Download Steam Heating Specification

Project Title
End User, Location
Job Number
STEAM HEATING
SPECIFICATION
Page 1 of 4
Revision: 1
Date: 7 Oct 2010
1. GENERAL
1.1.
This specification describes the minimum mandatory requirements governing the design
and installation of a steam heating system for process piping and equipment. The system
will be used to maintain incoming process temperature, prevent liquid processes from
freezing, and prevent vapor processes from condensing inside the pipe. Specific thermal
requirements are specified on the P&ID’s, piping line lists, piping isometric drawings,
and/or process data sheets.
2. STEAM HEATING ELEMENTS FOR PIPING
2.1.
The vendor is responsible for performing heat transfer calculations to determine the
number of heating elements required to achieve the thermal objective for each line. For
liquid processes, the analysis must show the heating system is sufficient to maintain the
bulk process temperature at or above the minimum temperature specified. For vapor
processes, the analysis must show the heating system is sufficient to maintain the pipe
wall temperature at or above the incoming vapor temperature at all locations to prevent
dew-point condensation which can lead to corrosion and plugging. The analysis must
consider heat loss to ambient, heat transfer to the process, and heat conduction through
the pipe wall. Piping components such as pipe supports, flanges, nozzles, spectacle
blinds, and valve stems/actuators all act as heat sinks in the piping system and pull heat
away from the pipe wall and process. Special consideration must be given to these areas
in the analysis. At a minimum, the analysis shall consider: (a) process design flow
conditions, (b) process convection coefficient, (c) pipe material and wall thickness, (d)
ambient conditions, (e) piping insulation type and thickness, and (f) steam conditions.
2.2.
The vendor is responsible for documenting the heat transfer calculations and providing
such documentation to client within ___ weeks of contract award.
2.3.
Since the heating elements are designed to contain pressure, all welders who fabricate
the heating elements shall be certified to the ASME Code, Section IX, latest addenda, for
the welding procedures used. Material traceability (MTR) is required.
2.4.
The heating elements shall have a minimum design pressure rating of 150 psig @ 400°F.
This rating shall be verified in accordance with the ASME Code, Section VIII, Div. 1,
latest addenda.
2.5.
The vendor is responsible for designing the heating element placement on the piping to
avoid obstructions, ensure the condensate can drain from the system, and prevent cold
spots.
Project Title
End User, Location
Job Number
STEAM HEATING
SPECIFICATION
Page 2 of 4
Revision: 1
Date: 7 Oct 2010
2.6.
The heating elements shall be attached to the process piping with either stainless steel
banding (minimum thickness of 0.030”) or a stronger method of attachment which will
prevent dislocation due to thermal and/or pressure expansion.
2.7.
If heat transfer compound or mastic is used to enhance heat transfer between the heating
element and the piping, it shall be of a thin layer which will not fall out from between
the heating element and the pipe wall due to repeated thermal cycling. A computer
analysis or experimental data shall be provided to support the improved thermal
performance claimed in the heat transfer calculations. The vendor shall also provide
experimental data on the long-term stability and thermal performance of any heat
transfer compound or mastic.
3. STEAM HEATING ELEMENTS FOR VALVES AND OTHER PIPING COMPONENTS
3.1.
The vendor shall also design, fabricate, and provide heating for valves and other piping
components contained in the piping system. The heating elements must provide an
integral fit between the heating elements and the specific process component that it will
heat to ensure good heat transfer contact. Bolt-on, cast aluminum jackets are an
acceptable method of heating valves and other piping components.
3.2.
Since the heating elements are designed to contain pressure, all welders who fabricate
the heating elements shall be certified to the ASME Code, Section IX, latest addenda, for
the welding procedures used. Material traceability (MTR) is required.
3.3.
The heating elements shall have a minimum design pressure rating of 150 psig @ 400°F.
This rating shall be verified in accordance with the ASME Code, Section VIII, Div. 1,
latest addenda.
4. STEAM CONNECTIONS
4.1.
Each heating element shall have an inlet and an outlet connection to enable the
unobstructed flow of steam and condensate through the element. The connections shall
be designed to extend beyond the insulation.
4.2.
The vendor will design some method of connecting in series the individual heating
elements along the piping in order to transfer the steam and condensate throughout the
heating system.
5. SYSTEM DESIGN
5.1.
The vendor shall design the heating system to achieve the client’s thermal requirements
as stated in the P&ID’s, piping line lists, piping isometric drawings, and/or process data
Project Title
End User, Location
Job Number
STEAM HEATING
SPECIFICATION
Page 3 of 4
Revision: 1
Date: 7 Oct 2010
sheets. The vendor shall specify the heating elements (number and location) for each
line type and line size combination to maintain the bulk process temperature and/or to
maintain the minimum pipe wall temperature (to prevent condensation) as specified.
5.2.
The steam shall be ___ psig (barg) saturated steam available at the outlet of the steam
manifold. The minimum steam pressure required at the inlet of the steam trap for
successful trap operation and condensate return shall be ___ psig (barg).
5.3.
Design ambient conditions are ___°F (°C) with a ___ mph (kph) wind speed. The
insulation type and thickness for each line will be as indicated on the P&ID’s, piping
line lists, piping isometric drawings, and/or process data sheets.
5.4.
The vendor shall perform steam pressure loss calculations to determine the maximum
allowable steam circuit lengths which can meet the thermal requirements. In so doing,
the vendor shall calculate the heat load for each circuit based on worst case operating
conditions. Both static and dynamic pressure loss components shall be considered. The
vendor shall design the steam routing to minimize the quantity of steam supplies and
steam without exceeding the temperature and pressure loss limitations necessary for
successful operation of the system.
5.5.
The heating system design shall be documented with detailed 3D or isometric
installation drawings showing each individual heating element for piping, valves, and
components along with each steam jumper. The installation drawings shall clearly label
each heating element/jumper as well as all steam supply and return locations.
5.6.
The vendor shall provide at time of final shipment an engineering report which
summarizes the thermal design of the system. The following points shall be included as
a minimum: (a) individual circuit heat loads and steam consumption, (b) minimum
allowable steam pressure at the end of any circuit by line and size combination, (c)
design assumptions, (d) design process conditions, (e) pipe wall temperature profile for
flowing process and/or stagnant process for each line and size combination, (f) net heat
input to the process and net heat loss to the ambient for flowing process and/or stagnant
process for each line and size combination, (g) individual circuit pressure loss under
worst case conditions, and (h) longitudinal process thermal profile of each flowing
process circuit showing process temperature change due to heating system heat input.
5.7.
Others will design and supply all utilities infrastructure including supply/return
manifolds, supply/return lines which connect the manifolds to the heating system
elements, and steam traps.
5.8.
The vendor shall calculate the pressure loss which can be allowed in the supply and
return pre-insulated tubing lines (which connect the steam/condensate manifolds to
Project Title
End User, Location
Job Number
STEAM HEATING
SPECIFICATION
Page 4 of 4
Revision: 1
Date: 7 Oct 2010
heating circuit) and determine the minimum allowable tubing size and the maximum
allowable length.
5.9.
The vendor shall confirm compatibility of the steam trap being specified by others. A
mechanical trap (inverted bucket, float, free-float) with continuous air purging capability
is the most robust choice for a heating system. If another type trap is being specified by
others, vendor shall approve or disapprove. If thermodynamic traps are preferred, the
condensate return absolute pressure must be less than half of the absolute steam pressure
at the trap inlet for successful operation. Thermostatic traps are generally not
recommended since they require condensate to back up in the heating system in order to
achieve adequate sub-cooling to allow the trap to open.
6. TESTING AND INSTALLATION
6.1.
The vendor shall pressure test each heating element and steam jumper in accordance
with ASME Code, Section VIII, Div. 1, latest addenda.
6.2.
The vendor will supply all hardware and heat transfer compound necessary for
installation of heating elements and jumpers.
6.3.
Upon contract award, the vendor shall provide an interference matrix to allow the piping
designers to check for potential interferences between the steam connections and
adjacent piping/components and floor penetrations.
6.4.
The vendor will provide an installation checklist to confirm the proper installation of
each component in the system.
6.5.
The client’s construction crew shall completely insulate all piping, flanges, pipe
supports, and process instrumentation such as valves, flow elements, and measurement
devices. The insulation type and thickness will be consistent with the system design
requirements as indicated on the piping line lists and/or piping isometric drawings.
7. PERFORMANCE GUARANTEE
7.1.
The vendor shall provide a thermal performance guarantee which will assure the
maintenance of the required bulk process temperature for liquid lines and/or the
maintenance of the required minimum pipe wall temperature for vapor lines. The vapor
line minimum pipe wall temperature shall be at or above the entering vapor temperature
under normal operating conditions.