Jacketed Piping System- Fully Jacketed, Partially Jacketed

1.0  General Introduction to Jacketed Piping

This specification covers the design of steam jacketed piping, continuous (fully jacketed)/discontinuous (Not fully jacketed), for use on process piping systems where solidification of medium may occur. It includes the requirement for the layout, materials, fabrication, erection and testing of jacketed piping system.

2.0 Steam Jacketing System

2.1  General

The steam jacketing system consists of:

• The steam supply piping to the jackets from steam supply manifold
• The individual steam jacket circuits
• The condensate outlet piping to condensate header, steam trap & trap
  installation upto condensate return manifold.

2.2 Types of Jacketing

a. Continuous Jacketing_

All straight lengths, flanges, fittings, valves and branch connections are fully jacketed.

b. Discontinuous Jacketing_
Only straight length of pipes are jacketed. Flanges, tees, elbows, branch connections and welds are not jacketed.

2.3 Identification

All piping requiring steam jacketing shall be shown on the P&IDs and Piping drawings indicating continuous  (fully)  or  discontinuous  (not  fully)  jacketed piping with double lines besides the main line.  Additionally insulation type  ‘IJ’ is given at the end  of  the  fine  number  of  the  jacketed lines  to  facilitate identification of the steam jacketed lines.
 Examples:
    a. Continuous (fully) Jacketed Lines:

b. Discontinuous (not fully) jacketed lines.
Location of centering guides, baffles supports and anchors must be specified on the isometric drawings.

2.4 Steam Supply to Jacket

1. The steam supply to each jacketed circuit shall be taken from the main header or subheaders or steam supply manifold for jacketing. The steam  header  or  sub-headers  or  steam  supply  manifolds  shall  be provided with steam traps.
2. Size to be 1/2″ NB for 4″x3″ jackets & smaller; and 3/4″ NB for 6″x4″ jackets & larger.
3. All take offs from the steam headers or subheaders or steam supply
   manifolds shall be taken from the top.
4. The valves at the steam supply stations and also the steam traps shall be provided with a name-plate with the line no. of the pipe being jacketed.
5. Arrangement of steam supply manifold is shown in Annexure-I.

2.5 Individual Steam Jacketed Circuits

2.5.1  Jacket circuits – Construction of pipe sections

1. A steam jacket pipe consists of a process line which passes through the contra of a large diameter steam line.   The nominal sizes of the inner pipe (core) and outerpipe (jacket) in inches are as given in the table below.

Inner Pipe	Outer
(Process)	(Jacket)
(In Inches)	(In Inches)
3/4	1 1/2
1	2
1 1/2	3
2	3
3	4
4	6
6	8
8	10
10	12

2. For continuous jacketing,

i.  the  outer  jacket  pipe  is  welded  to  the  back  of  the  end  flange (modified) of each  jacket section. The inner pipe is welded into the modified flange. For details refer.Annexure-lV

ii.  Valves are bought as jacketed valves, with flanged steam inlet & outlet connections. Jacketed valves shall have standard bore and oversized flanges.

3. For discontinuous jacketing, end of the jacketing is welded to the inner pipe. For detail of jacket to pipe joint, see Annexure-VIII. Valves flanges, tees, elbows, branch connections & welds are not jacketed.
4. Centering guides to support the inner pipes on long spans shall be made as shown in Annexure-IX.

2.5.2  Jacketed Circuits – Layout and connections

1. A steam jacket circuit is formed by a number of jacket sections (pipe,
   fittings, valves etc.) which are connected in series by jumpovers. Each
   steam jacket circuit has its own valved steam supply and condensate
   drains through steam traps.
2. In principle the steam inlet pipe must be connected to the uppermost
   point of the circuit.
3. Jumpovers connect the lowest tapping at jacket end over a welded or
   flanged joint to the top (or side) tapping in the adjoining jacketed section
   for horizontal piping. The steam and condensate are carried together
   from one section through the jumpover to the next section. In case of
   flanged joints the jumpover shall be provided with a breakup flange. The
   inlet & outlet to steam jacket shall be 1800 apart.
4. The maximum number of jacketed sections included in one circuit
   depends on layout, type of fittings or valves, size, insulations etc.
   Straight run of pipe shall have break-up flange joints at every 5M (max.)
5. The total length of one circuit shall not exceed 20M in case of
   continuous jacketing and 25M in case of discontinuous jacketing.
6. Although each circuit shall be arranged so that the flow of condensate is
   generally downwards, a small vertical rise, due to layout is permitted
   provided drainage at lowest point if possible. The total of individual
   vertical pipe rise per circuit shall not be more than 1 metro and each
   individual rise shall be less than 300mm.
7. The layout of piping and equipment must be such as to reduce potential
   congealing to a minimum. Dead-ended and non-circulating piping
   should be avoided where possible.
8.  Across shall be provided in case of direction change, however, jacketed elbows may be used if specially indicated in ISOS.
9. For continuous jacketed fittings, jumpovers, branch connections
   (including vents/drain/instrument connections) and for usage of baffles etc. Annexure-V, VI, VII.
10. For discontinuous jacketing details refer Annexure-VIII.
11. To keep proper concentricity between core and jacketed pipe internal guide (Rods or Bars) shall be provided at interval depending upon size of the Pipe.
12. Flanged joints or end caps shall be used to discontinue one feed length
    from the next. Intermediate partial baffles shall be provided if a separate
    branch portion is to be heated from the main tine steam.

2.6 Condensate outlet piping to condensate header; Steam  traps and Trap  installation

1. At the end of any circuit, the steam condensate is to be drained from
   lowest point in any circuit.
2. The steam traps shall be ‘Balanced pressure thermostatic’ steam traps with 40 mesh strainer & 100 subcool temperatures.
3. The condensate drain line shall be 1/2″ NB for 4″x3″ jackets and smaller
   and 3/4″ NB for 6″x4″ jackets or larger
4. Condensate drain lines from each circuit to steam traps to be as short
   as possible for gravity drainage.
5. The discharge line of the steam trap shall be as short as possible and
   self draining.
6. Each steam jacket circuit shall be provided with its own trap connecting
   to condensate recovery system.
7.  Arrangement of condensate manifold is shown in Annexure-I.
8.  The steam traps must be preferably installed in the horizontal line,
9. The discharge from a number of steam traps shall be combined into a
   condensate recovery manifold which is connected to main underground
   (open system) condensate header.

3.0 Material

All piping materials for Process line (inner core), outer jacket, steam supply
and condensate return shall be in accordance with material specifications.
Material specification for the Process line (inner core) shall be as per P&ID.
Material spec for the jacket shall be carbon steel when the jacketing is done with LP
Steam. Material for inlet lead line, jumpovers and outlet lines shall also be carbon steel.

4.0 Fabrication and Erection

1. Fabrication and erection of piping systems shall be done as per Company/Project
   Specification.
2. Each  weld of  the inner  pipe  shall  be  accessible  for  taking  X-ray  and shall  be  visible  during  hydrotesting.  Therefore split jackets shall be used to enable inspection of each inner pipe weld.
3. Longitudinal welds from the split pipe jackets and split tees or reducers shall be staggered to avoid cross weld.

5.0  Inspection Flushing and Testing

1. Hydrotesting, flushing, draining and inspection shall be done as per company/Project Specification.
2. Visual   and   nondestructive   examinations   of   all   welds   shall  be  in  accordance  with  the  requirements  of  Standard  Specification  for  non-destructive examination requirement of piping.
3. Welds of the process pipe shall be inspected and tested before jacket pipe is welded.
4. Jacket pipe shall be inspected and tested before steam supply and condensate return piping are connected to the jacket.

6.0  Fabrication Inspection   & Testing Sequence  for fully Jacketed  piping  items  ( Typical sequence  for  Jacketed  Pipe spool)

1. Weld one end flange onto inner pipe
2. Weld guide strips onto inner pipe
3. Weld wear plates onto inner pipe
4. Slide jacket pipe (minus split collar) over inner pipe
5. Weld remaining end flange to other end of inner pipe
6. Perform N.D.E of inner pipe as per Company/Project Specification
7. Hydrotest  inner pipe spool
8. Weld jacket pipe to one end flange
9. Weld split collar to jacket and end flange
10. Perform N.D.E of outer jacket as per Company/Project Specification
11. Hydrotest  jacket pipe spool

Notes:

1. For prefabrication purposes of a branch connection it is necessary to split the jacket pipe onto 4 longitudinal half pipe shells (dimensions as per the applicable T-fitting).  This enables welding of the inner pipe branch weld.
2. For prefabrication purposes of a branch connection it is necessary to split the jacket pipe onto 4 longitudinal half pipe shells (dimensions as per the applicable T-fitting).  This enables welding of the inner pipe branch weld.