OCTOBER 201326

For pipe cutting or weld preparationtasks related to maintenance ornew construction, there are prima-

rily two different methods commonlyused. The first is heat (thermal) cuttingwith subsequent hand grinding, and thesecond is portable machining, popularlyknown as cold cutting, which produces aweld ready surface — Fig. 1.

Reasons to Choose ColdCutting

While each has its adherents, cold cut-ting and beveling is considered by manya superior method due to its precision andinherent safety advantages. Machiningeliminates the risks associated with open

flame torch cutting, particularly impor-tant wherever volatile hydrocarbons arepresent. The cold cutting method alsoeliminates the undesirable heat-affectedzone (HAZ) created by thermal cutting,altering the molecular structure of themetal. Due to these factors, more indus-tries are specifying cold cutting as part oftheir project bid process.

Cold cutting in its simplest terms usesa portable machine tool to cut or prepprior to welding or flange assembly. Weldprep can take multiple forms: beveling,compound beveling (with two or morebevel angles), J prep, counterboring (ma-chining the inside of the pipe), facing(machining a square edge), and flangefacing (machining the mating surfaces ofbolted flanges) — Fig. 2.

Form Tooling vs. SinglePointing

There are two basic types of portablemachining, form tooling and single point-ing. Form tooling uses shaped tooling (orcutting bits) to create the final contouror profile of the finished prep. It tendsto pull larger chips and requires addi-tional machine rigidity and power thansingle pointing. The benefits of formtooling are it can be faster than singlepointing and may be easier to set up andoperate for a less experienced operator— Fig. 3.

Single pointing refers to machining,using the point of the tooling to take afine cut and pull a smaller chip. The ben-

Cold Cutting: A Clean and Repeatable Technology

MARK LESKA is Senior Marketing Coordi-nator, ITW Orbital Cutting and Welding,E. H. Wachs® (www.ehwachs.com)

Industrial Products Division.

Portable machine tools for coldcutting have many advantages forend prepping pipe prior to welding

BY MARK LESKA

Fig. 1 — Cold cutting produces a precise,

repeatable weld ready finish in a single

step.

Fig. 2 — Typical weld preparation profiles. Many profiles are only achievable by

machining.

27WELDING JOURNAL

efits of single pointing are the ability tomachine heavy wall or high-alloy mate-rial that tens to resist form tooling, andthe versatility of creating custom profiles.Another benefit is the choice of using a machine tool with a smaller power requirement.

In addition, single point cutting bitsare generally less expensive than formtooling cutting bits. They are often avail-able as an insert bit and holder arrange-ment, with multiple cutting points offer-ing a lower cost per cut. By its nature,single point machining tends to havelonger cut times than form tooling, andin certain instances may require set upcalculations by the operator to success-fully create the final prep.

Machining Technologies

Machining produces the consistent,repeatable weld preps needed to ensureweld integrity, critical to timely and prof-itable project outcomes. Machining ingeneral utilizes a wide range of technolo-gies to accomplish various tasks. Thesemachining technologies include lathe,milling, reciprocating, abrasive, chiplesscutting, drilling, and threading. No sin-gle technology is best for all applications,with some projects or tasks employingmultiple technologies. Portable machin-ing also offers the ability to apply vari-ous remote control and automationschemes where required.

Lathe

Lathe machining offers great accuracyand repeatability by utilizing a rigid, ro-tating frame with fixed tooling. Lathecutting and beveling is used where a proj-ect requires 360-deg machining of objectssuch as tube, pipe, vessels, cylinders, andconical objects. Lathe cutting producesa finish that in years past was only achiev-able in a well equipped machine shop.The best known pipe-cutting machinetool using lathe technology is the splitframe, a rotating ring pipe cutter andbeveler named for its ability to “split” inhalf for mounting to inline pipe.

Machining with a split frame (whichmay also be referred to as a "clamshell")is highly versatile. Properly configured,it can be used for cutting, beveling, com-pound beveling , counterboring, facing(or squaring), and flange facing. With itscomprehensive group of accessories, thesplit frame becomes a complete, inte-grated machining system that can tacklemost field machining tasks — Fig. 4.

Fig. 3 — Form tooling offers ease of setup and operation.

Fig. 4 — Versatile split frame machining systems utilize lathe technology to deliver per-

fect preps.

OCTOBER 201328

Milling

Milling utilizes a rotating cuttermounted to a carrier that follows a lin-ear or radial path. Compared to lathe ma-chining, milling produces fine chip de-bris and is not limited to 360-deg opera-tion. This is particularly useful for local-ized machining of pockets or windows,or partial segmentation. Milling opera-tions include cutting, beveling, facing,and grooving.

The modern market for pipe cold cut-ting technology goes back to 1949 withthe introduction of the Trav-L-Cutter®by E. H. Wachs. It is a portable millingmachine designed to cut, or cut and bevelsimultaneously, on most pipe materialsand schedules.

Reciprocating

Reciprocating cutting utilizes astraight blade moving in a repeated for-ward and backward motion to achieve thecutting action.

The advantages of reciprocating sawsare their relative simplicity and ease ofset up and operation. An example of thistype of reciprocating saw is the Guillo-tine®, which cuts horizontally, vertically,

or anything in between with an ellip-tical cutting motion that lifts theblade on the return stroke, enhanc-ing cutting efficiency and minimizingblade wear.

These saws can be configured withremote control with auto feed andauto clamping operation for subseaor hazardous environments.

Chipless Cutting

Chipless cutting, also known asforeign material exclusion (FME) isdesigned to prevent cutting contam-inants from entering the workpiece.Chipless cutting is often used in foodand dairy, high purity, and powergeneration applications where metalshavings cannot be tolerated. In sim-ple terms, FME utilizes a sharpedged wheel that orbits while inwardpressure is applied to sever (cut) thework piece, much like a householdcan opener. Other examples wherechipless cutting might be specifiedare hot cells, semiconductor, and de-activation and decommissioning(D&D) activities related to nuclearfacilities, chemical agents, and ex-plosive munitions.

Fig. 5 — One of the hottest technologies in cold cutting is abrasive cutting diamond wire saws.

Fig. 6 — Automated cutting technologies used

for demilitarizing WWII aerial bombs in Guam.

To illustrate, the U.S. Department ofDefense needed to destroy a WWIIstockpile of chemical agents stored in-side steel, cylindrical ton containers (TC)at a military storage facility. The projectrequired the TC to be remotely severedwithout generating additional contami-nates. Wachs’ FME technology helpeddestroy over 1800 TC, successfully end-ing over 60 years of agent storage at thefacility.

Abrasive Cutting

Abrasive cutting utilizes a hard ma-trix material bonded to the leading sur-face of various shaped cutting end effec-tors. The newest machine utilizing indus-trial abrasive cutting is the diamond wiresaw (DWS), which cuts with a diamondmatrix cable rotating at high speed, fedinto the workpiece with controlled force.Diamond wire cutting is useful where therisk of material collapse, known as com-pressive cutting, exists.

It’s the best solution when cuttingmixed material types such as concreteand steel, which tend to quickly dull con-ventional saw blades. In addition, DWSset up quickly, making them useful fordestructive cutting — Fig. 5.

Drilling and Threading

Drilling is a cutting process that uti-lizes a rotary cutting tool (drill bit) thatis advanced into a workpiece to cut orbore holes, or remove material to enlargea hole. Threading is a rotary cutting toolused to create screw threads. Traditionalhydraulic powered industrial drills fordrilling and threading are manufacturedby E. H. Wachs, plus a line of specializedsubsea drills.

Utilizing two hydraulically poweredopposed drills, the subsea drill is de-signed to drill inline holes for pin inser-tion used for installing solid rigging bars.This procedure facilitates decommission-ing and removal of structures such asmultiple string casings and oil platformlegs in near shore and subsea applica-tions, so they can be safely lifted in larger,stable assemblies.

Cutting Automation

Automation technologies can be ap-plied to cutting processes where humaninteraction is difficult or impossible, suchas zero visibility, radioactive environ-ments, explosive environments, and deep-water subsea operations. Automation op-tions can include remote, topside or re-

dundant controls, automatic feed, auto-matic clamping, ROV power and control,up to complete sequence automation withsystem integration — Fig. 6.

Repeatable Results

Properly machined weld preparationsare a vital prerequisite to achieving theprecise, high-integrity welds required intoday’s modern industries. Cold cutting,with subsequent or simultaneous bevel-ing, produces the repeatable weld prepsthat contribute to weld integrity.♦

29WELDING JOURNAL

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