Heat Shrink Sleeves

The field welded joints on coated pipe are exposed, and are protected by methods such as sleeves, cold tapes, epoxy, coal tar etc.  The use of heat shrinkable products or shrink sleeves is the most dominant method used to protect joints worldwide due to

a) Design flexibility and compatibility with pipeline conditions and pipe coatings.
b) High reliability and superior service performance.

The function of a sleeve is to protect the pipe joint from corrosion. The sleeve adhesive achieves this by preventing moisture and air ingress to the pipe surface. The outside Polyolefin backing mechanically protects the adhesive and the joint. The adhesive further acts to hold and anchor the backing around the joint through adhesion to the substrate and the backing.

SLEEVE DESCRIPTION

The heat shrink sleeve consists of a crosslinked and prestretched sheet, which upon heating, will shrink to its original length. This sheet is coated with a protective heat-sensitive adhesive.

When heat is applied to the sleeve wrapped around a joint, the adhesive melts and becomes a liquid, while the sleeve backing begins to shrink.

The radial shrinking forces of the sleeve squeezes the fluid adhesive into all the pipe surface irregularities, while the sleeve conforms tightly to the joint profile. On cooling, the adhesive solidifies, effecting a tough bond to the pipe and the coating.

A. Product Design

There are three basic types of sleeves used to protect joints:

WRAPID SLEEVE: One piece wraparound sleeve with built-in closure patch. CANUSAWRAP™: Wraparound sleeves with separate closure patch CANUSATUBE™: Tubular sleeves.  While HIGH SHRINK SLEEVES™   is designed for  corrosion protection of high profile joints

B. Sleeve Backing Types

Backings are available for normal or heavy duty service.

Yellow backing is typically used for buried application and also for hot climates to reflect the heat during prolonged exposure to the sun during construction. Black UV resistant backing is used for above ground applications. The yellow sleeves come with standard built-in thermochromic pigment which changes to orange at the correct temperature and then reverts to yellow upon cooling. The backing can optionally be supplied with a surface painted indicator.

C. Adhesive Types

The sleeve adhesives falls into two main categories; mastics and hotmelts.

1. Mastics

Mastics are tacky, pressure-sensitive, sticky, and softer adhesives. Therefore they bond relatively easily to substrates upon contact and pressure. The heat helps the adhesive flow and thus enhances the bonding action. They are more forgiving than hotmelt adhesives to installation conditions, such as pipe cleanliness and heat input.

Mastics have lower but still good peel strength and generally good cathodic disbondment resistance. Mastic sleeves are self healing; a puncture in the backing is sealed by the mastic.

2. Hot Melts

Hot melts are non-tacky, dry, hard adhesives based on semicrystalline resins.

They have very high shear strengths, and often high peel strengths. They are formulated to operate at high temperatures.

On the downside, they require a much higher degree of surface cleanliness and very high preheats. The preheat temperature can be reduced by using epoxy primer with appropriate sleeves.

The adhesive selection criteria are discussed in section 5

D. Sleeve Thickness

Thickness provides the mechanical protection, for example, impact and penetration resistance.

Sleeves typically are provided to give 2.8 mm (111 mils) applied thickness for normal applications, and 3.3 mm (131 mils) where extra mechanical protection is needed.