Nearly two years ago Bob Andrews of Childers Product Co. said "My best guess is that ASTM will keep renewing what they have forever." Today, some people may find his comment sadly accurate. His quote, now infamous, appeared in Al Hattal's article "Fabricators, Manufacturers Seek Perfect Fit" in August 1996 edition of Insulation Outlook. The article explored the differences in dimensional tolerances between two ASTM standards: C 450 and C 585, and Andrews' comment was referring to when he thought C 450 would be revised by the American Society for Testing and Materials.

C 585, the "Standard Practice for Inner and Outer Diameters of Rigid Thermal Insulation for Nominal Sizes of Pipe and Tubing (NPS System)," provides dimensional standards for pipe insulation to ensure a satisfactory fit on standard pipe sizes. C 450, "Standard Practice for Prefabrication and Field Fabrication of Thermal and Field Fabrication of Thermal Insulation Fitting covers for NPS Piping, Vessel Lagging and Dished Head Segments," provides dimensions for insulation fitting covers. All dimensions in C 450 are based on pipe insulation manufacture to conform to C 585, and as the 1996 article clearly points out, "The inconsistencies between the two wreak havoc when it comes to standardizing the method of insulation flanges and valves. Even though Andrew was right in his prediction regarding the revision of C 450, don't infer that there has been no action at all. The ASTM C 450 and C 585 committees have been very active in the past year and a half- yet, still no results of tighter tolerances have been achieved.

Most recently, the C 450 and C585 committees met at the ASTM meeting, which was held in Atlanta from April 19 to 23. The two committees met as one tack force, as both tolerance and fabrication standards are dependent on each other.

The main issues of the C 450 and C 585 committees are the following:

1. C 585 represents specification for the dimensional tolerances of each insulation material.
2. C 585 has no tolerances to pipe insulation outer diameter
3. C 585 insulation sizes do not have to "nest"
4. C 585 does not address concentricity of pipe insulation
5. C 450 governs dimensions for fitting fabrication, however, fittings may not fit metal or PVC covers if pipe outer diameters are too large
6. There exist multiple industry standards for number of elbow miters per fitting

TOLERANCES IN NEED OF CHANGE

A major change, and a much needed one, has taken place within C585. Each product standard, such as fiberglass, calcium silicate, perlite, mineral wool, polyisocyanurate, elastomeric, styrofoam, phenolic, now recognizes C585 for dimensional tolerances for pipe and tubing outer diameters. Prior to this, each material standard represented its own manufacturing tolerances. This change allows the battle for tolerances to ultimately rest within one standard: C585.

There are multiple tables for dimensional tolerances within C585. Tables 1 & 2 refer to inner diameters of pipe insulation, Tables 3 & 4 refer to outer diameters of pipe insulation, Tables 5 & 6 to the thickness of insulation and Tables 7 & 8 refer to jacketing. Sounds simple enough, doesn't it? Comprehensive? But what do the numbers within these tables really represent? What has been adopted through the years at ASTM?

The standard practice for C585 is intended as a dimensional standard for preformed rigid thermal insulation of pipes and tubing. The purpose of this practice is the following:

• to ensure satisfactory fit on standard sizes
• to accommodate radial expansion of pipes and tubes which are heated after being insulated, and,
• to minimize the number of insulation sizes and thicknesses to be manufactured and stocked.

C585-4.2 clearly states "While insulation may be manufactured to these recommended dimensions, care should be exercised in attempting to nest layers of different materials, or layers supplied by different manufacturers. Individual manufacturing processes may operate at slightly different tolerances. While the product will fit the pipe, it may not readily nest as the outer layer between the different materials or with different manufactures. Care should be exercised to determine these differences before specifying or ordering nesting sizes."

What is the real problem with C585? "There are no tolerances to Table 3A Outer Diameters of Insulation for Nominal Pipe Sizes." As pointed out by George Barnett of Stone and Webster, "Most people have inadvertently looked to the numbers within Table 7A "Outer Diameters of Insulation for Nominal Pipe Sizes" as the maximum outer diameter of the pipe insulation. However, Table 7A refers only to jacketing. Table 3A governs pipe insulation and no maximum tolerances have been set."

NESTING PROBLEM ADDRESSED

"If we follow the current dimensions and tolerances in ASTM C585 Table 1, along with the A.P.I. pipe tolerances, the pipe insulation will not nest. From a dimensional aspect, this problem must be fixed." Joe Bhavsar states, "The question is the re-tooling of dies, if required, could be very costly for the manufacturers. Because of that, we are trying to come up with new tables and new dimensional tolerances in conjunction with the manufacturers for an optimum solution on nesting."

The proposed Table 1 (not included in this article) "Inner Diameters" creates a gap to allow for the thermal expansion of pipes based on the A.P.I. allowances for piping tolerances on the inner diameter of the insulation and for the outer diameter of insulation to allows nesting of oversized pipe insulation with the tolerances listed in Figure 1 applied to Table 3A.

The proposed tolerances to Table 3A and proposed revision to Table 1 were voted down by the manufactures at the meeting in April. They voted to rework Table 3A with the following changes to tolerances shown in Figure 2, and, to rework Table 1 based on their die dimensions.

The result of this vote is that pipe insulation will not nest. Too large of tolerances will not allow nesting of pipe insulation due to the larger outer diameters of inner layers. This problem is compounded for the materials installed on process lines which require multiple layers and results in a dimensional problem when mitering elbows need to fit in stamped covers.

At this point, nesting sizes of Fiberglass, Calcium Silicate, Mineral Wool and Perlite are only guaranteed to fit when in fact the insulation is ordered to nest. A purchaser may not assume that the 2 X 2 will fit inside the 6 X 2 ordered from the supplier, unless it has been specifically manufactured to nest.

Figure 3 illustrates this, using the sizes mentioned earlier from Figures 1 and 2, compared with the proposed revisions.

How much of a problem is this? For many distributors or contractors who supply or use pipe insulation that is installed on moderate-ranged temperature systems, there is no problem. Insulation is not typically double layered.

Additionally, this type of dimensional problem is not typically found in the insulation materials supplied by fabricators, such as cellular glass, isocyanurate, styrofoam or phenolic. Fabricators follow ASTM C 585 Table 3A which is the same as the recommended outer diameter chart in ASTM C 450. As there are no tolerances in either specification, the saw blade cut becomes the tolerance. The fabricator, to realize maximum material usage, primarily provides all sizes as nesting sizes.

For the companies who provide pre-manufactured insulation that is installed on cold applications, or on the higher process temperature systems where multiple layers accommodate the expansion and/or the contraction of materials, nesting becomes an issue. Does the contractor wait until the material is available? Or, does he(She) "make do" with the material supplied from a distributor's inventory? What if one layer was manufactured from the high side and the other layer to the low side of the current tolerances? How tight did the joints fit? Was any extra labor incurred?

Many of the PVC fitting covers sold are installed over non-rigid insulations, so the tolerance issue becomes a problem primarily when PVC is installed over rigid insulation. The metal manufacturers find that their products are often installed over rigid insulations. Some metal manufacturers have already anticipated the renewal of C 585 without changes to tolerances. To reduce the number of complaints, they have to voluntarily increased their fitting outer diameters to accommodate some of the allowable larger sized pipe coverings being used to miter elbows.

REVISED MITER TABLES PROPOSED

The C 450 committee, chaired by John Kalis of Kalis Engineering Company, recently completed a study on the miter points of elbows. The study was conducted by committee member, Gary Sproule of Sproule Manufacturing. The issue? "There are multiple industry practices being used other than as provided in ASTM C 450. Why? Less miters equals less labor to fabricate a fitting. Typically, this is not a problem if the contractor makes his own gored metal covers with the same amount of miters to match the insulation gores. However, if premade metal or plastic covers were purchased, these covers have been produced to fit the amount of gores or miters. The result is that the insulation may not fit the cover. Compounding this problem of the fit of miters may be the maximum outer diameter of the insulation supplied."

According to Gary White of Taylor Insulation, the current president of the Midwest Insulation Contractors Association, the concept of revised miter tables has also received support from MICA. MICA has its own miter schedule in the National Commercial and Industrial Insulation Standards manual. This manual is published by MICA and sold through the National Insulation Association. According to White, "The intention is to ultimately have only one standard of fabrication. The fourth edition is currently under re-write. We do not know at this time if the miter issue will be addressed. The new release is schedule in October of 1998. It will be available in both print and on CD Rom."

Gary Sproule's study (see Figure 4) is a blend of the C 450 and the MICA Tables. Figure 4 identifies the current number of miters required in C 450 and the proposed number of miters for a long radius 90-degree elbow. It is based on having a maximum of 5/32" at the peak of the miter joint.

According to Gary's calculations, (see Figure 5) certain dimensions will allow clearance for installing the 2-piece metal ell-jac type fitting over the mitered insulation elbows. Some sizes will require more miters than are currently identified in the C 450 chart, while other sizes have reduced the number of miters required.

To ensure that the new proposed C 450 miter chart will work, it is based on the new proposed tolerance changes( see figure 1) to C 585 Table 3A "Outer Diameters of Insulation for Nominal Pipe Sizes." These tolerances were developed during the last 18 months at the task group level of ASTM C 450 and C585. Also, a new Table 1 "Inner Diameters of Insulation for Nominal Pipe Sizes" (chart not included in this article) was prepared by Joe Bhavsar of ABB Lummus, the C 585 chairperson, and presented in April meeting.

TOLERANCE BATTLE CONTINUES

What else is wrong within the dimensional tolerances of ASTM C 585? According to Joe Bhavsar, " The current standard does not address the concentricity of the pipe insulation. This means that the product does not have to be the same thickness from one end of the section to the other. Within C 585, the average measurement of a pipe section, through any variances in thickness of the pipe section, may not detect that the piece is not concentric. This needs to be addressed in future meetings."

In light of the urgency to renew this standard, the committee has decided there will be no changes to the C 585 ballot. The work to tighten tolerances will continue.

Gary Sproule states, C 585 Table 1 lists inner diameters and tolerances for those inner diameters while Table 3A lists outer diameters with no tolerances. Table 7A is used exclusively for jacketing purposes, not manufacturing purposes. I believe that C 585 should be submitted for another ballot with the proposed tolerances for 3A as set forth by the manufacturers at the April meeting and has been discussed the past 18 months. Although the tolerances could lead to nesting problems ( see Figure 2), they would be a step in the right direction. I believe that all manufacturers should continue to tighten tolerances when building (re-building) molds. The next revision to the outside diameter tolerances will hopefully eliminate nesting problems.

In conclusion, the C 585 Committee should work to add tolerances to Tables 3A, 3B, 4A, and 4B with the goal of a better fit between inner and outer diameters of pipe insulation. Tables 5, 6, 7A, 7B, 8A and 8B should be eliminated as they are not relevant to the dimensional tolerances. The committee must work with the manufacturers to identify just what tolerances are being met and what could be achieved to solve the inconsistencies in the adopted standards.

With all the consolidation going on in our industry, manufacturers are upgrading and must continue to perform routine maintenance during operation. The task group would like to see a move toward tightening tolerances, instead of the continual renewal of existing tolerances which do not nest.

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