Hot Tapping: Zero Down Time Modification & Remedial Work with Pressure Vessels
Table of Contents
1 Introduction to Hot Tapping
Few engineering procedures can modify, repair, and improve operating equipment while they remain in service; far less are the number of procedures that are also environmentally friendly, involve less risk, and firmly claim a 60%-80% expense reduction when compared with competing procedures. Nearly a century of widely practised hot tapping and plugging techniques confidently generate these facts. While hot tapping is not a recent invention of industries which use pipelines, piping, tanks, and other pressure vessels, its regularity of use has only increased over time; under the often uttered maxim, “Work smarter, not harder.” Leading authorities in the energy field, such as TransCanada Corp. (TC Energy) have extensively employed and refined the safe, highly effective, and economically beneficial uses of hot tapping for decades*, while the United States Environmental Protection Agency (EPA) has favourably evaluated hot taps for emission reduction and increased revenue in comparison to historical methods of achieving the same result*.
Making new connections to equipment while it remains in service and under pressure, is the end goal of any hot tapping enterprise; in the case of pipelines and piping, it is primarily used to tie in other pipeline systems. Existing, operational loaded facilities (usually tanks, piping, pipelines or water lines) undergo hot tapping to efficiently achieve several important goals. Remedial work without shutdowns, disruption of service, product loss, emission negation, and added risk to workers is achieved with this ingenious technique. Sometimes referred to as pressure tapping, wet tapping, or line tapping, the process involves an experienced crew, specialized equipment, and meticulously detailed analysis.
Hot tapping as an industry term originates from two distinct aspects of the procedure; hot work and precise drilling (tapping). Hot work encompasses heat generating or spark-producing equipment – welding, portable grinders, burning torches, abrasive blasting, etc. – which may be employed in a given “hot” procedure while tapping refers to the use of a hot tapping machine, which removes and recovers a curved cutout (coupon) of the pipe wall. Line stopping allows for greater degrees of modification and remedial work and uses different machinery to achieve this. This technique makes use of line stop machines, plugging heads, and a bypass line to maintain the complete operation of the loaded facilities while repair activities and further operations fully commence.
1.1 Pipeline and Piping Modification
Though hot tapping is versatile in its application to pressure vessels and storage tanks, the ability to engage in modification and remedial work without interrupting services makes it an indispensable skill in dozens, perhaps hundreds, of industries. Hot tapping can be applied to a broad spectrum of materials, including carbon steel, cement, and PVC – on land or underwater. Whether carrying crude oil, gasoline, water, natural gas, or sewage, commodity transportation and pressure remain unchanged, no matter how extensive modifications or repairs are. Broadly speaking, modification, could be defined as any planned and executed addition to an existing facility, though a distinction is worth noting for remedial work, or repairs (addressed later in detail), which technically could fall within such a general definition. The list of various modifications performed in the near-century through hot tapping exercises is lengthy, but there are several crucial, commonly performed modifications worth taking note of.
Tie in connections are among the most referenced concerning hot tapping, with sound reason. These common connections are essential to expanding existing infrastructure and utility of piping or pipeline – among the more routine modifications are extensions, bypass lines, main relocations, or even pig launcher and receiver stations. Perhaps less frequently, yet regularly installed modifications include: sample points, air relief points, pressure control switches, sensor installations, lateral lines, metering devices, sales taps, and much more can be added to existing facilities by way of hot tapping. As a versatile method for enacting timely modifications (or repairs), routine or rarified, “hot” connections have proven to be an invaluable service in industry toolkits around the world.
2 Hot Tapping: Preparation, Risk, and Risk Mitigation
Historical cold tee (shutdown interconnect) methods for creating pipeline connections or remedial work are still used, though often at the cost of disruption of service for days, increased emissions (particularly in the Natural Gas industry), millions of dollars in expense, and arguably more risk*. The decision to choose between a hot tap or a shutdown interconnect, hinges upon a comparative analysis of pros and cons. Potential installation difficulties and long term operating issues, against the beneficial economic, environmental, and operating impacts of either route. Though the comfort and familiarity of cold connections may hold some appeal, the regular use of hot connections has steadily increased. Largely due to ninety years of continuous refinement to standards, techniques, and regulations, risks associated with hot tapping have been mitigated to a significant degree. These advances have so significantly reduced hot connection risks that it is commonly deemed superior to the available alternatives.
Despite the “hot” nature of hot tapping and risks inherent in pressurized operational tanks, piping, and pipelines, it remains a thoroughly planned, calculated, and controlled procedure; exceptional investments in preparation, design, and proper installation are paramount in mitigating risk while completing a project.
Before commencing a hot tap, job-specific plans are written out in generous detail, and include a host of specifications which are intimately related to the procedure, at a minimum they include:
- Connection Location and Design (including gaskets, valves, and bolts)
- Thickness and Materials of the Vessel, Piping, or Pipeline to be tapped
- Detailed, Written Welding Procedures
- Health, Safety, Fire Protection, Emergency Response, Procedures and Instructions
- Owner and User Requirements
- Emergency Shut Off Procedures
- Contingency Seal Off and Isolation Plans (that maintain integrity for the system’s life)
When preparing for a hot tapping procedure, every minute detail must be rigorously accounted for, to ensure safe and effective operation. The highly trained and experienced crews that carry out hot connections address metallurgical concerns related to each operation, specifically as it pertains to welding. The wall thickness of these vessels can be measured with ultrasonic gauges, to properly marry welding techniques, temperature, and pressure concerns, to avoid a potential loss of containment near weld pools. Calculations are made regarding heat transfer. flow speed, and other variables to reduce any risk (of burn-through, hydrogen cracking, etc.) when welding branch connections onto pipe systems.
2.1 Branch Connections, High Pressure, and Low-Pressure Fittings
Aside from valves and hot tapping machines, fittings are one of the primary components of any hot tapping exercise; as the name suggests, they are designed with tremendous variety to make branch connections – a fit for every occasion. Dimensions such as the size and pressure of a vessel, as well as the bore size of the tap itself, are fundamental to determining the type of fitting. Expertly qualified personnel select a sized fitting to accommodate the operating pipeline. Once the appropriate fitting is selected, it is welded with incredible nuance and attention to detail, although mechanically attached fittings are rated as an alternative in instances where welds are not feasible.
High and low-pressure fittings are specialized for pressure variant used on pipelines, tanks, and storage vessels and can range from a welded nipple to a full-encirclement. The need for a case-by-case evaluation of appropriate fittings can be aided with the use of comprehensive equipment catalogues, vendor manuals, or graphs (similar to the T.D. Williamson charts below). These volumes are customarily broad spanning compendiums of relevant parts and their performance specifications. Branch connections are not, however, exclusively manufactured, quite often they are fabricated adaptively to an exacting specification, which can reduce project costs.
2.2 Valves
The humble and ever-present valve plays out its critical role between the fitting and the hot tapping machine. As with most aspects of a hot connection, this part of the hot tapping assembly is selected to perfectly conform with the specifics of a given vessel or line. Material composition, pressure, temperature, and size are some of the essential recurring factors. This valve must have adequate dimensions to allow the coupon retrieval after the cutting operation and can take the form of either a block or control valve.
While valves are genuinely ancient technology, many varieties have been masterfully adapted to the 20th and 21st-century tasks of regulating pressure and flow. Typically globular in shape, the stout, round-bodied silhouette of a gate valve (sometimes a ball valve) is found employed on pipelines, though many operations call for planed or flat (sandwich) valves to reduce the travel distance of a tap. Sandwich type valves are optimally applied in circumstances where space is a premium; they are fabricated and manufactured to exceed the necessary performance standards. Although these two valves do not exclusively dominate the hot-tap-horizon, they are prominent contenders.
The selected valve is properly secured to the fitting using one of several methods, usually welded (bolted or bonded), attached with a collar, or strapping device – depending on the need. Once attached structural and leak testing begins, usually in the form of hydrostatic pressure testing, though ultrasonic and X-ray techniques (among others) are possibilities.
3 Hot Tapping Machines
Capable workhorses, tapping machines avail themselves to hot tapping crews in a variety of sizes; dutifully persisting for 15 to 20 years with routine maintenance, they can be purchased from manufacturers or fabricated in-house. Pneumatically, hydraulically, electrically, or manually powered, these machines specialize in penetrating through vessel and piping walls while – critically – retaining and extracting the cutout or coupon once the cutting is completed. As with previous aspects of hot connections, hot tapping machines must be assessed by their merit for a particular job; accurate accounts must be taken of temperature, pressure, material compatibility, and mechanical stress parameters.
3.1 Hot Tapping Machine Considerations
Given the range of possible dimensions with vessels, piping, and pipelines a hot tapping machine may encounter the need for adaptability. This naturally promotes an equally large variety of adapter, cutter holder, cutter, and pilot drill sizes. Nested within the recess of the tapping adapter, the cutter and pilot bit await operation; specially designed with coupon retrieval in mind, these unique pilot bits feature a retention wire (often designated a U-wire), which toggles after cutting, catching the coupon and preventing its possible escape. This bent wire is recessed into a milled relief area on the bit, preventing its activation in the initial perforation of a pipe wall. Before saddling the machine to its designated valve, it is essential to scrupulously measure and detail these cutting dimensions: from pilot tip to cutter tip, from cutter tip to cutter base, from top of flange to pipe surface, and a wall thickness of the pipe.
For further reading on performing a successful hot tap follow the link below:
Hot Tapping – Advice on Successful Pipeline Tapping
3.2 The Hot Tapping Process: Step-by-Step
Married to the valve by the tapping adapter – which contains the pressure of the pipe system – the tapping machine stands at the ready. The machine is telescoped into cutting position on the surface of the pipe before actuation. The hot tap is then created with a smooth and continuous process, until the cutter clears the pipe wall, removing a section or coupon, which is swiftly captured and soon removed. The machine ceases cutting immediately upon piercing through the pipe wall, as proceeding could trap the cutter within the vessel. Subsequently, the cutting assembly is retracted. Pressure retained within the tapping adapter is bled out through a purpose-built relief valve, enabling a safe disconnection of the machine and the collection of a prized coupon – the token of a job well done.
The coupon may not be redeemed for a discount, but it certainly buys a successfully installed valve and shiny, new connection point to the network to other systems. Alternatively, it signifies the start of another hot tap, in a series of taps, for further action. During the lifetime of piping and pipelines damages are occasionally sustained due to natural events, flaws in maintenance, or exposure to corrosive elements and electrical forces – sometimes due to lack of applying for thorough cathodic protection. These damages can be resolved without interruption to service. Creating an additional hot tap is the first step towards conducting this sort of remedial work. Having two such taps presents the optimum scenario for establishing a line stop and bypass line to continue service, uninterrupted while work proceeds.
To read more about cathodic protection check out these EPCM articles below:
Cathodic Protection Case Study – Padma Bangladesh
4 Introduction to Line Stopping
Involving multiple hot taps, the service of line stopping is an essential part of modifying, repairing, or otherwise significantly adjusting piping and pipelines. Somewhat more involved than a hot tap, this operation uses multiple hot taps, line stop actuators, plugging heads, and a bypass line. Line stopping performs the temporary function of a valve, to isolate and neutralize a section of the pipe system, while allowing the commodity to freely flow through the bypass structure, into the rest of the pipe system.
Often requiring an even pipe-to-pipe, or size on size, fitting to accommodate the plugging heads large size, the latter two hot taps are typically larger in dimension. A line stop actuator and plugging head serve as a temporary valve – and as with hot taps – can be utilized with materials ranging from iron to PVC, concrete, steel, copper, and others. Relating to the size of piping and pipelines, line stops can be performed from ¾ of an inch to 80 inches, leaving little unaccounted for.
As with hot tapping, line stopping services have their origins in the early 20th century, though technologies had advanced considerably, the same techniques and principles apply – with notable advancements. Tried and true technologies related to line plugging are still commonly used, and serve the same undeniably central role when performing refurbishment, alteration, relocations, tie-ins, maintenance, or retrofits.
4.1 Line Stopping Machines and Plugging Heads
The machines used in line plugging and stopping bear a strong resemblance to the previously discussed aspects and equipment used in hot tapping – they are always suited precisely to the job at hand. Relatively straightforward in terms of machinery, line stop actuators can be manually – or more often hydraulically powered. Many applications that use line plugging machines require a size on size fitting, usually a welded tee fitting, to allow entry of a pivoting plug head. Whether employed in water lines, natural gas, oil, sewage, or other pipeline systems, these tools range a large span of dimensions, weights, pressure tolerances, and heat tolerances. Each line stopping machine is manufactured or fabricated with specifications for use with a range of piping or pipeline sizes (e.g. 14’’-20’’ or 36’’-48’’) and use complementary sized stopping heads.
Plugging heads are a varied technology, the selection of which hinges on the type of pressure vessel, piping, or pipeline at hand; selections are available for every material type and size of piping on the market, for commercial or industrial application. Though several common stopping heads have persisted throughout decades of use, they have all benefited from technological enhancement.
A pivoting plugging head is among the oldest employed, yet most widely used for its effectiveness, simplicity, and reliability. Folding headline stoppers can be used with a reduced branch hot tap, requiring a smaller entry point into the piping than a pivoting head.
There are well over a dozen widely used techniques for line plugging or stopping – including Sure-Stop, HTP Stop, freeze stops, triple line stops, positive sealing stops, inflatable stops, across-the-header stops, and many other specialities stops; these techniques are custom services for specific operations, and not as commonly employed as a double block and bleed line stop, regularly used for isolating a section of piping for work.
5 Performing A-Line Stop While Remaining in Service
Though line stopping is occasionally used as a single or emergency valve, to cease transport of a commodity and abandon a shutdown, it is most often employed with multiple hot taps, a pair of line stopping machines, and a bypass line. Engaging in a line stop operation helps a prospective company:
- Avoid Interruptions to Service
- Avoid Shutdowns and Associated Costs
- Prevent Emissions
- Prevent Loss of Product
- Provide Engineered Modifications
- Provide Increased Safety
- Provide Maintenance
- Reduce Operating Costs
5.1 Bypass Lines
Whether a few feet or a few miles, simple bypass lines are critical for companies wishing to stay in service throughout remedial work and modification. A bypass line has a simple function initially; maintain uninterrupted transportation of commodities. Several industries will opt to keep these bypass lines in place, as they often have a degree of utility with certain products.
Water lines, steam pipes, production facilities, and sewer systems frequently make use of bypass lines as a type of manifold or trap; in the case of municipal water supply, a bypass creates the possibility of diverting flow around a break, blockage, repair, or other issues. This application can provide a timely and secure flow of water, despite difficulties with infrastructure. Sewage or similar bypass lines may require a pump to move material through the line, yet they accomplish the same goal of continuing service, long after their installation.
Completing the necessary (usually four tapping points) hot taps allows the installation of a bypass line and the requisite valves for saddling up a pair of line stopping machines. Once the bypass line is in place and the line stopping actuators are fitted with housing, the line stopping procedure can begin in earnest.
5.2 Line Stopping Service
Selected far in advance of the procedure, the machine, housing, and accompanying components are chosen for their application to the unique circumstance of a given pressure vessel. Bolted to a line stop housing of appropriate length, the line stop actuator is secured to a line stop valve. Sandwich valves are the optimal choice in a line stopping operation, as they keep the travel distance for an actuator to the bare minimum.
Once actuated, the machine pushes the plugging head into the piping or pipeline. Pivoting-head stoppers feature a small wheel that makes contact with the pipe wall. When contact is made, the head rotates into the direction of the flow to form a leak-proof barrier, redirecting flow into the bypass line. At the same juncture, the second line stop machine performs an identical function, safely isolating the flow in a bypassed section of piping and effectively forming a temporary double block and bleed valve. Double bleed and block valves hold a particularly important role in oil and gas facilities, though they are broadly used across industries with piping to isolate sections for work on machinery or other aspects of the pipe system.
For more on double block and bleed (along with double block and isolation) valves, click the links below.
Introduction to Double Block and Bleed Valves
True Meaning of Double Block and Bleed
Left with an isolated section of the pipeline, containing product, bleeding or depressurizing must take place. Venting the isolated section of piping can take several forms, depending on the substance contained within, sometimes a temporary flare is used, other times the material may be piped into a containment vessel. This isolated section of pipeline is now available for extensive modification, replacement, or repair – while the pipe system remains incomplete operation.
6 Remedial Work and Modifications
Skilled and experienced crews always begin with the end in mind – ends that always include considerations for the anticipated remedial work. Complex systems such as those found in multi-product pipelines may require the addition of maintenance facilities, such as launching and receiving stations for pigging, pipe repair, complete replacement of pipeline sections, or any other modifications, including but not limited to:
- Valve Fitting
- Valve Replacement
- Decommissioning
- Leak Testing for Recommissioning
- Cold Cutting
- Pipe Welding and Weld Repairs
- Consulting Services
- Non-destructive Testing
- Risk Assessment
- Whole Site Procedures
- Redundant Line Sealing
- Relocations
- Retrofits
- Establishment of Routine Maintenance
After remedial work or other modification, the stopping heads are removed and completion plugs are set in place. These plugs seal at the flange on the pipe fitting, allowing removal of the gate valve. Once the valve is removed, a blind flange is securely installed, finishing the operation.
6.1 Pipeline Repair
Throughout the life of a pressure vessel, natural wear and tear necessitate the need for regular maintenance. Immediate intervention is required in instances where substantial damage is sustained to pipe systems. These situations call for a swift response with safety as a priority to prevent loss of containment. Isolating sections of piping with hot tapping and line stopping is a routinely indexed industry-standard put into frequent use around the globe.
A host of meticulously drafted regulations and high industry standards are closely observed during these operations. Once the isolated section is depressurized and ready for work, the required work is undertaken without hesitation. Cold cutting of the isolated section can begin, in the event of a replacement section of piping or pipeline; welding repairs, valve replacement, and other remedial work are safely completed.
6.2 Pipeline Modification
Modifications to pipelines or piping can include an array of systems, devices, or improvements to a running pipeline, each of which requires a skilled hot tapping team and the requisite knowledge to carry out these often highly beneficial and often necessary modifications.
Pipe systems are often comprised of relatively simple configurations, though this is not always the case. A veritable panoply of modifications is available once a double block and bleed are established. Retrofits, relocations, and maintenance additions are performed at this stage. Full site procedures can now take place while service continues, regardless of size or complication. Creating facilities for routine maintenance such as launching and receiving bays for pigging is an option, while consultation and extensive testing can freely move forward without impingement.
7 Knowing Parameters: Pipelines and Piping
A properly trained, experienced, and equipped crew can enact quick and reliable execution of both hot tapping and line stopping services on nearly any pressure vessel. The preparation for a hot tapping or line stopping job is both serious and thorough, as mistakes in some instances could be injurious or fatal in extreme cases. More than adequately prepared for, these parameters are checked in triplicate, if not more, as a standard operating procedure, to ensure the highest degrees of adherence to quality control and safety protocols.
Adapting underlying principles to a given scenario is the source and substance of engineering as a discipline. Adjusting techniques, machinery, and materials to adapt to a job are commonplace for these seasoned professionals; despite the routine nature of such changes, expert engineers know that the key to successful operations is to never underestimate the importance of these subtle changes, to ruthlessly observe the research, planning, and preparation for the job.
Hot tapping and line plugging projects are highly specific by nature. The tools and equipment used for each operation can be ordered from manufacturers or fabricated as needed. Manufacturers can be sourced for any number of fittings, valves, machines, pilot bits, or anything else required for these operations. Fabricating these tools is also routine, boasting the added benefit of being cost-effective and capable of providing a large degree of adaptability for both parties. Specialized for operation within finite ranges of size, temperate, and pressure, each tool and corresponding aspect of hot tapping and line stopping is planned for, configured, and accounted for at every step in the process.
8 Here to Stay
It is with the advent of such efficient and effective methods, safely enacted, that modern industry continues to thrive. This technique, almost a century old, is more relevant to energy systems at the present day than ever before. As the technologies used in these procedures become increasingly advanced, and techniques further refined, the degree of safety and reliable execution rises. The inevitable result is that the use of hot tapping and line stopping is growing across every sector it applies to.
Aside from the cost-saving practicality of hot tapping and line stopping, these practices represent a significant benefit to the environment. That benefit in the environment comes from a reduction of emissions associated with the venting of miles of pipeline necessary for cold tee shutdown procedures. This sort of environmental damage alone would likely dissuade most prospective parties from accommodating historical engineering practices. If, however, it did not – the enormous sum of expenses that arise from shutdowns, disruption of workers, lack of service to customers, and added risk posed to employees – through unnecessary transportation and installation using additional equipment – should more than serve as convincing arguments.
9 Hot tapping: Further Reading
For details on special fittings, components, and techniques involved in hot tapping and line stopping, investigate the Submenu Specials on this informative website:
10 Related Topics
Hot Tapping – Advice on Successful Pipeline Tapping
Cathodic Protection Case Study – Padma Bangladesh
11 Sources
Full Flow High-Pressure Hot Taps: The New Technology and Why It’s Indispensable to Industry or
Use of Hot Taps for Gas Pipelines Can Be Expanded
EPA.gov – Using Hot Taps For In-Service Pipeline Connections
