Stanley Yokell, P.E., Fellow of the ASME

Books by Stanley Yokell

2011-10-22T18:16:00.000-07:00

Viewers if this blog can purchase an illustrated print copy of An Old Timer's Scuba Tales, by Stanley Yokell from Amazon.com.

Stanley Yokell's novelette, "House of Mirrors" was published under his pen name Stanley Israel. It is available for purchase on Kindle and Nook and in paperback from bookstores, Amazon.com.

Stanley Israel's anthology, "Love, Sex and Erotica" will be published later this year.

Note to readers of these books

The genesis of House of Mirrors was a slip of the finger when I was searching for a book to read on my kindle. I inadvertently clicked on what was portrayed as an erotic story, mentally seeing the words as an exotic story. What I downloaded was a truly crude bit of pornography, written in language with which I am not comfortable. It was essentially street language that described sex acts in the crudest way, using crude language. I deleted it from my kindle.

That night, I began to think that over the years I have on occasion read erotic books, beginning as a boy with D. H. Lawrence’s “Lady Chatterley’s Lover” and later on one with a semi-erotic them “Being There” by Jerzy Kosinksi that was made into a movie starring Shirley McLane. I conflated that thought with the notion that I could write a more interesting erotic story than what I had inadvertently downloaded to my kindle. And that I could do it without using street language to describe self-love and other forms of amorous activity. I let my imagination rove and “House of Mirrors” is the result. This little book is the result. Subsequently I wrote the stories in the Anthology, "Love, Sex, and Erotica", which should be available for purchase shortly.

I submitted these works under my pen name, Stanley Israel to VP Publications and their subsidiary sent me contracts to publish the works. They are written under my pen name to avoid embarrassing family and friends who might be appalled that a man of my age and profession has and is capable of expressing such thoughts. Readers who might be offended by frank discussion of sexuality should not buy these books.

Stanley Yokell's murder mystery "Murder at Plato House" will be published later this year.

Stanley Yokell's autobiography "A Happy Life", has been published by Amazon.com. It is available on Kindle and in paperback from Amazon.com and from some bookstores.

Edith Yokell's book, "My Life Stories" has been published by Amazon.com. It is available on Kindle and in paperback from Amazon.com and from some bookstores.

Stanley Yokell's book, "A Working Guide to Shell-and-Tube Heat Exchangers", McGraw-Hill, 1990 is out of print but used copies may be available on Amazon.Com.

"Tubular Heat Exchanger Inspection, Maintenance and Repair" written with Carl F. Andreone remains available from McGraw-Hill and other sources.

PRESSURE TESTING FEEDWATER HEATERS AND POWER PLANT AUXILIARY HEAT EXCHANGERS

2011-07-24T06:21:00.001-07:00

On July 20, 2011, the ASME published online Stanley Yokell' article "Pressure Testing Feedwater Heaters and Power Plant Auxiliary Heat Exchangers," in the Journal of Pressure Vessel Technology (Vol.133, Iss.5).

Viewers can access the article at:

URL: http://link.aip.org/link/?JPV/133/054502
DOI: 10.1115/1.4003468

ASSURING TUBE-TO-TUBESHEET JOINT TIGHTNESS

2011-07-24T06:19:00.000-07:00

Stanley Yokell presented his paper Assuring Tube-to-Tubesheet Joint Tightness and Strength on Wednesday, July 13, 2011 at the ASME Power Conference in Denver, Colorado. Readers who would like a copy of the PowerPoint presentation should request one by email to Info@mgt-inc.com.

A FEW TIPS ON CLOSED FEEDWATER HEATERS

2011-04-15T18:09:00.000-07:00

In response to many inquiries about operating and troubleshooting closed feedwater heaters, we offer the following from the chapter "Achieving Reliability" of the course notes of our coppyrighted course, "Closed Feedwater Heaters-Mechanical Aspects":

Symptoms and Possible Causes of TTD and DCA Temperature Changes,

TTD Greater Than Design
A. Noncondensible buildup. Check Operating Vents.
B. Excessive pressure drop in desuperheating zone of horizontal heater.
Check condensing zone pressure.
C. Water leaking into DSH zone. Check for tube leaks or shroud leak in vertical channel head down heater. .
D. Shell side tube corrosion. Check for tube leaks.
E. Tubeside fouling. Check for snake skins inside tubes.
F. Tubeside pass-partition leaks. Check gasket on pass-partition covers or weld cracks at tubesheet.

DCA Greater Than Design
A. Low liquid leve. Check the liquid level.
B. Steam entering the drain cooler. Check for water hammer caused by steam collapsing in DC, It sounds like firecracker popping noise at the shroud welds and through tube holes at the end plate.
C. Horizontal split pass long drain cooler may have low liquid level or steam entering thrugh shoursd weld cracks, Check the liquid level. Check for shroud weld cracks. Listen for water hammer noise.
D. Vertical heater may have low liquid level or steam entering through shroud weld cracks. Check for shroud weld cracks. Listen for water hammer noise.

Check the Position of the Drain Valve Stem.
Knowing the position of the drain valve stem is useful because most drain lines and drain valve ststems are sized to carry much more flow than the normal drains flow rate. Consequently, if a minor tube break occurs, the drain system will probably be able to handle the extra drain flows. It is likely that the excessive drain flow will not have caused a noticable change in the DCA temperature, but it will be idicated by a cgange in the position of the drain valve stem.

Note: The HEI Closed Feedwater Heater Specification requires that the valve stem position should be checjed ib every shift.

Following are failures that can be repaired and ones that cannot be repaired but which can be treated so as to slow the rate of deterioration:

Repairable Feedwater Heater Failures

A. Tube-to-tubesheet joint attachment.
B. Impingement plate failures and damage.
C. Vibration failure damage.
D. Shroud weld failures when the flat divider plate is welded to the arcuate section.

Failures that are Not Repairable But Can be Treated so as to Slow the Rate of Deterioration

A. Tube failure in the top row of the DC in horizontal heaters at the end plate caused by steam entering the DC through the annular spaces betweeb the tube ODs and the tube hole IDs.
B. Tube failures in the top row of the DC in horizontal heaters at the back of the tubesheet caused by failure of the weld joining the DC flat divider plate to the back of the tubesheet.
C. Tube failures in the outer bends of U-tubes caused by vibration.
D. Tube failures in the inner bends of U-tubes caused by Stress Corrosion Cracking (SCC).
E. Tube failures at the back of the tubesheet caused by SCC and/or vibration.

On Line Feedwater Heater Replacemment

2011-03-22T13:59:00.000-07:00

Recently a question was circulated about how to safely install a feedwater heater on line. This consultant simply stated that it is necessary to have double block valves to protect pesonnel. However, Mr. Steven Kidwell,Project manager of Burns and McDonnal made a more informative comment. It is repeated here. This consultant is in complete agreement with Mr. Kidwell.

Here is Mr. Kidwell's comment

Double block and bleed is the only safe way of performing an on-line replacement. And it needs to be on all the pressurized (or vacuum) pipes, not just the mahor ones. The second block can be a spectacle flange to save money, but those spectacle flanges need to be installed ahead of time at an outage.

The other consideration is that normally the heater serves as an anchor for the pipe when the thermal stress analysis is done. If the heater is removed while the pipe is hog, the pipe will spring when the cut is made. So large temporary restraints need to be designed to hold the pipes in place so the new heater nozzles will mate up. Vof feedwater pipes and extraction pipes, these restraints will be massive. Commonwealth Edison pulled this off years ago, but because of the expense involved,they never considered it again.

GENERIC PROCEDURE SPECIFICATIONS

2011-02-10T08:22:00.000-08:00

MGT Inc. offers the service of preparing various procedure specifications using our generic procedure specifications for the following procedures:

Welding tubes to tubesheets whether full or partial strength or seal welding.

Post welding Roller Expanding tubes into tubesheets;

Roller Expanding tubes into tubesheets when tubes are not welded

Hydroexpanding tube into tubesheets;

Hybrid expanding tubes into tubesheets;

Hydro Testing Heat Exchangers and Pressure Vessels in accordance with ASME Paragraph UG-99;

Liquid Penetrant Examination of surfaces; and

Miscellaneous other procedures for nondestructive examinations.

Please contact Stanley Yokell at syokell@mgt-inc.com or phone him at 303-494-9608 or fax him at 303 499 1859 for prices and availability.

Telephone and email Consulting

2011-02-08T09:04:00.000-08:00

Many viewers of this blog are concerned with such things as tube-to-tubesheet joining, examinations of tube-to-tubesheet mockup specimens, hydrostatic testing requirements and procedures, the applicability of TEMA and API Standards, heat exchanger and closed feedwater heater problems such as level control and other drains cooler problems.

Although this blog has much information on these subjects, viewers who need more information or help with specific problems may find it adventageous to engage MGT Inc. for telephone or email consultations.

We are also available to examine tube-to-tubesheet joint specimens, using the digital microscope, and report on the acceptability or lack therof of the specimens.

The rates for such consultations are posted on the MGT Inc. website at www.mgt-inc.com.

MGT is located in the US Mountain time zone. Individuals requiring telephone consultation should be aware of the time differences between this location and theirs.

Inquiriers with webcam capability can use skype to communicate so we can see each other and if necessary view materials as we speak.

ON TUBE EXPANDING AND PERCENT WALL REDUCTION

2010-12-12T15:08:00.000-08:00

Background
Joining tubes to tubesheets and steam drums by mechanically expanding them to create an artificial shrink fit between the tubes and surrounding tubesheet or drum material has been a successful process since the 19th century. In this process, after the tube is inserted into the tubesheet or drum holes, the tube is first enlarged until it contacts the hole surfaces. Enlargement continues with the initial tube distortion elastic and further distortion plastic. After contact with the hole surface, the outside of the tube presses against the inside of the hole and distorts the surrounding metal. The distortion of the surrounding metal may be fully elastic or plastic near the tube and elastic farther out.

Upon release of expanding force, the tube and surrounding metal recover. Recovery is elastic but not to the original dimensions. If the tube and surrounding metal have substantially identical properties, after relaxation, there will be a residual stress field with zero magnitude at the tube I.D. and increasing magnitude to a maximum at some radius in the tube-hole structure, diminishing to zero magnitude farther out. The residual stress at the interface between the tube and hole is the equilibrium stress between the parts equal to an interfacial pressure. If the tubesheet or drum has twice the yield stress of the tubes, distortion of the tubesheet or drum remains elastic throughout the process. If the tubes have a yield stress higher than the tubesheet or drum, the position of maximum residual stress shifts depending upon the tube diameter and thickness. The equilibrium stress at the interface of tube and hole surfaces is lower than for constructions of equal tube-tubesheet or drum yield stresses or in which the tube or drum yield stress is higher that of the tube yield stress.

The axial shear strength of the expanded joint are approximately equal to the product of the tube-hole contact area, the interfacial pressure and the coefficient of static friction for the metal pair.

Although, most expanded joints have historically been made by roller expanding, most investigations of tube expanding have used the concept of uniformly applied pressure inside a capsulated length of tubing in contact with the tubesheet or drum. This simplifies the analysis by eliminating a many variables that define the roller expanding process.

How to Visualize Tube Expanding
The simplest way to visualize tube expanding is to picture an infinite number of infinitesimally thin cylinders in contact with each other. Here it is necessary to define the limits of elastic stress and plastic stress. The stress regime in the tubes will be elastic when the pressure inside the tubes is at the elastic limit as shown in equation (1) and will be plastic at the plastic limit shown in equation (2).
(1)

(2)

Any attempt to apply pressure greater than the plastic limit will be unsuccessful and will result only in extruding the tube end.

Roller Expanding
Now consider that when a rolling tool is inserted into the tube, there is a line of contact between each pin and the hole surface. Thrusting the mandrel into the tube applies greater pressure under each pin than the elastic limit pressure and quickly reaches the plastic limit pressure. Further application of the pin pressure causes the interior cylinders to extrude while applying pressure to adjacent cylinders. As the pressure on adjacent cylinders reaches the plastic limit they begin to extrude. There is a continuum of the pressure regime to the outer cylinders of the tube-tubesheet structure which may be at or less than the plastic limit and where there is no further extrusion. The extrusion is accompanied by tube wall thinning and strain hardening of the tubes. The strain hardening of the tubes prevents relaxation of residual stress during operation of the tubular.

In the 1940s several investigators examined whether the amount of tube extrusion or the degree of wall thinning (expressed as percent apparent wall reduction) would provide suitable parameters for determining the success of the roller expanding process. Because of measurement problems it was determined that percent wall reduction was more suitable and it is widely used as the controlling parameter for achieving joint strength and tightness suitable for the service of the boiler or heat exchanger.

Readers should be aware that although rolling tool manufacturers publish recommended percent wall reductions for various tube-tubesheet metal combinations and tube diameters and wall thicknesses, there is substantially no published literature that relates percent wall reduction to joint shear load strength or tightness. Depending upon the metal pair characteristics, tube diameter and thicknesses, expanding tool manufacturers’ recommended percent wall reduction vary from 5% to 12%.

Most heat exchanger and boiler manufacturers either have informally correlated percent wall reduction with making joints tight enough to be acceptable during hydrostatic testing or have made mockup specimens of tube-tubesheet combinations that represent production equipment to establish suitable percent wall reduction for roller expanding.

In the roller expanding process, shear load strength equal to the tube cross-sectional area times its yield stress is usually achieved in approximately 2-inches of rolled depth. If it is desired to seal the whole depth of thick tubesheets, rolling has to be done in steps (step rolling) and consideration has to be given to the effects of progressive VS regressive rolling (rolling from the outer tubesheet face toward the inner face or rolling from the inner face toward the outer face.

Uniform Pressure Expanding
There are two types of uniform pressure expanding in widespread use in tubular equipment manufacture: (1) applying pressure directly into the tube end with water encapsulated between two seals in a pressure chamber, and (2) exploding an explosive charge contained in a plastic cushioning cylinder inserted into the tube.

In neither process is the pressure or intensity of the charge so high that it causes the inner cylinders to extrude i.e the pressure or force applied is never greater than the plastic limit pressure or force. Rather than extruding the tubes become slightly shortened because of the Poisson effect as the elastic limit is reached and further shortened because of maintaining the metal volume as plastic deformation takes place. The degree of wall thinning expressed as percent wall reduction is considerably less that for roller expanding and is the result of the combination of Poisson effect and volume maintenance.

Although purchasers, not thoroughly familiar with either hydroexpanding or explosive expanding sometimes demand percent wall reduction in the same order of magnitude as are achieved in roller expanding, the typical limit for these processes is about 3%. Excessive pressure or excessively high explosive force tends to distort the surrounding ligaments. There are also limits to the pressure that hydroexpanding equipment can supply. However, both processes have been successful in producing strong, tight joints.

There are two major advantages to uniform pressure expanding: First, tubes can be expanded into the whole thickness of thick tubesheets in one application of pressure or exploding one explosive insert. The strain hardening effect of these processes is not so great as to preclude two stages of hydroexpanding or a second charge of explosive expanding. Two-stage uniform pressure expanding has the advantage that the first stage stiffens the tubesheet by increasing the ligament width by the amount of the tube wall. The second advantage is that there is considerably less residual tensile stress in the transition between the expanded and unexpanded tube. This is advantageous from the fatigue standpoint and also from the standpoint of Stress Corrosion Cracking in tube subject to SCC in the conditions of use.

Hybrid Expanding
Because the strain hardening created by roller expanding resists the tendency of residual stress in the tube joints to relax, combining a first stage of approximately 3% wall reduction by uniform pressure expanding with subsequent roller expanding to the final desired percent wall reduction can confer the benefits of both processes. Hybrid expanding is now widely used in such equipment as intermediate and high pressure feedwater heater manufacture.

ASME CODE REQUIREMENTS FOR PERCENT WALL REDUCTION
In response to the many requests for information about ASME Code requirements for wall thinning during expanding, expressed as percent wall reduction, readers are advised that the ASME COde does not specify percent wall reduction. As stated above, it is the Manufacturer's responsibility to determine the suitable percent wall reduction for the service.

ASME CODE DOES NOT COVER REPAIRS AND ALTERATIONS TO INSTALLED PRESSURE VESSELS

2010-11-16T10:13:00.000-08:00

Our response to many inquiries about ASME Code requirements for repairs and alterations to existing pressure vessels is as follows:

ASME Code jursidiction ends when the vessel is stamped.

Any subsequent changes, major repairs, temperature and/or pressure upratings after the pressure vessel has been shipped are covered by jurisdictional requirements that may invoke such codes as the National Board Inspection Code or similar codes such as those of the API.

The ASME Code does not cover tube plugging or sleeving without regard to the plugging or sleeving method.

In North America, there are no federal code requirements; each jurisdiction, state, province and sometimes county or city may have it own requirements for Code construction and stamping and for repairs and alterations to existing pressure vessels.

Most jurisdictions require repairs and alterations to be done in accordance with the National Board Inspection Code (NBIC), issued by the National Board of Boiler and Pressure Vessel Inspectors.

In addition to publishing the National Board Inspection Code (NBIC), the National Board of Pressure Vessel Inspectors publishes a Synopsis of Boiler and Pressure Vessel Laws, Rules and Regulations.

These publications are available from:

The National Board of Pressure Vessel Inspectors
1055 Crupper Avenue
Columbus, OH 43229-1183
Telephone 614-888-1183
Fax 614 888 9750
Website http://www.nationalboard.org/

CORRELATION BETWEEN % WALL REDUCTION AND TUBE JOINT STRENGTH AND TIGHTNESS

2010-11-06T10:13:00.000-07:00

TUBE EXPANDING - A VERY SUCCESSFUL PROCESS.
Tube expanding has been used successfully for joining tubes to tubesheets of boilers and tubular heat exchangers since the 19th century The history of tube expanding is long and interesting and covers methods such as Prossering, manually driving mandrels with hammer blows and hand rotation, electronic controls of rolling torque inputs, controls for air driven rolling equipment,hydraulically driven rollers with hydraulic insertion of mandrels, direct pressure applications such as explosive expansion, hydraulic expansion, hybrid expansion consisting of a first stage of hydraulic or explosive expansion and a second stage of roller expansion, hybrid expansion consisting of a first stage of either explosive or hydraulic expansion and a second stage of hydraulic after explosive or explosive after hydraulic expansion, inflating balloons inside tubes and compressing polymers inside the tubes.

PARAMETERS - INFORMATION LACKING
The strength and tightness of expanded tube-to-tubesheet connections depends upon the residual interfacial pressure, the tube-hole contact surface area and the coefficient of friction. There is no generally available means for calculating interfacial pressure created by direct application of hydraulic pressure, explosive expanding, roller expanding or combinations of these methods. There is no generally available information on coefficient of friction; it depends upon the surface finishes and the materials of construction of the tubes and tubesheets. Many of us who have worked in this field guess the coefficient of expansion to lie between 0.3 and 0.7 and the few papers on tube expanding that use values of coefficient of expansion generally guess at the mid point of the range or 0.5.

NO CORRELATION OF PERCENT WALL REDUCTION WITH EXPANDED JOINT STRENGTH OR TIGHTNESS
MGT Inc. has very extensive collection of papers on tube expansion including some by Stanley Yokell who also discussed it in his book "A Working Guide to Shell-and-Tube Heat Exchangers", that McGraw-Hill published in 1990. A thorough search of MGT's files and files published on the internet finds that there is no published correlation between percent wall reduction and expanded joint strength and tightness.

NO TECHNICAL BASIS FOR MANUFACTURERS' RECOMMENDATIONS OF PERCENT WALL REDUCTION.
Most roller expanding tool manufacturers publish recommended percent wall reductions for various tube metals, diameters and gages. But they do not and cannot offer a rational basis or bases for their recommendations. The responses to an email to six manufacturers of tube expanding equipment verified that they have no experimental basis for their recommendations. Possibly that explains some of the differences between some of the expanding tool manufacturers recommended percent wall reductions.

Q AND A. WHY ARE EXPANDED JOINTS SO SUCCESSFUL?
The question arises, "How then can we explain the widespread industry experience of consistently and regularly achieving strong tight expanded tube-to-tubesheet joints?"

The answer is that most exchanger manufacturers either formally or informally correlate tests of mockups or data garnered from manufacture of production equipment that produced joints tight enough and strong enough for the intended services.

ASME CODE TUBE JOINT EFFICIENCIES
With respect to Table A-1 of Appendix A of Section VIII Division 1 and Table 4.C.1 of Annex 4.C of Section VIII Division 2, it is generally recognized that the joint efficiencies shown in the tables were put together by people with long experience in tube joining. But there is no experimental work that underlies the joint efficiencies. There are some few papers that investigate such efficiencies but they do not form the bases of the efficiencies listed in these tables.

REQUEST FOR VIEWERS' INPUT
I have been searching diligently to see if there is any information in the literature that correlates percent expansion with joint strength and tightness. But so far with no success. Noting that there are substantial differences between the effects of explosive and hydraulic expansion and roller expansion and that rolling tools vary in the number of pins, shape of pins, slot orientation of mandrels, etc. I question whether the same correlation would apply for the uniform pressure percent wall reductions as for the roller expansion percent wall reductions or that it is possible to predict interfacial pressure produced by roller expanding.

If any reader of this blog has information that would even resemble such correlations I would appreciate your sharing it with me.

MORE ON EXAMINATION OF TUBE-TO-TUBESHEET JOINT MOCKUPS

2010-10-24T11:48:00.000-07:00

A recent examination of a specimen submitted for examination using the VAX digital microscope disclosed serious lack of penentration of tube metal into the grooves and major discontinuities at the interfaces of the tubes and holes. The following illustrate the unacceptable types of discontinuities.

The picture of the straight tube taken at 500X shows lack of contact between the tube and surrounding tubesheet metal.

The picture of the groove shows that tube metal did not fill the groove or contact the bottom of the groove.

TUBE-TO-TUBESHEET JOINT MOCKUPS

2010-10-06T09:34:00.000-07:00

For tubular heat exchangers in which tube-to-tubesheet joint tightness and strength are essential tubesheet mockups are useful in establishing appropriate welding and tube expanding procedures. The mockups must replicate the production tubesheets using tube and tubesheet material of the same specifications as will be used in producing the production unit. The drilling, annular grooving, preparation for welding and welding procedure used to produce the mockup must be those used on the production unit.

Once the mockup has been produced, our procurement specifications require the manufacturer to fill the tubes with a plastic that neither shrinks nor expands as it hardens. After the plastic sets, our specification requires cutting the specimen in the axial direction, making sure that the tubes to be examined are sawed on their centerlines. Our specification requires polishing to a mirror finish (#8).

The examination consists of examining the specimens using the VAX digital microscope at a magnifaction of 25X. We can increase the magnification to 150X to examine suspicious regions. We verify that the weld leak path is at least equal to the tube wall thickness and that te unexpanded gap behind the weld root is as specified. We check to see that the metal deformed into grooves bottoms out and that discontinuities where tube metal crosses groove edges is insignificant. We examine the tube-wall contact to make sure it is intimate and without discontinuities. The following photographs are of the VAX digital microscope, a typical specimen marked by the manufacturer, a weld examination, a groove examiation and the examination of an expanded region.

COMMENTS ON API 660 & ITS RELATIONSHIP TO THE TEMA STANDARDS

2010-09-29T09:03:00.000-07:00

Many questions addressed to MGT Inc. ask for comparisons of API 660 with the TEMA Standards.

EXCLUDED FROM THE SCOPE OF API 660.The scope of API 660 excludes vacuum-operated steam surface condensers and feedwater heaters.

STANDARDS NOT IN CONFLICT.Readers should be aware that these two standards are not in conflict with each other. Indeed, Paragraph 4.2 of API 660 requires construction to conform to TEMA Class R, unless the purchasers specifies another TEMA class.

CONSTRUCTION CODE REQUIREMENTS. Because API 660 is an international standard, it deviates from the TEMA requirement for construction to the ASME Boiler and Pressure Vessel Code (ASME Code), providing instead in its Paragraph 4.1 that the pressure design code shall be specified or agreed by the purchaser.

TUBE-TO-TUBESHEET JOINTS. With respect to tube-to-tubesheet joining, Paragraph 7.6.7 has three classifications of joints:

Strength-Welded Only
Strength-Welded and Expanded
Seal-Welded and Expanded

PARTIAL STRENGTH WELDS NOT COVERED. Users should note that API 660 does not cover Partial-Strength Welded joints as defined in Paragraph UW-20 of Section VIII Division 1 of the ASME Code.

EXPANDED TUBE-TO-TUBESHEET JOINTS. Paragrah 9.10 Tube-to-tubesheet joints subparagraph 9.10.1 of API 660 states, "If roller expanded joits are utilized, the tube wall thicknes reduction shall be in accordance with Table 4." Table 4 provides maximum allowable wall thickness reductions of 8% for carbon steel and low alloy (9% chromium) and non-work hardening non-ferrous tubing such as admiralty brass, 6% for stainless and high-alloy and 5% for titanium and work-hardening non ferrous materials. The table allows a further increase of 2% when agreed by the purchaser.

EXPLOSIVE EXPANDING, HYDROEXPANDING, HYBRID EXPANDING. API 660 does not discuss Explosive Expanding, Hydroexpanding or Hybrid Expanding but does not specifically exclude these processes. For such processes we have found that the maximum wall reductions listed in API Table 4 apply as well.

ANNULAR GROOVES. API 660 does not address annular groove widths and depths, requiring annular grooves only to be square-edged, concentric and free from burrs.

PRESSURE TESTING. API Paragraph 10.3 Pressure testing covers pressure testing. Unlike TEMA Paragraph 1.31 STANDARD HYDROSTATIC TEST, API 10.3 does not specify a hold time for the hydrostatic test. It refers the reader to the pressure design code for the temperature of the hydrostatic test. API Paragraph 10.3.8 limits supplementary pneumatic test pressure to 170 kPa (15 Psi).

2010 VERSIONS OF COURSES ARE NOW AVAILABLE

2010-08-15T12:22:00.000-07:00

The courses, "Closed Feedwater Heaters - Mechanical Aspects" and "Power Plant Auxiliary Heat Exchangers & Closed Feedwater Heaters" have been updated and are now available for purchase.

Each course consists of a set of course notes, suitable for printing in PDF format, a Power Point presentation for viewing in connection with the course notes and a bonus DVD showing a video of the installation of a feedwater heater bundle in the shell.

Prices are as shown on our website at www.mgt-inc.com.

Inquiries Regarding Hydrostatic Testing

2010-07-16T12:50:00.000-07:00

Many visits to this website are from people seeking information about hydrostatic testing pressure vessels.

PRESSURE VESSELS UNDER CONSTRUCTION. The best source of information on this subject for heat exchangers and other pressure vessels under construction is the ASME Boiler and Pressure Vessel Code. Section VIII Division 1 covers the vast majority of pressure vessels. Hydrostatic test requirements are described in its Paragraph UG99 STANDARD HYDROSTATIC TEST. The Code requires that there be no visible leaks but is silent about leaks that would not be visible such as those on the back face of the tubesheets of fixed tubesheet exchangers and feedwater heaters in which the channel is welded to the tubesheet.

The TEMA, API 660 and HEI Power Plant standards require testing in such a fashon that leaks at the tube joints can be detected from at least one side. Be aware that when the channel side is the higher pressure side, such testing will not disclose minute leaks from the channel to the shell because the pressure increments of the pressure gages in common use are too coarse to indicate such leakage by pressure loss.

The purpose of hydrostatic testing heat exchangers and other pressure vessels is to stress the structure to verify its integrity. Although the Code does not permit leakage during hydrostatic testing, the fact that a heat exchanger passes the hydrostatic test is not a guarantee that the tube-to-tubesheet joints are sufficiently leak tight for the service.

Users of fixed tubesheet heat exchangers and other exchangers in which the shell side face of the tubesheet is not visible during hydrostatic testing should be aware that the change in hydrostatic test presssure that would be required to indicate minute leaks is so small that the change in pressure resulting from such weeping will not be visible on the gages typically used during hydrostatic testing. Holding such equipment on hydrostatic test for a long period does not necessarily provide assurance that it is leak tight.

Where tube-to-tubesheet joint leak tightness is essential Users should consider seal or strength welding the tubes to the tubesheet followed by full depth expansion of the tubes with the expansion commencing about 1/2-inch behind the root of the weld. It is prudent to bubble test the joints after welding and follow the bubble testing with liquid penetrant examination. The most effective leak tightness test of tube-to-tubesheet joints is one that uses a mass spectrometer helium sniffer test described in section V, NONDESTRUCTIVE TESTING of the ASME Code. Purchasers should be aware that Manufacturers will not perform leak tests that the ASME Code does not require. Therefore, it is the Purchaser's obligation to specify such leak testing.

Many inquiries ask about the time on which the exchanger must be held on hydrostatic test pressure. The ASME Code does not specify how long the vessel must remain on hydrostatic test pressure. The TEMA Standards require holding the test pressure for a minimum of 30 minutes. The HEI Standard for Closed Feedwater Heaters simply requires testing in accordance with the ASME Code's requirements. The HEI Standard for Power Plant Heat Exchangers and the HEI's Standard for Steam Surface Condensers do not require leak testing beyond the ASME Code requirements too, that is they do not have a minimum time for holding the exchanger under test pressure.

Authorized inspectors do their inspections at a reduced pressure equal to the hydrostatic test pressure divided by 1.3.

INSTALLED PRESSURE VESSELS Users should be aware that the ASME Code's jurisdiction terminates once the Authorized Inspector accepts the pressure vessel and that the ASME Code does not cover inservice inspection. Most jurisdictions require inservice inspection and alterations and repairs performed by welding to meet the requirements of the Inspection Code of the National Board of Pressure Vessel Inspectors (NBIC.

SLEEVING PROCESS HEAT EXCHANGER TUBES

2010-04-16T19:58:00.000-07:00

Chemical Engineering Magazine has published Stanley Yokell's article on Sleeving Process Heat Exchanger tubes in the April, 2010 issue.

Availability of Information

2010-04-03T12:11:00.000-07:00

This site has received many inquiries about such matters as ASME Code and TEMA Standards hydrostatic testing requirements, tube-to-tubesheet weld joint requirements, leak testing and similar matters.

The only authoritative source of information on the ASME Code is the Code itself. We recommend going to the original source rather than websites that discuss the Code.

Tube-to-Tubesheet Welding is covered in Section VIII Div. 1 Subsection B Part UW, Paragraph UW-20.

Section IX covers welding requirements in general as referred to by other Code sections.

Requirements for Tube-to-Tubesheet Joints of heat exchangers in which the tubes stay the tubesheets are set forth in non-mandatory Appendix A. Requirements for tube expanding are in non-mandatory Appendix HH.

Pressure Testing is covered in Paragraphs UG-99 and UG-100 of the ASME Code. Readers should be aware that the ASME Code does not specify a minimum time for maintaining pressure during hydrostatic testing. However the TEMA Standards Paragraph RCB 1.31 specifies holding exchangers on hydrostatic test for at least 30 minutes.

Leak Testing including gas-bubble testing, helium leak (mass spectrometer) testing and other nondestructive testing are covered in Section V of the Code.

If a Code requirements is confusing, you can always follow the Code's format for requesting an Interpretation, Be aware that you cannot expect an answer to a request for interpretation of a Code rule until the request has been assigned to the appropriate committee, the committee has acted on it and it has gone up the chain for approval and the Code Secretary issues the interpretation to the requester.

The TEMA and HEI Standards require conformity to Section VIII Division 1. Viewers of this website should be aware that the ASME Code does not accept TEMA or HEI tubesheet design rules.

Be aware that ASME Code jursidiction ends when the vessel is stamped.

ASME Code jusrisdiction is not covered in the Code readers are refered to Interpretation No. VIII 79-01 as substantiation. Any subsequent changes, major repairs, temperature and/or pressure upratings after the pressure vessel has been shipped are covered by jurisdictional requirements that may invoke such codes as the National Board Inspection Code or similar codes such as those of the API.

In North America, there are no federal code requirements; each jurisdiction, state, province and sometimes city may have it own requirements for Code construction and stamping and for repairs and alterations to existing pressure vessels. In addition to publishing the National Board Inspection Code (NBIC), the National Board of Pressure Vessel Inspectors publishes a Synopsis of Boiler and Pressure Vessel Laws, Rules and Regulations available from:

The National Board of Pressure Vessel Inspectors

1055 Crupper Avenue

Columbus, OH 43229-1183

Telephone 614-888-1183

Fax 614 888 9750

Website http://www.nationalboard.org/

The ASME Code Committee responds to requests for interpretations. Address your inquiry to:

Secretary

ASME Boiler and Pressure Vessel Committee

Three Park Avenue

New York, NY 10016-5990

The ASME Code has specific requirements for submitting requests for interpretation:

Inquiry. Provide a condensed and precise question, omitting superflouous background information and when possible, composed in such a way that a "yes" or a "no" Reply, with brief provisos if needed, is acceptabl. The question should be technically and editorially correct.

Reply. Provide a proposed Reply that will clearly and concisely answer the Inquiry question. Preferably the Reply should be yes or "no", with brief provisos if needed.

Bacground Information. Provide any background information that will assist the Comittee in understanding the proposed Inquiry and Reply.

Requets for Code Interpretations must be limited to an interpretation of a particular requirement in the Code or a Code Case. The Committee cannot consider consulting type inquires such as the following:

1. A review of calculations, design drawings, welding qualifications, or descriptions of equipment or parts to determine compliance with Code Requirements.
2. A request for assistance in performing any Code-prescribed functions relating to, but not limited to, naterial selection, designs, calculations, fabrication, inspection, pressure testing, or installation.
3. A request seeking the rationale for Code requirements.

Viewers with specific questions may call MGT for telephone conversations as set forth in the MGT home page at http://www.mgt-inc.com/.

NOTE ON HEAT EXCHANGER FERRULES AND SLEEVES

2010-02-28T13:03:00.000-08:00

Recent inquires directed to MGT Inc. have revealed considerable confusion about what ferrules and sleeves are and and how heat exchanger users's employ them. The purpose of this short note is to try to clarify the differences between ferruling and sleeving.

Ferrules are used:

to protect tube ends from the effects of turbulence,
to bring a hot tubeside fluid past the inner face of the tubesheet,
to carry tubeside fluid through a ceramic or heat resistant tubesheet coating.

In just about every application, the end of the ferrule that is exposed is flared or flanged over to a small amount less than half the ligament width. Sometimes the flared-over end is welded to the ligament. And in some rarer applications, the inner end of the ferrule is welded to the tube ID. In almost all applications, the ferrule is expanded to intimate contact with the tube - preferably hydraulically but often by roller expanding.

Short sleeves, on the other hand, were developed in the power generation industry to cover discrete tube wall penetrations inside surface condenser tubes. The penetrations may be a considerable distance in from the inlet tube end. So the short sleeve was slid into the condenser tube so as to cover the perforation and expanded to intimate contact, sometimes with the sleeve ends welded to the tube to make sure there was no leakage between sleeve and tube.

Consequently, the definition of a ferrule is a short sleeve, flared or flanged at the tubesheet end and always installed in the tube inlet.

Eventually, full length sleeving was developed to:

Restore plugged tubes to approximately 70% usefulness by effectively restoring the tubes' integrity. The effective loss of surface results from the increased wall thickness and resistance to heat flow across the interface boundary of sleeve and tube.
Restore insurance plugged tubes to service. In the power generation industry, where it is common to monitor the wall thickness of feedwater heater tubes and other tubular equipment tube walls, it is common practice to "insurance plug" tubes with walls thinner than can safely operate without the risk of failure, or if a tube has failed, to plug the surrounding tubes to make sure that jets of high-pressure water escaping through a tube wall penetration has not damaged an adjacent tube. Here again, restoration is only about 70% because of increased wall thickness and the interfacial barrier to heat flow.

For more information on sleeving, see, S. Yokell, "Get more Life Out of Heat Exchangers", Chemical Engineering, January, 2005. A forthcoming article by the author discusses the effects of temperature when sleeves that have a higher coefficient of thermal expansion are installed in the original tubes.

LIFE MEMBERSHIPS

2009-12-02T15:25:00.000-08:00

Stanley Yokell is now a Life Member of the American Society of Mechanical Engineers and the American Welding Society.

ON HYDROSTATIC TESTING HEAT EXCHANGERS

2009-11-14T13:11:00.000-08:00

INTRODUCTION

Section VIII Division 1 of The ASME Boiler and Pressure Vessel Code (Code)[i] requires testing the integrity of pressure vessels by subjecting them to a hydrostatic pressure test of 1.3 times the maximum allowable working pressure (MAWP) corrected for the difference between allowable stress at the test temperature and the design temperature. The Code provides for testing at higher hydrostatic test pressures but most pressure tests are at the 1.3 multiple. For shell-and-tube heat exchangers built to the TEMA

Standards, Paragraph RCB-1.31 Standard Test, the holding period is at least 30 minutes[ii]. The TEMA Standards require testing the shell and tube sides separately in such a manner that leaks at the tube joints can be detected at least from one side.

The Code does not permit any visible leakage through the joints during the Authorized Inspector’s (AI’s) examination during and after the holding period on hydrostatic test pressure. Paragraph UG-99(g) states in part, “Following the application of the hydrostatic test pressure, an inspection shall be made of all joints and connections. This inspection shall be made at a pressure not less than the test pressure divided by 1.3. Except for leakage that might occur at temporary test closures for those openings intended for welded connections, leakage is not allowed at the time of the required visual inspection.” (Italics added.)

This means that the AI must reject any visible leakage of exposed tube-to-tubesheet joints such as weeping around the tube-to-tubesheet connections during testing. Inspection is with the shell side of the exchanger under the hydrostatic test pressure divided by 1.3 and the tube side at atmospheric pressure with the tube-to-tubesheet joints visible.

Tube-to-tubesheet joints of some types of shell-and-tube heat exchangers, such as fixed tubesheet designs and closed feedwater heaters in which the channel is welded to the shell, are visible only from the channel side with the shell side under pressure and the channel side at atmospheric pressure.

The ASME Code’s Paragraph U-99(g) states, “The visual inspection of joints and connections for leaks at the test pressure divided by 1.3 may be waived: provided (1) a suitable gas leak test is applied; (2) substitution of the gas leak test is by agreement reached between the Manufacturer and Inspector; (3) all welded seams which will be hidden by assembly be given a visual examinations for workmanship prior to assembly; and (4) the vessel does not contain a “lethal substance”. This is particularly pertinent for heat exchangers in lethal service because literal interpretation of the waiver would preclude using fixed tubesheet exchangers for lethal service applications. But many such exchangers have been Code stamped and this practice continues throughout the industry.

Users and designers should be aware that the purpose of the Code’s standard hydrostatic test described in Paragraph UG-99 is to test the capacity of the vessel to withstand the design pressure; it is not to determine whether the tube-to-tubesheet joints are sufficiently leak tight to prevent leakage of process fluids with low viscosities through the joints. (Leak rates vary inversely with fluid viscosity.) Users must recognize the hazards of process fluids leaking from the channel into the shell and where hazards exist, specify further leak testing as described in Section V of the Code. This includes the possibility of wiredrawing (wormholing) in high pressure closed feedwater heaters in which a leak of high pressure feedwater through the tube-to-tubesheet welds can erode the steel under the weld overlay to which the tubes are welded. Severe wormholing can shorten feedwater heater life.

Current practice is for Manufacturers to use loss of pressure in the channel to determine whether there is leakage from the channel side to the shell side when the shell side is not visible for inspection. However, the gradations on pressure test equipment in common use are too coarse to indicate very small leaks or weeping. It follows that users should specify that Manufacturers use other methods to verify non-visible leakage when such leaks could be hazardous or harmful during operation of the heat exchanger. See Table 1 for typical test pressures and pressure gage graduations.

Because the ASME Code rules and the API and TEMA Standards do not require gas leak testing to verify that there are no-leaks from the channel side to the shell side, Manufacturers will not perform such tests unless the User or the User’s Agent specifies that they do so. Therefore, when they hydrostatically test the tube side, they rely on pressure loss in the tubes and channel during the holding period to indicate leakage through the tube-to-tubesheet joints. The gages in widespread use in the heat exchanger and pressure vessel industries for hydrostatic testing to meet the Code requirements are dial type Bourdon tube gages. Some Manufacturers use strip chart or circular recording gages but the graduations are similar to those of dial gages.

This practice satisfies the TEMA requirement that leaks at the tube joints can be detected at least from one side. API 660 also accepts this practice[iii]. Although gas leak testing is not onerous and costly, heat exchanger manufacture is a very competitive business and it is not likely that Manufacturers will perform testing that the ASME Code does not require unless the procurement specification requires it.

For constructions in which the Authorized Inspector cannot visibly examine the shell sides of tubesheets, heat exchanger users are cautioned that pressure loss to determine whether there are leaks from the channel into the shell does not indicate weeping through the tube-to-tubesheet joints because the gages in common use are not sufficiently sensitive to indicate a pressure loss that discloses such small leaks. This is especially so when the tube side hydrostatic test pressure is substantially higher than that of the shell side.

An analysis of the pressure testing process which hydrostatic test water is applied in the tubeside of an exchanger where the backside of the tubesheet is not visible was adapted from material previously published on the MGT Inc. website. It demonstrates that relying on gage indication of pressure loss to assess leaks (weeping) that would not be visible during hydrostatic testing does not indicate whether there are such small leaks.[iv] It shows that using test gage pressure loss to determine if there is leakage through the tube joints from the channel to the shell of heat exchangers in which the back side of the tubesheet is not visible does not disclose weeping leakage from the channel into the shell through the tube-to-tubesheet joints. Such leakage does not comport with the implication of the language of the Code’s Paragraph U-2(g) that leakage is not permitted. In this discussion weeping is defined as a leak of 20 drops per hour or approximately 1 cm³ (0.061 in³) which if visible would be 10 drops of water on the tubesheet face after the half-hour TEMA minimum holding period.

If the exchanger service is for a fluid less viscous than water the likelihood of leakage in services may be very high if the Manufacturer relies on changes in the pressure gage reading to assess whether there is leakage from the channel side into the shell during hydrostatic testing.

ISSUES ABOUT HYDROSTATIC TESTING HEAT EXCHANGERS

Should the User or the User’s agent or a Manufacturer with knowledge about the hazards of the service be required to specify further leak testing and the kind of leak testing the Manufacturer must use and whether the API-660 and TEMA Standards requirements meet the Code’s requirements?
Despite the Code rules about the unacceptability of leakage through the joints of pressure vessels and heat exchangers, the TEMA and API standards do not require leak testing every heat exchanger and Manufacturers will not perform such leak tests unless Users request them. It is necessary to understand the service of the exchanger and the degree of hazard such leakage presents. when determining whether to require the Manufacturer to perform leak tests. For example, a minor tube joint leak in a water-to-water cooler presents no hazard, whereas leakage of a volatile, flammable or explosive fluid could cause damage such as wire drawing, injury or death. How should users deal with the possibility of such leaks?
What constitutes a suitable leak test if the standard Code hydrostatic test cannot disclose very small leaks (weeping)?
Are only leak tests described in the Code’s Section V acceptable for meeting the Code’s no-leak requirement?

The simplest and least costly additional test is gas-bubble testing (often erroneously described as soap bubble testing.) Typically, the Manufacturer pressurizes the shell with air or nitrogen at 30 to 50 psi and applies a commercial bubble former to the tube-to-tubesheet joints. This is a very effective way to disclose leaking tube-to-tubesheet joints. When the User or User’s agent or knowledgeable Manufacturer is aware of the potential hazard of a leak in service, or when the channel side design pressure is substantially higher than that of the shell side, it is reasonable to specify halogen or helium sniffer leak testing to satisfy a no-leak requirements. For tubes welded to the tubesheet and subsequently expanded, the prudence suggests that in addition to such leak testing the welds should be fluid penetrant examined.

When the channel side design pressure is very high – in the order of 1500 lb/in² and above - it is prudent to require cycle testing. Typical procurement specifications for high-pressure feedwater heaters require 10 cycles of bringing the channel to the hydrostatic test pressure followed by dropping the pressure to atmospheric for each cycle. (Figure 1) Such testing has beneficial effects on the structure in addition to possibly cracking subsurface porosity bubbles and disclosing cracks in the welds. For such equipment small leaks of high-pressure feedwater through the tube-to-tubesheet joints leads to wire drawing (wormholing), which when severe can be extremely expensive to repair, especially when considering the loss of cycle efficiency when the heater is bypassed to allow access for repairs. Therefore, typical feedwater heater procurement specifications require helium leak sniffer testing (mass spectrometer) testing the tube-to-tubesheet joints during manufacture.

COMMENTS AND RECOMMENDATIONS

The Code is a pressure containment safety code and the hydrostatic test represents only a test adequate for the typical heat exchanger not in a specific service where leakage is an issue. Users should be aware of these facts.
Loss of test gage pressure during ASME Code required hydrostatic testing does not disclose very small leakage (weeping) from the channel side to the shell side because of the insensitivity of the test gages used industry wide for hydrostatic testing.
Users of the Code should also be aware that, although the TEMA Standards require a minimum of one-half hour hold time of hydrostatic pressure, the Code does not specify a hold time, which would be important for detecting leakage through welds and joints. Because hold time does not guarantee that a joint is 100% free from leaks, Designers, Users, and Manufacturers need to agree on the suitable test(s) for the service conditions.
Designers, Users, and Manufacturers should agree on the definition of joint type and to the nondestructive Tests (NDT) for all welded joints.
Designers, Users and Manufacturers of heat exchangers should consider the specific language of the Code’s no-leak requirement of UG-99(g) and the differences between it and the requirements of API 660 and the TEMA Standards.
When preparing procurement specifications, Engineers should consider the service of the exchanger and the UG-99(g)’s requirements and determine the appropriate leak tests for meeting them. Users and Manufacturers should agree beforehand on the suitable leak detection system when invoking the waiver provisions of the Code’s Paragraph UG- 99(2)(g).
The language of the waiver in UG-99(2)(g) needs clarification with respect to using fixed tubesheet exchangers for lethal service, possibly with a specific exception allowing their use with appropriate precautions.

[i] The ASME issues the ASME Boiler & Pressure Vessel Code is issued at three-year intervals and issues Addenda annually.

[ii] Standards of the Tubular Exchanger Manufacturers Association, 9th Ed., 2007, The Tubular Exchanger Manufacturers Association, Tarrytown, New York

[iii] ANSI/API 660/ISO 16812, 8th Ed., August 1, 2007, the American Petroleum Institute, Washington, D.C.

[iv] This analysis was based on work done by Dr. Ted Anderson of Quest Reliability and published on Tips, Volume 1 Number 7, MGT Inc. website at http://www.mgt-inc.com.

TROUBLESHOOTING FEEDWATER HEATER DRAIN COOLER PROBLEMS

2009-04-17T11:14:00.000-07:00

Recently a Client called to ask what might be the cause of loud noises coming from the vicinity of the Subcooler in a Closed Feedwater Heater. Here is a summary of the possible causes and actions the plant may take to deal with the problem:

CAUSES

Tubes passing through the endplate of the subcooler are not expanded tightly in place to allow them to expand and contract axially as the heater works. The annular space between the tubes and the holes in the endplate will allow steam to intrude into the subcooler if the tube surface contained within the endplate is insufficient. In some very old Closed Feedwater Heaters, the subcooler end plate is too thin (less than 3-inches thick) to condense steam that passes around the annuli. Consequently, when there is sufficient pressure differential between the condensing zone and the subcooling zone, uncondensed, wet steam will enter the Subcooler. The wet steam erodes the cross-flow baffles, especially in the vicinity of the tube holes. As the tube holes enlarge due to the erosion, the effect is to significantly increase the unsupported tube span, making the tubes more vulnerable to vibration and subsequent failure. As the tube holes enlarge due to the erosion, of the tubes making the tubes more vulnerable are subject to vibration and subsequent failure. Current practice is to specify a minimum of 3-inch thick end plates as shown in the figure and modest pressure drops across the end plate. It might seem to be reasonable to plug tubes as they begin to leak. But this is self-defeating because doing so does not allow for cooling/condensing any steam passing through the annuli. A better way to deal with this problem is to fix it as shown below in Fixes. As shown in the sketch, the clearance between the tube and hole is ~0.0045-inch. We recommend holding all end plate drilling to the TEMA Special Close Fit Tolerances with no exceptions for out of tolerance holes that the TEMA Standards allow for drilling tubesheets (4% oversize).

The welds of the Subcooler shell to the flat roof plate have failed as shown in the photograph.

The welds of the Subcooler to the back face of the tubesheet have failed.

FIXES

Fix the problem with thin end plates by having the tubes expanded into the end plate so they just contact the hole interiors, thereby reducing the volume of steam that can pass between the tubes and hole.
Fix the problem with failed longitudinal welds by cutting a window in the shell of sufficient size to expose the whole roof plate-to-closure weld. Grind out the failed weld. Attach clamps to pull the roof plate to contact with the enclosure, reweld and examine the weld with fluid penetrant. Replace the removed section in the shell and hydrostatically test. Note that this kind of repair meets the National Board Inspection Code (NBIC) requirements for repairs. Most jurisdictions require such work to be performed only by Repair Organizations that possess the NBIC-issued R Symbol stamp and Certificate of Authorization.
Attempts to fix the problem of failed Subcooler enclosures to tubesheets have not bee successful. Various schemes have been tried, including injecting sealants at the position of the failed welds. But to our knowledge, none have been successful. We recommend replacing the heater, or in the case of a heater installed in the condenser neck, replacing the bundle and channel.

COMMENT

It goes without saying that careful and proper level control is the best way to operate Closed Feedwater Heaters. Improper or inadequate level control can also lead to Subcooler problems. But this Technical Tip does not address such problems.

Stan Yokell's book Dog Stories is now Available for Purchase

2009-02-03T10:38:00.000-08:00

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Posted by Stanman at 9:23 AM

Revised Interpretation 07-2005

2008-09-19T07:49:00.000-07:00

In a letter to Stanley Yokell dated September 18th, the Code Secretary advised that the ASME Subcommittee of Power Boilers has made a correction to the wording of Interpretation 07-2007 previously issued to him. Here is the corrected Interpretation:

Our understanding of the questioning in your inquiry and our reply are as follows:

Question (1): Do the requirements of PFT 12.2.1 for the joining of tubes to tubesheets of firetube boilers apply to the joining of tubes to tubesheets of shell-and-tube heat exchangers constructed to Section VIII Division 1?

Reply (1): No.

Question (2): May the tubes of firetube boilers built in accordance with Section I PFT-12 be welded to the tubesheets prior to expanding and subsequently expanded?

Reply (2): No. Stanley Yokell disagrees with this interpretation because expanding the tubes before welding leaves no path for welding generated gases to escape except through the weld puddle which can cause weld porosity. In addition any foreign matter introduced by the expanding process can lead to porosity and weld cracking.

Question (3): May manufacturers use tube expansion methods other than roller expanding, such as hydraulic, explosive or combinations of methods in which the uniform pressure expansion precedes roller expanding (hybrid expanding) in the construction of firetube boilers built
in accordance with Section I PFT-12?

Reply (3): Yes.

ASME procedures provide for reconsideration of this interpretation when or if additional information is available which the inquirer believes might affect his interpretation. Further, persons aggrieved by this interpretation may appeal to the cognizant ASME committee or subcommittee. As stated in the foreword of the code documents, ASME does not "approve," "certify, ""rate," or "endorse" any item, construction, proprietary device or activity.

Sincerely,
Umberto D’Urso
Secretary, B&PV SC-I
Phone: (212) 591-8535
Fax: (212) 591-8501
E-Mail: dursou@asme.org

Stanley Yokell's Article in March 2008 Chemical Engineering

2008-03-14T10:01:00.000-07:00

The Operations and Maintenance section of the March 15, 2008 Chemical Engineering Magazine has Stanley Yokell's article, "Maintaining and Repairing Heat Exchanger Tubes." Its eight pages describe various types of plugs and their advantages and disadvantages and the following subjects:

Locating Tube Failures

Assessing Failure

Tube Plug Maps

Plugging Techniques

Sleeves and Ferrules

Heat and Erosion Shields

Illustrations include:

Two-piece taper plugs

Breakaway plugs

Thimble plugs

Three types of plugs for welding

Removable Plugs

Tube stabilizers

Plug maps and

Typical plots of Numbers of Plugs VS Months of Operation and Percent of Plugs VS Months of operation useful for determining when to retube, rebundle or replace an exchanger.

The MGT Website can be found at http//www.mgt-inc.com. Copy and past the URL to your browser window to access the MGT website.

ASME Code Section I Interpretation No. 07-2005

2008-03-10T08:35:00.000-07:00

On March 10, 2008, Umberto D'Urso forwarded to Stanley Yokell Interpretation No. 07-2005 which reads as follows:

Subject: ASME Section I 2007 Edition, PFT-12

Reference: Your letter dated October 30, 2007

Item: 07-2005

Dear Sir:

Our understanding of the questioning in your inquiry and our reply are as follows:

Question (1):

Do the requirements of PFT 12.2.1 apply to the joining of tubes to tubesheets of shell-and-tube heat exchangers constructed to Section VIII Division 1?

Reply (1): No.

Question (2):

May the tubes of firetube boilers built in accordance with Section I PFT-12 be welded to the tubesheets prior to expanding and subsequently expanded?

Reply (2): No.

Question (3):

May manufacturers use tube expansion methods other than roller expanding, such as hydraulic, explosive or combinations of methods in which hydraulic or explosive welding and roller expanding in which the uniform pressure expansion precedes roller expanding (hybrid expanding) in the construction of firetube boilers built in accordance with I PCT-12?

Reply: (3): Yes

Note that I believe there is an inadvertent error in that hydraulic or explosive welding should really read hydraulic or explosive expanding. I have so advised the Code Secretary and asked him to pass it on to SC-1 for a correction. (I don't know of any method of hydraulically welding tubes to tubesheets.)

I disagree with the proscription against welding the tubes to the tubesheets of firetube boilers before expanding because in all the years of my experience in dealing with welded and expanded tube-to-tubesheet joints, I have found that rolling before welding is a sure way to create bad tube-to-tubesheet welds. I do not understand why SC-I responded as they did but do not intend to pursue the matter.

ASME Code Section VIII Division 1 Interpretation No. 02-4113

2008-02-25T08:47:00.000-08:00

Viewers of the blog are advised of the ASME Boiler Code Committee's Interpretation No. 02-4113 which reads as follows:

Subject: Section VIII, Division 1 (2007 Edition); UG-20(a)

Ref: Your Inquiry of 12/03/02

Item: 02-4113

Dear Mr. Yokell.

Our understanding of the question in your inqury and our reply is as follows:

Question:
Does the ASME Section VIII, Division 1 require a user to consider the effects of startup, shutdown or other abnormal conditions listed in U-2(a) when determining the design temperature as per UG-20(a), and the design pressure as per UG-21?

Reply:
Yes

Very truly yours,

Daniel R. Sharp
Secretary, Subcommittee on Pressure Vessels
Ph: (212) 591-8538
Fax: (212) 591-8501
sharp@asme.org