FAQs

The weld-free Snap Ring Joint (SRJ) solves many of the problems commonly associated with welded and flanged joints in pipelines and process piping. It can be used in both new lay and established pipework, as a temporary or permanent solution.

Snap Ring Joints

FAQs

FAQs

  • Metallurgy
  • Mechanical Issues
  • Corrosion Issues
  • Seals

METALLURGY

Can the SRJ be used to connect, for example, Inconel pipe or Superduplex pipe?

Yes. It is possible to connect any material with sufficient wall thickness. In the case of Inconel and super duplex the most important considerations are the materials of construction of the coupling and retaining wires, which must be compatible with the pipe material and the process fluid.

Can SRJ technology be applied to fibre pipes?

Technically it is possible to use the SRJ on fibre / composite pipes and SRJ hope to develop a suitable product in the near future.

MECHANICAL ISSUES

What is the SRJ’s resistance to torsion?

The SRJ is an 'unstressed' connection and as such its resistance to torsional loads once assembled, and not pressurised is limited to the friction generated by the radial seals. Once the connector is pressurised it locks to the pipe due to the hydrostatic end force being withstood by the retaining rings / pipe grooves, this 'locking' also provides high torsional rigidity.

How is the depth of the pipe groove determined?

The depth of groove in the pipe is determined by several factors – 1 - The longitudinal stress in the pipe, under the groove does not exceed 20,000 psi (grade B) at design pressure (increases when pipe material yield increases). 2 - The pipe with the coupling installed is capable of withstanding the tensile pull test specified in the IACS P2 test regime, which states that the coupling must withstand a tensile load equal to the hydrostatic end force generated by the design pressure whilst the coupling is pressurized to its design pressure. These calculations are constant across the pipe diameter range. In the event it is not possible to keep the stress below that specified the number of retaining wires used is increased.

These calculations ensure that after grooving and installation of the coupling that sufficient pipe wall thickness exists to ensure the pipe is capable of withstanding the full range of operational loads.

The actual wall thickness of a pipe varies due to the allowable manufacturing tolerances (specified in API 5L) do these tolerances impact the depth of groove calculations?

The maximum design pressure allowable for the pipe is calculated by subtracting the pipe manufacturing tolerance for wall thickness according to API 5L (-12.5%) along with any corrosion allowance. (Calculation 304.1.2 ASME B31.3) In this way the strength of the coupling and the required pipe groove is based upon minimum metal conditions and not the nominal wall thickness of the pipe. This will ensure that sufficient strength is left in the pipe after grooving if the pipe is supplied with minimum wall thickness and at the end of the pipes operational life.

CORROSION ISSUES

Can the SRJ connector handle corrosive fluids?

The SRJ is capable of handling a wide range of pipe media. The main considerations are the selection of the seal and the couplings material of construction. For general process fluids please refer to James Walkers Oilfield media compatibility chart. When requesting a connector proposal SRJ require full application details which includes the composition of the process fluid so that we can ensure that the materials of construction are correctly determined.

What consideration is there for sand erosion inside the pipe and the risk of it passing between the pipe ends?

The pipe ends are in close proximity and as such the likely hood of the sand passing through is unlikely. The main concern with sand erosion would be due to any restrictions / protrusions in the line of flow, which is not a concern with the SRJ as it has a smooth bore.

If the coupling is made of the same material as the pipe, is there potential for galling?

The coupling needs to be manufactured from similar materials as the pipe to ensure that is compatible with the pipe media. The potential for galling is only considered a problem if a stainless steel connector is being installed onto a stainless steel pipe. In the scenario to prevent galling the connector would be manufactured from a different grade of stainless to that of the pipe.

What considerations are there for external corrosion entering the grooves and its impact on pressure constraint?

The fitting of an environmental seal will prevent ingress into the connector and thus prevent corrosion of the retaining wires. When installed the retaining wires are coated in a suitable corrosion inhibitor which will assist with corrosion prevention.

Certain types of internal corrosion can typically occur at the 6pm position due to the accumulation of sedimentary matter. How much wall thickness can be lost due to internal corrosion at this position before the SRJ fails?

Corrosion occurring at the '6 o'clock' position depends on the type of corrosion occurring within the system. In the event that this type of corrosion does occur and allowed to go beyond the pipes corrosion limit then the pipe will fail in the area under the grooves (thinnest section) if insufficient pipe strength is left to withstand the pressure.

What consideration is there regarding the bare metal underneath the seals?

SRJ recommend that the area under the seals is bare metal as sealing on any painted surface cannot be guaranteed (manufactures specification).

SEALS

What material are the environmental seals made of?

The external / environmental seal is a low pressure seal and is designed to prevent ingress into the coupling, thus protecting the retaining wires from corrosion. The material is an elastomer, typically Nitrile or PTFE.

Is age hardening a problem with HNBR?

Some elastomers do have a shelf life due to age hardening. SRJ ensures, by its material specification that the environmental seal does have a suitable design life.

Why does SRJ have a Casing Seal and Lip Seal?

The casing seal is a good robust seal and well suited to the SRJ. It is used for downhole / drilling type applications, it is capable of being resistant to pipe stab in operations and is self-energised. The downside is the load required to insert the pipes into the coupling and the limited range of materials that the seal can be produced from.

The Lip Seal was developed to offer a wider range of materials – initially Viton due to a higher temperature requirement but the seal is available in PTFE, filled PTFE, Elastomers, metallic etc. and the seals composition is dependent upon the pressure, temperature and process media of the application.

The current operation g range of the SRJ with either seal type is -27 to +177 Deg C but ongoing developments will see this range expanded to -50 to +350 Deg C.

Snap Ring Joint Limited, 9 The Esplanade, St.Helier, Jersey, JE2 3QA, UK.
tel: +44 (0) 1534 626 818
e-mail: info@srj-technologies.com
Snap Ring Joint Limited. All rights reserved