INTRODUCTION CHAPTER 1 1.1 Accepted Industry Practices For Sheet Metal Lagging  First Edition 1.1 INTRODUCTION 1.2 SCOPE Thisdocumentcontainsacceptedpracticesforthefab- rication and installation of sheet metal lagging. This document serves to establish standard methods to fab- ricate and install sheet metal lagging systems. This document does not provide designs nor does it address safety issues. While it is not practical to include every conceivable lagging detail, most commonsituations areaddressed. As in the case of all design, construction and installa- tion procedures, proper engineeringjudgment mustbe exercised in conjunction with the specific engineering anddetailinformationbeingfurnishedbythedesigner. 1.3 USES Lagging is used to cover and protect insulated areas of equipment. Fabrication practices are provided herein to illustrate the requirements of the configurations most commonly encountered such as boiler walls, flues, ducts, precipitators, bag houses, selective cata- lytic reduction systems, air heaters, economizers, scrubbers, wind boxes, fans, etc. and to provide suffi- cient examples that reflect industry practices for lag- ging design and application. Although standardized componentsofanygivenlaggingdesignmayberepre- sentative of industry practices, the lagging system it- self shall be individually designed for the particular installation, its configurations and its operating re- quirements. 1.4 TERMS AND DEFINITIONS 1.4.1 Glossary See the Glossary for a complete list of terms and defi- nitions related to sheet metal lagging. 1.4.2 Selected Terms and Definitions 1.4.2.1 Lagging A sheet material, typically steel or aluminum, used to cover a variety of types of insulation. Sheet metal lag- ging ranges in thickness from 20 gage (1.01mm) to16 gage (1.61 mm) for galvanized steel and 0.032 in. (0.81 mm) to 0.063 in. (1.60 mm) for aluminum, and generallydoesnot includea vaporbarrier. Bothribbed and flat sheets are used. Thinner or thicker materials may be selected at the discretion of the specifier. All sheetmetallaggingshallbesufficientlystrong anddu- rable to protect the underlying materialsfor thedesign life of the lagging. 1.4.2.2 Cladding Anambiguousandarcanetermalsosometimesusedto describe sheet materials that cover insulation. In the sheet metal industry, “cladding” has traditionally re- ferred to a protective metallic coating installed over, or bonded directly to, thermal insulation. This is pri- marily with applications involving round industrial duct. A 1999 SMACNA survey of members revealed multi- ple and potentially confusing uses of terms that varied by region. For the purposes of this document, the term “cladding” will not be employed, and in the interests of unifying the industry’s terminology, “lagging” will beusedexclusivelyinthisandfutureSMACNApubli- cations. 1.4.2.3 Jacketing A light gage covering material (usually over pipe in- sulation). Jacketing refers toa steelor aluminumsheet and ranges in thickness from 0.010 inch (0.26 mm) to 0.024 inch (0.61 mm) thick. A factory-applied mois- ture barrier is usually included on the back or under- side of the jacketing material. 1.4.2.4 Casing Ifthethicknessofthesteelcoveringmaterial isgreater than 16 gage (1.61 mm), it is not considered lagging but is referred to as “casing”. 1.5 PURPOSE The purpose of this document is to establish accepted industrypracticesfor sheetmetal laggingconstruction and installation. Lagging, as previously defined, is the material, typically steel or aluminum, ribbed or flat, used to cover insulation especially on large flat sur- faces such as boiler walls, flues, ducts, precipitators, bag houses, selective catalytic reduction systems, air heaters, economizers, scrubbers, wind boxes, fans, etc.