1 Scope
NOTE This specification covers steam supply and condensate return distribution piping systems for institutional, campus, healthcare, industrial, and central-plant facilities, addressing three pressure classes: low-pressure steam (0-15 psig), medium-pressure steam (15-100 psig), and high-pressure steam (100-300 psig). Coverage includes above-grade and underground steam supply mains and branches, condensate return mains and drip legs, expansion compensation, drip pockets and steam traps, condensate receivers and pumps, pressure-reducing and pressure-regulating stations, strainers, isolation and check valves, safety relief valves, flash tanks, system insulation requirements, high-temperature pipe supports, slope, and commissioning hydrostatic testing. The system boundary begins at the high-pressure or low-pressure boiler outlet connection and ends at the inlet flange of the terminal equipment served, including heat exchangers, unit heaters, steam coils, and process loads. (1.1)
NOTE The pressure class is the governing decision for this standard: it determines the applicable design code, the pipe material and schedule, the joining method, the valve and flange ratings, and the welder qualification requirements. Low-pressure building-services steam at or below 15 psig is governed by ASME B31.9; steam above 15 psig is power piping governed by ASME B31.1, which imposes more stringent material, examination, and welder-qualification requirements. (1.2)
NOTE This standard applies to all project scales, from a single-building low-pressure heating plant to a multi-building campus distribution system. (1.3)
1.4The pressure class of each system shall be established by the Engineer of Record and indicated on the drawings before pipe material and code basis are selected.
1.5Steam piping above 15 psig steam shall be designed, fabricated, examined, and tested in accordance with ASME B31.1.
1.6Low-pressure steam piping at or below 15 psig steam shall be designed, fabricated, and tested in accordance with ASME B31.9.
1.7The boiler external piping for a power boiler shall comply with ASME B31.1 and the boiler-external-piping jurisdictional boundary defined therein.
2 Referenced Standards
2.1Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
2.2Where referenced standards conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
| Standard |
Title |
| ASME B31.1 |
Power Piping (primary code for steam above 15 psig and boiler external piping) |
| ASME B31.9 |
Building Services Piping (low-pressure steam at or below 15 psig) |
| ASME BPVC Section IX |
Welding, Brazing, and Fusing Qualifications |
| ASME B16.9 |
Factory-Made Wrought Buttwelding Fittings |
| ASME B16.11 |
Forged Fittings, Socket-Welding and Threaded |
| ASME B16.34 |
Valves - Flanged, Threaded, and Welding End |
| ASME B16.5 |
Pipe Flanges and Flanged Fittings NPS 1/2 through NPS 24 |
| ASTM A106/A106M |
Seamless Carbon Steel Pipe for High-Temperature Service |
| ASTM A53/A53M |
Pipe, Steel, Black and Hot-Dipped, Zinc-Coated, Welded and Seamless |
| ASTM A234/A234M |
Piping Fittings of Wrought Carbon Steel and Alloy Steel for Moderate and High Temperature Service |
| ASTM C547 |
Mineral Fiber Pipe Insulation |
| ASTM C533 |
Calcium Silicate Block and Pipe Thermal Insulation |
| ANSI/ASHRAE/IES 90.1 |
Energy Standard for Buildings Except Low-Rise Residential Buildings (Tables 6.8.3-1 and 6.8.3-2) |
| NFPA 70 |
National Electrical Code (NEC) |
| IMC |
International Mechanical Code, adopted edition |
3 Submittals
3.1 Action Submittals
3.1.1The Contractor shall submit the following for the Engineer's review and approval prior to procurement and fabrication.
- Pipe and fitting material data for each pressure class, including ASTM specification, grade, schedule or wall thickness, and manufacturing method (seamless or ERW)
- Valve data for each valve type and service, including ASME B16.34 pressure-temperature rating, body and trim materials, end connections, and pressure class
- Flange data, including ASME B16.5 class, facing, and gasket material for the operating temperature
- Welding procedure specifications (WPS), procedure qualification records (PQR), and welder performance qualification records (WPQ) per ASME BPVC Section IX for all pressure-containing welds
- Steam trap schedule listing each trap by service (drip, equipment, end-of-main), type (inverted-bucket, float-and-thermostatic, thermodynamic), pressure rating, orifice or capacity, and connection size
- Pressure-reducing valve (PRV) station data, including reducing-valve type and capacity, single- or two-stage configuration, strainer, downstream safety relief valve set pressure and capacity, bypass, and gauges
- Condensate receiver and pump set data, including receiver volume, pump type and arrangement (simplex or duplex), capacity, head, motor horsepower, and electrical characteristics
- Flash tank data, including ASME pressure-vessel rating, dimensions, vent and outlet connections, and relief device
- Expansion compensation data: expansion loop dimensions and anchor/guide locations, or expansion joint type, cycle rating, movement rating, and manufacturer's installation requirements
- Pipe support details for high-temperature service, including insulated supports, anchors, guides, and any variable- or constant-spring supports, coordinated with Hangers And Supports
- Insulation system data by service: operating temperature range, insulation material (mineral fiber, calcium silicate, cellular glass), minimum thickness per ASHRAE 90.1 Table 6.8.3-1, and jacket type
- Hydrostatic (or pneumatic) test plan, including test medium, test pressure, hold duration, and the boundaries of each test section
☑ Pipe and fitting material data by pressure class
☐ Valve data with B16.34 pressure-temperature ratings
☐ Flange data (B16.5 class and facing)
☐ WPS / PQR / WPQ welder qualification (Section IX)
☐ Steam trap schedule by service and type
☐ PRV station data with downstream relief valve
☐ Condensate receiver and pump set data
☐ Flash tank data (ASME-stamped)
☐ Expansion compensation calculations and details
☐ High-temperature pipe support details
☐ Insulation system data by service
☐ Hydrostatic / pneumatic test plan
3.1.2Fabrication and procurement shall not proceed until action submittals have been reviewed and returned.
3.2 Closeout Submittals
3.2.1At substantial completion, the Contractor shall provide the following before the system is accepted.
- As-built drawings showing pipe routing, valve and trap locations, anchor and guide locations, and pressure class of each section
- Welding records for each pressure-containing weld, including the welder identification, WPS used, and examination results
- Hydrostatic (or pneumatic) test report for each section, recording test pressure, hold time, and acceptance
- Steam trap survey at startup confirming each trap discharges condensate and holds steam
- PRV station setting record listing the as-set reduced pressure and downstream relief valve set pressure for each station
- Condensate pump set startup report, including alternator operation, float-switch settings, and alarm verification
- Operation and maintenance manuals for traps, PRV stations, condensate pumps, and flash tanks
- Insulation completion record confirming valves, strainers, PRV stations, and trap stations are insulated
☑ As-built drawings with pressure class indicated
☐ Welding records and examination results
☐ Hydrostatic / pneumatic test reports
☐ Steam trap startup survey
☐ PRV station setting record
☐ Condensate pump set startup report
☐ O&M manuals
☐ Insulation completion record
3.3.1The Contractor shall submit the following for information.
- Mill test reports (MTRs) for pipe and fittings used in medium- and high-pressure service
- Manufacturer's installation instructions for expansion joints, PRV stations, and steam traps
- Condensate quality and treatment provisions where condensate is returned for boiler make-up, including conductivity monitoring and chemical-injection arrangement, coordinated with Hvac Water Treatment
☑ Mill test reports for pipe and fittings
☐ Manufacturer installation instructions
☐ Condensate quality and treatment provisions
4 Quality Assurance
4.1 Welder and Procedure Qualification
NOTE Steam piping welds are pressure-containing and the leading cause of in-service failure when unqualified; documented qualification is therefore mandatory, not a formality. (4.1.1)
4.1.2All pressure-containing welds shall be made in accordance with a welding procedure specification (WPS) qualified per ASME BPVC Section IX.
4.1.3Each WPS shall be supported by a procedure qualification record (PQR) demonstrating the mechanical properties of a test weld.
4.1.4Each welder and welding operator shall hold a current welder performance qualification (WPQ) for the process, position, and material covered by the work.
4.1.5Qualification records shall be available at the project site for review before welding begins and shall remain available for the duration of the work.
4.1.6A weld made by an unqualified welder, or under an unqualified procedure, shall be cut out and replaced at no cost to the Owner.
4.2 Examination
NOTE Welds shall be examined to the extent and by the methods required by the governing code for the pressure class. (4.2.1)
4.2.2Welds on systems governed by ASME B31.1 shall be visually examined, with radiographic or other volumetric examination performed to the percentage required by B31.1 for the design conditions.
4.2.3Welds on low-pressure systems governed by ASME B31.9 shall be visually examined in accordance with B31.9.
4.2.4Defects revealed by examination shall be repaired and re-examined by the same method before the system is pressure-tested.
4.3 Code Compliance
NOTE Applying ASME B31.9 to a system that operates above 15 psig is a code violation; the building-services code does not impose the welder qualification and examination that power piping requires. (4.3.1)
4.3.2Where the operating pressure of any portion of the system exceeds 15 psig steam, that portion shall be designed, fabricated, examined, and tested to ASME B31.1.
4.3.3Pipe wall thickness for medium- and high-pressure service shall be verified against the pressure design rules of ASME B31.1 for the design pressure and temperature.
5 Environmental and Service Conditions
5.1 Design Pressure and Temperature
NOTE The design pressure and design temperature define the code basis, the pipe schedule, and the valve and flange ratings, and shall be fixed before material selection. (5.1.1)
5.1.2The design pressure shall be not less than the maximum operating pressure at the point of use, including the maximum setting of any upstream pressure-reducing or relief device.
5.1.3The design temperature shall be the saturation temperature corresponding to the design pressure unless superheat is present, in which case the maximum operating temperature shall govern.
○ Low-pressure steam (0-15 psig) - ASME B31.9
● Medium-pressure steam (15-100 psig) - ASME B31.1
○ High-pressure steam (100-300 psig) - ASME B31.1
5.2 Slope
NOTE Steam mains and condensate return lines must drain by gravity to their drip and collection points; insufficient slope leaves condensate standing in the main, which is then carried into the pipe as a slug on the next pressure change. (5.2.1)
5.2.2Steam supply mains shall slope a minimum of 1/4 in. per 10 ft (1:480) in the direction of steam flow.
5.2.3Condensate gravity return lines shall slope a minimum of 1/4 in. per 10 ft toward the receiver or collection point.
5.2.4Where a steam main must rise in the direction of flow, the main shall be dripped at the base of the rise and the slope reversed so condensate drains back to a trapped low point.
5.3 Velocity Limits
NOTE Excessive steam velocity erodes fittings, increases pressure drop, and entrains condensate; the following limits are design targets for sizing. (5.3.1)
5.3.2Steam supply mains shall be sized for a maximum design velocity of 8,000 fpm.
5.3.3Steam branch lines shall be sized for a maximum design velocity of 6,000 fpm.
5.3.4Two-phase condensate return lines shall be sized for a maximum velocity of 4,500 fpm, accounting for flash steam volume and not condensate mass flow alone.
6 Pipe, Fittings, and Joining
6.1 Pipe Material by Pressure Class
NOTE ERW A53 pipe is acceptable for low-pressure building-services steam but is not suitable for the temperatures and pressures of medium- and high-pressure service, where seamless A106 Grade B is required. (6.1.1)
6.1.2Low-pressure steam (0-15 psig) pipe shall be ASTM A53 Grade B black steel, electric-resistance-welded or seamless.
6.1.3Medium-pressure steam (15-100 psig) pipe shall be ASTM A106 Grade B seamless carbon steel.
6.1.4High-pressure steam (100-300 psig) pipe shall be ASTM A106 Grade B seamless carbon steel.
6.1.5Condensate return piping for pressurized return above 30 psig shall be Schedule 80 steel; gravity return piping shall be not less than Schedule 40.
ASTM A53 Gr. B black steel (low-pressure)
ASTM A106 Gr. B seamless (medium/high-pressure)
6.2 Pipe Schedule
NOTE The schedule must be matched to the pressure class and verified against the code pressure-design rules; the defaults below are the 80% case and do not relieve the engineer of the wall-thickness calculation for high-pressure service. (6.2.1)
6.2.2Low-pressure steam piping 2 in. and smaller shall be Schedule 40, joined by thread or flange.
6.2.3Low-pressure steam piping larger than 2 in. shall be Schedule 40, joined by butt-weld.
6.2.4Medium-pressure steam piping shall be Schedule 80 in all sizes.
6.2.5High-pressure steam piping 2 in. and smaller shall be Schedule 160.
6.2.6High-pressure steam piping larger than 2 in. shall be Schedule 80, with wall thickness verified by ASME B31.1 stress calculation.
Schedule 40 (low-pressure)
Schedule 80 (medium-pressure / high-pressure > 2 in.)
Schedule 160 (high-pressure ≤ 2 in.)
6.3 Fittings
NOTE Fitting type follows the joining method, which in turn follows the pressure class and size; mismatched fittings are a common source of leaks and pressure-rating shortfalls. (6.3.1)
6.3.2Butt-weld fittings for medium- and high-pressure steam shall conform to ASME B16.9 and ASTM A234 Grade WPB.
6.3.3Socket-weld and threaded fittings for small-bore steam shall conform to ASME B16.11.
6.3.4Fittings shall match or exceed the pressure rating and material grade of the connected pipe.
6.4 Joining Method
NOTE The joining method is selected by pressure class and pipe size: welded joints for medium and high pressure, with threaded joints permitted only on low-pressure small-bore lines. (6.4.1)
6.4.2Medium- and high-pressure steam piping larger than 2 in. shall be butt-welded.
6.4.3Medium- and high-pressure steam piping 2 in. and smaller shall be socket-welded.
6.4.4Threaded joints shall be used only on low-pressure steam piping 2 in. and smaller.
6.4.5Connections to equipment, valves, and removable components shall be flanged.
● Butt-weld (medium/high pressure)
○ Socket-weld (medium/high pressure ≤ 2 in.)
○ Threaded (low pressure ≤ 2 in. only)
○ Flanged (equipment connections)
6.5 Flanges
NOTE Flange class must be rated for both the design pressure and the design temperature; carbon-steel ratings derate with temperature, so a flange that passes a pressure check at ambient may be under-rated at the operating temperature. (6.5.1)
6.5.2Flanges shall conform to ASME B16.5 and shall be rated for the design pressure and temperature of the connected service.
6.5.3Class 150 flanges may be used where the design conditions fall within the carbon-steel Class 150 rating at the design temperature.
6.5.4Class 300 flanges shall be used for systems above 150 psig or above 400°F.
● Class 150 (campus steam within rating)
○ Class 300 (above 150 psig or above 400°F)
○ Class 600 (high-pressure service)
7 Steam Traps and Drip Legs
7.1 Drip Legs
NOTE A drip leg is a vertical collecting pocket at the bottom of a steam main that lets gravity pull condensate out of the fast-moving steam so a trap can discharge it; without drip legs at low points and ahead of equipment, condensate accumulates and is driven through the pipe as a destructive slug on startup. (7.1.1)
7.1.2Drip legs shall be provided at all low points, at the base of risers, ahead of each pressure-reducing station, ahead of each isolation valve that may close against trapped condensate, and at the end of each steam main.
7.1.3Drip leg depth shall be a minimum of 12 in. below the centerline of the steam main.
7.1.4Drip legs on mains 4 in. and smaller shall be full size of the main.
7.1.5Drip legs on mains larger than 4 in. shall be a minimum of half the main size, but not less than 4 in.
7.1.6Each drip leg shall be fitted with a steam trap and a strainer upstream of the trap.
7.2 Steam Trap Selection
NOTE Trap type is selected by service: drip service on the mains, continuous high-volume discharge at equipment, and compact drip service on high-pressure lines each favor a different trap mechanism. (7.2.1)
7.2.2Inverted-bucket traps shall be used for drip service on steam mains.
7.2.3Float-and-thermostatic (F&T) traps shall be used on heat exchanger and unit heater condensate where discharge is continuous and high-volume.
7.2.4Thermodynamic disc traps shall be used for compact drip service on high-pressure lines.
7.2.5Each trap shall be selected for the differential pressure across it at the design condition and for the condensate load it serves, with a safety factor applied per the manufacturer's sizing method.
● Inverted-bucket
○ Thermodynamic disc
○ Float-and-thermostatic (F&T)
● Float-and-thermostatic (F&T)
○ Inverted-bucket
7.3 Trap Station Arrangement
NOTE A trap station that can be isolated, cleaned, and tested without shutting the system is the difference between a trap that is maintained and one that fails open and wastes steam indefinitely. (7.3.1)
7.3.2Each trap station shall include an upstream strainer, isolation valves upstream and downstream, a test or inspection means, and a union or flange for trap removal.
7.3.3A check valve shall be provided downstream of each trap discharging into a common return where back-flow from other traps is possible.
8 Condensate Return
8.1 Return Configuration
NOTE Condensate returns by gravity where the layout and back-pressure permit; where it does not, a receiver and pump set lift the condensate back to the boiler plant. (8.1.1)
8.1.2Gravity return shall be used where the condensate can drain to the receiver or boiler without lift and against the system back-pressure.
8.1.3A pumped return with a condensate receiver and a duplex condensate pump set shall be used where gravity return is not feasible.
○ Gravity return
● Pumped return (receiver + duplex pump set)
8.2 Condensate Receiver and Pump Set
NOTE A duplex pump set with an alternator keeps condensate moving when one pump fails and is standard for any return that cannot tolerate an outage; the receiver volume must buffer the condensate load between pump cycles. (8.2.1)
8.2.2The condensate pump set shall be duplex.
8.2.3The pump set shall include an automatic alternator that alternates the lead and lag pumps and starts the lag pump on high level.
8.2.4The receiver shall be sized to hold not less than one minute of the connected condensate load at the receiver.
8.2.5Pump and motor electrical characteristics shall be coordinated with the electrical scope before installation.
8.2.6Float-switch and alarm wiring shall be confirmed to be in the project electrical scope before installation.
NOTE Condensate pump controls frequently fall into a coordination gap between mechanical and electrical scopes; confirm scope boundaries explicitly during design. (8.2.7)
● Duplex (lead/lag with alternator)
○ Simplex
Cast iron
Fabricated steel
Stainless steel
8.3 Flash Tanks
8.3.3The flash tank shall be an ASME-stamped pressure vessel sized to separate the flash steam from the condensate at the flash pressure.
8.3.4Flash steam shall be vented or recovered to a low-pressure use, and the residual condensate shall drain to the return through a trap.
○ Yes - high-pressure condensate to low-pressure return
● No - single-pressure return
9 Pressure-Reducing Stations
9.1 Station Arrangement
NOTE A pressure-reducing valve (PRV) station drops steam from a distribution pressure to a use pressure; it is a small assembly, not a single valve, because it needs a clean inlet, a means to maintain service during PRV maintenance, and overpressure protection on the reduced side. (9.1.1)
9.1.2A PRV station shall include an upstream strainer, an upstream isolation valve, the pressure-reducing valve, a downstream isolation valve, a bypass with a globe valve, and inlet and outlet pressure gauges.
9.1.3A drip leg with a trap shall be provided upstream of the station to remove condensate before the reducing valve.
9.1.4Single-stage reduction shall be used where the pressure ratio across the station is within the reducing valve's recommended single-stage range.
9.1.5Two-stage reduction shall be used where the pressure ratio exceeds the single-stage range or where close downstream pressure control is required.
● Single-stage
○ Two-stage
9.2 Downstream Relief
NOTE A reducing valve can fail open and pass full upstream pressure to the low-pressure side; ASME B31.1 and the IMC therefore require a relief valve downstream of every reducing station, sized to pass the full PRV capacity. (9.2.1)
9.2.2A safety relief valve shall be provided downstream of every pressure-reducing station.
9.2.3The downstream relief valve shall be set at or below the maximum allowable working pressure of the downstream piping and equipment.
9.2.4The relief valve shall be sized to relieve the full capacity that the reducing valve can pass with its seat fully open at the inlet design pressure.
10 Valves and Strainers
10.1 Isolation Valves
NOTE Isolation valves must carry the pressure-temperature rating of the service, which for steam means a B16.34 rating verified at the design temperature, not just the design pressure. (10.1.1)
10.1.2Isolation valves shall conform to ASME B16.34 and shall be rated for the design pressure and temperature of the service.
10.1.3Gate or ball valves shall be used for isolation service where full-bore shutoff is required.
10.1.4Globe valves shall be used where throttling or bypass control is required.
10.1.5Valve end connections shall match the piping joining method for the service.
● Gate
○ Ball
○ Globe (throttling/bypass)
10.2 Check Valves
NOTE Check valves prevent reverse flow into condensate pumps and back-flow between traps discharging into a common return. (10.2.1)
10.2.2Check valves shall be provided on the discharge of each condensate pump and where required to prevent back-flow in common return headers.
10.2.3Check valves shall be rated for the pressure and temperature of the service and selected for the flow direction and orientation of the installation.
10.3 Strainers
NOTE A strainer ahead of each trap, control valve, and reducing valve keeps scale and weld slag out of close-clearance seats, which are otherwise wire-drawn and fail open. (10.3.1)
10.3.2A strainer shall be installed upstream of each steam trap, pressure-reducing valve, and control valve.
10.3.3Strainer screens in steam service shall be stainless steel with a perforation or mesh suited to the protected device.
11 Expansion Compensation
11.1 General
NOTE Steam pipe grows roughly 3/4 in. per 100 ft at 100 psig; unrelieved thermal growth cracks flanges, shears bolts, and pulls supports loose, so every run must be analyzed and compensated. (11.1.1)
11.1.2Thermal expansion of each pipe run shall be calculated for the temperature change from installation to operating temperature.
11.1.3Expansion compensation shall be provided by expansion loops, bellows expansion joints, or slip-type expansion joints, with anchors and guides arranged to direct the movement.
11.1.4Expansion loops shall be the preferred method of compensation where space permits, as they require no moving seals.
● Expansion loops
○ Bellows expansion joints
○ Slip-type expansion joints
11.2 Expansion Joints
NOTE Where a loop will not fit, an expansion joint is used, but a joint has a finite cycle life and movement rating and must be sized to the actual analyzed movement, not a nominal value. (11.2.1)
11.2.2Expansion joints shall be selected and rated by engineering analysis for the calculated movement and the design number of thermal cycles.
11.2.3Anchors and guides shall be provided at the spacing required by the joint manufacturer to keep the movement axial and within the joint's rating.
11.3 Anchors and Guides
NOTE Anchors fix the pipe at intended points so expansion is directed into the loop or joint rather than into equipment; guides keep the pipe aligned between anchors. (11.3.1)
11.3.2Main anchors shall be provided at the points required to direct thermal movement into the compensation devices, coordinated with Hangers And Supports. 11.3.3Pipe guides shall be provided on each side of expansion joints and along long runs at the spacing required to prevent buckling and to keep movement axial.
12 Insulation Requirements
12.1 General
NOTE This standard specifies the insulation requirements by service - operating temperature, minimum thickness, and jacket - and delegates material specification and field application detail to
Mechanical Insulation.
(12.1.1) 12.1.2Steam and condensate piping shall be insulated to not less than the minimum thickness required by ASHRAE 90.1 Table 6.8.3-1 for the service operating temperature.
12.1.3Insulation material shall be selected for the surface operating temperature of the service.
● Mineral fiber (up to ~850°F)
○ Calcium silicate (high temperature, above ~400°F surface)
○ Cellular glass
12.2 Material by Temperature
NOTE Fiberglass has a continuous service limit near 850°F; on the hottest high-pressure mains the surface temperature exceeds the practical limit and calcium silicate or cellular glass is required instead. (12.2.1)
12.2.2Mineral fiber insulation conforming to ASTM C547 shall be used for steam and condensate lines within its service temperature limit.
12.2.3Calcium silicate insulation conforming to ASTM C533 shall be used on steam mains operating above approximately 400°F surface temperature, where mineral fiber is inadequate.
12.3 Insulation of Fittings and Accessories
NOTE Valves, strainers, PRV stations, and trap stations are the largest single source of heat loss and the primary burn hazard in a steam system; leaving them bare or only partly insulated wastes steam and creates a safety hazard. (12.3.1)
12.3.2Valves, strainers, flanges, pressure-reducing stations, and steam trap stations shall be insulated.
12.3.3Insulation at these components shall be furnished with removable, reusable insulation covers where the component requires periodic access for maintenance.
● Required at all valves, strainers, traps, and PRV stations
○ Required at PRV and trap stations only
13 Routing and Underground Distribution
13.1 General Routing
NOTE The routing decision - above-grade, direct-buried, or walk-through tunnel - drives the entire insulation and protection approach and is set by the campus layout and the locations shown on the drawings. (13.1.1)
13.1.2Above-grade steam piping shall be insulated and provided with a weatherproof metal jacket where exposed to weather.
13.1.3Underground steam piping shall be a factory pre-insulated, direct-buried conduit system with a continuous steel or HDPE outer casing and a drainable, dryable air space or foam carrier insulation.
● Above-grade (insulated, metal jacket)
○ Underground direct-buried (pre-insulated conduit)
○ Walk-through tunnel
13.2 Underground Pre-Insulated Systems
NOTE A buried steam line that takes on water fails fast through corrosion of the carrier pipe; the conduit system must keep the carrier dry and be testable for leaks before backfill. (13.2.1)
13.2.2The pre-insulated conduit system shall be furnished by a single manufacturer as a complete system, including straights, fittings, anchors, and field joint closures.
13.2.3The outer casing shall be tested for leak-tightness in accordance with the manufacturer's requirements before backfill.
13.2.4Drainage and venting provisions of the conduit air space, where furnished, shall be installed in accordance with the manufacturer's requirements.
14 Pipe Supports
14.1 High-Temperature Support
NOTE Steam piping needs supports designed for high temperature and thermal movement; ordinary clevis hangers at insulation crush points cause corrosion under insulation and thermal bridging, so insulated supports are used at hot lines. (14.1.1)
14.1.2Pipe supports shall be coordinated with Hangers And Supports and shall be suitable for the operating temperature and the thermal movement of the run. 14.1.3Insulated pipe supports (shoes or saddles with insulating inserts) shall be used at support points on insulated hot piping to prevent thermal bridging and corrosion under insulation.
14.1.4Variable-spring or constant-spring supports shall be provided at heavy fittings and at points of significant vertical thermal movement where rigid supports would impose unacceptable load changes.
15 Testing
15.1 Hydrostatic Test
NOTE A hydrostatic test proves the joints before the system carries steam; it is performed at a pressure above the design pressure and held long enough to find leaks. (15.1.1)
15.1.2The system shall be hydrostatically tested at 1.5 times the design pressure, but not less than 100 psig, in accordance with ASME B31.1.
15.1.3The test pressure shall be held for a minimum of 10 minutes, and longer as required to complete the examination.
15.1.4The system shall show no leakage and no drop in pressure attributable to leakage during the hold.
15.1.5Strainers, traps, and pressure-sensitive components that could be damaged by the test pressure shall be isolated or removed during the test.
● 1.5 x design pressure (minimum 100 psig)
○ Per ASME B31.1 for the design conditions
15.2 Pneumatic Test
NOTE Where a hydrostatic test cannot be done - for example where the system cannot be drained or freezing is a risk - a pneumatic test at a lower multiplier is permitted, with the added precautions that stored gas pressure requires. (15.2.1)
15.2.2A pneumatic test shall be used only where hydrostatic testing is not feasible and shall be performed at 1.1 times the design pressure in accordance with ASME B31.1.
15.2.3A pneumatic test shall be conducted with the safety precautions required for stored-energy testing, including a preliminary low-pressure check and exclusion of personnel from the test area.
15.3 Startup and Trap Verification
NOTE Bringing a steam system up requires warming the pipe slowly and draining condensate as it forms; a fast startup against a cold, condensate-filled main is the classic water-hammer event. (15.3.1)
15.3.2The system shall be warmed up gradually at startup, draining condensate through the drip legs and traps as the piping comes up to temperature.
15.3.3Each steam trap shall be verified at startup to discharge condensate and to hold steam, and any trap found blowing steam or failing to discharge shall be repaired or replaced.
16 Installation
16.1 General
NOTE Field practice on steam piping is unforgiving: a missed drip leg, a back-pitched run, or an unrelieved expansion turns into water hammer or a cracked joint in service. (16.1.1)
16.1.2Piping shall be installed to the slopes, drip-leg locations, anchor and guide locations, and pressure class shown on the drawings and specified herein.
16.1.3Eccentric reducers shall be installed flat-on-bottom on horizontal steam mains so condensate is not trapped at the reduction.
16.1.4Branch connections from a steam main shall be taken from the top of the main so condensate is not carried into the branch.
16.1.5Dirt pockets and drip legs shall be installed so they can be cleaned and so the trap can be removed without cutting the pipe.
16.2 Cleaning
NOTE New steam piping carries weld slag, scale, and oil that will lodge in trap and valve seats; the system is blown down and strainers are cleaned before it is placed in service. (16.2.1)
16.2.2The system shall be blown down or flushed to remove construction debris before traps and control valves are placed in service.
16.2.3Strainer screens shall be removed, cleaned, and reinstalled after initial operation and again as directed during the startup period.
17 Delivery, Storage, and Handling
17.1 Protection
NOTE Pipe ends and pre-insulated conduit sections take on dirt and water if left open in the yard; corrosion and wet insulation that start in storage are carried into the finished system. (17.1.1)
17.1.2Pipe and fittings shall be stored off the ground, with end caps or plugs left in place until the pipe is installed.
17.1.3Pre-insulated conduit sections shall be stored to keep the insulation dry and shall not be installed if the insulation has become wet.
17.1.4Valves, traps, and PRV components shall be stored in their original packaging, protected from dirt and weather, until installation.
18 Warranty
18.1 Warranty
18.1.1The Contractor shall warrant the steam and condensate piping system against defects in materials and workmanship for a period of not less than one year from the date of substantial completion.
18.1.2Manufactured components, including steam traps, condensate pumps, PRV stations, and expansion joints, shall carry the manufacturer's standard warranty, which shall be transferred to the Owner.
18.1.3Defects in welds, joints, or components discovered within the warranty period shall be repaired or replaced at no cost to the Owner, including restoration of insulation disturbed by the repair.
19 Spare Parts
19.1 Spare Parts
NOTE Steam traps and strainer screens are the routine wear items; a small on-hand stock keeps a failed trap from being left blowing steam while a replacement is procured. (19.1.1)
19.1.2The Contractor shall furnish spare steam trap internals or complete spare traps for each trap type and size used, in the quantity scheduled.
19.1.3The Contractor shall furnish spare strainer screens for each strainer type and size used.
19.1.4The Contractor shall furnish spare gaskets for each flange size used at removable connections.