Raising the bar on oil-rig pipe testing

A testing process using electro-hydraulic motion controllers gives drillers confidence that rigs can stand up to the most extreme subsea conditions.

10/21/2014


Figure 1: The Dril-Quip test stand uses two large hydraulic cylinders, mounted horizontally, to apply large amounts of bending and tension force to an assembled pipe stand (center). Courtesy: Delta Computer Systems Inc.Subsea oil well pipe stands undergo tremendous stresses in operation. They must bear the weight of attached equipment, such as oil well blowout preventers, as well as stand up to the force applied by the constant motion of the oil rig. Then there are forces of nature, such as tidal waves and other storm-like conditions.

Knowing the environments in which they operate forces the companies that manufacture oil well pipes and pipe connectors to employ rigorous tests to make sure that their products will perform as designed in the field.

Historically, structural qualification testing of subsea pipe connectors has been performed by machines with limited capability of applied axial and bending loads, but one threaded connector manufacturer, Dril-Quip Inc. of Houston, believes that qualification testing of its equipment should not be limited by the capacity of currently available test machines. To verify the integrity of such assemblies, the company has developed a test system that is capable of producing millions of pounds of axial and bending force on an assembled pipe stand.

Applying such large forces is the domain of the largest of hydraulic rams, and controlling them requires an electro-hydraulic motion controller with special capabilities for closed-loop force control. Following an extensive search, company engineers found the right controller for this task. "We saw that using an 8-axis motion controller could save us a lot of time and effort in implementing our hydraulic controls," said Mike Lynch, PE, Dril-Quip senior scientist engineer.

The testing apparatus the company designed uses two large hydraulic rams, mounted on either side of a pipe stand assembly that can be in excess of 25 ft long (see Figure 1). The rams are operated in concert to exert bending and tension or compression forces on the pipe stand specimen of more than 6 million pounds.

"We need to repeatedly test the specimen to 95% of its yield force (the force required to bend the pipe assembly without failing to return to its original shape)," said David Trevas, Ph.D., Dril-Quip senior scientist engineer.

The test sequence

Figure 2: Dril-Quip system block diagram shows pressure transducers P1A and P2A mounted on cylinder 1, and D1 is the input from cylinder 1’s displacement transducer. Cylinder 2’s connections also are noted. Courtesy: Delta Computer Systems Inc.To set up a typical test sequence, the specimen pipe stand is filled with a fluid or gas test medium. The test cycle is initiated and the system moves as controlled by the 8-axis motion controller. During this operation, the system is monitored for leakage. The test limits (such as allowable leakage) are standardized by the American Petroleum Institute (API). Maintaining functional integrity of the connection at such close proximity of yield is a motivating factor behind developing a powerful and highly precise test apparatus.

Figure 2 is a block diagram showing how the main control components are connected. The setup includes a Microsoft Windows-based PC operating in a control room, providing a safe, noise-free environment for the test operator.

The test specimen and the hydraulic cylinders are located in a test pit for safety. The motion controller receives commands over an Ethernet link from a NI LabWindows/CVI program running on the PC. These commands provide instructions to the motion controller on how to move the hydraulic cylinders and at what pressure.

The motion controller's manufacturer developed a special software package that allows other applications on the PC to communicate with the controller—both sending and receiving data—over an Ethernet connection.

The motion controller's role

Figure 3: This 8-axis electro-hydraulic motion controller provides direct interfaces to position and pressure sensors and can connect to other systems via Ethernet or serial ports. Courtesy: Delta Computer Systems Inc.The motion controller (Figure 3) reads the differential hydraulic pressure across the piston of each cylinder to calculate and control the force being applied to the specimen. The controller uses position feedback from magnetostrictive displacement transducers (MDTs), mounted between the cylinder housing and the cylinder rod, to measure the deflection of the specimen. Because it's a multi-axis controller, it can simultaneously control different motion profiles for each axis.

To complete the instrumentation of the system, strain gauges mount directly onto the specimen at specific places and send the strain signal to strain gauge module in the chassis. Pressure and temperature transducers mount on various parts of the test fixture and connect to another data acquisition chassis. The transducer signals are converted to engineering units inside of the software. Process status, parameter values, and limit warnings are updated on operator screens attached to the PC.

Test sequence, a step at a time

Before conducting a test on a specimen, the test engineer sets up a schedule of test points to load and/or bend the specimen. These test points are converted into a series of steps for the motion controller to carry out. These steps are organized in a Microsoft Excel spreadsheet residing on the PC. The development software program then transfers one test step at a time to the motion controller and the motion controller executes the step. The PC program monitors the status registers within the controller and determines if the controller is operating within specified parameters as it completes the step. The development software program also logs test data.

Figure 4: Plot of the motion of the two cylinders in a typical test. Courtesy: Delta Computer Systems Inc.To gain optimal performance from the motion control system, the control loops need to be tuned, with the control loop coefficients set to minimize the error between target profiles specified by the PC test program and actual motion profiles observed by the motion controller. To assist with the tuning process, engineers used the plotting application that also came with the motion controller. Figure 4 shows a typical plot of the motion of the system.

With the use of the test system, the company can simulate field conditions with load, bending, and pressure that wouldn't otherwise be possible in a lab setting. In doing so, the company has increased its understanding of the wellhead performance and gained knowledge to give its customers confidence in the subsea wellhead system.

- Bill Savela is a Professional Engineer with Delta Computer Systems Inc. Edited by Sidney Hill, Jr., a CFE Media contributing content specialist. This article is part of the oil and gas coverage from Control Engineering and Plant Engineering, CFE Media publications. 

Key concepts

  • Verifying that pipes and connectors can withstand the forces applied to them in subsea drilling environments requires extremely rigorous testing.
  • Conventional testing equipment has limited capabilities when it comes to applying force, which sometimes prevents equipment manufacturers from testing products to their maximum limits.
  • Test system can produce millions of pounds of axial and bending force on an assembled pipe stand, comparable to the harshest subsea drilling conditions.

Consider this

Given the potential loss of dollars associated with the failure of pipe or connector in the field, doesn't make sense to have those products undergo the most rigorous tests possible? 

ONLINE extra

This online version adds relevant links and additional product information.

www.api.org 

www.deltamotion.com 

www.dril-quip.com 

www.ni.com/lwcvi 

Data acquisition test system for oil drill rig testing

Dril-Quip Inc. of Houston, performs qualification testing of its oil rig equipment with instrumentation including NI LabWindows/CVI strain gauge module in the chassis, mounted onto the specimen at specific places and send the strain signal to a strain gauge module in the chassis. Pressure and temperature transducers mount on various parts of the test fixture and connect to another NI LabWindows/CVI data acquisition chassis. The transducer signals are converted to engineering units inside of the NI LabWindows/CVI program, which transfers one test step at a time to the motion controller and the motion controller executes the step. The LabWindows/CVI program, from National Instruments, also logs test data. 



The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by Control Engineering subscribers. Vote now (if qualified)!
The System Integrator Giants program lists the top 100 system integrators among companies listed in CFE Media's Global System Integrator Database.
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
This eGuide illustrates solutions, applications and benefits of machine vision systems.
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
This eGuide contains a series of articles and videos that considers theoretical and practical; immediate needs and a look into the future.
HMI effectiveness; Distributed I/O; Engineers' Choice Award finalists; System Integrator advice; Inside Machines
Women in engineering; Engineering Leaders Under 40; PID benefits and drawbacks; Ladder logic; Cloud computing
Robotic integration and cloud connections; SCADA and cybersecurity; Motor efficiency standards; Open- and closed-loop control; Augmented reality
Programmable logic controllers (PLCs) represent the logic (decision) part of the control loop of sense, decide, and actuate. As we know, PLCs aren’t the only option for making decisions in a control loop, but they are likely why you’re here.
This digital report explains how motion control advances and solutions can help with machine control, automated control on assembly lines, integration of robotics and automation, and machine safety.
This article collection contains several articles on how advancements in vision system designs, computing power, algorithms, optics, and communications are making machine vision more cost effective than ever before.

Find and connect with the most suitable service provider for your unique application. Start searching the Global System Integrator Database Now!

Control room technology innovation; Practical approaches to corrosion protection; Pipeline regulator revises quality programs
Cloud, mobility, and remote operations; SCADA and contextual mobility; Custom UPS empowering a secure pipeline
Infrastructure for natural gas expansion; Artificial lift methods; Disruptive technology and fugitive gas emissions
Automation Engineer; Wood Group
System Integrator; Cross Integrated Systems Group
Jose S. Vasquez, Jr.
Fire & Life Safety Engineer; Technip USA Inc.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by Control Engineering subscribers. Vote now (if qualified)!
The System Integrator Giants program lists the top 100 system integrators among companies listed in CFE Media's Global System Integrator Database.
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
This eGuide illustrates solutions, applications and benefits of machine vision systems.
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
This eGuide contains a series of articles and videos that considers theoretical and practical; immediate needs and a look into the future.
HMI effectiveness; Distributed I/O; Engineers' Choice Award finalists; System Integrator advice; Inside Machines
Women in engineering; Engineering Leaders Under 40; PID benefits and drawbacks; Ladder logic; Cloud computing
Robotic integration and cloud connections; SCADA and cybersecurity; Motor efficiency standards; Open- and closed-loop control; Augmented reality
Programmable logic controllers (PLCs) represent the logic (decision) part of the control loop of sense, decide, and actuate. As we know, PLCs aren’t the only option for making decisions in a control loop, but they are likely why you’re here.
This digital report explains how motion control advances and solutions can help with machine control, automated control on assembly lines, integration of robotics and automation, and machine safety.
This article collection contains several articles on how advancements in vision system designs, computing power, algorithms, optics, and communications are making machine vision more cost effective than ever before.

Find and connect with the most suitable service provider for your unique application. Start searching the Global System Integrator Database Now!

Control room technology innovation; Practical approaches to corrosion protection; Pipeline regulator revises quality programs
Cloud, mobility, and remote operations; SCADA and contextual mobility; Custom UPS empowering a secure pipeline
Infrastructure for natural gas expansion; Artificial lift methods; Disruptive technology and fugitive gas emissions
Automation Engineer; Wood Group
System Integrator; Cross Integrated Systems Group
Jose S. Vasquez, Jr.
Fire & Life Safety Engineer; Technip USA Inc.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by Control Engineering subscribers. Vote now (if qualified)!
The System Integrator Giants program lists the top 100 system integrators among companies listed in CFE Media's Global System Integrator Database.
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
This eGuide illustrates solutions, applications and benefits of machine vision systems.
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
This eGuide contains a series of articles and videos that considers theoretical and practical; immediate needs and a look into the future.
HMI effectiveness; Distributed I/O; Engineers' Choice Award finalists; System Integrator advice; Inside Machines
Women in engineering; Engineering Leaders Under 40; PID benefits and drawbacks; Ladder logic; Cloud computing
Robotic integration and cloud connections; SCADA and cybersecurity; Motor efficiency standards; Open- and closed-loop control; Augmented reality
Programmable logic controllers (PLCs) represent the logic (decision) part of the control loop of sense, decide, and actuate. As we know, PLCs aren’t the only option for making decisions in a control loop, but they are likely why you’re here.
This digital report explains how motion control advances and solutions can help with machine control, automated control on assembly lines, integration of robotics and automation, and machine safety.
This article collection contains several articles on how advancements in vision system designs, computing power, algorithms, optics, and communications are making machine vision more cost effective than ever before.

Find and connect with the most suitable service provider for your unique application. Start searching the Global System Integrator Database Now!

Control room technology innovation; Practical approaches to corrosion protection; Pipeline regulator revises quality programs
Cloud, mobility, and remote operations; SCADA and contextual mobility; Custom UPS empowering a secure pipeline
Infrastructure for natural gas expansion; Artificial lift methods; Disruptive technology and fugitive gas emissions
Automation Engineer; Wood Group
System Integrator; Cross Integrated Systems Group
Jose S. Vasquez, Jr.
Fire & Life Safety Engineer; Technip USA Inc.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
click me