Until the mid of 90-s of the last century the main approach applied was use of steel patches and frames designed to extend the useful life of the pipe before overhaul, when the replacement of damaged section becomes feasible.
Although the modern approach to piping spool replacement provides for more radical solution, it is sometimes considered as not the best one, especially in large diameter pipes cases.
However, the major financial costs related to halt of product transportation may be avoided by means of hot tapping and bypassing, the use of heavy machinery resulting in high labor costs are unavoidable. Additionally, in some cases it is not possible to bring machinery and equipment to the repair site. Though setting aside the financial and other cost issues we will face the problem of repair term, which is usually limited either by the seasonality or by production halt period.
Issue of Repair Approach Selection
Pipeline owner is at cross-road: either to perform traditional diagnostic providing only for Technical Inspection Board permit on pipeline operation, though giving no hint on effective pipeline condition in other words putting owner asleep on volcano; or to carry out the in-line inspection, which will identify numerous defects making the repair compulsory. This is high time for making decision on the approach to repair.
Seemingly there is a large variety of sleeve fittings. However, the closer inspection results in only two major types of fittings: compression and non-compression ones, which types are equally applicable to steel and composite fittings. Thus, according to RD (Ruling Documents) of Transneft JSC, repair performed with use non-compression steel fitting is referred to temporary repair, whereas that with use of compression steel fitting – to overhaul one. The fundamental difference of compression fittings is in ability to offset the internal pressure at the defective area due to creation of external contact pressure.
The repair technology of British Gas Company, i.e. CFT (composite-fitting technology) is in some way standing apart. The sectional steel sleeve with internal diameter larger than that of pipeline is aligned and welded by longitudinal welds at the defective area. Bearing faces of fitting are filled with quick-settling sealant, and the annular distance is filled through temporary opening with polymer setting compound. This universal repair technology applicable to all types of defects also allows avoiding halts in product transportation. Though, the implementation of such technology assumes need in extensive resources.
Figure 1 clearly illustrates the scale of earth moving works and need in special purpose and heavy machinery, and labor requirements at CFT installation. Additionally, the quality of repair works is in heavy dependence on strict adherence to technology, e.g. the filling of annular distance with polymer setting compound may be accompanied with air bubbles formation, which will result in deterioration of mechanical properties of fitting.
Having in mind the desire to avoid use of heavy machinery, the engineers of repair frames directed their attention to composite materials. Thus, density of fiberglass is 4 times higher than that of steel, and by far, the endurance limit is 2 times higher than that of steel.
First repair frame with use of scrolled fiberglass was designed by Argus Limited Company (U.S.A.). Engineers of the company developed repair approach making use of Clock Spring sleeve. The main idea of the approach lays in application on defective area of bandage of scrolled fiberglass by spooling through glue compound (see fig. 2). The fiberglass belt is made of unidirectional high-modulus glass roving providing materials with coefficient of elasticity close to that of steel.
However, considering the need in free annular space (defined by the pipe diameter) required for belt spooling at the defective area, this approach provides no relief from use of heavy machinery and earth moving.
Russian engineers went farther, and at the end of 1990-s Novie Tekhnologii (New Technologies) CJSC offered construction of compression fiberglass fitting RSM (see fig. 3). Using as basis application of fiberglass of unidirectional glass roving alike to Clock Spring, the company manufactured two half-fittings with embedded steel parts instead of flanges. The half-fittings are screwed up by alternating screwing of eight pins with multi-faceted thread. High external compression is created due to high screwing momentum of bolted assembly and reliefs the pipe walls in the defected area. Though the main drawbacks of this frame comprise:
- limitation in dimensions scale, the frame is applicable to pipes of 720…1420 mm;
- impossibility of tight application along the whole perimeter of the pipe due to screwing node construction peculiarities;
- unscrewing when subjected to continuous oscillation, as a result of multi-faceted thread pins use and impossibility of split washers application.
Promising approach – Reinforcing composite sleeve for pipelines (Smart Lock)
Considering 20 years of development of fiberglass constructions, as well as using technologies of pipelines repair which existed in 2005, the engineers of PSO Neftegazdiagnostika LLC designed, manufactured, certified and put in series production in 2008 a reinforcing composite sleeve for pipeline Smart Lock, which allowed to eliminate the above drawbacks. The Smart Lock sleeve were admitted for use in oil and gas industry and are supplied with hygienic certification. Use of Smart Lock provides for surgical, inexpensive, relatively easy but reliable repair of pipelines.
Operation principle of Smart Lock lays in compensation of internal pressure of the pipeline by creation of contact external compression due to high screwing momentum of bolted assembly, which provides for mounting at operational pressures at predefined quality, unlike the fittings installed without preliminary tension. Fitting comprises two half parts joined by hinge on one side and four bolted connectors. The fitting is tightened by bolts manufactured in series using GOST (State Standard) 11738-78. The main distinction from all types of fittings currently used comprises wide scale of dimensions of repaired pipes from 89 to 1420 mm, complete coverage of damaged area, ease of mounting, high speed of repair and insignificant volume of earth moving works. The relatively small diameter pipes repair with Smart Lock sleeve may be performed in manually made small opening and will take some 15-20 minutes, which is very important, e.g. when the repair operations are subjected to need of underground water pumping, thus making dimensions of opening and time of repair critical.
The reinforcing composite sleeve Smart Lock are used to repair external and internal pipelines with steel loss of up to 100% of the nominal wall thickness. This approach to repair is referred to overhaul, providing for use of Smart Lock by some oil and gas companies for the purposes of liquidation of pipeline tears, including repair without pressure reduction. The repair with use of Smart Lock allows to avoid the use of steel collars completely, as well as in some cases – to avoid the pipelines spools replacement. The Smart Lock sleeves are also applicable for deep sea pipelines repair.
The sleeve is completely manufactured at production facility, thus eliminating influence of external (weather) conditions and human factor on the quality of the repair performed with such fitting use. Steel parts of Smart Lock are made of stainless steel and are not subject to corrosion. Subject to requirements applicable, after repair the technological cavities and openings are filled with special purpose polymer material making sleeve a monolith fiberglass construction reinforced by embedded parts of stainless steel.
- RD 153 39.4-067-00 “Approaches to Repair of Defective Areas of Operated Oil Trunk Pipelines”.
- VSN (Russian Construction Rules) 39-1.10-001-99 “Rules on Repair of Gas Trunk Pipelines with Use of Polymer Compound Materials”.
- Materials from official site of Clock Spring Company (www.clockspring.com).
- Patent for Invention No. 80530 “Device for Pipeline Repair” dated 21.10.2008.
- Opinion of Industrial Safety Inspection No. TU-AS-237/659-10 “Reinforcing Composite Sleeve Smart Lock”, VNIISERTIFIKATSIYA, Moscow, 2010.
- TU (Specification) No. 2296-001-70552764-2007 “Reinforcing Composite Sleeve”, Moscow, 2007.
- Kazakhstan Industry Standard “Guidelines on Application of Reinforcing Composite Sleeve at Pipeline Repair”, Astana, 2008.
General Director of
PSO Neftegazdiagnostika LLC
Victor LESCHENKO, PhD in Technical Sciences,
General Director of
NTC Neftegazdiagnostika LLC
PhD in Technical Sciences,
Development Director of
NTC Neftegazdiagnostika LLC