What is the scope of API 685?

API 685 covers sealless centrifugal pumps for petroleum, petrochemical, and gas industry process service. It applies to both Magnetic Drive Pumps (MDP) and Canned Motor Pumps (CMP), specifically single-stage overhung (OH) type pumps.

What is the current edition of API 685?

The current edition is API 685 3rd Edition, published in July 2022 with 197 pages. Key updates include expanded datasheet requirements, normal operating point definition, and additional annexes for multistage pumps.

What is the difference between API 685 and API 610?

API 610 covers sealed centrifugal pumps with mechanical seals, while API 685 specifically addresses sealless pumps (mag-drive and canned motor). API 685 includes additional requirements for containment shells, internal bearings, temperature monitoring, and zero-emission design.

What testing is required by API 685?

API 685 requires hydrostatic testing at 1.5× MAWP for 30 minutes minimum, and mandatory performance testing (non-witnessed by default). NPSH testing is optional and must be specified if required.

API 685 Requirements for Sealless Pumps - Complete Engineering Guide

Overview of API 685

API STD 685 - Sealless Centrifugal Pumps for Petroleum, Petrochemical, and Gas Industry Process Service

Attribute	Details
Current Edition	3rd Edition (July 2022)
Pages	197 pages
Scope	Magnetic Drive Pumps (MDP) and Canned Motor Pumps (CMP)
Pump Types	Single-stage overhung (OH) type only

Key Features

100% leakage-free performance for safe handling of hazardous and volatile fluids
Containment shell requirements with secondary containment
Internal flushing system for cooling and lubrication
Temperature monitoring and protection systems
Back pullout design for simplified maintenance

Standard Structure

API 685 is organized into common and specific requirements:

Section	Content	Applies To
Sections 2-8	Common requirements	Both MDP and CMP
Section 9.1	MDP-specific requirements	Magnetic Drive only
Section 9.2	CMP-specific requirements	Canned Motor only
Section 10	Additional common requirements	Both types

Key Annexes

Annex	Content
D	Cooling water and circulation system schematics
E	Instrumentation and protective systems options
F	Piping design criteria
G	Material class selection guidance
H	Materials selection requirements
I	Magnetic materials for magnetic couplings
L	Lateral analysis; Spare parts (Table L1)
N	Inspector’s checklist
O	Vendor drawing and data requirements
P	Test data recording forms
Q	Multistage sealless pump considerations (informative)

API 685 vs API 610

Understanding the key differences helps in proper specification:

Aspect	API 610	API 685
Seal Type	Mechanical seal	Sealless (zero-emission)
Pump Types	OH, BB, VS types (multiple sub-types)	OH types only
Emissions	Controlled leakage via seals	Zero emission design
Applications	General service	Hazardous, toxic, volatile fluids
Efficiency	Higher	Lower (eddy current/friction losses)
Maintenance	Regular seal observation	No seal maintenance

When to Specify API 685 vs API 610

Condition	Recommended Standard
Hazardous/toxic fluids	API 685
Zero emission required	API 685
VOC compliance	API 685
General hydrocarbon service	API 610
High solids content	API 610
Cost-sensitive general service	API 610

Design Requirements

Pressure Boundary Components

For Magnetic Drive Pumps, pressure boundary components include:

Casing
Casing plate
Containment shell

3rd Edition Material Changes:

Cast iron (columns I-1 and I-2) deleted - no longer manufactured
Carbon steel minimum for repairable pressure boundary parts
Additional materials added for containment shells

Containment Shell Requirements

Requirement	Specification
Primary material	Alloy C4 (nickel-based) for corrosion resistance
Secondary containment	Required for added safety
Design pressure	Must meet MAWP requirements
Burst pressure	Per Section VIII requirements

Magnetic Coupling Requirements

Parameter	Requirement
Torque rating	Must exceed hydraulic + motor kW with service factor
Service factor	Per Table in API 685
Decoupling protection	Power monitor recommended
Temperature rating	Above max process + eddy current heating

Bearing Design Requirements

Component	Requirement
Type	Hydrodynamic sleeve bearings
Location	In pumped liquid (process-lubricated)
Standard material	Pure alpha-grade Silicon Carbide (SiC)
Alternative materials	Carbon/SiC, Carbon/Stellite
L3/D4 ratio	Minimum requirements for shaft stiffness

Internal Flushing System

API 685 requires internal circulation paths for:

Cooling magnetic coupling
Lubricating sleeve bearings
Preventing vapor formation

Material Requirements

Containment Shell Materials

Material	Max Temp	Eddy Losses	Application
Alloy C4 (Hastelloy)	400°C+	Medium	API 685 standard
Titanium	315°C	Lower	High efficiency
Carbon Fiber/PTFE	200°C	Zero	Non-conductive
Ceramic	250°C	Zero	Maximum efficiency

Bearing Materials

Material	Properties	Application
Pure SiC	Corrosion-proof, extreme hardness	Standard
Carbon/SiC	Self-lubricating	Dry-run capability
Carbon/Stellite	Hard facing	Alternative

Magnet Materials

Material	Max Temp	Strength	Application
NdFeB	150-200°C	Highest	Standard service
SmCo	300-350°C	High	High temperature
AlNiCo	450-550°C	Moderate	Very high temp

Testing Requirements

Hydrostatic Test

Parameter	Requirement
Test Pressure	1.5 × Maximum Allowable Working Pressure
Duration	Minimum 30 minutes
Acceptance	No leak or seepage from pressure-containing parts
Gauge Range	1.5× to 4× test pressure (preferred 2×)

Performance Test

Parameter	Requirement
Default	Non-witnessed performance test (mandatory)
Witness Option	Optional - must be specified by purchaser
Rated Point	Point where vendor certifies tolerances
End of Curve	120% of BEP (105-110% for low Ns pumps)
BEP Position	Preferred between rated point and normal flow

Performance Tolerances

Parameter	Tolerance
Flow at rated point	±2%
Head at rated point	±2%
Efficiency at rated point	-5% (no positive limit)
NPSHr	-0% / +10%
Power	+4%

Optional Tests

NPSH Test: Must be specified if required
Mechanical running test: Per purchaser specification
Witness points: Performance test (mandatory if specified)

Instrumentation and Protection

Clause 7.4.2.1 Requirements

Protective/condition monitoring instrumentation SHALL be provided (default requirement):

Monitoring Type	Purpose	Status
Pump power monitor OR flow monitoring	Detect dry-run or deadhead	Shall be considered
Leakage monitoring in secondary containment	Early leak detection	Shall be considered
Temperature monitoring of containment shell	Prevent overheating	Shall be considered

Recommended Protection Systems

Protection	Type	Function
Power monitor	Under-current/over-current	Detect decoupling, dry-run
Temperature sensor	RTD or thermocouple	Bearing/shell protection
Flow detection	Flow switch or paddle	Minimum flow protection
Level switch	Tank level	Prevent dry suction

Typical Alarm/Trip Settings

Parameter	Alarm	Trip
Bearing temperature	80°C	100°C
Containment shell temperature	90°C	110°C
Power drop (decoupling)	-	>30% drop
Low flow	20% of rated	15% of rated

Documentation Requirements

With Quotation

Document	Purpose
Completed Data Sheet (Annex R format)	Technical specification
Deviation List	Exceptions to specification
Preliminary Performance Curves	Hydraulic verification
General Arrangement Drawing	Interface verification
Reference List	Vendor experience

Final Documentation (Databook)

Document	Content
Final Data Sheets	As-built specifications
Performance Curves (as-tested)	Verified hydraulics
GA Drawing (certified)	Final dimensions
Sectional Drawing	Component identification
Material Certificates	Mill test reports
Test Reports	Hydrostatic, performance
O&M Manual	Operation/maintenance
Spare Parts List	Ordering information

Vibration and Noise Requirements

Vibration Limits

Category	Criteria
Preferred Operating Region	Vibration within base limit
Allowable Operating Region	Vibration within 130% of base (30% above preferred)

Shaft Stiffness

Minimum L3/D4 ratio requirements specified
Ensures adequate shaft stiffness relative to unsupported span
Prevents excessive deflection leading to bearing failures

Noise Requirements

Parameter	Requirement
SPL Control	Joint purchaser-vendor responsibility
Reference Standards	ISO 3740, ISO 3744, ISO 3746
Maximum SPL	As specified by purchaser

3rd Edition Key Updates (2022)

Data Sheet Enhancements

Expanded information requirements
Normal operating point now addressed (not in 2nd Edition)
SI and USC measurement systems supported
Additional fields for proper selection and scope

New Annexes

Annex Q: Multistage sealless pump considerations (informative)
Requires purchaser-supplier agreement for multistage applications

Material Updates

Cast iron options removed (no longer manufactured)
Additional materials for containment shells
Updated magnetic material specifications (Annex I)

TBE Quick Reference

Must-Verify Items

Item	API 685 Clause	Acceptance
Hydrostatic test	Section 8	1.5× MAWP, 30 min, no leak
Performance test	Section 8	Mandatory, tolerances per spec
Containment material	Section 6, Annex H	Per specification
Bearing material	Section 6, Annex H	SiC or approved equivalent
Temperature monitoring	Clause 7.4.2.1	Shall be considered
Flow/power monitoring	Clause 7.4.2.1	Shall be considered
Spare parts	Annex L, Table L1	Per list

Common Compliance Issues

Issue	Impact	Resolution
No power monitor	Critical - reject	Add to scope
Incomplete data sheet	Minor	Request completion
Missing deviation list	Moderate	Request before evaluation
Non-compliant materials	Critical	Reject or obtain waiver
Insufficient references	Moderate	Request extended warranty