facilities be
integrated into the existing system. In such cases, the information requested in Section 12.3 shall be
developed for the new facilities by the contractor from unit process flow and P&I diagrams supplied by
SABIC. This information shall be included in the completed design package.
12.3 Required Information and Documents
The following information or documents shall be submitted to SABIC for preliminary review. This procedure
facilitates processing of the contractor’s designs before the single-design package is assembled for final
review and approval.
12.3.1 Summary Sheet. A pressure relief valve and depressuring valve load summary sheet (see Figure 8),
by units, shall include the following data. Numbers match the columns in Figure 8.
a. Pressure relief valve or depressuring valve tag number
b. Tag numbers for the major equipment that is protected. Several equipment items may exist in a
protected system.
c. Equipment or system design pressure/temperature
d. Equipment or system operating pressure/temperature
e. Pressure relief device type, metallurgy, set pressure and discharge temperature
f. Maximum allowable/calculated backpressure on the pressure relief valve
g. Molecular weight of the relief stream
h. Disposition of the discharge (to atmosphere, LP flare, HP flare)
i. Maximum individual loads due to:
(i) Local cooling water failure
(ii) Power failure
(iii) Blocked outlet
(iv) Fire
(v) Instrument failure
(vi) Steam failure
(vii) Other (vapor depressuring or other)
j. Maximum simultaneous load due to:
(i) Total cooling water failure
(ii) Total power failure (show mol weights, temperature and compositions separately)
(iii) Total steam failure (show mol weights, temperature and compositions separately)
k. Other loads (show mol weights, temperature and compositions separately)
l. Remarks.
Figure 8
Typical Relief and Depressuring Load Summary – SI (Metric) Units – Single-Line Diagrams
Single-line diagrams, which include pressure relief and vapor depressuring valves and piping to the flare
(see Figure 9), shall include the following information:
a. Line sizes and line slope
b. Equivalent lengths of line segments
c. Vessel numbers
d. Pressure relief and depressuring valve numbers
Show all pressure relief valves that are connected to the closed system. Identify those that simultaneously
contribute to the maximum emergency relief load that is used to design the main header flare knockout
drum, flare stack and tip. Show all depressuring valves.
12.3.3 Flare System P&I Diagrams. Flare P&I diagrams shall show the following data:
a. Flare stack height
b. Flare stack diameter
c. Flare tip diameter
d. Knockout drum size, pumpout facilities and liquid level
e. Type of flashback protection
f. Utility supply lines
g. Pilots and igniters
h. Slope of pressure relief piping
12.3.4 Additional Requirements. Other documents required are:
a. Data Sheets: Completed data sheets, including the type and method of operation for
depressuring valves.
b. Calculations: Pressure relief and depressuring assumptions and calculations made to establish
loads and valve sizes for the three worst case contingencies.
c. Unit Diagrams: The latest unit P&IDs, process flow diagrams and plot plans.
d. Vessels: A list of vessels that require vapor depressuring (see Section 9.1.1).
Figure 9
Closed Pressure Relief System and Flare – Typical Single-Line Diagram – SI (Metric) Units
Figure 10
Closed Pressure Relief System and Flare – Typical Single-Line Diagram – Customary Units
