Upgrading Two Slop Water Transfer Pumps to Improve Reliability Case Study

In this case study, we’re discussing how we upgraded two slop water transfer pumps which had been failing after reactivation following the long COVID shutdown. 

Our client was having significant problems with two progressing cavity pumps which had suffered frequent seal damage, with the rotors becoming stuck because they weren’t in operation. The remoteness of the site meant it would be too expensive to go out and frequently rotate the slop oil pumps.  

The site had been mothballed during Covid, and had experienced a number of issues since the produced water transfer pumps were brought back into service.  

What is slop water? 

The two pumps were needed to transfer slop water. This is water that’s contaminated with hydrocarbons, other chemicals and waste produced on offshore oil and gas rigs, and is produced when the pipe and drill deck is cleaned.  

On drill decks, slop water can also contain erosive substances such as highly corrosive salts, drilling muds including chemicals and water, salt, rain and formation water as well as sand, floating solids, stones and large particles. 

The produced water transfer pumps are important because global regulations for slop water state that no oily water is to be discharged overboard. All slop waters must be shipped to shore for treatment and disposal or be re-injected offshore. This means that the traditional management of offshore drilling slop water can be costly and wasteful, which is why efficient working of the transfer pumps is crucial. 

Problems with the existing process pumps 

There are situations where a progressing cavity pump is the best choice for use in applications like this, as we discussed in a previous case study. Here, progressing cavity pumps had been chosen as the ideal technology for the project.  

Not only do they handle the oil droplets gently, but they produce a constant volume of flow at varying pressures, are largely unaffected by changes in viscosity and can handle solids without issue. 

Irregular use was a major problem 

However, progressing cavity pumps need to have the pump head rotating at regular intervals to prevent the seal faces sticking, and stop the rotor and stator sticking together. In addition, because of the tight tolerances within the pump head, the parts can rest on each other making separation difficult. 

At the site we’re discussing today, the progressing cavity pumps hadn’t been used very often, and had been unreliable since being brought back on line after the Covid lockdown.  

So our client, an oil extraction company, wanted to change the progressing cavity pumps to single stage centrifugal pumps which would be easier to maintain, and would not suffer damage from being out of use or used only occasionally. They wanted two slop oil pumps for their processing facility, to feed an oily water separator, as well as inject produced water into a well.  

In addition, they wanted to upgrade the current produced water transfer pumps without making any modifications to the existing electrical architecture. This meant that any pump selected as an upgrade would need to have a motor power of 7.5Kw or less. They also wanted the pumps in less than 13 weeks. 

Demanding criteria 

Moreover, there were a number of strict requirements which would need to be met. These included ANSI Class 150 flanges, and a Mechanical Seal Plan to API PLAN 11. This is where fluid is recirculated from the pump discharge through a pipe into the seal chamber, where it acts as a flush for keeping seal faces clean and cool. There would also have to be a self-venting plant for horizontal process pumps.  

Here at North Ridge Pumps, we’re not restricted to a single pump technology, so we can provide the best pump for a particular application and designed for the lowest lifetime cost. We use our expertise to offer a tailored solution, not something which just comes straight off the shelf. 

We upgraded with our XCP end suction horizontal centrifugal pumps  

The process pumps chosen were our XCP end suction horizontal centrifugal pumps designed for clean or contaminated fluids with low viscosity. This is a robust process pump with additional bearings in the pump head in an oil bath designed for heavy duty 24/7 operation.  

The XCP end suction, long-coupled, single stage centrifugal chemical process pump is standardised to EN 22858 and ISO 2858, and can be used for a wide range of applications in the industrial and marine markets.  

It’s designed to pump low viscosity, clean or slightly contaminated fluids without the presence of solid or fibrous solids. These fluids include fresh water, sea water and fuels like diesel, petrol and kerosene. Common applications include fuel transfer, chemical, energy plants, mining, firefighting, irrigation, water supply, water treatment, pressurisation, grey water, dewatering, and marine situations. 

Complying with EN 22858 and ISO 2858 means they can be used in installations where existing older ISO2858 chemical pumps can be replaced without modification to pipework, and users get the same pumping performance in their application. 

Our produced water transfer pumps were built to ATEX standards with a brass coupling guard, anti-static paint, with earthing connections on the baseplate. They were designed with ductile iron GGG40 casing, AISI 316 stainless steel impeller, AISI420 shaft and sleeve. 

After construction, the slop oil pumps achieved all of the specified performance requirements and remained below the electrical limits of the installation. The client requested third party BV Witness testing and inspection, performance test, hydrostatic test and material test inspection.  

The process pumps were built in 13 weeks and despatched to the client along with all of the required testing and inspection documentation. 

For more information on Upgrading Two Slop Water Transfer Pumps to Improve Reliability Case Study talk to North Ridge Pumps Ltd