PUMPS, VALVES & ACTUATORS
OVERHAUL OPERATIONS Samuel Eccles, SPx FLOW, UK, describes the overhaul of a pump for a critical diethyl amine pumping process, exploring the technology developments that helped to ensure a successful project outcome.
This article will outline a brief history of the BB3 pump for the refining industry, before examining some of the key issues end users face with common failures on multi-stage equipment, as well as potential solutions. These will be examined in the context of a pump overhaul case study, carried out in order to improve the safety, reliability and efficiency of the amine pumping process within an operator’s desulfurisation unit.
Pump developments and standards The initial development of SPx FLOW’s BB3 pump began in Penistone, near Sheffield – located at the industrial heart of the UK. In the 1960s, Penistone was transformed from an old foundry into a pump manufacturing facility that, for many years, has produced pump engineering solutions.
As the world has become increasingly globalised and lower end technologies have moved to lower cost regions, Penistone’s manufacturing focus has shifted to higher end, higher energy multi-stage horizontal pumps for critical applications.
The BB3 is an axially split multi-stage pump that operates in a variety of areas, from reverse osmosis plants through water injection, boiler feed and high pressure refinery applications.
The pumps are used when sufficient pressure cannot be attained by using a one or two stage machine, as they operate at significantly higher pressures. The units have existed since 1954, when classified by API, but multi-stage pumps were first patented in the nineteenth century. The pump design ensures ease of maintenance for the user, but it requires high end manufacturing skills to provide higher quality and efficiencies.
The first units were supplied during the very early 1960s, after API had approved
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the BB3 designation in 1954. Although non-standardised across vendors before the first edition of API 610 appeared in the mid-1950s, this type of design had been in existence since the turn of the century.
The introduction of API provided standard design criteria and guidance for customers. This has led to a safer more reliable industry, but in some cases an over conservative approach to new innovation.
A variety of changes have occurred during the past 50 years that have all focused on providing better value to the end user, whilst making the product easier to manufacture. The typical issues that cause downtime for multi-stage pumps are overhaul times, seal failure and bearing failures. Each issue poses a particular engineering challenge to overcome, which have, through time, been addressed and improved upon.
Overhaul times As with any type of rotating equipment, wear is unavoidable within a centrifugal pump. The timescale required between overhauls will vary drastically depending on the application and quality of the installed solution. Whilst a clean liquid running at constant speed is ideal for the pump, these are rarely the requirements of a refinery. As such, overhauls may consist of anything from routine replacement of common wear parts through to an internal re-design due to excessive corrosion on an aggressive service, or a change in operator requirements.
There are several updates to API that have been designed to prolong operating life, such as moving from stainless to nickel alloy bronze through to duplex and super duplex materials.
SPx FLOW’s ClydeUnion Pumps and, specifically, Mather & Platt, were pioneers in this field through the Mather & Platt’s foundry’s development of Zeron 25, which became a standard within the industry. Several updates have been made to the BB3 range to reduce overhaul time.
These have ranged from minor changes, such as adding case lifting lugs for quick disassembly and integral bosses to help prevent stub pipework becoming damaged during commissioning, through to a unique cartridge bearing that enabled a 25% reduction in overhaul time.
Seal failure
The seals are one of most important components in the package as the last line of product containment. As the clearances are tightest at the rotating seal faces, a very small contamination can cause rapid wear, resulting in the seal beginning to leak and impacting safety and performance. As such, the seal lifespan is normally the limiting factor when a pumpset requires an overhaul.
Whilst seal failures happen for a varied and complex array of reasons, ClydeUnion Pumps has worked to reduce failures and provide an optimum environment for the seal to operate through adding 360˚ bearings. These are fitted to all BB3 designs to ensure vibration performance, as well as tasks designs that enable a better performance than is required by international standards. It also further reducesthe vibration levels. These factors are crucial, as vibration standards lower following more demanding API requirements.
At present, to reduce costs for suppliers (but which increase costs for end users), a number of pump manufacturers use only 180˚mounts on these units.
Bearing failure Secondary to seals, bearing issues are the next most common issues limiting overhaul duration. Pumps will often experience excessive bearing vibration
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