Valves, Gages and Instruments

    Valves gages and instruments are used in piping for measuring, controlling and directing the fluids in the piping. The following is a partial list of valves:

1. Gate valve

2. Globe valve

3. Stop valve

4. Safety valve

5. Safety relief valve

6. Control valve

7. Elbow-down valve

1. Level gage

2. Flow measuring device

3. Temperature gage

4. Pressure gage

1. Steam purity gage

2. pH meter

3. Water chemistry measuring device

4. Temperature probe

5. Ventury meter

6. Flow nozzle

7. Pitot tube

8. Flow orifice

26. Fittings and Attachments

    The piping uses several fittings and attachments. These are used for flow direction and load transfer. The following gives a list of fittings:

1. Short radius elbow

2. Long radius elbow

3. Equal TEE

4. Unequal TEE

5. Pregnant TEE

6. Y piece

7. Branch

8. Concentric reducer

9. Eccentric reducer

10. End cap

1. Circumferential lug

2. Longitudinal lug

3. Inclined lug

4. Saddle

5. Trunnion

6. Erection attachment

7. Compensating pad

8. Stiffener plate

9. Clamp

10. Limit stop

27. Supports and Restraints

    The supports and restraints of the piping are provided to resist various loads and load combinations. Some of the supports are listed below.

1. Rigid hanger

2. Variable load hanger (VLH)

3. Constant load hanger (CLH)

4. Semi-constant load hanger (SCLH)

5. Saddle

6. Slide bearing

7. Roller

8. Double hanger

9. Swinging hanger

10. Rocker

1. Unidirectional restraint

2. Bi-directional restraint

3. Angular restraint

4. Sway brace

5. Limit stop

6. Vibration snubber

7. Tie

8. Strut

9. Spar

10. Wind brace

28. Anchors and Guides

The piping is provided with several types of anchors and guides. The following gives a partial list of anchors:

1. Rigid anchor

2. Floating anchor

3. Anchor with rotational movements

1. Rotational guide

2. Linear guide

3. Guide with springs

4. Guide with initial movements

5. Directional guide

The loads on the anchors are to be limited to those acceptable by the equipment suppliers. The allowable forces and moments on the equipment are provided by the equipment suppliers. The equipment supplier will indicate the linear and angular movements expected during the plant operation. The piping analyst shall carry-out the piping stress analysis to find-out the forces and moments induced on the equipment. These are limited to those allowed.

    For all systems, a greater allowance in percentage variation is permissible at points of support where the variation n supporting effect is transferred directly to a rigid support or terminal connection specifically designed for the resulting loading condition.

    When the load and movement at each selected support location are determined, detailed design of the individual supports can be undertaken. The movement determiners the basic type of support (such as spring or rigid, slide or roller); the piping, its temperature, and ambient temperature determine the pipe attachment and remaining support material, respectively; the proximity to supporting structure and available clearance determines the support configuration such as single-or double-rod hanger, stanchion, or bracket-type support; and the load determines the required size for each component of the support.

    The design should take full advantage of commercially available load-rated and tested support components to the greatest extent possible. An effort should be made to maintain uniformity and simplicity in design. The support should be functional, provide means for piping elevation adjustment, and be easily installed using normal field labor and equipment.

MSS SP-58 Hanger and Support Types

Refer to Fig. B5.1.

Type 1	Adjustable steel clevis hanger A pipe attachment for suspension of horizontal stationary lines and providing a means for vertical adjustment.
Type 2	Yoke-type pipe clamp A pipe attachment for suspension of horizontal stationary insulated lines. This type of clamp is also made to accommodate pipe of nonstandard size when designed with a filler plate.
Type 3	Carbon-or alloy-steel three-bolt pipe clamp A pipe attachment for suspension of horizontal stationary lines.
Type 4	Steel pipe clamp A pipe attachment for suspension of horizontal stationary insulated lines.
Type 5	Pipe hanger A pipe attachment for suspension horizontal stationary lines either using hanger rod or bolting to wall from the T slot provided in the side of the strap.
Type 6	Adjustable swivel pipe, split ring type or solid ring type A pipe attachment for suspension of horizontal stationary lines.
Type 7	Adjustable steel band hanger A pipe attachment for suspension of horizontal stationary lines and providing a means for vertical adjustment.
Types of pipe supports (MSS SP-58)
Type 8	Extension pipe or riser clamp A pipe attachment for suspension of vertical stationary lines without the use of hanger rods. The transfer of piping load is accomplished by resting the ears of the clamp on a bearing surface.
Type 9	Adjustable band hanger A pipe attachment for suspension of horizontal stationary lines.
Type 10	Adjustable swivel ring, band type A pipe attachment for suspension of horizontal stationary lines and providing a means for vertical adjustment.
Type 11	Split pipe ring with or without turnbuckle adjustment A pipe attachment for suspension of horizontal stationary lines permitting installation before or after pipe is in place.
Type 12	Extension split pipe clamp, hinged or two-bolt A pipe attachment for suspension of horizontal stationary lines used in conjunction with a pipe nipple.
Type 13	Steel turnbuckle A device with one left-hand internal threaded end and one right-hand internal threaded end, used to join two threaded rods and providing for vertical adjustment.
Type 14	Steel clevis A device which provides for the attachment of a threaded rod to a bolted or pinned connection.
Type 15	Swivel turnbuckle A device which provides flexibility at the pipe connection and a means of vertical adjustment.
Type 16	Malleable iron socket A device for attaching threaded rods to various types of building attachments.
Type 17	Steel weldless eye nut A forged-steel device which provides for the attachment of a threaded rod to a bolt or pin connection.
Type 18	Steel or malleable concrete insert A cast-in-place device which provides for a rod attachment capable of nominal lateral adjustment.
Type 19	Top beam C-clamp A device requiring no welding which attaches to the top flange of a structural shape where the vertical rod is required to be offset from the edge of the flange.
Type 20	Side beam or channel clamp A device requiring no welding which attaches to the bottom flange of a structural shape where the vertical rod is required to be at the edge of the flange.
Type 21	Center beam A device requiring no welding which attaches to the bottom flange of a structural shape where the vertical rod is required to be centered on the structural shape.
Type 22	Welded beam attachment (as shown or inverted less bolt) A structural attachment welded to the bottom of steel beams and used as a means for connecting hanger rods to the beams.
Type 23	C-clamp A device requiring no welding which attaches to a flange of a structural shape and provides for attaching a threaded rod.
Type 24	U-bolt A U-shaped rod with threaded ends used as a support or guide.
Type 25	Top beam clamp A device requiring no welding which attaches to the top flange of a structural shape where the vertical rod is required to be at the edge of the flange.
Type 26	Pipe clip A pipe attachment for suspension of horizontal stationary lines by bolting the clip directly to a structure. Also referred to as a pipe strap or strap.
Type 27	Side beam clamp A device requiring no welding which attaches to the bottom flange of a structural shape where the vertical rod is required toe be offset from the center of the shape.
Type 28	Steel beam clamp with eye nut A device requiring no welding which attaches to the bottom flange of a structural shape where the vertical rod is required toe be centered on the structural shape.
Type 29	Linked steel clamp with eye nut A device requiring no welding which attaches to the bottom flange of a structural shape where the vertical rod is required to be centered on the structural shape.
Type 30	Malleable beam clamp with extension piece A device requiring no welding which attaches to the bottom flange of a structural shape where the vertical rod is required to be centered on the structural shape.
Type 31	Light welded steel bracket A braced cantilever device intended for supporting a gravity load from rod-type hangers. This device is typically bolted to a wall and may be installed with the brace either above or below the horizontal member.
Type 32	Medium welded steel bracket A braced cantilever device intended for supporting maximum gravity loads and/or horizontal loads up to 1500 lb (6670 newton. N). Loads may be applied anywhere along the main member. This device is typically bolted to a wall and may be installed with the brace above, below, or on either side of the main member.
Type 33	Heavy welded steel bracket A braced cantilever device intended for supporting maximum gravity loads and/or horizontal loads up to 3000 lb (13,340 newton. N). Loads may be applied anywhere along the main member. This device is typically bolted to a wall and may be installed with the brace above, below, or on either side of the main member.
Type 34	Side beam bracket A device requiring no welding which attaches to the sides of steel or wooden members and provides a means for vertical adjustment.
Type 35	Pipe slide and slide plate A device for supporting piping having horizontal movements and where a low coefficient of friction is necessary.
Type 36	Pipe saddle support A device having a curved base for cradling horizontal pipe and which slips into a nominal diameter pipe stanchion.
Type 37	Pipe stanchion saddle A device having a curved base for cradling horizontal pipe and which slips into a nominal diameter pipe stanchion. The U-bolt yoke provides stability.
Type 38	Adjustable pipe saddle support A device having a curved base for cradling horizontal pipe and which threads into a nominal diameter pipe stanchion. This device provides vertical adjustment.
Type 39	Steel pipe covering protection saddle A device used on insulated piping which is designed to minimize heat losses and prevent damage to insulation.
Type 40	Protection saddle A metal device intended to prevent crushing of insulation and/or breaching of the vapor barrier. It is typically used at support points.
Type 41	Single pipe roll A device used for supporting horizontal piping from two rods, allowing for vertical adjustment and consisting of a roller that allows for axial movement with virtually no frictional resistance.
Type 42	Carbon-or alloy-steel riser clamp A pipe attachment for supporting vertical piping through the use of shear lugs welded to the pipe. Load bolts are provided to transfer the pipe load toe the rod hanger assembly.
Type 43	Adjustable roller hanger with or without swivel A device used for supporting horizontal piping from a single rod, allowing for vertical adjustment and consisting of a roller that allows for axial movement with virtually no frictional resistance.
Type 44	Pipe roll complete A device used for supporting horizontal piping where vertical adjustment is unnecessary and consisting of a roller that allows for axial movement with virtually no frictional resistance.
Type 45	Pipe roll and plate A device used to support horizontal piping, having minimal axial movement, from beneath and where no vertical adjustment is necessary.
Type 46	Adjustable pipe roll and base A device used to support horizontal piping, having axial movement, from beneath and where vertical adjustment is necessary.
Type 47	Restraint control device A rigid, mechanical, spring, or hydraulic device used for absorbing shock loading and/or controlling sway in piping systems.
Type 48	Spring cushion A noncalibrated, rod-type, single-coil spring support used where a cushioning effect is desired.
Type 49	Spring cushion roll A noncalibrated, rod-type, double-coil rod spring support used where a cushioning effect is desired along with a pipe roll.
Type 50	Spring sway brace A spring device used for absorbing shock loading and or controlling sway in piping systems.
Type 51	Variable spring hanger A device having a single-spring coil which supports the gravity loads of piping systems that are subjected to vertical thermal movements. This device produces a varying load when the piping moves from the cold position to the hot position. This type of spring hanger supports the pipe from above.
Type 52	Variable spring base support A device having a single-spring coil which supports the gravity loads of piping systems that are subjected toe vertical thermal movements. This device produces a varying load when the piping moves from the cold to the hot position. This type of spring hanger supports the pipe from below.
Type 53	Variable spring trapeze hanger A device having double-spring coils which support the gravity loads of piping systems that are subjected to vertical thermal movements. This device produces a varying load when the piping moves from the cold position to its hot position. This type of spring hanger supports the pipe fro above with two rods.
Type 54	Constant support hanger, horizontal type A device having a single-spring coil working in conjunction with counterbalancing mechanisms to support the gravity loads of piping systems that are subjected to vertical thermal movements. This device produces a constant load when the piping moves from the cold position to the hot position. This type of constant hanger has the spring coil in the horizontal position and supports the pipe from above.
Type 55	Constant support hanger, vertical type A device having a single-spring coil working in conjunction with counter balancing mechanisms to support the gravity loads of piping systems that are subjected to vertical thermal movements. This device produces a constant load when the piping moves from the cold position to the hot position. This type of constant hanger has the spring coil in the vertical position and supports the pipe from above.
Type 56	Constant support hanger, trapeze type A device having double-spring coils working in conjunction with counter balancing mechanisms to support the gravity loads of piping systems that are subjected to vertical thermal movements. This device produces a constant load when the piping moves from the cold position to the hot position. This type of constant hanger has the spring coil in the vertical position and supports the pipe from below with two rods.
Type 57	Plate lug A structural attachment which provides a means of connecting rod-type hangers to structural steel members via a pin or bolt through the hole of the lug.
Type 58	Horizontal traveler A device which permits the structural attachment end of rod-type hangers to accommodate horizontal piping movements in conditions where offsetting of conventional structural attachments is not practical due to limited space.

121.2 121.7.1

stress value during hydrostatic testing shall not exceed 16,000 psi (110.3 MPa).

121.3 Temperature Limitations

    Parts of supporting elements which are subjected principally to bending or tension loads and which are subjected to working temperatures for which carbon steel is not recommended shall be made of suitable alloy steel, or shall be protected so that the temperature of the supporting member will be maintained within the appropriate temperature limits of the material.

121.4 Hanger Adjustments

    Hangers used for the support of piping, NPS 2 and larger, shall be designed to permit adjustment after erection while supporting the load. Screwed adjustments shall have threaded parts to conform to ASME B1.1.

    Class 2 fit turnbuckles and adjusting nuts shall have the full length of thread in engagement. Means shall be provided for determining that full thread length is in engagement. All screw and equivalent adjustments shall be provided with suitable locking devices.

121.5 Hanger Spacing

    Supports for piping with the longitudinal axis in approximately a horizontal position shall be spaced to prevent excessive sag, bending and shear stresses in the piping, with special consideration given where components, such as flanges and valves, impose concentrated loads. Where calculations are not made, suggested maximum spacing of supports for standard and heavier pipe are given in Table 121.5. Vertical supports shall be spaced to prevent the pipe from being overstressed from the combination of all loading effects.

121.6 Springs

    The springs used in variable or constant effort type supports shall be designed and manufactured in accordance with MSS SP-58.

121.7 Fixtures

    121.7.1 Anchors and Guides

    (A) Anchors, guides, pivots, and restraints shall be designed to secure the desired points of piping in relatively fixed positions. They shall permit the piping to expand and contract freely in directions away from the anchored or guided point and shall be structurally suitable to withstand the thrusts, moments, and other loads imposed.

(a) Suggested maximum spacing between pipe supports for horizontal straight runs of standard and heavier pipe at maximum operating temperature of 750°F (400°C).

(b) Does not apply where span calculations are made or where there are concentrated loads between supports, such as flanges, valves, specialties, etc.

(c) The spacing is based on a fixed beam support with a bending stress not exceeding 2300 psi (15.86 MPa) and insulated pipe filled with water or the equivalent weight of steel pipe for steam, gas, or air service, and the pitch of the line is such that a sag of 0.1 in. (2.5 mm) between supports is permissible.

(B) Rolling or sliding supports shall permit free movement of the piping, or the piping shall be designed to include the imposed load and frictional resistance of these types of supports, and dimensions shall provide for the expected movement of the supported piping. Materials and lubricants used in sliding supports shall be suitable for the metal temperature at eth point of sliding contact.

(C) Where corrugated or slip-type expansion joints, or flexible metal hose assemblies are used, anchors and guides shall be provided where necessary to direct the expansion into the joint or hose assembly. Such anchors shall be designed to withstand the force specified by the manufacturer for the design conditions at which the joint or hose assembly is to be used. If this force is otherwise unknown, it shall be taken as the sum of the product of the maximum internal area times the design pressure plus the force required to deflect the joint or hose assembly. Where expansion joints or flexible metal hose assemblies are subjected to a combination of longitudinal and transverse movements, both movements shall be considered in the design and application of the joint or hose assembly.

29. Hangers and Limit Stops

    The piping is provided with several types of hangers. The hangers are usually top supported. Where structures are not available above the piping, saddle supports are used (bottom support). The following gives a list of commonly used hangers:

1. Rigid hanger 2. Flexible hanger 3. Hanger with trunnion 4. Hanger with rockers

The following gives a list of commonly used limit stops.

1. Linear limit stop 2. Angular limit stop 3. Unidirectional limit stop 4. Bi-directional limit stop

Use and application of the hangers and limit stops are based on past experience. In the design of piping supports, the following principles of design are to be addressed:

a) Performance b) Safety c) Economy d) Environmental considerations e) Aesthetics f) Contractual requirements g) Legal requirements h) Standard practices i) Material availability j) Shop and field facilities

30. Variable Load Hangers (VLH)

    The Variable Load Hangers (VLH) is used as flexible supports. The load on the VLH varies during the operation of the piping. The load from cold condition to hot condition can increase or decrease. The change in load depends on the value of the piping movement from cold to hot condition. If the vertical thermal movement is down-ward, the load from cold to hot will increase. If the vertical thermal movement is upwards, the load from cold to hot will decrease.

    The variable load hangers use helical springs. The helical springs are used in compression. Helical springs are not used in tension. This is based on safety considerations. Several makes of variable load hangers are available as ready-made products. The piping engineer selects from the available standard VLH which is economical for the particular application.

    After selection and ordering of the VLH, the VLH is to be set properly in the filed. The following types of setting are available:

1. Hanger rod vertical in cold condition (Zero % pre-setting) 2. Hanger rod vertical in hot condition (100% pre-setting) 3. Hanger rod setting with 50% pre-setting 4. Design load = hot load 5. Design load = cold load

   The usually allowed load variation is 25% of the design load.

31. Constant Load Hangers (CLH)

    The Constant Load Hangers (CLH) is used as flexible supports. The load on the CLH does not vary substantially during the operation of the piping. The load from cold condition to hot condition can increase or decrease, marginally. The change in load depends on the value of the piping movement from cold to hot condition.

    The constant load hangers use several types of designs. Some of the popularly used constant load hangers are indicated in the following.

1. Crank mechanism 2. Band type CLH 3. Cam type CLH 4. Dead weight type CLH 5. Dead weight with lever CLH

    The load variation in the constant load hanger, from cold to hot, is usually les than 6% of the design load. Selection and setting of the constant load hanger requires experience and expertise. The type of constant load hanger to be used for a particular application depends on the economics and availability.

    The constant load hangers can be used for piping, ducts, flues, boilers and equipment. The setting of the CLH is done at shop. The CLH is re-set again in the field based on the actual performance. The CLH are ready-made products. These are available in various size and load ranges. In the piping industry many components are standardized.

    The work of a piping designer is to carry-out the piping stress analysis and finalize the design. From the list of CLH required (based on piping stress analysis), applicable CLH are selected. After selecting the CLH, these are set in shop and field, based on the recommendations of the CLH maker.

    CLH are widely used for high thermal movements in vertical direction. The CLH are costlier than the Variable Load Hangers (VLH). A judicious selection of rigid support, VLH and CLH will give an economical piping design.

32. Bends and Elbows

    The bends and elbows are used for changing the fluid flow direction. The elbows are of the following angles: 180°, 90°, 45°, 22.5° and 11.25°. The bends can be of any angle from 1° to 180°. The fabrication process of the bend and the elbow are different. The bends are usually constructed using bending machines. The elbows are usually made by the forging machines or the pressing machines.

    The bends can be of curves in three dimensions. The elbows are usually a two dimensional component. For a given application, bends or elbows can be used. The piping designer selects an elbow or a bend, depending on the availability and economy.

    The behavior of elbows and bends are different. Various codes and standards stipulate the design requirement for elbows and bends. The recommendations for elbows and bends by the same code are different. The economics of bends and elbows and different.

    The stresses and the fluid flow distribution in the elbows and bends depend on the following five parameters:

Do = Outside diameter of bend / elbow, mm T = Nominal thickness of the bend / elbow, mm R = Bend radius to the neutral axis of bend / elbow, mm 4. Dead weight type CLH 5. Dead weight with lever CLH

Oval shape (Ovality0, % = 100 x (Maximum outside diameter Minimum outside diameter)

Average outside diameter

 

Thinning, % = 100 x (Actual pipe thickness Minimum pipe bend thickness)

Actual pipe thickness

33. TEE and Y Piece

    TEE pieces are used in piping to collect or distribute fluids. The following types of TEE pieces are used:

1. Equal TEE 2. Unequal TEE 3. Pregnant TEE

    The TEE is a part of the piping fittings. The Tee pieces are fabricated using any one of the following process:

a) Forming from straight pipe b) Forged TEE c) Machined and welded TEE d) Extruded TEE

    The stresses induced on the TEE are higher than that of the straight pipe. Hence, the thickness of the TEE is more than the thickness required for an equivalent straight pipe. To take care-of this effect, TEE is made of higher thickness. Since the TEE has change of shape, Stress Concentration Factor (SCF) is to be computed and used. In the piping industry, the Stress Intensification Factor (SIF) is used. This is due the reason that the TEE is made of ductile material. Also, TEE is subjected to low cycle fatigue. Hence, the method of using SCF, widely used in Mechanical construction industry, is not used for TEE. The SIF is usually lower than the SCF.

    The Y piece is used in place of TEE. The Y piece is costlier than the TEE. However Y piece is used to reduce the pressure drop in the piping. The Y piece is technically superior to the TEE. But, TEE is commercially superior to the Y piece. The following gives a comparison of the TEE and the Y pieces.

A) Cost of Y piece is higher than the TEE. B) Pressure drop and pumping power are higher in TEE than the Y piece. C) TEE is easier to fabricate, compared to Y piece. D) The Indian Boiler Regulation, 1950 (with amendments) has no rules for Y piece design.

34. Temperature and Effects

    The piping is subjected to temperature changes. The temperatures at various points in the piping are different. The temperature at various points in the piping change during start-up and shut-down. The temperature change leads temperature differentials. The temperature differential leads to thermal stress. The stresses induced in the piping can be classified into the following categories:

1. Primary stress (Sustained load) 2. Secondary stress (Expansion loads) 3. Occasional stress (Example: Wind, Earth-Quake, Pressure Surge, etc.) 4. Hydraulic test stress (During hydraulic testing at shop or field)

    The primary stress leads to failure by short-term rupture. The secondary stress leads to rupture by fatigue. The occasional stress leads to rupture by repeated application. The occasional loads induce primary stress. But, the probability of rupture by occasional load is low. Hence, higher stresses are allowed for occasional stresses. During hydraulic loads, pressures higher than the design pressure (Working Pressure), are imposed. Also, during hydraulic testing, the cold water is filled in the complete piping. These lead higher stresses. The hydraulic testing is a load of long duration. This aspect is to be considered in the design and analysis of piping.

    The raise in temperature leads to thermal expansion. As the thermal expansion is restrained in the piping, thermal stresses are induced in the piping. The thermal stresses are divided into the following two categories:

    a) Expansion stress

    b) Local thermal stress

    The calculation and allowable stress due to the above-mentioned two stresses are different. In the piping design and analysis, the expansion stress is considered. The local thermal stress is not generally considered. This is due to the fact that the start-up rate and the shut-down rate of the piping are small. In piping, like the Heat Recovery Steam Generator (HRSG) piping, the start-up rates are high. Hence, suitable precautions are to be taken for this. The thermal expansion of the piping induces forces and moments on the equipment. These are to be suitably addressed.

35. Creep and Fatigue

    The piping used in engineering applications is subjected to creep and fatigue. The creep of piping is taken care-of by suitable factors of safety. The following factors of safety are used, as per ASME B31.1 (Code for Power Piping, as per the American Society of Mechanical Engineers):

    1. Average stress to produce creep rupture in 100,000 hours => 1.5 (Factor of safety)

    2. Minimum stress to produce creep rupture in 100,000 hours => 1.25 (Factor of Safety)

    3. Minimum stress to produce 0.01% creep strain in 1,000 hours => 1.0 (Factor of Safety)

    The allowable stresses are calculated using the above-mentioned three Factors of Safety. The minimum allowable stress obtained above is used for design of piping.

    The fatigue of piping is taken care-of by use of suitable computer based stress analysis. The allowable stress for fatigue is based on the fatigue life considerations. The piping is subjected to creep and fatigue. The interaction of creep and fatigue is complex. The Power Piping code ASME B31.1 uses simplified methods to take care-of the creep and fatigue. Suitable creep-fatigue interaction rules are used to asses the acceptability of the piping. The following parameters influence the safety of the piping:

a) Pipe diameter b) Pipe thickness c) Working pressure d) Working temperature e) Pipe material f) Piping fabrication process g) Life of piping h) Codes of design and construction i) Occasional loads j) Hydraulic test loads k) Piping layout l) Piping joints m) Equipment interface n) Additional loads due to valves, fittings and equipment