Permalok® Steel Casing Pipe

NWP-PermalokLogoPermalok®, because Time is Money

The most effective innovations are often the most simple in design. Permalok® is a proprietary steel casing pipe joining system that employs a press-fit interlocking connection system for joining casing pipe sections in the field, faster than any other system.

Since 1997, over 2 million feet of Permalok® Steel Casing pipe has been installed on jobs where failure was not an option. That’s why Permalok® stands as the product of choice for trenchless contractors and engineers for their most important and challenging projects.

Permalok® Steel Casing Pipe from Northwest Pipe Company is installed easily using various trenchless jacking construction methods including microtunneling and pipe jacking, auger boring, pipe ramming, Direct Pipe®, and others.

  • Eliminate field butt-welding, and associated down time … no more waiting 4 to 5 hours while a 60-inch casing pipe is butt-welded in the field before moving on to the next pipe section
  • Save time and money, lower labor and equipment intensive processes of various pipe jacking methods
  • Flush on both the ID and OD
  • Reduced costs by significantly increasing productivity in the field
  • Unequaled precision and accuracy provided by a joint of consistent quality and integrity
  • Available in any length and size – up to 150-inch OD and 2½-inch wall thickness
  • Quick and easy installation

Permalok®‘s precision machined ends create a time-savings benefit, cutting jointing time by 90% or more from field butt welded joints. This means overall tunneling duration is significantly reduced, and periods of non-movement of the tunnel are kept to a minimum, reducing potential for ground loss at the face or ceasing the tunnel due to ground squeeze or friction. Pipe is still flush on OD and ID, so pipe jacking and stringing of carrier pipe is unaffected.

Permalok® Fits Your ProjectNWP-PermalokLogo

The system is approved for both steel casing and with modifications, pressure pipe applications. The T-5, T-7 and Type HDD joints each bring a different application- specific solution to the pipe connections. Standard specifications ensure that all pipe manufactured by Permalok® meet stringent guidelines. Joint quality is further enhanced because the Permalok® connector is consistently round, true and perpendicular to the pipe axis. Its unique machined groove makes stabbing and aligning easy and expeditious.

Permalok® Steel Coatings and Linings

Permalok® uses several options for our coatings and linings. The primary materials applied to Permalok® products are:

Coal Tar Epoxy – A catalyzed, two-component lining that combines the corrosion-resistant characteristics of coal tar pitch with those of epoxy resin, resulting in a cured lining that will tolerate reasonable impact abrasion and flexing.

Bitumastic – Bitumastic is made from coal tars and blends of resins such as epoxy. A trade name often associated with long-term protection from water penetration, Bitumastic is an economical, heavy-duty material which protects piping subjected to water immersion.

Polyurethane – Polyurethanes are used extensively in the pipe coating industry because they exhibit excellent corrosion resistance, abrasion resistance, toughness and chemical resistance, as well as a wide range of useful mechanical properties. Fast-setting, high-solids polyurethane has been used to line and coat steel pipe for various demanding trenchless and open-cut applications.

Power Lonestar “Powercrete®” – An epoxy based polymer concrete which protects the steel pipe under severe handling conditions. It is highly abrasion-resistant, and provides a smooth surface that allows for less drag resistance than standard concrete.

Efficiency Comparison

Save Time and Money – Permalok®’s time saving benefits are significant. Two examples of how you can save time and money in common installations are detailed below.


Case Studies

Permalok® T-5 Joint

The Permalok® T-5 joint utilizes a precision machined interference fit that eliminates the need for time-intensive field-applied butt welds on trenchless installations of casing pipes. The pre-installed precision joint connection, which is flush with the interior and exterior surfaces of the pipe, quickly, easily, and permanently joins each piece of steel casing pipe on a project.

Permalok® T5 Female to Male Joint
Permalok® T5 Female to Male Joint

Permalok T-7 Joint

The Permalok® T-7 joint utilizes a precision machined interference fit similar to the T-5 joint, but incorporates two rubber o-ring
gaskets. The pre-installed precision joint connection, which is flush with the interior and exterior surfaces of the pipe, quickly
and easily joins each piece of steel casing pipe on a project. Its unique stepped profile makes stabbing and aligning simple and

Permalok® T-7 Female to Male joint
Permalok® T-7 Female to Male joint

A One-Pass system with the Permalok® T-7 joint is possible, eliminating the need for a casing pipe. The T-7 Permalok® pipe in this
case serves as the carrier pipe, for low to medium pressure applications. Following installation typically by microtunneling, a
1/8-inch single-pass seal weld is applied at each of the joints where a pre-existing v-groove is chamfered at the joints from the
manufacturing facility

Permalok® T-7 Female to Male joint
Permalok® T-7 Female to Male joint

Permalok® Type HDD Joint

Permalok®’s HDD joins sections of the 12″ in diameter and under pipe quickly, using your Drill Rig

Permalok® Type HDD Female to Male Joint
Permalok® Type HDD Female to Male Joint

The Type HDD profile incorporates an additional locking key on the male portion of the joint to greatly increase pull-apart resistance. The HDD profile is considerably longer for more flexibility in bending. Also, by increasing the joint length, the spacing between interlocking ribs is greater, making the connection easier and faster. Less force is required to complete the joint makeup.

With the Permalok® Type HDD profile, contractors can install steel pipe from the rig side of the bore path, using the drill rig to make up the sections and advance them, similar to installing drill stem.

Northwest Pipe Engineering Services

Let Northwest Pipe assist your underground construction project with its engineering requirements. Our professional staff members can
assist with:

  • the design of new products for specialty applications
  • shop drawings
  • engineering submittals
  • coordinating outside sources for specialty fabrications
  • non-destructive testing
  • product recommendations
  • coating and lining recommendations

For more information on our engineering services, please contact us directly:


Request for Permalok Sales Quote - Temporary

  • Your Company Information

  • Quote Requirements

    Please complete a line item for each requirement. If you need more than three line items, please complete the form more than once.
  • Line Item 1
  • Line Item 2
  • Line Item 3
  • Shipping Information

  • Important Dates

  • Date Format: MM slash DD slash YYYY
  • Date Format: MM slash DD slash YYYY
  • Date Format: MM slash DD slash YYYY