Specifying heavy duty pumps for critical industries

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by Ron Astall, PIA Immediate Past President and Sales & Contracts Manager, United Pumps

API 610 pumps are expensive, normally custom built and are often on a long delivery. So why would you specify an API 610 pump? Ron Astall explains why.

When is API 610/ISO 13709 a logical requirement, and how are these pumps different from ordinary centrifugal pumps? In this article, I will be discussing where this specification came from, why you might specify this standard, and how pumps to this standard differ from conventional centrifugal pumps. As ISO 13709 is identical to and is fundamentally an adoption of API 610, I will simply refer to the standard as API 610 for from now on.

There are various exciting centrifugal pump standards that you may come across such as ISO 2858, DIN 24255, ANSI B73.1 and ISO 5199. These are great reading if you suffer from insomnia, so I have summarised the basics in Figure 3.

You can see that some are dimensional and performance envelope standards, while others are constructional; addressing reliability aspects. ANSI/ASME B73.1 covers both dimensional and constructional aspects. Some of the key differences between the constructional standards are shown in Figure 4.

In practice, the major points of difference with API 610 are rigidity (nozzle loadings), extreme reliability requirements, and bearing life, noting that in practice API designers normally consider “worst case conditions” to be zero flow.

The American Petroleum Institute (API) was founded in 1919 to cooperate with government in matters of national concern, to promote the general interests of the petroleum industry and, in particular, issue and maintain more than 500 standards and recommended practices for the petroleum industry. Today the world’s petroleum industry uses API standards as the mainstay of design and installation specifications for almost all operational equipment and plant. So, what exactly is API 610?

It is primarily about centrifugal pump safety and integrity. API 610 is normally specified where the pumped product is dangerous, hot, high pressure, flammable, toxic and for critical services (see Figure 5).

It is a tough specification, with a required pump design life of 25 years, and a requirement for uninterrupted operation for at least three years (see Figure 6).

It is too ambitious to cover all the requirements of a 221 page standard in this article, but some of the basics are shown in Figure 7.

Let’s look at one of these requirements in a little more detail. Nozzle loads and base plate rigidity were dramatically increased by the 6th edition of the standard, and are such that shaft deflection shall be negligible under the worst combination of nozzle loadings. This means that not only the pump itself has to be strong, but the baseplate as well (see Figure 8).

Basically, you can park a large car on the pump nozzles, and the shaft must not move more than 0.178mm vertically or 0.076mm horizontally! A properly designed API 610 pump from the late 1980s onwards is recognisable by the massive mounting feet and strong base plate pedestals (see Figure 9).

API 610 has various pump type designations with coding “OH” for overhung pumps, “BB” for between bearings and “VS” for vertically suspended pumps.

An overview of some of the most common types and what they look like is provided in Figure 10.

As well as tough constructional requirements for the pumps, API 610 references API 682 (ISO 21049) for mechanical seals and their associated, often complex systems. Where the liquids are hot, dangerous and toxic, the sealing systems can sometimes rival or exceed the cost of the pumps.

So why, and when would you specify an API 610 pump? The answer is ultimately pretty simple: when you have a dangerous, difficult or critical service and when safety and reliability are the highest priorities.

fig1

Figure 1. A BB3 style API 610 pumpset

fig2

Figure 2. Comparison between Din/ISO and an API pump

Centrifugal Pump Standards

Dimensional & Performance standards

 

Basic standards that set out dimensions and performance envelope

 

ANSI B73.1

ISO 2858

DIN 24255

DIN24256

Constructional standards
Stricter standards that outline properties such asDesign stresses (API 610)

Nozzle loads

Min bearing life

Shaft stiffness

Baseline  stiffness (API 610)

ANSI B73.1

API 610

ISO 5199

Figure 3. Comparison between various pump standards.

SIMPLIFIED COMPARISON
ISO 5199 ANSI B73.1 APl 610
Critical Speed Margin 10{87a03eb4327cd2ba79570dbcca4066c6d479b8f7279bafdb318e7183d82771cf} 20{87a03eb4327cd2ba79570dbcca4066c6d479b8f7279bafdb318e7183d82771cf} 20{87a03eb4327cd2ba79570dbcca4066c6d479b8f7279bafdb318e7183d82771cf}
Basic Pressure Rating 16 Bar 19.5 Bar 40 Bar
Min  Bearing Life
(hrs -B10)
17,500

(over allowable operating range)

17,500

(over allowable operating range)

25,000 at rated duty
16,000 worst case conditions
Vibration
(Horizontal Pumps)
3mm/s 4.8mm/s 3mm/s
Balance Grade G6.3 G6.3 G2.5
Shaft Deflection
(at Seal Chamber face)
50µm

(over alllowable operating range)

130µm

(over alllowable operating range)

50µm

worst case Conditions

Allowable Shaft Runout 50µm 25µm 25µm
Lubrication Grease Grease Oil lube
Nozzle Loads Per Annex B

modified by materials & other factors

Similar to
lSO 5199
Per Table 5

basic table values lower than ISO 5199, but no modifiication allowed. Option of
s2 x Table 5 loads is commonly applied

 

Figure 4. Simplified comparison of the key differences between the constructional standards.

WHY END USERS SPECIFY API PUMPSfig5

(NOT ONLY OIL & GAS)

  • Dangerous liquids
  • Hazardous
  • Flammable
  • Poisonous
  • High temperatures
  • High pressures
  • Critical service
  • High cost of pump failure
  • Compulsory in oil & gas

Figure 5. Why end users specify API pumps.

KEY SPECIFICATION REQUIREMENTSfig6

  • Pump design life of 25 years
  • Designed to run uninterrupted
    for three years
  • 40 Bar minimum design pressure
  • Oil lube bearings
  • 25,000hr L10 minimum
    bearing life
  • Renewable wear rings
  • Shaft rigidity: Maximum deflection 50 µm
    (0.002 in) at the seal faces
  • Tough vibration criteria
  • Material certification & testing
  • Performance tested

Figure 6. Key specification requirements.

API 610 BASIC DESIGN PROPERTIES

6.1.1 Minimum service life of 20 years (excluding normal wear parts). Pumps to operate uninterrupted for a minimum of 3 years.

6.3.3 Pressure cases shall be designed to operate without leakage or internal contact while subject simultaneously to the MAWP and twice the allowable nozzle loads.

6.3.5 MAWP to be at least maximum discharge pressure plus 10{87a03eb4327cd2ba79570dbcca4066c6d479b8f7279bafdb318e7183d82771cf} of maximum differential pressure. MAWP shall not be less than 4,000 kPag

6.3.7 Minimum corrosion allowance of 3mm

6.3.3 Pressure cases shall be designed to operate without leakage or internal contact while subject simultaneously to the MAWP and twice the allowable nozzle loads.

6.3.5 MAWP to be at least maximum discharge pressure plus 10{87a03eb4327cd2ba79570dbcca4066c6d479b8f7279bafdb318e7183d82771cf} of maximum differential pressure. MAWP shall not be less than 4,000 kPag

6.3.7 Minimum corrosion allowance of 3mm

6.5 External nozzles are required to withstand the high nozzle loads (forces and moments)

6.8 Minimum Seal Chamber dimensions – for better cooling, ease of installation of dual seals.

6.6.9 Shafts to be machined and finished so the TIR is not more than 25 µm (0.001 in)

6.9.1.3 The shaft stiffness shall limit the total deflection under the most severe dynamic conditions (max impeller diameter, speed and fluid) to 5O µm (0.002 in) at the primary seal faces.

6.10.1 Bearing basic rating life L10, is to be at least 25,000 hours at rated conditions and at least 16,000 hours at maximum radial and axial loads and rated speed.

7 .3.20 Strict design properties are placed on the baseplate. Table 13 (API 610 11th Edn) outlines the stiffness test acceptance criteria.

Figure 7. API 610 basic design properties.

NOZZLE LOADS AND BASEPLATE RIGIDITYfig8

WHAT DOES IT REALLY MEAN?

FOR 150mm (6”) NOZZLES

MAXIMUM COUPLING DEFLECTION WITH ANY COMBINATION OF  FORCES & MOMENTS:

VERTICAL : 0.178mm (0.007”) LATERAL : 0.076mm (0.003”)

MOST API 610 CUSTOMERS SPECIFY DOUBLE THESE LOADS

Figure 8.

fig9

Figure 9. Identifying an API 610 pump from the 1980s onwards.

fig10

Figure 10. Common types of API 610 pumps.

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