5.5 Pipe Hangers, Supports, Rigid Restraints & Spring Can Installation/Adjustment

5.3 Pipe Hangers, Supports, Rigid Restraints & Spring Can Installation/Adjustment

Core Trade Concept: As high-temperature power piping transitions from ambient shutdown conditions to full operating steam temperatures ($1{,}000^\circ\text{F}+$), thermal expansion causes pipe runs to expand significantly in three dimensions. Rigid pipe supports cannot accommodate vertical expansion without imposing destructive bending moments on boiler headers, turbine casings, and pump nozzles. Boilermakers must install, calibrate, adjust, and commission precision variable and constant effort spring support systems to carry pipe deadweight continuously throughout the thermal expansion cycle.

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1. Functional Classifications of Pipe Supports (MSS SP-58 / ASME B31.1)

Every industrial pipe support belongs to one of three distinct mechanical categories:

                      PIPE SUPPORT CLASSIFICATIONS
                      
     1. DEADWEIGHT SUPPORTS      2. THERMAL EXPANSION GUIDES      3. DYNAMIC RESTRAINTS
        +-----------------+         +---------------------+          +-----------------+
        | Clevis Hangers  |         | PTFE / SS Slide Shoe|          | Hydraulic Snub. |
        | Rod Suspensions |         | Directional Guides  |          | Mechanical Snub.|
        | Spring Cans     |         | Hold-Down Clamps    |          | Rigid Struts    |
        +-----------------+         +---------------------+          +-----------------+
        (Carries gravity            (Controls expansion axis;        (Absorbs shock,
         weight of pipe)             allows low-friction slide)       water hammer, EQ)

1. Deadweight (Gravity) Supports: Carry the sustained downward gravity load of the pipe, inline valves, insulation, cladding, internal process fluid, and hydrostatic test water.
   • Examples: Standard rigid rod hangers, clevis hangers, roller hangers, pipe saddles, trapeze supports, and spring hanger assemblies.
2. Thermal Expansion Guides & Sliding Supports: Direct piping growth along designated geometric axes while preventing unwanted lateral or upward displacement.
   • Examples: Pipe slide shoes resting on low-friction PTFE (Teflon) on polished stainless steel or bronze/graphite slide plates; structural guide angles; hold-down pipe clamps.
3. Dynamic Restraints & Shock Arrestors: Protect piping systems against high-energy dynamic transient events, including steam hammer, water hammer, rapid safety relief valve (SRV) discharge thrust, and seismic ground acceleration.
   • Rigid Struts: Stiff structural tie-rods fitted with spherical ball-joint bushings on each end. Resists both tension and compression loads along a single axis while permitting $\pm 5^\circ$ of angular rotation.
   • Sway Braces: Dual opposed spring assemblies that exert a push/pull centering force to dampen steady-state acoustic and mechanical vibration in pump discharge lines.
   • Snubbers (Shock Arrestors): Specialized dynamic restraints that provide zero resistance to slow, steady thermal movements ($< 1.0\text{ in/min}$), but lock rigidly into a solid structural brace when subjected to rapid dynamic acceleration ($> 0.2\text{ g}$) or sudden velocity changes.

Hydraulic vs. Mechanical Snubbers

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2. Variable Spring Supports vs. Constant Effort Supports

          VARIABLE SPRING HANGER                      CONSTANT EFFORT SPRING HANGER
           +-----------------+                            +-------------------+
           |  Helical Coil   |                            | Counterbalanced   |
           |     Spring      |                            | Cam / Lever Arm   |
           +--------+--------+                            +---------+---------+
                    |                                               |
                    v Force varies with travel                      v Constant Force Output
              F = k * delta_x                                F = F_design (+/- 6%)

Variable Spring Hangers

• Operating Physics: Contains a heavy helical coil spring enclosed within a steel canister. The upward supporting force exerted by the spring varies linearly with vertical displacement according to Hooke's Law: $\Delta F = k_{spring} \cdot \Delta x$.
  • Downward Pipe Thermal Movement: Compresses the spring, increasing the upward support force.
  • Upward Pipe Thermal Movement: Extends the spring, decreasing the upward support force.
• Variability Formula & 25% Rule (ASME B31.1 / MSS SP-58):

$\text{Variability } (\%) = \frac{|\text{Hot Load} - \text{Cold Load}|}{\text{Hot Load}} \times 100$

Critical Code Rule: For critical power piping, the calculated variability must not exceed $25%$. If variability exceeds $25%$, the load shed onto adjacent rigid supports or equipment nozzles during thermal expansion will cause pipe overstress, flange leaks, or nozzle failure.

Constant Effort (Constant Support) Hangers

• Operating Physics: Combines a high-capacity helical spring coil with a counterbalanced mechanical cam, bell-crank, or toggle lever arm.
  • As the spring compresses (increasing internal spring force), the mechanical moment arm decreases proportionately: $F_{spring} \cdot r_1 = F_{pipe} \cdot r_2 = \text{Constant Moment}$.
  • The resulting supporting force delivered to the pipe remains $100%$ constant (within $\pm 6%$ manufacturing tolerance) across the entire travel stroke.
• Application: Mandatory when vertical thermal movement exceeds $\frac{1}{2}\text{ inch}$ ($13\text{ mm}$), when variability exceeds $25%$, or on piping directly connected to strain-sensitive equipment (steam turbine inlets, boiler feedwater pump discharges, boiler superheater outlet headers).

Engineering Comparison

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3. Spring Can Installation, Travel Stops & Commissioning Protocols

                 SPRING CAN POSITION INDICATOR & TRAVEL STOPS
                 
                 +-------------------------------------+
                 |  [O] TOP TRAVEL STOP (Locking Pin)  |
                 |                                     |
                 |      -- H (Hot Load Setting)        |
                 |     |                               |
                 |    [X] Pointer (Current Cold State) |
                 |     |                               |
                 |      -- C (Cold Load Setting)       |
                 |                                     |
                 |  [O] BOTTOM TRAVEL STOP             |
                 +-------------------------------------+

The Role of Travel Stops (Locking Pins / Shipping Stops)

Spring hangers are delivered from the factory with rigid steel travel stops (locking pins or locking plates) inserted into the canister body. These stops mechanically lock the internal spring piston at the engineered Cold (C) position.

• Hydrostatic Testing Protection: A piping system filled with water for hydrostatic testing weighs 2 to 3 times more than an operating steam line. Without travel stops, the heavy hydrostatic water load would completely bottom out the spring coils, causing permanent plastic deformation of the springs and destroying their calibration.

Systematic Travel Stop Removal Protocol

1. Complete All Mechanical Work: Ensure all piping is fully welded, non-destructive examination (NDE) is complete, and permanent inline components (valves, strainers) are installed.
2. Hydrostatic Testing & Complete Draining: Conduct the hydrostatic pressure test with travel stops installed. Fully drain and purge all hydrotest water from the piping system.
3. Install Complete Insulation & Cladding: Apply all permanent thermal insulation, refractory, lagging, and metal cladding to achieve full operating deadweight.
4. Check Pin Load Balance: Attempt to slide out the travel stop pins by hand or with a light tap of a brass mallet.
   • Critical Inspection Rule: If a travel stop pin is bound tightly and cannot be removed, the hanger rod is either under-tensioned or over-tensioned.
   • Adjust the hanger rod turnbuckle until the pin becomes loose and slides out effortlessly by hand. Never drive out bound travel stops with a heavy sledgehammer or torch cut them off!
5. Store Travel Stops: Pin the removed travel stops to the storage brackets provided on the side of the canister for future hydrostatic re-testing.

Cold-to-Hot Indicator Verification

• Cold Walkdown (Ambient / Cold Plant): Verify the external position pointer aligns exactly with the stamped "C" (Cold) mark on the scale.
• Hot Walkdown (Full Operating Temperature & Pressure): After the unit reaches steady-state operating temperature, inspect every spring hanger. The position pointer must have migrated to the stamped "H" (Hot) mark.

+--------------------------------------------------------------------------+
|                     SPRING POINTER TROUBLESHOOTING                       |
|                                                                          |
| - Pointer at Top Limit (Topped Out): Spring is completely unloaded.     |
|   Causes: Pipe moving upward more than calculated, adjacent hanger loose, |
|   or incorrect cold setting. Turnbuckle adjustment required.             |
| - Pointer at Bottom Limit (Bottomed Out): Spring is fully compressed.    |
|   Causes: Pipe carrying water/condensate, unexpected downward expansion, |
|   or missing insulation weight. Extreme risk of overloading nozzles.     |
+--------------------------------------------------------------------------+

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4. Rigid Hardware, Clamps, Shoes & Insulated Pipe Supports

                  VERTICAL RISER CLAMP & SHEAR LUGS
                  
                     Hanger Rod       Hanger Rod
                         |                |
                     +---+----------------+---+
                     |   | [ Riser Clamp] |   |
                     |===+================+===|
                     |   |  # Shear Lug # |   | <- Welded to Pipe Wall
                     |   |  # (Full Load) #   |
                     |   |  |            ||   |
                     |   |  | Vertical   ||   |
                     |   |  | Pipe Run   ||   |

1. Vertical Riser Clamps & Shear Lugs:
   • Vertical pipe runs cannot rely on clamp friction alone to resist downward gravity loads.
   • Heavy structural steel shear lugs are welded directly to the vertical pipe wall immediately above the riser clamp ears. The riser clamp bears directly against the underside of the shear lugs, transferring $100%$ of the vertical weight into the hanger rods.
2. Horizontal Pipe Shoes:
   • Structural WT or fabricated steel saddles welded or clamped to the underside of horizontal pipe runs. Elevates the pipe $4\text{--}6\text{ inches}$ above supporting structural steel beams, creating clear space for continuous thermal insulation.
3. Hot vs. Cryogenic Insulated Pipe Shoes:
   • Hot Service Shoes: Utilize internal high-density calcium silicate, cellular glass, or microporous insulation blocks positioned between the pipe clamp and outer structural base. Prevents thermal conduction from overheating structural building steel.
   • Cryogenic / Cold Service Shoes (LNG & Liquid Oxygen): Utilize high-density polyurethane foam (HD PUF) or compressed phenolic-impregnated wood (Permali) blocks combined with a continuous 360-degree vapor barrier. Prevents ambient heat gain, eliminates pipe sweating and ice buildup, and protects the carbon steel clamp from freezing and Corrosion Under Insulation (CUI).

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5. Decoding Spring Hanger Nameplates & Worked Load Calculations

+-------------------------------------------------------------------+
|                INDUSTRIAL SPRING HANGER NAMEPLATE                 |
|  +-------------------------------------------------------------+  |
|  | MANUFACTURER: LISLE-BERGEN PIPE SUPPORTS                    |  |
|  | MARK / TAG NO: 2-MS-H-014        TYPE: VARIABLE B-CAN       |  |
|  | SPRING SIZE: 14                  SPRING RATE: 320 LBS/IN    |  |
|  | COLD LOAD (LC): 4,800 LBS        HOT LOAD (LH): 5,440 LBS   |  |
|  | DESIGN TRAVEL: 2.0 IN. DOWN      TOTAL SCALE RANGE: 4.0 IN  |  |
|  +-------------------------------------------------------------+  |
+-------------------------------------------------------------------+

Worked Trade Example: Variability Verification

Given:

• Cold Load ($L_C$) = $4{,}800\text{ lbs}$
• Hot Load ($L_H$) = $5{,}440\text{ lbs}$
• Spring Rate ($k$) = $320\text{ lbs/in.}$
• Vertical Travel = $2.0\text{ inches downward}$

Step 1: Verify Load Delta from Spring Rate and Travel $\Delta F = k \cdot \Delta x = 320\text{ lbs/in.} \times 2.0\text{ in.} = 640\text{ lbs}$ $L_H = L_C + \Delta F = 4{,}800\text{ lbs} + 640\text{ lbs} = 5{,}440\text{ lbs} \quad (\text{Matches Nameplate})$

Step 2: Calculate Load Variability Percentage $\text{Variability} = \frac{|L_H - L_C|}{L_H} \times 100 = \frac{|5{,}440 - 4{,}800|}{5{,}440} \times 100 = \frac{640}{5{,}440} \times 100 = 11.76\%$

Conclusion: Because $11.76% \le 25%$, this variable spring hanger complies with ASME B31.1 code requirements.

Turnbuckle Adjustment & Thread Engagement Verification

• All hanger rod assemblies utilize forged steel turnbuckles (or clevis fittings) to adjust piping elevation and balance spring loads.
• Sight Window Verification: Both threaded rods entering the turnbuckle body must be visible inside the open central inspection window.
• Equal Thread Engagement: Both upper and lower rods must engage the turnbuckle threads by at least $1.5 \times \text{rod diameter}$.
• Jam Nuts: Once the cold setting is verified, tighten upper and lower jam nuts firmly against the turnbuckle body to prevent thread backing-out caused by acoustic piping vibration.