STEP BOLT

1. Industry Context

Step bolts are specialized structural and mechanical fasteners designed to perform dual functional roles:

1. Primary Mechanical Fastening
2. Integrated Load-Bearing Step or Support Surface

Unlike conventional bolts intended solely for clamping, step bolts form functional structural interfaces, commonly acting as:

• Ladder climbing steps
• Tower access footholds
• Transmission structure steps
• Equipment access supports
• Structural positioning stops
• Alignment or load transfer studs

They are widely deployed in industries where human access, repeat load cycling, and environmental exposure coexist.

Primary Industrial Sectors

Industry	Functional Purpose
Transmission & Telecom Towers	Climbing footholds
Power Generation	Boiler access & maintenance steps
Oil & Gas	Platform access systems
Infrastructure	Bridge inspection access
Railways	Signal and gantry structures
Petrochemical	Reactor platform climbing systems
Shipbuilding	Vertical access structures
Heavy Equipment	Maintenance access points

Step bolts must simultaneously satisfy:

• Structural fastening requirements
• Human safety load requirements
• Corrosion resistance expectations
• Fatigue durability criteria

This dual requirement differentiates them from standard hex bolts or carriage bolts.

SM Fasteners manufactures step bolts under controlled ISO 9001 quality systems, ensuring compliance with global EPC procurement expectations.

2. Technical Definition

Engineering Definition

A Step Bolt is a headed threaded fastener incorporating an extended cylindrical or formed shoulder designed to function as a load-bearing step or spacer while maintaining threaded clamping capability.

Basic Geometry Elements

1. Head section
2. Load-bearing step/shoulder
3. Transition fillet radius
4. Threaded shank
5. Nut engagement zone

The shoulder diameter is intentionally larger than the thread diameter.

This provides:

• Increased bending resistance
• Reduced contact stress
• Stable foot engagement
• Controlled load transfer

Typical Geometry Representation

Feature	Function
Head	Installation torque application
Step/Shoulder	Human or mechanical load support
Threaded Portion	Structural attachment
Fillet Radius	Fatigue stress reduction
Bearing Surface	Load distribution

3. Functional Role in Assemblies

Step bolts operate in combined loading environments.

They must resist:

• Axial tensile forces
• Shear forces
• Bending loads
• Cyclic fatigue loads
• Dynamic human impact loads

Unlike conventional bolts, failure risks include:

• Step bending
• Shoulder fatigue cracking
• Thread root stress concentration
• Slip-induced wear

4. Load Mechanics & Force Behavior

4.1 Load Types Acting on Step Bolts

Load Type	Source
Tensile Load	Nut preload
Shear Load	Lateral force from climbing
Bending Moment	Off-center foot load
Impact Load	Worker stepping action
Fatigue Load	Repeated access cycles

4.2 Combined Stress Model

Step bolts rarely experience pure tension.

They operate under combined stress conditions:$$\sigma_{combined} = \sigma_t + \sigma_b + \tau_s$$

Where:

• $\sigma_t$​ = tensile stress
• $\sigma_b$​ = bending stress
• $\tau_s$​ = shear stress

Design must satisfy:$$\sigma_{equivalent} < Yield\ Strength / Safety\ Factor$$

4.3 Bending Mechanics

Critical design consideration:

Human weight applied at step center generates bending.$$M = F \times L$$

Where:

• F = applied load
• L = distance from mounting face

Increasing shoulder diameter significantly reduces bending stress.

5. Preload and Clamping Behavior

Proper tightening ensures:

• Joint rigidity
• Reduced vibration loosening
• Controlled fatigue life

Torque–Tension Relationship

$$T = K \times F \times D$$

Where:

• T = tightening torque
• K = nut factor
• F = preload
• D = nominal diameter

Typical Nut Factor Values:

Condition	K Factor
Dry	0.20
Zinc Plated	0.18
Lubricated	0.15
PTFE Coated	0.10–0.12

Worked Preload Example

M16 Step Bolt — Property Class 8.8

$$F_p = 580 \times 157 = 91,060N$$

Recommended preload = 70%$$F = 63,742N$$

Torque (lubricated):$$T = 0.15 \times 63,742 \times 0.016$$

$$T ≈ 153 Nm$$

6. Joint Design Principles

6.1 Thread Engagement Rule

Minimum engagement:

Material	Engagement
Steel	1 × Diameter
Aluminum	1.5 × Diameter
Cast Iron	1.25 × Diameter

6.2 Step Projection Design

Projection must balance:

• Ergonomics
• Structural strength
• Clearance
• Safety regulations

Typical projection:

100–250 mm depending on application.

6.3 Safety Factors

Application	Safety Factor
Static Structural	2.0
Access Structures	3.0
Offshore	4.0
Critical Maintenance Access	5.0

7. Failure Mechanisms

7.1 Fatigue Failure

Repeated climbing cycles induce microcracks at fillet radius.

Mitigation:

• Rolled threads
• Proper fillet radius
• Controlled hardness

7.2 Shear Failure

Occurs when lateral load exceeds shoulder capacity.

Prevention:

• Increased shoulder diameter
• High-strength alloy steel grades

7.3 Hydrogen Embrittlement

Risk increases with:

• High strength steels (>1000 MPa)
• Electroplating processes

SM Fasteners applies controlled baking procedures per ISO standards.

7.4 Stress Corrosion Cracking

Common environments:

• Chloride exposure
• Sour gas service (H₂S)

Material upgrade required:
Duplex / Super Duplex / Nickel alloys.

8. Functional Selection Criteria

Engineers must evaluate:

• Required step load rating
• Environmental corrosion level
• Structural thickness
• Maintenance frequency
• Inspection accessibility
• Applicable international standards

9. Engineering Advantages of Step Bolts

• Integrated structural + access function
• Reduced component count
• Faster installation
• High fatigue resistance
• Improved worker safety
• Long service life in harsh environments

10. Product Types and Variants

Step bolts are engineered according to functional loading requirements, installation methods, and structural interface design. Unlike conventional fasteners governed by a single standard geometry, step bolts are primarily application-engineered components manufactured under controlled dimensional frameworks.

SM Fasteners supplies both standardized and custom-engineered step bolts, aligned with global EPC specifications.

10.1 Classification by Functional Design

Type	Description	Typical Application
Single Shoulder Step Bolt	One load-bearing shoulder	Towers, ladders
Double Step Bolt	Dual offset shoulders	Access platforms
Anti-Slip Step Bolt	Knurled or serrated step	Offshore & wet environments
Heavy Duty Structural Step Bolt	Increased diameter shoulder	High-load access systems
Safety Head Step Bolt	Dome/rounded head	Worker safety compliance
Extended Projection Step Bolt	Long step projection	Transmission towers
Insulated Step Bolt	Non-conductive sleeve	Electrical infrastructure
PEEK Step Bolt	Polymer high-performance step	Chemical & electrical zones

10.2 Classification by Installation Method

Installation Type	Features
Through Bolt	Nut secured opposite side
Tapped Hole Step Bolt	Direct threaded installation
Welded Base Step Bolt	Permanent structural fixation
Anchor Bolt	Concrete embedment applications
Flange Bolt	Improved load distribution

10.3 Head Style Variations

Head Type	Engineering Purpose
Hex Head	Standard torque application
Square Head	Anti-rotation support
Button Head	Safety & snag prevention
Countersunk	Flush mounting
Custom Forged Head	EPC specification compliance

11. Dimensional Logic and Geometry Design

Step bolt geometry is governed by ergonomic safety, structural strength, and manufacturing feasibility.

Key Dimensional Parameters

Symbol	Parameter
d	Nominal thread diameter
P	Thread pitch
Ds	Shoulder diameter
L	Overall length
Ls	Step projection length
Lt	Threaded length
H	Head height
F	Across flats dimension

Engineering Design Relationship

Critical design rule:$$D_s \geq 1.5d \text{ to } 2.5d$$

This ensures adequate bending resistance under human load.

Step Projection vs Load Capacity

Projection Length	Load Condition
80–120 mm	Light access
120–180 mm	Standard climbing
180–250 mm	Heavy industrial access
>250 mm	Special engineered systems

12. Standard Dimensional Specification Table

(Typical SM Fasteners Engineering Range)

Thread Size	Pitch (mm)	Shoulder Dia (mm)	Projection (mm)	Head AF (mm)	Head Height (mm)	Thread Length (mm)
M10	1.5	20	100	17	6.5	30
M12	1.75	24	120	19	7.5	35
M16	2.0	30	150	24	10	40
M20	2.5	36	180	30	12.5	45
M24	3.0	45	200	36	15	50
M30	3.5	55	250	46	18.7	60

(Dimensions may be customized according to project drawings.)

13. Applicable International Standards

Step bolts combine multiple standard references rather than one exclusive specification.

13.1 ISO Standards

Standard	Scope
ISO 4014	Hex bolts – partial thread
ISO 4017	Fully threaded bolts
ISO 898-1	Mechanical properties
ISO 965	Thread tolerances
ISO 3506	Stainless steel fasteners
ISO 3269	Acceptance inspection
ISO 10683	Zinc flake coatings
ISO 6157	Surface discontinuities

13.2 ASTM Standards

Standard	Application
ASTM A307	General structural bolts
ASTM A325 / A490	High-strength structural
ASTM A193	High temperature service
ASTM A320	Low temperature service
ASTM F568M	Metric mechanical properties
ASTM B633	Zinc plating
ASTM F1136	Zinc/Al coatings

13.3 DIN Standards

Standard	Description
DIN 931	Hex bolt partial thread
DIN 933	Fully threaded
DIN 267	Technical delivery
DIN EN 10204	Inspection documentation

13.4 British Standards (BS)

Standard	Scope
BS 3692	Metric precision fasteners
BS 4190	Hexagon bolts
BS EN ISO 898	Mechanical properties
BS EN 14399	Structural bolting assemblies

14. Property Class Systems (Mechanical Grading)

Property Class	Yield Strength (MPa)	Tensile Strength (MPa)	Application
4.6	240	400	Light structures
5.8	400	500	General equipment
8.8	640	800	Structural access
10.9	900	1040	Heavy duty industrial
12.9	1080	1220	High stress environments

SM Fasteners validates mechanical properties via certified testing aligned with ISO 898-1.

15. Thread Systems & Global Interchangeability

Global EPC projects require compatibility across regional standards.

Thread Standard Comparison

System	Angle	Units	Region
Metric	60°	mm	Global
UNC	60°	inch	USA
UNF	60°	inch	USA aerospace
BSW	55°	inch	Legacy UK
BSF	55°	inch	Mechanical legacy
NPT	60° taper	inch	Pressure systems

Thread Tolerance Classes

Thread	External	Internal
Metric Standard	6g	6H
Precision	4g6g	4H
Structural	8g	7H

Thread tolerance selection influences:

• Preload accuracy
• Assembly friction
• Fatigue resistance

16. Thread Engagement Engineering

Minimum engagement must prevent stripping failure before bolt fracture.$$L_e \geq \frac{2F}{\pi d \tau}$$

Where:

• $L_e$​ = engagement length
• $F$ = preload
• $τ$ = allowable shear stress

17. Dimensional Tolerance Control

SM Fasteners maintains dimensional consistency through:

• CNC machining verification
• Forging die control
• Statistical process control
• ISO 9001 inspection procedures

Typical tolerances:

Parameter	Tolerance
Diameter	±0.02 mm
Shoulder Length	±0.5 mm
Projection	±1.0 mm
Thread Pitch	ISO Class compliant

18. Proof Load & Tensile Strength Table

(Representative Engineering Values)

Size	Stress Area (mm²)	Proof Load 8.8 (kN)	Proof Load 10.9 (kN)	Ultimate Tensile (kN)
M10	58	34	49	58
M12	84	49	71	84
M16	157	91	132	157
M20	245	142	206	245
M24	353	205	298	353
M30	561	325	474	561

19. Dimensional Engineering Considerations for EPC Projects

Procurement engineers typically evaluate:

• Standard compliance equivalence
• Interchangeability across suppliers
• Field installation tooling compatibility
• Safety certification requirements
• Replacement availability

SM Fasteners supports custom dimensional alignment based on:

• Transmission tower drawings
• Offshore platform specifications
• OEM equipment layouts
• Infrastructure authority standards

20. Design Interchangeability Considerations

Step bolts frequently replace:

• Ladder rung assemblies
• Welded steps
• Structural pins

Key interchangeability checks:

Parameter	Requirement
Shoulder Diameter	Must match ergonomic spec
Projection Length	Critical safety dimension
Thread Class	Must match nut grade
Property Class	Equal or higher allowed
Coating System	Compatible with environment

21. Engineering Advantages of Custom Step Bolt Geometry

SM Fasteners’ custom manufacturing capability enables:

• Optimized shoulder stress distribution
• Reduced fatigue concentration
• Improved corrosion performance
• Enhanced worker safety compliance
• Project-specific tolerancing

Custom production supported through:

• ISO 9001 design verification
• Material traceability systems
• Advanced forging and machining operations
• Global export readiness

22. Material Grades and Selection Criteria

Material selection for step bolts is a critical engineering decision because these fasteners operate under:

• Combined tensile and bending stresses
• Repeated fatigue loading from climbing cycles
• Outdoor atmospheric exposure
• Chemical or offshore corrosion environments
• Safety-critical human load applications

Unlike standard structural bolts, step bolts must maintain mechanical integrity and surface safety performance simultaneously.

SM Fasteners manufactures step bolts across a full industrial material spectrum, supported by ISO 9001 controlled procurement and traceability systems.

22.1 Industrial Material Categories

Material Category	Typical Grades	Key Characteristics
Carbon Steel	IS 2062, ASTM A307	Economical, structural use
Medium Carbon Steel	C35, C45	Improved strength
Alloy Steel	4140, 4340, EN19	High strength & fatigue resistance
Stainless Steel	SS304, SS316	Corrosion resistance
Duplex Stainless Steel	2205	High strength + corrosion resistance
Super Duplex	2507	Offshore & seawater resistance
Nickel Alloys	Inconel, Monel, Hastelloy	Extreme environments
SMO 254	High Mo alloy	Chloride resistance
PEEK Polymer	Reinforced PEEK	Electrical & chemical isolation

22.2 Material Selection Criteria

Engineering evaluation considers:

Mechanical Requirements

• Required proof load
• Bending resistance
• Fatigue life
• Impact resistance

Environmental Requirements

• Atmospheric exposure
• Chloride contamination
• Acidic process environment
• H₂S sour service

Operational Factors

• Temperature range
• Inspection interval
• Maintenance accessibility
• Galvanic compatibility

22.3 Material Comparison Table

Material	UTS (MPa)	Yield (MPa)	Corrosion Resistance	Temp Limit °C	Relative Cost	Typical Application
Carbon Steel	400–600	250–350	Low	300	Low	Transmission towers
Alloy Steel	900–1200	700–1000	Moderate	450	Medium	Heavy industry
SS304	515	205	Good	425	Medium	General outdoor
SS316	515	205	Very Good	500	Medium-High	Marine exposure
Duplex 2205	800	550	Excellent	300	High	Offshore
Super Duplex 2507	950	650	Outstanding	300	Very High	Seawater systems
Inconel 625	827	414	Exceptional	980	Premium	High temperature
SMO 254	650	300	Extreme chloride	400	Premium	Chemical plants
PEEK	100	—	Chemical inert	260	High	Electrical isolation

23. Corrosion Resistance vs Environment

Environment	Recommended Material
Rural atmosphere	Carbon Steel + HDG
Industrial pollution	SS304 / SS316
Marine atmosphere	SS316 / Duplex
Seawater immersion	Super Duplex / SMO254
Acid processing	Hastelloy
LNG cryogenic	ASTM A320 grades
Sour service (H₂S)	NACE compliant alloys
Electrical insulation	PEEK Step Bolts

SM Fasteners supports NACE MR0175 / ISO 15156 compliant material selection for oil & gas applications.

24. Mechanical Properties by Property Class

Property Class	Tensile Strength MPa	Yield Strength MPa	Hardness (HRC)
4.6	400	240	12–22
5.8	500	400	18–25
8.8	800	640	22–32
10.9	1040	900	32–39
12.9	1220	1080	39–44

Hardness control is essential to prevent hydrogen embrittlement in coated step bolts.

25. Heat Treatment Processes

Heat treatment directly determines mechanical reliability and fatigue life.

25.1 Typical Heat Treatment Sequence

1. Austenitizing
2. Quenching
3. Tempering
4. Stress relieving
5. Hardness verification

25.2 Heat Treatment Objectives

Process	Purpose
Normalizing	Grain refinement
Quenching	Strength increase
Tempering	Toughness restoration
Induction hardening	Local wear resistance
Solution annealing	Stainless steel corrosion resistance

25.3 Hardness Limits for Sour Service

To avoid sulfide stress cracking:

Material	Max Hardness
Carbon/Alloy Steel	22 HRC
Low Alloy NACE Service	248 HV
Stainless Steel	Solution annealed condition

SM Fasteners validates hardness through calibrated testing aligned with project specifications.

26. End-to-End Manufacturing Workflow

Step bolt reliability depends heavily on manufacturing precision.

26.1 Raw Material Control

Incoming material verification includes:

• Mill Test Certificate (EN 10204 3.1)
• Chemical composition analysis
• Ultrasonic inspection (if required)
• Positive Material Identification (PMI)

Traceability maintained from heat number to final product.

26.2 Forging vs Machining

Process	Advantage
Hot Forging	Superior grain flow & fatigue strength
Cold Forging	Dimensional precision
CNC Machining	Custom geometry flexibility
Hybrid Manufacturing	Optimal strength + precision

SM Fasteners selects process routes based on project specification.

26.3 Shoulder Formation

Critical process for step bolts:

• Closed-die forging preferred
• Smooth radius transition mandatory
• Controlled fiber flow reduces crack initiation

26.4 Thread Manufacturing

Thread Rolling (Preferred)

Advantages:

• Increased fatigue resistance
• Compressive surface stresses
• Improved surface finish

Thread Cutting

Used when:

• Large diameters
• Exotic alloys
• Small production volumes

Control stages:

26.5 Dimensional Verification During Production

1. First article inspection
2. In-process gauging
3. Thread ring gauge verification
4. Shoulder concentricity checks
5. Final dimensional audit

All processes operate under ISO 9001 documented procedures.

27. Surface Finishing and Coatings

Step bolts are commonly exposed to aggressive outdoor conditions; surface engineering is therefore critical.

27.1 Common Surface Finishes

Finish	Thickness	Corrosion Protection	Typical Use
Black Oxide	Minimal	Low	Indoor
Zinc Plating	8–12 µm	Moderate	General use
Hot Dip Galvanizing	70–100 µm	High	Towers
Mechanical Galvanizing	50 µm	High	Structural
Zinc Flake (Geomet/Dacromet)	8–20 µm	Very High	Automotive
PTFE/Xylan	20–40 µm	Chemical resistance	Oil & Gas
Epoxy Coating	80–200 µm	Severe corrosion	Marine
Passivation	—	Stainless enhancement	SS bolts

27.2 Surface Finish Performance Comparison

Coating	Corrosion Life	Hydrogen Risk	Torque Stability
Zinc Plated	Medium	Moderate	Good
HDG	High	Low	Variable
Zinc Flake	Very High	Very Low	Excellent
PTFE	High	None	Excellent
Epoxy	Extreme	None	Moderate

28. Hydrogen Embrittlement Prevention

High-strength step bolts require strict control:

• Controlled electroplating chemistry
• Post-plating baking (200°C)
• Hardness limitation
• Coating selection review

SM Fasteners integrates preventive controls within certified production procedures.

29. Surface Preparation Prior to Coating

1. Degreasing
2. Shot blasting
3. Pickling
4. Rinsing
5. Activation
6. Coating deposition
7. Curing / baking

Uniform coating ensures consistent torque-preload performance.

30. Temperature Capability by Material

Material	Continuous Service Temperature
Carbon Steel	300°C
Alloy Steel	450°C
SS304	425°C
SS316	500°C
Duplex	300°C
Inconel	980°C
PEEK	260°C

31. Engineering Role of PEEK Step Bolts

PEEK fasteners supplied by SM Fasteners are used where metallic fasteners cannot operate safely:

• Electrically isolated access systems
• MRI facilities
• Chemical plants
• Semiconductor equipment
• Offshore corrosion-sensitive areas

Advantages:

• Non-conductive
• Lightweight
• Chemical inertness
• No galvanic corrosion

32. Manufacturing Traceability System

SM Fasteners maintains full lifecycle traceability:

• Heat number stamping
• Batch control records
• Process route documentation
• Inspection records
• Export documentation linkage

This ensures suitability for EPC and third-party inspection environments.

33. Inspection & Quality Control Philosophy

Step bolts are categorized as safety-critical structural fasteners, especially when used for:

• Human access systems
• Elevated structures
• Offshore installations
• Maintenance platforms

Failure may result in severe operational or safety consequences; therefore inspection must verify:

• Mechanical integrity
• Dimensional compliance
• Material authenticity
• Surface performance
• Traceability

SM Fasteners operates under an ISO 9001 certified Quality Management System, integrating inspection at every manufacturing stage.

34. Incoming Material Inspection

Verification Procedures

Inspection Activity	Method
Material Identification	Heat number verification
Chemical Composition	Spectrometer analysis
Mill Test Certificate	EN 10204 3.1 validation
Ultrasonic Examination	Internal defect detection
PMI Testing	Alloy confirmation

All raw material batches remain traceable throughout production.

35. In-Process Quality Control

Stage	Inspection Control
Forging	Grain flow & surface inspection
Machining	Dimensional gauging
Thread Rolling	Go/No-Go gauges
Heat Treatment	Hardness & microstructure
Coating	Thickness measurement
Final Assembly	Visual & dimensional audit

Statistical Process Control (SPC) ensures repeatability across large EPC quantities.

36. Mechanical Testing Requirements

Step bolts undergo mechanical verification aligned with ISO 898-1 and ASTM standards.

Test	Purpose
Tensile Test	Verify UTS & yield
Proof Load Test	Confirm elastic behavior
Hardness Test	Heat treatment validation
Bend Test	Shoulder integrity
Impact Test (Charpy)	Low temperature service
Fatigue Evaluation	Cyclic load reliability

37. Non-Destructive Testing (NDT)

Used for critical projects such as offshore or nuclear installations.

NDT Method	Application
Magnetic Particle Inspection (MPI)	Surface cracks
Dye Penetrant Testing (DPT)	Non-magnetic alloys
Ultrasonic Testing (UT)	Internal flaws
Eddy Current	Surface discontinuities
Radiography (RT)	Critical forgings

38. Dimensional Inspection Parameters

Parameter	Inspection Method
Thread Pitch	Profile gauge
Major Diameter	Micrometer
Shoulder Diameter	Digital caliper
Projection Length	Height gauge
Concentricity	Dial indicator
Surface Finish	Visual + Ra measurement

Inspection frequency defined per ISO 3269 acceptance sampling.

39. Documentation & Certification

SM Fasteners supplies complete EPC documentation packages.

Standard Documentation

• EN 10204 3.1 Material Test Certificate
• Heat Treatment Report
• Coating Thickness Report
• Mechanical Test Reports
• Dimensional Inspection Records
• Certificate of Conformity (CoC)
• PMI Reports (when required)

Optional Third-Party Inspection

Supported agencies typically include:

• Lloyd’s Register
• Bureau Veritas
• TUV
• DNV
• SGS

40. Industry Applications Mapping

40.1 Construction & Structural Steel

• Transmission tower climbing systems
• Bridge inspection access
• High-rise maintenance structures

Requirements:

• Hot-dip galvanizing
• Property Class 8.8
• Long corrosion life

40.2 Oil & Gas (Upstream, Midstream, Downstream)

Applications:

• Offshore platforms
• Pipe rack access ladders
• Refinery equipment access

Engineering Needs:

• NACE compliant materials
• Zinc flake/PTFE coating
• Fatigue resistance

40.3 Power Generation

• Boiler access systems
• Turbine maintenance platforms
• Cooling tower structures

Preferred Materials:
Alloy steel / Stainless steel.

40.4 Petrochemical & Chemical Processing

Challenges:

• Acid exposure
• Chlorides
• Temperature cycling

Typical Selection:
SS316, Duplex, SMO 254, Hastelloy.

40.5 LNG & Offshore

Critical Considerations:

• Seawater corrosion
• Cryogenic exposure
• Worker safety access

Materials:
Duplex / Super Duplex / Inconel.

40.6 Railways & Infrastructure

Used in:

• Signal towers
• Gantry structures
• Maintenance platforms

Requirements:
High vibration resistance and long fatigue life.

40.7 Automotive & Heavy Equipment

Applications:

• Service access steps
• Mining equipment platforms
• Agricultural machinery

Typically Alloy Steel 10.9.

40.8 Shipbuilding & Marine

Challenges:

• Salt spray
• Cyclic loading
• Galvanic corrosion

Preferred:
SS316 / Super Duplex.

40.9 PEEK Step Bolt Applications

SM Fasteners manufactures PEEK step bolts for:

• Electrical substations
• Semiconductor facilities
• MRI installations
• Chemical isolation zones

Advantages:

• Electrically non-conductive
• Non-magnetic
• Corrosion immune

41. Export Capability & Global Supply Readiness

SM Fasteners supports international EPC and OEM procurement programs.

Industrial Packaging Standards

Packaging Type	Purpose
VCI Packaging	Corrosion prevention
Thread Protectors	Damage prevention
Oil Coating	Transit protection
Heat Sealed Bags	Moisture control
Wooden Crates	Export shipping

Export Compliance

• ISPM-15 compliant fumigated wooden crates
• Containerized bulk shipments
• Batch segregation labeling
• Barcode traceability

Export Documentation

• Commercial Invoice
• Packing List
• Certificate of Origin
• Inspection Certificate
• Material Test Certificates
• Coating Certification
• Compliance Declaration

ENGINEERING TABLES

42. Tightening Torque Chart

(Metric Step Bolts — Typical Values)

Size	Torque Nm (Dry) 8.8	Lubricated 8.8	Dry 10.9	Lubricated 10.9
M10	49	37	70	52
M12	85	64	120	90
M16	210	160	300	225
M20	410	310	580	435
M24	710	530	1000	750
M30	1420	1060	2000	1500

43. Preload Calculation Formula

$$F = \frac{T}{K \times D}$$

Where:

• F = preload force
• T = tightening torque
• K = nut factor
• D = bolt diameter

Worked Example

M20 Step Bolt
Torque = 410 Nm
K = 0.20$$F = \frac{410}{0.20 \times 0.02}$$

$$F = 102,500 N$$

44. Thread Standards & Tolerances

Standard	Thread Angle	External Class	Internal Class
ISO Metric	60°	6g	6H
UNC	60°	2A	2B
UNF	60°	3A	3B
BSW	55°	Medium	Medium
BSF	55°	Close	Close

45. Surface Finish Performance Comparison

Coating	Salt Spray Resistance	Typical Life
Zinc Plated	72–120 hrs	Indoor
HDG	500–1000 hrs	Structural outdoor
Zinc Flake	1000+ hrs	Automotive/offshore
PTFE	Chemical resistant	Oil & Gas
Epoxy	Severe marine	Long-term offshore

46. Mechanical Properties Table (Summary)

Property Class	Proof Stress MPa	Yield MPa	Tensile MPa
5.8	380	400	500
8.8	580	640	800
10.9	830	900	1040
12.9	970	1080	1220

47. Weight Chart — Step Bolts

(Aligned with SM Fasteners Manufacturing Data — Approximate Values)

Size	Length (mm)	Weight/Pc (kg)	Weight /100 pcs (kg)
M10 × 100	0.09	9
M12 × 120	0.15	15
M16 × 150	0.32	32
M20 × 180	0.58	58
M24 × 200	0.95	95
M30 × 250	1.75	175

(Custom weights available per drawing.)

48. Final Engineering Selection Checklist

Engineers and procurement teams should confirm:

✔ Load capacity requirement
✔ Step projection dimension
✔ Property class verification
✔ Environmental corrosion rating
✔ Coating compatibility
✔ Thread standard alignment
✔ Inspection documentation requirement
✔ Traceability compliance

49. SM FASTENERS — ENGINEERING & MANUFACTURING CAPABILITY

SM Fasteners integrates:

• ISO 9001 certified manufacturing systems
• MSME registered industrial production
• UKAF accredited quality processes
• Advanced alloy manufacturing capability
• Custom step bolt engineering
• PEEK and exotic material fasteners
• Global EPC supply readiness

Capabilities include:

• Forged & machined step bolts
• Custom shoulder geometry
• Special coatings
• Project-specific documentation
• Batch traceability
• International export logistics