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Monday, August 31, 2015

Shrink Sleeve Selection Criteria

How To Select The Proper Shrink Sleeve

     Covalence (formerly Raychem) heat shrinkable sleeves are the world leader in corrosion protection of pipeline girth welds.  They are specifically designed to combine ease of field installation with a level of performance that matches, or exceeds, that of the mainline coating. 

     Project specifications and or local standards must be observed, when specifying a shrinkable sleeve for protection of girth welds.  To ensure optimal choices, the following parameters must be considered.

Pipe Operating Temperature

As temperature increases, the overall resistance of a coating generally decreases.  Therefore, in order to ensure adequate lifetime, it is important to select a coating that has been correctly performance tested at maximum operating temperature.  Covalence mastic coated sleeves are available for temperatures up to 100C.  Hotmelt sleeves are available for temperatures up to 120C.

Pipe Coating Type

Covalence / Raychem heat shrinkable sleeves are compatible with all commonly used pipe coatings, although somewhat different installation procedures may be required, depending on the line coating employed.  The sleeves will adhere to FBE, PE, PP, ARO and CTE coatings.  Some polypropylene coated pipes require special heat shrink sleeves.  When using polypropylene pipe coating, please consult Joint Specialists for assistance in selecting the appropriate heat shrinkable joint protection sleeve.

The HTLP three layer system is often used on three layer PE pipe coatings to provide factory original quality to the field applied girth weld protection.  The same system can also be applied on two layer PE. 

Cutback Distance

Different pipe coatings require different coating cutbacks at the weld joints.  Our standard sleeve widths are 11", 17", 24" and 34".  Custom widths are generally available for no extra charge.

Outside Pipe Diameter

When buried, larger diameter pipes incur higher soil stress due to the weight of the soil above them. These stresses create tangential forces, which in low performance coatings tend to cause wrinkling at the two, four, eight and ten o clock positions on the pipe.  The best way to combat these forces is with high modulus polymer shrink sleeves coated with high shear strength adhesive.

Covalence heat shrinkable sleeves possess the highest modulus in the industry, while the hotmelt adhesives are made of the finest copolymers.  Raychem hotmelt coated shrink sleeves provide the greatest resistance to soil stresses on all diameters.  Below 20 inches diameter, Raychem's high performance mastic coated shrink sleeves often provide a good balance of performance, economy and easy of installation.

Adverse Soil Conditions

In adverse soil conditions where heavy soil stresses, corrosive soils or water logged areas are expected, the use of soil stress free coatings with excellent cathodic disbondment and long term water immersion resistant is essential.

HTLP60, HTLP80, WPC120 and ROCS / DIRAX are all outstanding in this respect.  They have consistently been rated the best girth weld coatings in tests carried out by major pipeline companies worldwide.

Pipe Laying Method

Directional drilling places tremendous stress on a pipe coating - and especially on the girth weld coatings.  Raychem DIRAX kits are designed to protect girth welds in this punishing environment.  The DIRAX system starts with the application of an epoxy primer coating, on top of which the DIRAX sleeve is installed.  The sleeve is a fiberglass reinforced polymer laminate with an edxtremely high shear resistant crystalline adhesive.  In numerous tests and customer trials, DIRAX surpasses even the toughest conditions.

For laybarge installed pipelines, WPCT, WPCZ, WPC100M are ideal girthweld coatings, being easy and quick to install and fully resistant to the pour of hot marine mastic infills and the heat generated by polyurethane foam infills.  They are compatible with all commonly used main pipe coatings.  For elevated temperature lines use WPC100M which has a 100C continuous rating subsea.

For reelship installed pipelines, HTLP80 has a proven track record on three layer PE lines, even when reeled or unreeled under tropical conditions.

Climatic Conditions

Extreme climatic conditions (hot, cold, wet, etc) can have an impact on the sleeve selection and the installation method.  In cold conditions it will be necessary to organize proper field storage; rain requires a tent.  In hot climates it may be beetter to select a high temperature sleeve, even for a low pipe operating temperature, as the pipe could be exposed to very high ambient temperatures for an extended time during construction.

Recommended Pipe Preparation

Pipe preparation depends upon the project specification and the resulting choice of products.  In order to obtain the desired performance, pipe preparation must be carried out in accordance with the relevant product installation instructions.

Mechanical Resistance Class

Depending on the mechanical requirements of the local or project specification, the appropriate sleeve construction (thickness) is selected.  

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