Pressure Systems Reference

NPS sizes covered

1/8" through 12"

Schedules shown

Sch 10 to Sch 160/XXH

OD is fixed

per NPS

Wall thickness varies by Sch

Standard

B36.10

ASME / ANSI

Wall thickness by schedule (inches)

NPS	OD (in)	Sch 10	Sch 20	Sch 40 (Std)	Sch 80 (XH)	Sch 120	Sch 160	XXH	Material note
1/8"	0.405	—	—	0.068	0.095	—	—	—	CS / SS
1/4"	0.540	—	—	0.088	0.119	—	—	—	CS / SS
3/8"	0.675	—	—	0.091	0.126	—	—	—	CS / SS
1/2"	0.840	0.083	—	0.109	0.147	—	0.187	0.294	CS / SS / Alloy
3/4"	1.050	0.083	—	0.113	0.154	—	0.219	0.308	CS / SS / Alloy
1"	1.315	0.109	—	0.133	0.179	—	0.250	0.358	CS / SS / Alloy
1-1/4"	1.660	0.109	—	0.140	0.191	—	0.250	0.382	CS / SS / Alloy
1-1/2"	1.900	0.109	—	0.145	0.200	—	0.281	0.400	CS / SS / Alloy
2"	2.375	0.109	—	0.154	0.218	—	0.344	0.436	CS / SS / Alloy
2-1/2"	2.875	0.120	—	0.203	0.276	—	0.375	0.552	CS / SS / Alloy
3"	3.500	0.120	—	0.216	0.300	—	0.438	0.600	CS / SS / Alloy
4"	4.500	0.120	0.188	0.237	0.337	0.438	0.531	0.674	CS / SS / Alloy
6"	6.625	0.134	0.250	0.280	0.432	0.562	0.719	0.864	CS / SS / Alloy
8"	8.625	0.148	0.250	0.322	0.500	0.594	0.906	0.875	CS / SS
10"	10.750	0.165	0.250	0.365	0.500	0.594	1.125	1.000	CS / SS
12"	12.750	0.180	0.250	0.406	0.500	0.688	1.312	1.000	CS / SS

Note: OD is fixed for a given NPS regardless of schedule. All dimensions in inches. CS = Carbon Steel (A53/A106), SS = Stainless Steel (A312), Alloy = Chrome-Moly (A335). Wall thickness determines pressure rating in conjunction with material grade and temperature. Calculated per ASME B31.3: P = (2·S·E·W·t) / (D − 2·Y·t).

Thread standards comparison

Standard	Full name	Thread angle	Profile	Seal method	Region	Common sizes	Typical application
NPT	National Pipe Taper	60°	Tapered	Thread interference + sealant	North America	1/8" – 4"	General process, utility, instrumentation
NPTF	National Pipe Taper Fuel	60°	Tapered	Thread crests crush for dry seal	North America	1/16" – 2"	Fuel, hydraulic, pneumatic — no sealant needed
NPS	National Pipe Straight	60°	Parallel	O-ring or face seal (no self-seal)	North America	1/8" – 4"	Mating with NPT female (NPS male into NPT female)
BSPT	British Standard Pipe Taper	55°	Tapered	Thread interference + sealant	Europe / UK / Asia	1/8" – 4"	European process, imports, OEM equipment
BSPP	British Standard Pipe Parallel	55°	Parallel	Bonded seal / O-ring face seal	Europe / UK / Asia	1/8" – 4"	European hydraulic, pneumatic
Metric (ISO)	ISO 228 / DIN 3852	60°	Parallel	O-ring or soft insert	Global (ISO)	M10×1 – M52×2	Machine tools, European OEM, compressed air
JIC / AN	Joint Industry Council / Army-Navy	37°	Straight	37° flare metal-to-metal	North America	-2 to -32 (dash size)	Hydraulics, aerospace, instrumentation tubing
SAE ORB	SAE O-Ring Boss	—	Straight	O-ring compressed on boss face	North America	-2 to -32 (dash size)	High-pressure hydraulic, mobile equipment
ORFS	O-Ring Face Seal (SAE J1453)	—	Straight	O-ring on flat face — zero-leak	Global	-4 to -32	Leak-critical hydraulic, high-pressure, vibration
Autoclave HP	Autoclave Engineers Coned & Threaded	—	Cone seat	Metal-to-metal cone + gland	Global	1/16" – 1"	Ultra-high pressure, lab, reactor systems

NPT thread dimensions by pipe size

Pipe size	TPI	Pitch (in)	Taper (in/in)	Engagement length (in)	Threads to engage	Notes
1/8" NPT	27	0.03704	1:16	0.180	4.87	Very fine — use PTFE tape, 2–3 turns
1/4" NPT	18	0.05556	1:16	0.200	3.60	Common instrumentation size
3/8" NPT	18	0.05556	1:16	0.240	4.32	Same TPI as 1/4" — not interchangeable
1/2" NPT	14	0.07143	1:16	0.320	4.48	Most common small process size
3/4" NPT	14	0.07143	1:16	0.339	4.75	Same TPI as 1/2" — not interchangeable
1" NPT	11.5	0.08696	1:16	0.400	4.60	Utility / process standard
1-1/4" NPT	11.5	0.08696	1:16	0.420	4.83
1-1/2" NPT	11.5	0.08696	1:16	0.420	4.83
2" NPT	11.5	0.08696	1:16	0.436	5.01	Consider flanged above this size
2-1/2" NPT	8	0.12500	1:16	0.682	5.46	Coarse thread — careful torque control
3" NPT	8	0.12500	1:16	0.766	6.13
4" NPT	8	0.12500	1:16	0.844	6.75	Upper limit of practical NPT use

Note: NPT taper is 1°47' per side (1/16 in/in). BSPT taper is identical at 1:16 but thread angle is 55° and pitch differs — the two standards are NOT interchangeable. Always use thread sealant (PTFE tape or anaerobic compound) on NPT; engagement depth controls sealing, not torque alone.

FILTER:

All

Directional

Branch

Size change

Termination

Union / coupling

Special

90° Long-Radius Elbow

Directional

End typesBW · SW · Thd · Flg

Radius1.5 × nominal diameter

Sizes1/2" – 24" (BW)

StandardASME B16.9 (BW) · B16.11 (SW/Thd)

Tags Low ΔPPreferred

Preferred over SR elbow for most services. Lower pressure drop due to gentler turn. Required for pigging service.

90° Short-Radius Elbow

Directional

End typesBW · SW · Thd

Radius1.0 × nominal diameter

Sizes1/2" – 24"

StandardASME B16.9

Tags Higher ΔPSpace-limited

Used where space is constrained. Higher turbulence and pressure drop than LR. Avoid in slurry or erosive service.

45° Elbow

Directional

End typesBW · SW · Thd

Radius1.5 × nominal diameter

Sizes1/2" – 24"

StandardASME B16.9

TagsLow ΔP

Used for gentle direction changes. Two 45° elbows with an offset spool are often used instead of one 90° to reduce vibration.

Street Elbow

Directional

End typesMPT × FPT (or MPT × SW)

Angle90° or 45°

Sizes1/8" – 2"

StandardASME B16.11

TagsCompactLow pressure

Male thread on one end, female on the other. Eliminates one nipple in tight spaces. Limit to utility/instrument service.

Return Bend (180°)

Directional

End typesBW · Thd

RadiusLR or SR

Sizes1/2" – 12"

StandardASME B16.9

TagsHeat exchanger

Common in heat exchangers, coils, and snake-pass configurations. Available close-pattern (tight U) and open-pattern.

Equal Tee

Branch

End typesBW · SW · Thd · Flg

ConfigAll three outlets same size

Sizes1/2" – 24"

StandardASME B16.9 / B16.11

TagsFull bore

Splits or combines flow. Branch flow creates pressure drop and turbulence. Consider flow direction when sizing.

Reducing Tee

Branch

End typesBW · SW · Thd

ConfigBranch outlet smaller than run

Sizes2" × 1/2" through 24" × 8"

StandardASME B16.9

TagsMost common tee

Most branch connections use a reducing tee (branch smaller than the header). Specified as run × run × branch.

Lateral / Wye

Branch

End typesBW

Config45° branch angle off run

Sizes2" – 24"

StandardASME B16.9

TagsLow ΔPSlurry

Lower pressure drop than a 90° tee branch. Preferred for slurry, high-velocity, and sewer applications.

Cross (4-way)

Branch

End typesBW · SW · Thd

ConfigEqual or reducing outlets

Sizes1/2" – 12"

StandardASME B16.11

TagsUse sparingly

Four-way fitting. Under cyclic or thermal loading, the intersection becomes a high-stress point — use with caution in elevated temp/pressure.

Concentric Reducer

Size change

End typesBW · SW · Thd

CenterlineShared (both ends aligned)

SizesFull range

StandardASME B16.9

TagsVertical runs

Centered reduction — both pipe centerlines align. Used in vertical runs where accumulation of liquid or gas is not a concern.

Eccentric Reducer

Size change

End typesBW

CenterlineOffset — one flat side

SizesFull range

StandardASME B16.9

TagsPump suctionDrain

Flat on bottom (FOB) prevents air pockets at pump suction. Flat on top (FOT) prevents liquid traps in gas lines. Critical to specify orientation.

Swage Nipple

Size change

End typesPlain × plain, Thd × Thd, or combo

Sizes1/4" – 3"

StandardASME B16.11 / MSS SP-95

TagsCompact

Short forged reducer used in smaller pipe. Eliminates a separate fitting and nipple, saving weight and leak points.

Cap

Termination

End typesBW · SW · Thd

Sizes1/2" – 24"

StandardASME B16.9 / B16.11

TagsDead-endPermanent

Permanent end closure. BW cap is preferred for high pressure — no leak path. Threaded cap is removable for inspection/cleaning.

Blind Flange

Termination

End typesFlanged (bolted)

Sizes1/2" – 24" (all classes)

StandardASME B16.5 / B16.47

TagsRemovableInspection

Removable end closure. Preferred for ends that may need to be opened (future connections, hydrotesting, pig launching).

Plug

Termination

End typesMPT (screws into FPT outlet)

Sizes1/8" – 4"

StandardASME B16.11

TagsThreaded outlets

Used to close off threaded outlet ports on tees, crosses, and body connections. Square head, hex head, and round head types available.

Union

Union / coupling

End typesThd × Thd · SW × SW

Sizes1/8" – 4"

StandardASME B16.11

TagsRemovable3-piece

Three-piece fitting: two end pieces weld/thread to pipe, a nut draws them together. Allows disassembly without cutting pipe.

Full Coupling

Union / coupling

End typesThd × Thd · SW × SW

Sizes1/8" – 4"

StandardASME B16.11

TagsPermanent join

Joins two pipes or a pipe and a fitting. Cannot be disassembled once welded/threaded. Use union if serviceability needed.

Half Coupling

Union / coupling

End typesThd or SW on one end; BW stub on other

Sizes1/8" – 4"

StandardASME B16.11

TagsBranch weld

Welded onto the main pipe body to create a threaded or socket-weld branch outlet. Used for small instrument connections.

Weldolet®

Special

End typesBW branch outlet

Sizes1/2" – 24" branch

StandardMSS SP-97

TagsFull strengthHigh pressure

Integrally reinforced branch fitting welded directly to the main pipe. Stronger than a cut-in tee for equal-size branches, and avoids pipe weakening.

Sockolet® / Threadolet®

Special

End typesSW or Thd branch outlet

Sizes1/8" – 2" branch

StandardMSS SP-97

TagsInstrumentSmall bore

Reinforced branch outlets for small-bore connections. Sockolet for socket-weld branch, Threadolet for threaded instrument/drain taps.

Nipple

Special

End typesMPT × MPT

LengthClose, short, long (6" to 12"+)

Sizes1/8" – 6"

StandardASME B1.20.1

TagsExtension piece

Short threaded pipe used as a spacer between fittings. Close nipple has threads meeting in the middle (no exposed pipe). Avoid in corrosive service.

Bushing

Special

End typesMPT (large) × FPT (small)

Sizes1/4" × 1/8" up to 4" × 2"

StandardASME B16.11

TagsSize adaptLow pressure only

Hex or face bushing reduces a female threaded opening. Not recommended for elevated pressure — prefer reducing coupling or swage nipple.

ASME B16.5 pressure-temperature ratings — carbon steel (A105 / Group 1.1) in psi

≤ 500 psi

501–1500 psi

1501–3000 psi

> 3000 psi

Class	-20 to 100°F	200°F	300°F	400°F	500°F	600°F	750°F	1000°F	Typical use
150	285	260	230	200	170	140	105	50	General service, utilities, low-P steam
300	740	680	655	640	600	550	465	130	Mid-pressure process, steam to 600°F
600	1480	1360	1310	1280	1200	1110	930	260	High-pressure process, refinery service
900	2220	2040	1970	1920	1800	1660	1395	390	High-pressure hydrocarbon, HP steam
1500	3705	3400	3295	3195	3000	2765	2325	650	Very high pressure process, injection
2500	6170	5670	5490	5330	4995	4610	3875	1080	Wellhead, ultra-HP, reactor systems

Flange face types

Face type	Abbrev.	Gasket contact	Classes	Typical use
Raised Face	RF	Raised ring seats on gasket	All	Default for most process piping; full-face gasket or ring gasket
Flat Face	FF	Full face — mates across entire flange face	150, 300	Required when mating to cast iron, ductile iron, or flat-face equipment flanges
Ring Type Joint	RTJ	Oval or octagonal ring seated in groove	300–2500	High-pressure, high-temperature; wellhead; API service. Metal-to-metal seal
Tongue & Groove	T&G	Interlocking male/female faces confine gasket	All	Self-centering; good for volatile or hazardous fluids where gasket blowout is a concern
Male & Female	M&F	One raised face fits into recessed face	All	Used in heat exchangers and specialty equipment; must have matching pair

Flange end types

Type	Abbrev.	Connection to pipe	Best for	Notes
Weld Neck	WN	Butt-weld to pipe end	High pressure / high temp / cyclic	Strongest flange type; bore matches pipe bore; preferred for critical service
Slip-On	SO	Slips over pipe end, fillet-welded inside & out	Lower pressure, general service	Lower material cost; two welds required; weaker than WN; easier to align
Socket Weld	SW	Pipe inserted into socket, fillet-welded	Small bore (≤ 2"), high pressure	Strong connection; crevice between pipe and socket can trap corrosives
Threaded	Thd	Screws onto external NPT threads	Low pressure utility, instrumentation	No welding required; weaker than weld types; not for cyclic or high-temp service
Blind	BL	No pipe connection — end closure	Dead ends, future connections	Solid disk bolted to mating flange; rated same as flange class
Lap Joint	LJ	Stub end butt-welded; flange slips over stub	Alloy piping, frequent disassembly	Flange rotates freely for bolt-hole alignment; stub end is the sealing surface
Orifice Flange	OR	Weld neck or slip-on; paired flanges	Flow measurement	Includes tapped ports for differential pressure measurement across orifice plate

Note: Ratings shown for ASME Group 1.1 (A105 / A216 WCB carbon steel). Ratings differ for alloy steels — always consult B16.5 Tables for actual material group. Ratings drop significantly above 750°F. For sizes above 24", use ASME B16.47 (Series A or B). RTJ ratings are same as RF of the same class.

Valve type selection guide

Valve type	Service	Flow control	Pressure drop	Sizes	End types	Key advantage	Limitation
Gate	On/off only	None (fully open / fully closed)	Very low	1/2" – 60"	BW · Flg · SW · Thd	Full bore, minimal restriction	Never throttle — disc erodes
Globe	Throttling	Good (disc position = flow)	Moderate–high	1/2" – 24"	BW · Flg · SW · Thd	Precise flow control	High ΔP; S-shaped flow path
Ball	On/offThrottle	Poor (not recommended for throttle)	Very low	1/4" – 48"	BW · Flg · SW · Thd	Fast operation, tight shutoff	Seat erosion if throttled
Butterfly	On/offModulate	Fair–good (disc angle)	Low	2" – 120"	Flg (lug/wafer)	Compact, lightweight, low cost	Lower pressure rating; seat erosion
Plug	On/offMulti-port	Poor	Low	1/2" – 24"	Flg · Thd	Multi-port configurations (3-way, 4-way)	High operating torque
Diaphragm	On/offThrottle	Good	Moderate	1/2" – 20"	Flg · Clamp	No packing — no stem leak; sanitary	Limited to 200°F / 150 psi typically
Needle	Precision throttle	Excellent (fine adjustment)	High	1/8" – 2"	Thd · Flg (HP body)	Very fine flow regulation	Small bore only; high ΔP
Check (swing)	Backflow prevention	N/A	Low	1/2" – 36"	BW · Flg	Simple; full bore	Cannot use in vertical downflow
Check (lift)	Backflow prevention	N/A	Moderate	1/2" – 6"	Thd · SW · Flg	Responds quickly; vertical line capable	Requires minimum flow velocity
Check (dual plate)	Backflow prevention	N/A	Low	2" – 60"	Wafer (between flanges)	Compact; fast-closing, low water hammer	Spring-loaded — not suitable for slurry
PRV (safety relief)	Overpressure protection	Automatic (spring set point)	Set < MAWP	1/2" – 8"	Thd · Flg	Required by code (ASME Sec. I / VIII)	Must be inspected / tested periodically
Control valve	Modulating	Excellent (actuated)	Designed ΔP	1/2" – 24"	Flg · BW	Remotely actuated; flow/pressure/temp control	Complex; cavitation risk if undersized

Valve body materials — service compatibility

Material	ASTM grade	Temp range	Compatible services	Avoid
Carbon steel	A216 WCB	-20°F to 800°F	Hydrocarbons, steam, general process	Wet H₂S, strong acids, seawater
316 Stainless	A351 CF8M	-425°F to 1000°F	Corrosives, acids, chlorides (moderate), cryogenic	High chloride concentration
304 Stainless	A351 CF8	-425°F to 1000°F	Food, pharma, mild corrosives	Chloride environments (use 316)
Duplex SS	A995 4A	-60°F to 570°F	Seawater, H₂S/CO₂ sour service, offshore	High-temp service above 570°F
Chrome-Moly	A217 WC6 / WC9	-20°F to 1100°F	High-temp steam, catalytic cracking, refinery	Wet H₂S without special heat treatment
Bronze / brass	B62 (bronze)	-50°F to 400°F	Water, seawater, marine utility	Ammonia, acetylene, strong acids
Hastelloy C-276	N10276	-423°F to 1000°F	Highly corrosive acids, chlorides, oxidizing media	Cost-prohibitive for general use

Note: PRVs must be set at or below MAWP and above normal operating pressure. Minimum overpressure allowance is 10% or 3 psi (whichever is greater) per ASME Sec. VIII. All valve selections should consider fluid properties, temperature, pressure class, end connection, actuator requirements, and applicable codes (ASME B16.34, API 600/602/608).

Gasket types — construction and use

Type	Construction	Flange face	Pressure limit	Temp limit	Key characteristic	Common service
Full-face (soft)	Flat sheet — full flange OD	Flat face only	150 psi	250–400°F	Covers all bolt holes; protects flanges from bending	Water, low-P steam, cast iron flanges — REQUIRED for flat-face Class 150
Raised-face ring (soft)	Flat ring — ID to OD of raised face	Raised face	300 psi	400–500°F	Higher bolt load concentrated on smaller area = better sealing	General process, utility, low–mid pressure
Spiral wound (SW)	V-profile metal + filler wound in spiral; inner/outer rings	Raised face	2500+ psi	-330°F to 1500°F	Self-centering inner ring; recovers under bolt load cycling	Refinery, chemical, steam, Class 300–2500 — most common process gasket
Kammprofile	Serrated solid metal core + soft facing layers	Raised faceT&G	2500+ psi	-330°F to 1500°F	Very high seating stress; excellent blowout resistance; reusable	Critical flange joints, heat exchangers, toxic or hazardous fluids
Ring joint (RTJ)	Solid metal oval or octagonal ring in groove	RTJ groove only	10,000+ psi	-100°F to 1200°F	Metal-to-metal seal; extremely high pressure capable	Wellhead, API flanges, Class 900–2500 HP/HT service
Corrugated metal	Corrugated thin metal sheet (bare or with soft facing)	Raised face	1500 psi	-330°F to 1100°F	Good for uneven flanges; requires lower bolt load than SW	Heat exchangers, steam, piping where SW is oversized
Double-jacketed	Soft filler inside metal jacket (two half-shells)	Raised faceT&G	1500 psi	-330°F to 1100°F	Filler protected from fluid contact; good for heat exchangers	Heat exchangers with tongue-and-groove channel covers
Solid metal flat	Flat solid ring — soft metal (Cu, Al, soft iron)	Raised faceM&F	Extreme HP	-330°F to 1500°F+	Used only where high bolt load is achievable; no recovery	Autoclave, ultra-HP reactors, special flanges

Gasket filler / facing materials — selection guide

Material	Type use	Max temp	Max pressure	Chemical resistance	Avoid	Notes
PTFE (pure)	Sheet, ring, envelope	450°F	300 psi	Excellent — nearly universal	High temp above 450°F; cold flow under high bolt load	Most chemical resistant soft gasket; creep under load at elevated temp
Expanded PTFE	Sheet, tape, ring	500°F	1500 psi	Excellent — nearly universal	Strong oxidizers at high temp (fluorine, liquid oxygen)	Lower creep than pure PTFE; good for irregular flange surfaces; FDA compliant
Flexible graphite	Sheet, SW filler, tape	850°F (oxidizing) / 5400°F (inert)	3000+ psi	Excellent for acids, steam, hydrocarbons	Strong oxidizing acids (HNO₃, H₂SO₄ fuming), chlorine gas	SW filler of choice for high-temp process; low seating stress; not for strong oxidizers
Compressed fiber (CAF)	Sheet, ring	750°F	1000 psi	Moderate — hydrocarbons, steam, water	Strong acids, chlorinated solvents	Legacy material; being replaced by PTFE/graphite; check asbestos-free spec
Neoprene / EPDM	Sheet, ring	300°F	150 psi	Water, dilute acids/alkalis, weather	Hydrocarbons, oils, solvents — swell or degrade	EPDM: water / steam / dilute chemicals. Neoprene: weather / ozone / moderate chemicals
Viton (FKM)	Sheet, ring, O-ring	400°F	300 psi	Excellent in fuels, oils, chlorinated solvents, acids	Ketones (acetone), esters, amines	Best elastomer for hydrocarbon and fuel service; expensive
316 SS winding	SW outer / inner ring; RTJ rings	1500°F	Full flange class	Broad — matches 316 SS corrosion envelope	High chloride at elevated temp (SCC); reducing acids	Standard SW winding metal; paired with graphite or PTFE filler
Inconel 625 winding	SW winding / RTJ rings	2000°F	Full flange class	Excellent — acids, chlorides, sea water, oxidizing	Cost — use only when 316 SS fails	Specified for sour gas (H₂S), high-chloride, and extreme-temperature service
Soft iron / low-C steel	RTJ ring joint only	1000°F	10,000+ psi	Dry hydrocarbons, steam, non-corrosive	Wet H₂S, chlorides, acids — corrodes	Lowest hardness RTJ ring — seats into groove; must be softer than flange material

Spiral wound gasket — dimensional reference (ASME B16.20)

NPS	Class 150 ID×OD (in)	Class 300 ID×OD (in)	Class 600 ID×OD (in)	Class 900–1500 ID×OD (in)	Thickness (in)	Min seating stress (psi)
1/2"	0.84 × 1.38	0.84 × 1.38	0.84 × 1.38	0.84 × 1.66	0.175	10,000
3/4"	1.05 × 1.69	1.05 × 1.69	1.05 × 1.69	1.05 × 1.88	0.175	10,000
1"	1.32 × 2.00	1.32 × 2.00	1.32 × 2.00	1.32 × 2.19	0.175	10,000
1-1/2"	1.90 × 2.62	1.90 × 2.62	1.90 × 2.62	1.90 × 3.00	0.175	10,000
2"	2.38 × 3.38	2.38 × 3.38	2.38 × 3.38	2.38 × 3.62	0.175	10,000
3"	3.50 × 4.50	3.50 × 4.75	3.50 × 4.75	3.50 × 5.00	0.175	10,000
4"	4.50 × 5.56	4.50 × 5.88	4.50 × 6.19	4.50 × 6.50	0.175	10,000
6"	6.63 × 7.88	6.63 × 8.50	6.63 × 8.75	6.63 × 9.69	0.175	10,000
8"	8.63 × 10.62	8.63 × 11.00	8.63 × 11.50	8.63 × 12.50	0.175	10,000
10"	10.75 × 13.00	10.75 × 13.50	10.75 × 14.25	10.75 × 15.12	0.175	10,000
12"	12.75 × 15.00	12.75 × 16.00	12.75 × 17.00	12.75 × 17.75	0.175	10,000

Note: SW gasket minimum seating stress is per ASME B16.20 with 316 SS winding + flexible graphite filler. RTJ ring material hardness must be less than the flange groove hardness — soft iron (HRB 68 max) for standard carbon steel flanges. Never reuse RTJ rings. SW gaskets with inner centering rings are mandatory for Class 900+.

Stud material (std)

B7 / 2H

A193 studs + A194 nuts

HT service studs

B16 / 7M

A193 B16 for >1000°F

Stainless option

B8M / 8M

A193 B8M (316 SS)

Lubrication

Always

Moly paste or anti-seize

ASME B16.5 stud bolt data — Class 150 & 300

NPS	Cl 150 — No. bolts	Cl 150 — Stud dia.	Cl 150 — Stud length (in)	Cl 300 — No. bolts	Cl 300 — Stud dia.	Cl 300 — Stud length (in)	Torque (ft·lb) B7/2H lubed
1/2"	4	1/2"	3.00	4	5/8"	3.50	Cl150: 30 · Cl300: 60
3/4"	4	1/2"	3.25	4	5/8"	3.75	Cl150: 30 · Cl300: 60
1"	4	1/2"	3.50	4	5/8"	4.00	Cl150: 30 · Cl300: 60
1-1/2"	4	1/2"	3.75	4	3/4"	4.50	Cl150: 30 · Cl300: 105
2"	4	5/8"	4.25	8	5/8"	5.00	Cl150: 60 · Cl300: 60
2-1/2"	4	5/8"	4.75	8	3/4"	5.50	Cl150: 60 · Cl300: 105
3"	4	5/8"	4.75	8	3/4"	5.75	Cl150: 60 · Cl300: 105
4"	8	5/8"	5.25	8	3/4"	6.25	Cl150: 60 · Cl300: 105
6"	8	3/4"	5.75	12	3/4"	7.00	Cl150: 105 · Cl300: 105
8"	8	3/4"	6.25	12	7/8"	7.50	Cl150: 105 · Cl300: 160
10"	12	7/8"	6.75	16	1"	8.25	Cl150: 160 · Cl300: 215
12"	12	7/8"	7.25	16	1-1/8"	9.00	Cl150: 160 · Cl300: 300

ASME B16.5 stud bolt data — Class 600, 900 & 1500

NPS	Cl 600 — No.	Cl 600 — Dia. / Length	Cl 900 — No.	Cl 900 — Dia. / Length	Cl 1500 — No.	Cl 1500 — Dia. / Length	Torque range (ft·lb) lubed
1/2"	4	3/4" / 4.25	4	3/4" / 4.50	4	7/8" / 5.50	105 · 105 · 160
1"	4	7/8" / 5.25	4	1" / 5.75	4	1" / 6.50	160 · 215 · 215
1-1/2"	4	1" / 6.25	4	1-1/8" / 7.00	4	1-1/4" / 8.25	215 · 300 · 420
2"	8	7/8" / 6.50	8	1" / 7.25	8	1-1/8" / 8.50	160 · 215 · 300
3"	8	1" / 7.50	8	1-1/8" / 8.75	8	1-1/4" / 10.00	215 · 300 · 420
4"	8	1-1/8" / 8.50	8	1-1/4" / 9.75	8	1-1/2" / 11.25	300 · 420 · 690
6"	12	1-1/8" / 9.75	12	1-3/8" / 11.50	12	1-5/8" / 13.25	300 · 530 · 870
8"	12	1-1/4" / 11.25	12	1-1/2" / 13.00	12	1-7/8" / 15.50	420 · 690 · 1200
10"	16	1-1/4" / 12.25	16	1-1/2" / 14.50	16	2" / 17.00	420 · 690 · 1550
12"	20	1-1/4" / 13.25	20	1-5/8" / 16.00	20	2" / 18.50	420 · 870 · 1550

Stud material grades — quick reference

Stud grade	Nut grade	ASTM spec	Material	Min yield (ksi)	Max temp	Typical use
B7	2H	A193 / A194	Cr-Mo alloy steel (4140)	105	1000°F	Standard process piping — most common combination
B7M	2HM	A193 / A194	Cr-Mo alloy steel, controlled hardness	80	1000°F	Sour service (NACE MR0175 / ISO 15156) — H₂S environments
B16	4	A193 / A194	Cr-Mo-V alloy steel	125	1100°F	High-temperature steam, Class 600+ above 750°F
B8M / B8M Cl.2	8M	A193 / A194	316 stainless steel	30 / 80	1000°F	Corrosive service, cryogenic; Cl.2 is strain-hardened (higher strength)
B8 / B8 Cl.2	8	A193 / A194	304 stainless steel	30 / 80	1000°F	Low-chloride corrosive; cryogenic; lower cost than B8M
L7 / L7M	4	A320 / A194	Cr-Mo (impact tested)	105	-150°F	Low-temperature / cryogenic service (LNG, propane, ethylene)

Torque notes: Values shown are guidelines for B7/2H studs with molybdenum disulfide (moly) paste lubricant. Dry torque values are ~40% higher. Always follow project-specific bolt torquing procedures. Cross-pattern torquing in minimum 3 passes (30% → 70% → 100%). For RTJ flanges add additional pass to seat the ring. Galvanic isolation washers required when using SS studs in CS flanges. B7M required per NACE MR0175 for any sour service (H₂S partial pressure > 0.05 psia).

B31.3 Pressure Rating Calculator

Calculates MAWP from pipe dimensions and material, or required wall thickness for a target pressure. Uses ASME B31.3 formula.

▶ How to use this calculator

What this does

This calculator applies the ASME B31.3 pipe wall thickness formula. Use it in two directions: given a pipe you already have, find its MAWP (maximum safe pressure). Or given a target pressure, find the minimum wall thickness you need to order.

Key inputs explained

Corrosion allowance (CA) — how much wall thickness you set aside for corrosion over the design life. Typical values: 0.063" (1/16") for general service, 0.125" for mild corrosive, 0.250" for aggressive environments. This gets subtracted before calculating pressure capacity, so the MAWP result reflects the pipe at end-of-life, not when new.

Mill tolerance — pipe manufacturers are allowed to under-deliver on wall thickness by a set percentage (12.5% for most ASTM specs). The calculator accounts for this automatically. If you've measured the actual wall with UT, select 0%.

Weld quality factor E — seamless pipe = 1.0 (no longitudinal weld seam to worry about). ERW pipe from reputable mills is also 1.0 per B31.3 Table A-1B. Older furnace-welded pipe uses 0.85 or 0.80. If in doubt, use 1.0 for seamless and verify your ERW pipe's E factor from the mill cert.

Y coefficient — a temperature correction from B31.3 Table 304.1.1. For most carbon and stainless steel at temperatures below 900°F, this is 0.4. It only changes at very high temperatures (950°F+). Leave it at 0.4 unless you're working at elevated temperatures.

Allowable stress S — this is the most temperature-sensitive input. The presets cover common cases, but for critical work always verify against the official B31.3 Appendix A tables. Stress drops significantly above 600°F.

Worked example — finding MAWP

Pipe: 4" Sch 40 carbon steel (A106-B)
OD = 4.500" · Nominal wall = 0.237"
Mill tol. 12.5% → min wall = 0.237 × 0.875 = 0.207"
CA = 0.063" → effective wall = 0.207 − 0.063 = 0.144"
S = 20,000 psi (A106-B to 400°F) · E = 1.0 · Y = 0.4
P = (2 × 20,000 × 1.0 × 0.144) / (4.500 − 2 × 0.4 × 0.144) = ~1,300 psi

Worked example — finding required wall

Target: 600 psi design pressure in 4" line, A106-B at 400°F
CA = 0.063" · Mill tol. = 12.5%
t_min (pressure only) = (600 × 4.500) / (2×20,000×1.0 + 2×0.4×600) = 0.067"
Add CA: 0.067 + 0.063 = 0.130"
Apply mill tol.: 0.130 / 0.875 = 0.149" nominal required
→ Select Sch 40 (0.237") — next schedule above 0.149"

Important notes

This formula covers straight pipe only. Fittings, branches, and bends have separate calculations.
The result is the pressure-containing wall only. Structural loads, nozzle loads, and thermal stress are separate checks.
Always have results reviewed by a qualified engineer before use in design.

P = (2·S·E·W·t) / (D − 2·Y·t)

P = internal design pressure (psi) · S = allowable stress (psi)
E = weld quality factor · W = weld strength reduction factor
t = wall thickness (in) · D = outside diameter (in) · Y = temp coefficient

Calculation mode

Pipe size (NPS) — sets OD automatically

Outside diameter (D) inches

Nominal wall thickness (t) inches

Material & allowable stress (S) psi at temperature

Weld quality factor (E)

Temperature coefficient (Y) per B31.3 Table 304.1.1

Mill tolerance deduction % (subtract from wall)

Corrosion allowance (CA) inches — subtracted from wall before calc

Typical: 0.063" (1/16") general · 0.125" (1/8") mild corrosive · 0.250" severe

—

Pipe Weight Calculator

Calculates pipe weight per foot and total run weight. Includes fluid fill weight option.

W/ft = 10.69 × (D − t) × t

Steel pipe (carbon or alloy). For SS multiply by 1.02.
Fluid fill: W_f/ft = 0.3405 × d² where d = bore (in)

Pipe size (NPS)

Outside diameter (D) inches

Wall thickness (t) inches

Run length feet

Material

Fluid fill (add to total)

—

lb/ft (pipe only)

Flow Velocity Estimator

Calculates fluid velocity in a pipe for a given flow rate. Flags against typical design velocity limits.

v = Q / A = (0.321 × GPM) / d²

v = velocity (ft/s) · Q = flow rate · d = bore (in)

Flow rate

Pipe bore (ID) inches — or select NPS + Sch

Fluid type sets velocity limits

—

ft/s flow velocity

Flange Class Selector

Enter your design pressure and temperature to find the minimum required ASME B16.5 flange class for carbon steel (A105 / Group 1.1).

Design pressure psi

Design temperature °F

Design margin

—

Minimum flange class

Darcy-Weisbach Pressure Drop

Calculates frictional pressure drop across a straight pipe run plus fittings equivalent length. Uses Darcy-Weisbach with Colebrook-White friction factor.

▶ How to use this calculator

What this does

This calculates the frictional pressure drop from fluid flowing through a pipe run — the pressure you lose to friction that a pump or compressor must overcome. It uses the Darcy-Weisbach equation with the Colebrook-White friction factor (industry standard for turbulent flow).

The result tells you how much pressure your pump needs to provide beyond just the static head. A rule of thumb for liquid service: keep pressure drop below 2 psi per 100 ft of equivalent length. Gas lines vary more widely.

Fittings equivalent length — the most misunderstood input

Every fitting (elbow, valve, tee) causes extra pressure drop beyond its physical length. We model this as an equivalent length of straight pipe that would cause the same drop. The formula is: L_eq = (L/D ratio) × pipe ID in feet.

Typical L/D values:

90° LR elbow: ×16 — e.g. 4" pipe (ID 4.026") → 4.026/12 × 16 = 5.4 ft each
Gate valve (fully open): ×8 → 2.7 ft per valve (4" line)
Globe valve (fully open): ×340 → 114 ft per valve (4" line) — this is why globe valves hurt
Tee (flow through branch): ×60 · Tee (run): ×20
Check valve (swing): ×50 · Ball valve (fully open): ×3

Add up all fittings' equivalent lengths and enter the total in the fittings field. The calculator adds it to the straight pipe length for a combined equivalent length.

Worked example

4" Sch 40 CS pipe (ID 4.026"), water at 60°F
Straight run: 250 ft · Flow: 350 GPM
Fittings: 4× 90° LR elbows + 1× gate valve + 1× swing check
Equiv. length: (4×16 + 8 + 50) × (4.026/12) = ~39 ft
Total equiv. length: 250 + 39 = 289 ft
Result: velocity ≈ 8.8 ft/s · Re ≈ 280,000 (turbulent)
ΔP ≈ 4.9 psi total · 1.7 psi/100 ft ✓

Understanding the results

Reynolds number (Re) — below 2,300 is laminar (very viscous or slow flow, high friction), above 4,000 is fully turbulent (typical process service). The transition zone 2,300–4,000 is unpredictable and should be avoided in design.

Darcy friction factor f — a dimensionless number typically between 0.01 and 0.05 for turbulent flow. Higher for rough pipe or low Re. Calculated iteratively using Colebrook-White.

ft of head — equivalent water column height. Useful for pump sizing (pump curves are often in ft of head).

What this doesn't include

Static head (elevation change) — add separately: ΔP_static = ρgh / 144
Minor losses from entrance/exit conditions
Two-phase flow, flashing, or compressible gas flow at high Mach numbers

ΔP = f · (L/D) · (ρv²/2) · (1/144)

f = Darcy friction factor (Colebrook) · L = equiv. length (ft)
D = ID (ft) · ρ = density (lb/ft³) · v = velocity (ft/s)

Pipe bore (ID) inches

Straight pipe length feet

Fittings equivalent length feet — add L/D × ID for each fitting

Typical L/D: 90° LR elbow ×16 · Gate valve ×8 · Globe valve ×340 · Tee branch ×60 · Check (swing) ×50

Flow rate GPM

Fluid

Pipe roughness (ε)

—

psi pressure drop

Thermal Expansion Calculator

Calculates pipe elongation due to temperature change and sizes an expansion loop to absorb the movement without exceeding allowable stress.

▶ How to use this calculator

Why thermal expansion matters

All pipe grows when heated. A 300 ft carbon steel line heating from 70°F to 450°F will expand by roughly 3 inches. If both ends are rigidly fixed — anchored at a vessel nozzle on one end and a pump on the other — that 3 inches has nowhere to go. The pipe buckles, flanges leak, or nozzle loads exceed equipment allowables. Expansion must be accommodated in the layout design.

What the calculator outputs

ΔL (thermal expansion) — the total elongation of the pipe run in inches. This is the movement the piping system must be able to absorb through layout flexibility, expansion loops, or expansion joints.

U-loop half-leg length — if you're using an expansion loop (a U-shaped detour in the pipe run), this is the minimum leg length on each side of the loop. The full loop is roughly twice this value wide. This is an estimate based on the guided cantilever method — sufficient for preliminary sizing but pipe stress software (CAESAR II, AutoPIPE) is required for final design.

Expansion loop — what it looks like

An expansion loop is a rectangular detour in the pipe that acts as a spring. The pipe run goes: straight → 90° elbow → loop leg → 90° elbow → loop leg → 90° elbow → back on original route. The loop absorbs the growth by bending slightly. The longer the legs, the more flexible the loop.

Main run direction: →→→→ [loop] →→→→
Loop shape: ↑ leg → across → ↓ leg
Half-leg = each vertical section length
Rule of thumb: loop legs ≥ half-leg result from calculator

Worked example

6" Sch 40 CS pipe (OD 6.625")
Run length: 200 ft · Install temp: 70°F · Operating: 400°F
ΔT = 330°F · α (CS) = 6.3 × 10⁻⁶ /°F
ΔL = 6.3e-6 × (200×12) × 330 = 5.0" of growth
Loop leg = 0.65 × √(6.625 × 5.0) = ~3.7 ft per side
→ Use 4 ft minimum loop legs, full loop ≈ 8 ft wide

When a loop isn't enough — other solutions

Natural offsets — L-shaped or Z-shaped pipe runs absorb some expansion through the corners. Often sufficient for small ΔL (<1").
Bellows expansion joints — compact axial expansion absorbers. Require thrust restraint (anchor blocks). Not suitable for all fluids.
Sliding/slip joints — telescoping pipe sections. Used on large-diameter low-pressure lines (steam distribution, flue gas).
Cold spring — deliberately cutting the pipe short by half the expected expansion, so it's pre-stressed in the cold condition and balanced in the hot.

Stainless vs. carbon steel

Stainless steel expands ~50% more than carbon steel (α ≈ 9.6 vs 6.3 × 10⁻⁶ /°F). A SS line will need significantly longer loop legs or more frequent offsets than an equivalent CS line. Select the correct material in the dropdown — the difference is not trivial.

ΔL = α · L · ΔT

L_loop = 3 · √(D · ΔL / 0.00026·S)

α = thermal expansion coeff. · L = pipe length (in) · ΔT = temp rise (°F)
D = OD (in) · S = allowable stress · Loop leg = U-loop half-leg length

Pipe material

Pipe OD inches — for loop sizing

Pipe run length feet

Installation temperature °F

Operating temperature °F

—

inches of thermal expansion

Disclaimer: These calculators are reference tools only. All design calculations for pressure-containing equipment must be reviewed by a qualified engineer and comply with the applicable code (ASME B31.3, B31.1, etc.). Mill tolerance deduction, corrosion allowance, and weld joint examination factor are the designer's responsibility. Do not use these results as sole basis for fabrication or procurement.

Basis

MSS SP-69

ASME B31.1 / B31.3 guidance

Span limit criteria

L/240

Max sag (deflection) at midspan

Stress check

Required

Spans are starting points only

Insulated pipe

−25%

Reduce span for insulation weight

Maximum pipe support span — carbon steel, water-filled (ft)

NPS	Sch 40 — gas / air	Sch 40 — water-filled	Sch 80 — gas / air	Sch 80 — water-filled	Sch 160 — water-filled	Notes
1/2"	7	5	7	6	7	Min span — use continuous support in rack if possible
3/4"	7	6	8	7	8
1"	9	7	10	8	10
1-1/2"	10	9	11	10	12
2"	13	10	14	11	14	Common small process line
2-1/2"	14	11	15	12	16
3"	15	12	16	13	17
4"	17	14	18	15	19	Most common mid-size process line
6"	21	17	22	18	23
8"	24	19	25	21	26
10"	26	22	28	23	29	Verify stress at each support
12"	30	24	32	26	33	Verify stress at each support

Maximum span — stainless steel, water-filled (ft)

NPS	Sch 10S — gas	Sch 10S — water	Sch 40S — gas	Sch 40S — water	Sch 80S — water	Notes
1/2"	6	4	7	5	6	SS is ~3% denser than CS — slightly shorter spans
1"	8	6	9	7	9
2"	11	9	13	10	13
3"	13	10	15	12	16
4"	15	12	17	13	18
6"	18	15	20	16	22
8"	21	17	23	19	24
12"	26	21	29	23	31	Confirm with stress analysis for critical lines

Support type selection guide

Support type	Function	Movement allowed	Best for	Avoid when
Resting / shoe support	Gravity support — carries weight	Axial + lateral slide	General pipe racks, most process lines	Lines needing rigid lateral restraint
Anchor (fixed)	Fully restrains all movement	None	At equipment nozzles; between expansion loops; branch points	Mid-run without expansion analysis — will induce stress
Guide	Allows axial movement; restrains lateral	Axial only	Every 3rd–4th span on hot lines; directs thermal growth toward loops	Lines needing lateral freedom
Limit stop	Limits travel in one direction	Partial (to stop)	Seismic restraint; blast; slug flow lines needing sway restraint	Lines with large thermal growth in restrained direction
Spring hanger (variable)	Supports weight while allowing vertical movement	Vertical (spring travel)	Lines with significant vertical thermal movement; riser supports	Lines where constant load is critical — use constant hanger instead
Constant effort hanger	Constant load regardless of position	Vertical (full travel)	Equipment nozzle connections; tall risers; sensitive rotating equipment	Horizontal pipe runs (overkill and expensive)
Clamp / U-bolt	Secures pipe to structure, no sliding	None (clamp) / slight (U-bolt)	Low-temp utility, instrument lines, insulated lines	High-temp lines — thermal growth will fight the clamp
Pipe roller	Weight support with axial and rotational freedom	Axial + some lateral roll	Long horizontal runs, hot steam lines, large-bore process lines	Small-bore lines — overkill

Span adjustment factors

Condition	Multiplier on base span	Notes
Bare pipe, gas / air filled	1.0× (base)	Reference condition — tables above
Water-filled	0.82×	Water adds ~8.33 lb/gal; dominates at larger sizes
Insulated (1"–2" thick)	0.75×	Insulation + jacket weight; reduce further for heavier insulation
Insulated + water-filled	0.65×	Worst case for support spacing — hydro test condition
High temperature (> 750°F)	0.85×	Creep reduces allowable stress; verify with pipe stress software
Concentrated load (valve, flange cluster)	0.5–0.7×	Support within 1–2 ft of each side of a heavy inline component
Vibrating / pulsating service	0.5×	Compressor discharge, pump discharge with slug — reduce span aggressively
Seismic zone (high)	0.75×	Add lateral bracing per ASCE 7; reduce spacing

Note: Spans shown are starting-point estimates based on MSS SP-69 and B31.3 Appendix guidance. Final support spacing must be verified by pipe stress analysis (Caesar II, AutoPIPE, or equivalent) for all lines designated as critical, high-temperature, cyclic, or connected to rotating equipment. Always support within 2 ft of inline components (valves, flanges, instruments) weighing more than 50 lb. Spans for SS pipe reflect lower modulus of elasticity (28×10⁶ psi vs 29.5×10⁶ for CS) and slightly higher density.