1.1 Process Critical Lines
A process critical line is any line where the physical run of the piping can adversely influence the process performance,
safety, line sizing and/or pressure drop allowances. For example:
Serial No.
Description
Responsibility
1.
Critical line list
FTH
2.
Pump suction lines
FTH
3.
Re-boiler and two phase flow piping
EIL
4.
Overhead condensing system
EIL
5.
Relief valve piping and critical venting systems including flaring facilities
EIL
6.
Plant blow-down, cleaning and drainage for certain processes
FTH
7.
Reactor circuits
EIL
8.
Compressor piping systems
EIL
9.
Vacuum piping
EIL
10.
Concentrated solutions, high fouling systems etc.
11.
Steam piping systems for process and turbine drives
EIL
12.
Jacketed piping
MODELING BY FTH/
ANALYSIS BY EIL
1.2 Piping Critical Lines
A piping critical line is any line for which a flexibility review is required to be carried out by a Piping Stress Engineer, or the
line supporting is deemed critical and similarly merits the attention of a Stress Engineer. Lines 50 mm (2") NB and smaller
are not normally considered critical — in the following definitions, “lines” means lines 80 mm (3") NB and above, unless
otherwise stated.
1.2.1 Category 1: Stress Critical Lines
Critical lines in this category are defined as follows:
Serial No.
Description
Responsibility
13.
Lines with a minimum temperature below -29°C (-20°F)
EIL
14.
Lines 80 mm (3") NB and 100 mm (4") NB operating above 250°C (480°F)
FTH
15.
Lines 150 mm (6") NB and larger operating above 110°C (230°F)
FTH
16.
Non-ferrous lines operating above a “critical” temperature established for the
material and contract (as a general rule, above 100°C)
EIL
17.
Non-metallic lines above a “critical” temperature established for the material and
contract (as a general rule, above 50°C)
EIL
18.
Jacketted lines — all sizes
FTH/EIL
19.
Lines for which a probable requirement for an expansion joint (e.g. bellows) has
been pre-determined by Process Group, and shown on the P&ID, as a result of
their experience on a similar plant
EIL
20.
Any line for which formal calculations are specified, either by Client or Local
Authorities
EIL/FTH
21.
Lines that, although not themselves critical, tie in to critical lines and have a
significant effect on their flexibility. As a general rule such lines are added to the
Critical Line List at the initial review stage if their nominal size exceeds one-third
FTH
Serial No.
Description
Responsibility
of that of the critical line (and they exceed 50 mm NB); the remainder are
established and added during the design stage (see 5.2.5.4). These lines cease to be
considered critical beyond the nearest anchor to the tie-in point.
22.
Any other line that the piping engineer and/or lead stress engineer consider should
be referred to the stress and support group for clearance
FTH
1.2.2 Category 2: Equipment Critical Lines
These are lines connecting to equipment regarded as strain sensitive, as listed below:
Serial No.
Description
Responsibility
23.
Rotating machinery, e.g. pumps, turbines, centrifugal and reciprocating
compressors, fans
EIL
24.
Fired heaters and reforming furnaces (*labelled 2.3.2.1 in the source document)
EIL
25.
Air-cooled exchangers
EIL /FTH
26.
Shell and tube exchangers with a bellow in the shell
FTH
27.
Vessels fabricated from non-ferrous or non-metallic materials
EIL
28.
Vessels with lining of a brittle nature, e.g. glass, brick or refractory materials
EIL
29.
Special items of equipment where the manufacturer specifies low nozzle loading
FTH /EIL
Note: lines classified as critical solely because they connect to strain-sensitive equipment cease to be considered critical
beyond the anchor nearest to the equipment connected.
1.2.3 Category 3: Support Critical Lines
Lines to which special care and consideration must be given are defined as follows:
Serial No.
Description
Responsibility
30.
Rotating machinery, e.g. pumps, turbines, centrifugal and reciprocating
compressors, fans
FTH
31.
Lines to which field welding are prohibited
FTH
32.
Lines subject to two-phase flow
FTH
33.
Lines in reciprocating service, irrespective of whether a pulsation analysis is
carried out
FTH
34.
Non-ferrous lines
FTH
35.
Non-metallic lines
FTH
36.
Lines of wall thickness schedule 160 or greater
FTH
37.
Lines having an outside diameter over wall thickness ratio (D/t) less than 10
FTH
38.
Lines 500 mm (20") NB and larger having a D/t ratio greater than 90
FTH
39.
Lines having coating or lining of a brittle nature, e.g. glass, concrete
FTH
1.2.4 Category 4: Relief Critical Lines
The following lines are considered critical because of the possibility of their being subject to dynamic shock loads or reaction
forces:
Serial No.
40.
Description
Relief valve discharges
Responsibility
EIL
Serial No.
Description
Responsibility
41.
Lines downstream of bursting discs
EIL
42.
Lines downstream of control valves that connect into vent or flare system headers,
or discharge to atmosphere
FTH
43.
Vent and flare system headers
FTH
44.
Liquid blow-down lines required for process reasons, i.e. not drain lines
FTH
1.2.5 Category 5: Category M Fluid Service
Serial No.
45.
Description
Lines 40 mm (1 ½") NB and larger, at any temperature, with piping spec codes
identified in the Contract Piping Specification as Category M Fluid Service
Responsibility
FTH/EIL
1.2.6 Category 6: Lines Subjected to Settlement Loads
Serial No.
Description
46.
Lines connected to any vessel or tank which may undergo settlement in the course
of its working life
Responsibility
FTH
1.2.7 Category 7: NUCLEAR
Clause
Description
Responsibility
47.
NCD AS PER ASME SEC III
EIL
48.
NINS PIPING AS PER ASME B 31.1
FTH
0
