Table of Contents
|Design of Cryogenic Pipe Systems||2|
|Vacuum-Jacketed Piping (LOX, LIN, and LAR Service)||4|
|Insulated Pipe Duct||6|
|Cryogenic Storage Tanks (Excluding Hydrogen)||7|
|Trailer Fill Piping||8|
|Liquid Hydrogen and Liquid Helium Piping Systems||9|
|Horizontal Expansion Loops||11|
|Pipe Duct Layout||13|
|Supports Inside Pipe Duct||14|
|Pipe Duct Pipe Support Details||15|
|Underground Trailer Loading Arrangement||16|
|Details of Underground Loading Lines||17|
DOUBLE CLICK ON GREEN “TOC” TO RETURN TO TABLE OF CONTENTS
1.1 This guideline highlights typical problems and design considerations associated with piping systems that are used to transfer cryogenic liquids and gases. Cryogenics is a science relating to very low temperatures.
2.1 This guideline applies to cryogenic piping in air separation and hydrocarbon plants that are designed by or for Air Products.
2.2 Cryogenic liquefied gases included in this guideline are nitrogen, oxygen, argon, hydrogen, natural gas, as well as gases such as helium, neon, and krypton. Temperatures for these liquefied gases range from -161°C (-258°F) for natural gas (methane) to -269°C (-452°F) for helium.
- RELATED DOCUMENTS
3.1 Air Products Engineering Documents
3CB00005 Perlite Loading
3CB30005 Purge Systems for Air Separation Process Cold Boxes
3PI01001 Design Criteria for Plant Layout
3PI25010 Venting of Nontoxic and Nonflammable Substances
3PI45002 Specifying Static Vacuum Jacketed Piping
4EL64401A Electric Heating for Cryogenic Equipment Foundations
4ES60101A Separation Distances for Storage Systems and Process Equipment
4ES85001A Fire Protection Requirements for GEG-USA Facilities
4PI00003A Piping Flexibility and Thermal Movement
4PI20001A Trailer Pull-Away Protection System Using Instrument Air Shut-off Cable
4PI20004A Cryogenic Vapor Dispersal System for Tanker Loading Areas
4WCB-30001 Cold Box Penetrations Standard Details
Å 4WPI-INS001 Cellular Glass Thermal Insulation System for Cold and Cryogenic Piping and Equipment Material Symbol C
Å 4WPI-INS007 Installation of Multi-Layer Thermal Insulation of Cryogenic Piping With PIR (Polyisocyanurate foam) Symbol P1
Å 4WPI-INS008 Installation of Single-Layer Thermal Insulation of Cold Piping and Equipment With PIR (Polyisocyanurate Foam) Symbol P4
4WCB-50002 Mineral Wool for Cold Box Insulation
311708 Standard Pipe Support Details
312447 Tanker Loading Arm Assembly
312448 Tanker Loading Arm Hose Clamp Assembly
320009 Standard Piping Details
326280 Standard VJ Piping Details
Å Provided for background information only (not referenced in the text)
- DESIGN OF CRYOGENIC PIPE SYSTEMS
4.1.1 Vertical pipe loops should be avoided because vaporized gas will collect at the high point and restrict liquid flow. This is most critical for cryogenic piping systems with marginal pressure differential, for example, liquid to storage, liquid from storage to pumps, liquid to pressure buildup coils (PBU) or product vaporizers.
4.1.2 Liquid oxygen lines with intermittent flow should be designed to free drain. Low points should be avoided because repeated oxygen boil off at low points creates the hazardous condition of hydrocarbon accumulation. The addition of a low-point drain will be required when low points cannot be avoided.
4.1.3 Equipment should be located to minimize cryogenic pipe runs. This is important for cryogenic systems with low flow rates and when minimum product loss to boil off is a requirement.
4.1.4 Expansion loops or offset pipe runs might be necessary to compensate for thermal movement of cryogenic piping (see Figure 1). Refer to 4PI00003A for information on piping flexibility and expansion when designing cryogenic piping systems. The stress engineer shall review all cryogenic piping designs.
4.1.5 The design of a cryogenic piping system shall consider insulation requirements associated with cryogenic temperatures when locating valves and instrumentation (see Figure 2).
4.1.6 Basic design requirements for plant layouts are discussed in 3PI01001.
4.2 Valves in Cryogenic Service
4.2.1 Automatic valves and hand valves in continuous cryogenic service must include an extended‑stem design to protect the packing area of the valve from cryogenic temperatures and ice buildup. The extended stem provides a vapor seal within the valve. The use of chain operators should be avoided on extended-stem valves.
4.2.2 Preferably, valves should be installed with the operator, or hand wheel, in a vertical position. Rotating the valve stem from vertical to a minimum of 15 degrees above horizontal is an acceptable alternative.
4.2.3 Valves shall not be installed in vertical pipe runs in continuous cryogenic service, thereby avoiding damaging ice buildup on valves.
4.3 Relief Devices In Cryogenic Piping
4.3.1 Spring-operated relief valves shall be installed vertically to allow reseating of the valve in case of a discharge. The relief device must be positioned above the pipe run to provide vapor‑seal protection. Paragraphs 4.4.2 and 4.4.4 provide installation guidelines.
4.3.2 Sections of cryogenic piping that are blocked in by valves, check valves, or equipment shall be protected with a thermal relief device to prevent overpressurization resulting from liquid boil off. Thermal relief valve discharge piping must be directed away to protect personnel and equipment (see 320009-62).
4.3.3 Cryogenic liquid discharging from full-flow relief devices must be directed to either a disposal system or a safe spill area for disposal.
4.3.4 Cryogenic gas discharging from full-flow relief devices shall be routed according to 3PI25010.
4.3.5 Flammable gas relief devices (hydrogen and methane) shall discharge to a safe elevation or into a disposal-header system. Flammable gas vents shall not be discharged at or directed to grade.
4.4 Branch Connections From Cryogenic Pipe
4.4.1 Instrument and process branch connections should be from the top of horizontal pipe runs. Horizontal and bottom branch connections should be avoided except for process considerations such as pump suction piping. The vertical extension of the branch pipe provides a vapor seal configuration for nonflowing lines, which minimizes boil off loss and ice buildup and provides an ambient-temperature zone for instrument devices.
4.4.2 The minimum vertical extension should be the greater of either 175 mm (9 in) or 5 diameters of the branch size above the top of the header pipe. Insulation thickness and installation must be considered in the design of the branch pipe.
4.4.3 Branch connections shall be combined when possible. An example would be a vent valve and relief valve assembly. See 320009 for the piping and insulation requirements for typical installations.
4.4.4 Horizontal branch connections from vertical pipe runs shall include a vertical 90-degree elbow to affect a required vapor seal. The branch configuration shall allow for both the header and branch piping to be insulated independently. Paragraphs 4.4.2 and 4.4.3 apply to the complete assembly.
4.4.5 Bottom branch connections terminating with a valve must be configured to allow both the header and branch to be independently insulated. The valve must be an extended-stem valve installed according to paragraph 4.2.2. Check to ensure the necessary hand wheel clearances are maintained. Insulation of the branch run shall extend a minimum of one insulation thickness downstream of the valve body.
4.5 Supporting of Cryogenic Pipe
4.5.1 Insulated cryogenic pipe shall be supported from the outside of the insulation to minimize insulation penetrations. See 311708-I061 through 311708-I070 for standard insulated pipe support details.
4.5.2 Noninsulated cryogenic pipe in contact with carbon steel material can cause embrittlement and structural failure. Either a stainless steel member or a stainless steel shoe will be required to support the piping. See 311708-C021 through 311708-C023 for standard shoe support details. A minimum “A” dimension of 150 mm (6 in) is required.
4.5.3 Anchors on cryogenic piping must connect directly to the pipe wall. Standard support drawings 311708A-001, 311708A-C021, and 311708A-C038 are acceptable anchors. Consult the pipe stress engineer when selecting an anchoring system.
4.5.4 The pipe stress engineer must review and approve all pipe support systems.
4.6 Piping at Vaporizers
4.6.1 The liquid lines that gravity feed to the vaporizer shall be short and continuously slope upward towards the vaporizer. Vertical pipe loops should be avoided because vaporized gas will collect at the high point and restrict liquid flow. A pumped line to a vaporizer may have some upward loops. These lines must be reviewed for sufficient pump “head” and for adequate line velocity.
4.6.2 In the case of multiple vaporizers, the inlet header must always run full of liquid. The lines to the individual vaporizers shall branch off of the top of the header.
- The liquid line to vaporizer shall be insulated up to and including its shut-off valve, only. The rest of the line(s) downstream from this valve shall remain uninsulated. All the pressure, vent, thermal relief valve and other small branches off of main line shall be in accordance with the applicable Air Products Engineering Standard Piping Details located on the 320009A Detail Drawings.
- A minimum clearance under these lines shall be 300 mm (12 in) from the bottom of the pipe to the concrete pads to allow for some ice buildup.
- VACUUM-JACKETED (VJ) PIPING (LOX, LIN, AND LAR SERVICE)
Note: See paragraph 9.2 for liquid hydrogen and liquid helium VJ pipe.
5.1.1 This guideline applies to VJ piping systems manufactured and installed in the US. Limitations or variances in construction and sizing might vary for international applications.
5.1.2 See 3PI45002 for general information relating to the design, construction, and purchase of VJ pipe.
5.1.3 The following is a schedule of common VJ pipe sizes; the VJ supplier will determine final pipe size. For sizes not listed, consult the VJ supplier.
|Carrier x Casing||Carrier x Casing|
|1 x 2 1/2||3 x 5|
|1 1/2 x 3||4 x 6|
|2 x 4||6 x 10|
5.1.4 Vacuum-jacketed spools are assembled using field-insulated butt welded joints. See standard VJ piping details drawing 326280. Spools might vary in length depending on configuration. The maximum shippable spool length shall be as specified in 3PI45002, Section 5, or as limited by project-specific conditions.
5.1.5 The piping designer shall furnish the VJ pipe specifier with isometric drawings of the VJ pipe routing to be included with the VJ bid specification. The pipe stress engineer must approve the isometric drawings before they are sent to the VJ supplier. Supports for the VJ pipe must be located and identified (see paragraph 5.3).
5.1.6 Piping Design and the pipe stress engineer shall review and approve in writing the drawings submitted by the VJ pipe fabricator for conformance to design drawings and specifications.
5.2 Routing Vacuum-Jacketed Pipe
5.2.1 VJ pipe runs should be as short as possible. Boil-off losses are less than for insulated pipe, but material costs are greater.
5.2.2 Pipe runs should use changes in direction to compensate for thermal pipe movement. Vacuum‑jacketed, braided metal hoses used at these points can absorb pipeline movement with minimum offset length.
5.2.3 All branch connections, valves, relief valves, or other in-line components add cost to VJ piping. When practical, these items should be located outside the VJ piping runs.
5.2.4 Branch connection and VJ termination details must be shown on the VJ isometrics. See 326280 for standard VJ piping connections and termination details.
5.3 Supporting VJ Piping
5.3.1 The inner line size must be used to determine the maximum span between supports for VJ pipe. See 4PI00004A for maximum support spacing.
5.3.2 Slide plates should be used to reduce friction loads on vacuum-jacketed pipe. See drawing 311708, details C026 and C027, for typical guide and anchor details.
5.3.3 Anchor and support location information shall be furnished to the VJ-pipe fabricator to aid in locating casing bellows and spool joints. This information shall be part of the routing drawing referenced in paragraph 5.1.5.
5.3.4 The pipe stress engineer shall review and approve in writing the VJ-piping isometrics. The final design is the responsibility of the VJ supplier.
- INSULATED PIPE DUCT
6.1.1 Insulated pipe duct may be used for cryogenic piping when three or more lines are routed together and when insulated or VJ pipe is either not available or considered to be too expensive. Customer requirements might also dictate the use of insulated duct.
6.1.2 Typical duct construction shall be an angle frame with plate sides. Duct shall be all-welded construction with removable top plates (see Figure 3). The top plate shall be sealed with a rubber gasket and fastened with bolts or spring clips to provide a weather-tight installation. The cross‑sectional strength of insulated duct allows for long unsupported spans of duct to be used. Straight run of pipe duct is the most cost-effective use of insulated duct. The use of bends shall be minimized.
6.1.3 Lines within the insulated duct may be copper, stainless steel, or aluminum pipe and fittings.
6.1.4 The duct interior shall be packed with granulated, mineral fiber or perlite insulation after installation and testing of the piping (see 3CB00005). To specify mineral wool, 4WCB-50002 may be used.
6.1.5 The duct interior shall be continuously purged with nitrogen using an internal purge distribution system. Nitrogen supply shall have a meter to control flow (see 3CB30005 for duct purge systems guideline).
6.2 Pipe Routing (Inside Duct)
6.2.1 Pipe runs should be arranged in a tight pattern using multiple layers to accommodate a larger number of lines (see Figure 3). Duct cross section shall be kept square, if possible. Line spacing should be 150 to 200 mm (6 to 8 in) on centers. To ensure adequate insulation cover*, a minimum distance of 380 mm (1 ft 3 in) shall be maintained from the centerline of any pipe run to face of duct panel for lines DN100 (NPS 4) and smaller.
(Note*) A value of 19.4°C (35°F) should be applied to each 25 mm (1 in) of insulation (from ambient to operating temperature) to determine adequate cover.
Example: 100°F at the duct wall to -320°F operating temperature of the pipe, equals
[100-(‑320) = 420] divided by 35 for a required cover from outside of pipe of 300 mm (12 in) rounded up.
6.2.2 Process lines (with continuous flow) that penetrate the duct wall will require a thermal break detail (to specify thermal breaks, see 4WCB-30001). The limited area inside the duct requires that the thermal break assembly be applied outside the duct wall.
6.2.3 Branch connections penetrating the duct will require a penetration plate (to specify plates, see 4WCB-30001). Branch connections are lines that in normal operation have no flow, relief valve connections, and pressure connections. Vents and drains are branch connections. Branch connections may originate from the top or bottom of the pipe but must rise a minimum of 175 mm (9 in) to form a vapor seal. Piping shall be routed near the duct exterior before exiting the duct to provide a warm-up leg (see Figure 3). Branch connections must allow for thermal movement of piping inside the duct.
6.2.4 Valves installed in insulated duct shall have plain extended stems with enough length to install a seal boot at the duct penetration. Seal boot details may be specified as shown in 4WCB-30001. All valves penetrating the duct or located inside (check valves) shall be identified with a 90 mm (3 1/2 in) x 13 mm (1/2 in) x 1.5 mm (1/16 in) thick laminated plastic nameplate secured to the duct with #4 x 3/16″ Large Round Head Stainless Steel self-tapping screws. The nameplate will be engraved with the valve tag number.
6.2.5 The piping designer shall consider thermal movement of the piping inside a duct when routing the pipe. The charts in 4PI00003A shall be used to determine line movements. Changes in direction or offsets in the duct arrangement should be used for thermal movement. Braided flexible hoses, when installed at these offsets, compensate for large amounts of movement. When straight pipe runs are necessary, expansion joints designed for axial movement may be used. Anchor design and guide locations are important when this type of expansion joint is used. The pipe stress engineer must review all cryogenic pipes inside of duct runs.
6.3 Support of Pipes Inside Insulated Duct
6.3.1 Mineral fiber insulation of the pipe duct will generally support the piping. Supports are required at anchor and guide points as well as for support of the pipe during construction. Perlite insulation, on the other hand, could require additional weight supports.
6.3.2 Internal duct supports shall be 80 x 80 x 6.5 mm (3 x 3 x 1/4 in) stainless steel angle with 13 mm (1/2 in) thick laminated plastic pad. The support angles span the width of the duct and are welded to duct sides. Supports are to be installed by the piping contractor (see Figure 4).
6.3.3 Support locations should satisfy anchor and guide requirements first, with additional supports added as needed to support piping (see 4PI00004A).
6.3.4 Stainless steel U-bolts shall be used to anchor and guide piping inside the insulated duct. See 311708, standard supports C015 and C016 and Figure 5.
- CRYOGENIC STORAGE TANKS (EXCLUDING HYDROGEN)
7.1 Flat Bottom (Field-Erected Tanks)
7.1.1 Storage tanks should be located close to the cold box and trailer loading areas. If liquid argon storage is required, location nearer the cold box is desired to minimize length of fill line, thereby reducing costs resulting from boil-off of this expensive product.
7.1.2 The spacing between field-erected tanks should be half the diameter of the largest tank with a minimum distance of 4 500 mm (15 ft 0 in) to accommodate construction of the tanks. See 3ES60101 for minimum spacing requirements to other plant equipment.
7.1.3 Tank nozzle orientation and pump placement should facilitate piping from the plant to storage and from storage to loading. Venting should be positioned away from operating areas to avoid fogging and icing problems.
7.1.4 Field-erected tanks with soil-bearing foundations (anchoring slab directly on grade) shall have a cable heating system installed according to 4EL64401A.
7.2 Shop-Fabricated Tanks (Horizontal or Vertical)
7.2.1 Shop-fabricated product storage tanks (low pressure) shall be located according to paragraph 7.1.1. High‑pressure storage tanks associated with pipeline backup should be located close to related pumps and vaporizers.
7.2.2 Horizontal tanks may be arranged side by side with a minimum distance between tanks of 1 500 mm (5 ft) to allow for maintenance. Foundation requirements could also dictate tank spacing.
7.2.3 Horizontal storage tanks might have the control piping factory installed. When control piping is field installed, the comments in Section 2 of this guideline shall be applied when locating valves and instrumentation.
7.2.4 Refer to 3PI25010 for venting of shop-fabricated storage tanks.
7.3 Design Consideration For Cryogenic Storage Tanks
7.3.1 Maintaining net positive suction head (NPSH) pressure requirements of storage-area pumps will ensure optimum pump performance. NPSH is the primary criterion used to establish the storage tank elevation. The positioning of the pressure-buildup coil relative to the bottom of the storage tank is also critical. This information is provided via a “critical elevation drawing” prepared by the process engineer.
7.3.2 Pumps, buildup coil, and other storage-area equipment and pipe supports shall be supported from a common foundation to avoid differential-settlement issues. This also facilitates shorter pipe runs and reduces product loss due to boil off.
7.3.3 Differential settlement between a “cryogenic storage system” and adjacent pipe rack or storage system must be considered in the design of storage tank piping.
- TRAILER FILL PIPING
8.1.1 The preferred location of the fill pad is adjacent to the storage area with the loading end (back) of the trailer visible from the control room.
8.1.2 When multiple load stations are required, the design should place the argon loading nearest the storage area and also include the flexibility of loading multiple products from each load point.
8.1.3 Each trailer fill point must be equipped with trailer pullaway protection. See 4PI20001A for pullaway-protection requirements. Customer station fill points and other product unloading connections with intermittent use within a facility are exempt from pullaway protection.
8.1.4 Trailer fill pads not equipped with an automatic-fill system must install a disposal system to safely manage an overfill event (see 4PI20004A).
8.2 Drive-Thru Trailer Loading
8.2.1 Drive-thru loading promotes one-directional truck traffic within a facility. Equipped with load-on scales and auto load, it provides a fast, safe, and efficient loading procedure.
8.2.2 A loading arm equipped with a load-balanced fill-hose caddy system is used to facilitate drive-thru trailer loading.
8.2.3 Typical piping arrangements and related details associated with drive-thru loading are stored with the Engineered System TKA000 and are also referenced in paragraph 8.4 of this guideline.
8.3 Back-In Trailer Loading
8.3.1 Back-in loading requires less plant area and is an alternate to drive-thru loading. On-scale loading and auto load are options that can also be used with back-in loading.
8.3.2 Back-in loading can be designed as a system to accommodate either aboveground or underground loading lines.
8.3.3 The aboveground installation is similar to the drive-thru loading described in paragraph 8.2. The hose length, support arm, breakaway coupling, anchor, and piping arrangement are common.
8.3.4 Underground loading is an option when multiple loading stations are required and unobstructed access is desirable. Figures 6 and 7 show a typical arrangement and details for underground loading. The arrangement may be adjusted to satisfy project requirements. For example, the auto load would eliminate the need of the vent line, or the load station spacing may vary.
8.4 Related Design Details
8.4.1 Available reference details are as follows:
Trailer Loading Hose – 320009A-111
2 ½ Inch Loading Connection – 320009A-97
Pipe Anchor for Breakaway Coupling – 311708A-P097
Overhead Drive Thru LOX Trailer Load Metal Hose Specification – 312443A
Overhead Drive Thru LIN & LAR Trailer Load Metal Hose Specification – 312444A
Break Away Coupling Specification for Pull Thru Trailer Applications – 314245A
Tanker Loading Guard Rail Assembly – 312446
Tanker Loading Arm Assembly – 312447
Tanker Loading Arm Hose Clamp Assembly – 312448
2 ½ ” Hose End Assembly Argon Service – 314251
2 ½ ” Hose End Assembly Nitrogen Service – 314253
2 ½ ” Hose End Assembly Oxygen Service – 314251
- LIQUID HYDROGEN AND LIQUID HELIUM PIPING SYSTEMS
9.1.1 The paragraphs in Section 4, describing routing of cryogenic pipe, apply to the design of liquid hydrogen (LH2) and liquid helium (LHe) piping systems.
9.1.2 The cryogenic temperature of LH2 and LHe will liquefy the air around exposed piping, thereby creating a hazard for operating personnel and equipment. The oxygen content of liquefied air can increase the risk of fire. Piping shall be arranged to minimize and contain formation of liquid air.
9.1.3 Vent piping and relief valve discharges shall be routed to a disposal system or away from operating areas and designated walkways.
9.2 Vacuum-Jacketed (VJ) Pipe and Components
9.2.1 Hydrogen and helium piping systems with an operating temperature below -198°C (-325°F) must be VJ. In‑line components such as hand valves, control valves, and filters must be VJ. Bellows are required in the outer jacket between valves and branch connections to compensate for inner line movement. Spacing requirements are similar to those for insulated pipe (see Figure 2).
9.2.2 VJ pipe for liquid hydrogen or helium service is designed for -254° to -269°C (-425° to -452°F) operating temperature and shall include design features not provided with other cryogenic systems. Special internal thermal wrapping, triple wall pipe, and liquid nitrogen tracing are items that might need to be considered. VJ-pipe design requirements are established before starting design. The stress engineer shall select the type of VJ piping to be used (see 3PI45002).
9.2.3 A VJ bayonet joint is the typical method used to assemble LH2 and LHe VJ systems in the field. Bayonet assembly details and dimensional data are available in the VJ-pipe supplier catalog data.
9.2.4 A welded joint with a field-installed and field-evacuated canister is an alternate method of assembly. This type of joint requires additional field work and added cost, but does permit adjustment for field fit up. See 326280 for details of a butt welded VJ-spool assembly.
9.2.5 Branch connections for relief valves, pressure taps, purge connections, and temperature probes must be vacuum jacketed. See standard VJ-piping details for details of typical branch connections.
9.2.6 See paragraph 5.3 for VJ-pipe support requirements and details.
9.3 LH2 Storage (Shop-Fabricated and Field-Erected Tanks)
9.3.1 Shop-fabricated liquid hydrogen storage tanks may be located side by side. Care shall be taken to allow for maintenance and foundation requirements. Tanks can be installed at grade level since liquid withdrawal from storage is normally a pressure transfer procedure.
9.3.2 A containment or dike system for LH2 storage is not required by Air Products; however, local regulations might require containment. The storage area should be graded to direct spills away from property lines, operating areas, and plant equipment.
9.3.3 Storage tank relief valves discharging liquid or cold vapor shall be directed to a safe area or into a disposal system. Liquid and cold vapor discharges are hazardous to personnel and equipment. As an example, cold vapor discharging against the carbon steel outer wall of a storage tank can cause embrittlement and failure of the tank.
9.3.4 Field-erected and shop-fabricated LH2 storage tanks might require a deluge system for fire protection (see 4ES85001A for details).
9.4 LH2 Trailer Loading
9.4.1 LH2 trailer loading shall be back-in loading with aboveground piping. All pipe, valves, and hoses in the loading system shall be VJ with bayonet connections. Project-specific requirements might alter the design of trailer loading.
9.4.2 LH2 trailers shall be spaced a minimum 6 m (20 ft 0 in) on centers with a distance of 2.5 m (8 ft 0 in) from center of trailer to edge of pad. See 3ES60101 for minimum spacing criteria for LH2 loading within a facility.
9.4.3 A load-on scale with an auto-load system is included with each load station pad. Pull-away protection and a deluge system shall be provided to protect operating personnel and adjacent equipment and piping (see 4ES85001A for deluge requirements).
9.4.4 The trailer-vent connection and other vents and drains in the trailer-load area shall be piped back to the process system or to a safe disposal system. Liquid air condensing on exposed vent piping must be considered when routing the trailer vent system.
Horizontal Expansion Loops
Pipe Duct Layout
Supports Inside Pipe Duct
Pipe Duct Pipe Support Details
Underground Trailer Loading Arrangement
Details of Underground Loading Lines