Pipe Plugs


Mechanical Research & Design, Inc. has been providing innovative and proven Pipe Plugs all over the world for nearly 25 years. Also called pressure test plugs, pipe stoppers, pipe bungs, line stops, or inline isolation tools, pipe plugs are a common pipeline pressure test and isolation barrier tool for both newly fabricated or existing piping systems. Mechanical Research & Design, Inc. designs and manufactures many standard, off the shelf configurations as well as custom, application specific barrier options for low, medium, and high pressures (most styles from vacuum test pressures through several thousand PSI). We supply round plugs, rectangular plugs, irregularly shaped plugs that can be used in pipelines (carbon steel, stainless steel, ductile iron, polymer, composite, ceramics, concrete, to name a few), tubing, tunnels, shafts, bores, hoses, assembled components, water intakes, and nearly any part that requires pressure or leak testing.


MRD supplies several types of Pipe Plug sealing systems, the most popular being Mechanical Pipe Plugs, Inflatable Pipe Plugs, and Combination Mechanical + Inflatable Pipe Plugs. The tools can be manufactured from nearly any material imaginable for temporary or long term installations, in standard test configuration use or even in corrosive, temperature extreme environments. Our Pipe Plugs are designed to last and are rugged enough to be used again and again in remote location field services, offshore oil & gas, subsea and for underwater construction, as well as in heavily regulated industries, such as nuclear power.


SEALFAST® Pipe Plugs set themselves apart from the competition as they implement both integral, tested restraint systems, holding the tool in place reliably against back pressures and our own in-house designed and fabricated SEALFAST® Elastomers. At Mechanical Research & Design, Inc. we vulcanize our own SEALFAST® Mechanical and Inflatable Seals in-house which allows us to offer short lead times and flexible design options, sizes, and profiles. We do the best work under pressure!



Have Specific Requirements?

We specialize in custom solutions! Take a look at a few of our proven custom solutions or let us know your requirements. Our engineers and production staff are equipped to travel around the world at a moment’s notice to assist you with your needs!

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The above detail illustrates the operation of a standard in-line Mechanical and Inflatable Pipe Plug. Though Mechanical and Inflatable Pipe Plugs can rely upon the seals for restraint, typically, secondary mechanical restraint is required to prevent slippage – in the form of friction screw dogs that engage to the pipe, by utilizing strong back supports, anchors, or other user added blocking methods. Both MRD Mechanical and Inflatable Pipe Plugs are typically provided with integral restraint systems, which is shown by the annotated Restraint Screws. Prior to actuating any seal, it is required that the user tightens all restraint screws to the required torque to safely hold the tool in place in the event pressure builds behind the plug. Next, the SEALFAST® Mechanical or Inflatable Seal is actuated, creating the pressure boundary. Mechanical plugs typically require the tightening of seal actuation nuts to a required torque to set the Mechanical Seal. Inflatable plugs require inflation pressure in the form of liquid or gas to set the Inflatable Seal. The tool is ready to add test pressure to the pipeline — begin by adding fluid through the tool bypass while venting air through the vent port (usually located near the top of the tool). Fill the region behind the plug with water until a clear stream of water exits the vent, then close the vent. Pressurize the region behind the plug to full test pressure and monitor pressure decay or leakage through the pipeline via the test gauge on the vent port or bypass line.
Mechanical Research & Design, Inc. | Innovation Redefined | Manitowoc Wi



You may have heard the terms normal and reverse pressure, previously, with regards to pipe plugs and isolation barriers.  The terms have special meaning, particularly with respect to mechanical pipe plugs, as not all plugs are designed for positive pressure differentials applied from both front and rear of the plug; special care must be taken to identify the location of the plug installer and the side of the plug receiving net differential pressure during isolation or product failures may occur!  Please consider the below as typical convention, as there are exceptions.


• A NORMAL PRESSURE PLUG is typically defined as the net positive differential pressure being isolated on the side opposite of the installer (see detail above). In simpler terms, the installer is in front of the plug and the fluid being isolated or tested is behind the plug.  In this orientation, there is typically a pressure assist for a mechanical plug that will aid in active sealing — the more pressure upstream of the plug, the better the mechanical seal functions due to the geometry of the mechanical pipe plug and location of the integral restraint.


• A REVERSE PRESSURE PLUG is typically defined as the net positive differential pressure being isolated on the same side as the installer (see detail above). In simpler terms, the installer is in front of the plug and the fluid being isolated or tested is also in front of the of the plug.  This application is commonly found in underwater construction where a diver is installing the plug and the pipeline behind the plug is de-watered (for example, a dam inlet isolated from a reservoir so that a valve downstream can be replaced).


SEALFAST® Pipe Plugs can be designed for pressure isolation or testing in a very large variety of applications and configurations.


•Mechanical and Inflatable Pipe Plugs can be designed for vaccum testing through several thousand psi pressure rating. See our Low, Medium, and High Pressure Plug options which optimize for weight, function, and cost for your needs.


•SEALFAST® Pipe Plugs can be manufactured for a variety of different shapes and sizes, including round, rectangular, and irregular shapes. MRD provides plugs for carbon steel, stainless steel, ductile iron, cast iron, concrete, polymer, and composite piping systems as well as thin wall tubular systems, industrial assemblies, tunnel and drift wall isolation, and many more applications!


• Our Mechanical and Inflatable Pipe plugs can come with a variety of different SEALFAST® Elastomer Seals, chosen specially for your application, including: Viton®, EPDM, Buna-N, Silicone, Natural Rubber, Urethanes, and Neoprene, to name a few.


SEALFAST® Pipe Plugs are used in numerous industries and applications including:

• General transport pipeline testing, isolation, and repair
• Pressure vessel isolation and hydrotesting
• Construction Isolation and Test Plugs
• Refinery vapor isolation and maintenance
• Municipal force and water mains
• Lift and Pump station service
• Conventional and Nuclear Power process line isolation and pressure test
• Fire Protection Pipeline test plugs
• HVAC system isolation and test plugs
• Subsea pipeline repair, maintenance, and de-commissioning
• Hydroelectric Dam Penstock Isolation
• Water intake lines and valve isolation
• General industrial leak testing, verification, and maintenance


Mechanical Research & Design, Inc. can design our SEALFAST® Mechanical and Inflatable pipe plug for most of the same applications, however, each tool and overall seal type has functional, safety, and cost benefits depending upon the actual use. Both sealing types can be effective solutions in most applications and they are often used together on the same tool to maximize redundancy and safety in single point isolation tooling.


• SEALFAST® Mechanical Seals have an inherent advantage over inflatable seals in that there is no inflation medium (they are not pressurized internally with a liquid or gas to create the sealing pressure boundary). Typically, SEALFAST® Mechanical Plugs do not require any utilities in the field for installation (pressurized gas, pumps, etc.) unless the fluids are required for pressure testing. Mechanical seals are typically bulk rubber that are actuated mechanically so there is no chance of release of activation pressure critical for sealing. Mechanical seals are also great for high temperatures and pressures since there is little chance of seal creep if designed appropriately, over the duration of the sealing application. One of the negatives of Mechanical seals is that they can take a bit longer to actuate, or set the seal, unless more automated methods such as hydraulics are utilized. Unlike Inflatable Seals, Mechanical Seals will require more actuation points to allow them to handle gap clearance between the tool and a variable distance sealing surface. Mechanical seals are ideal for long-term, safety critical applications when you cannot afford for things to go wrong.


• SEALFAST® Inflatable Seals’ major advantage over mechanical seals is that they are typically faster to actuate, the only limiting factor being the availability of an actuation or “filling” fluid. Most inflatable seals can be inflated with pressurized gases, water, or even hydraulic fluids, so they are very flexible with commonly available utilities. As stated elsewhere in this page, inflatable seals do not need to be compressed to function, meaning the seal will by default flow to the area of least resistance during inflation. This is particularly important when a tool is installed in a location where the distance varies between the plug O.D. and the pipe I.D., for example, as you would find using a round tool in an out-of-round pipe. The seal will flow to fill all gaps and, with the correct inflation pressure, naturally seal a bit better than a more rigid mechanical seal. The requirement of an inflation medium for sealing efficacy, however, must be observed over long periods of time, as if inflation pressure is lost, sealing effectiveness can dissipate, unlike with a mechanical seal.

SEALFAST® Mechanical Pipe Plugs are ideal for long term installations, in applications where single point isolation safety is paramount, and for many other low, medium, and high pressure applications. These tools are also less likely to be effected by temperature over time then tools that require inflation medium. See our many design configurations, some with integral restraint systems and all provided with our industry leading SEALFAST® Mechanical Seals.


SEALFAST® Inflatable Pipe Plugs are ideal for rapid, frequent installations, such as in applications including pressure testing, short term isolations, and for unknown geometry sealing environments.  These plugs are easily adaptable for remote or beyond line-of-sight installations and we have multi-seal versions for long term isolations.  See our design configurations tailored to your application specific needs, many provided with integral pressure restraint and tools including our active SEALFAST® Inflatable Seals. 

Mechanical Research & Design, Inc. | Innovation Redefined | Manitowoc Wi


Mechanical Research & Design, Inc. is the expert when it comes to pressure isolation and test solutions! We have a wealth of application and product experience in industrial fabrication, pipeline maintenance, underwater construction, conventional and nuclear energy, and have manufactured tools for nearly every problem or need you can encounter! We design and vulcanize our own SEALFAST® elastomers on-site to offer incredible design and lead-time flexibility, allowing us to build nearly any product at a moment’s notice. Our products and ideas are shop validated and have withstood the rigors of time in the most demanding industries. Have a basic isolation or test tool need or can’t come up with a solution for your remote access isolation? Give us a call — we have the products and ideas you need!

• See our other Isolation and Test Tools here.
• See our large Isolation Barriers and Bulkheads.
• Interested in diver-installed products? See our Underwater Construction and ROV Tools.
• See our Nuclear Industry tool products
• For Control Panels, Utilities, Turnkey Test and Operational Systems, please see our Controls and Accessories page.