Dundas, Ontario,

16 April 2012

Well guys spring is here and good times for pipers are back again. Activity in both the process and power industries have spawned a shortage in Piping Designers and Engineers. As we all know this business is very cyclic and when things get moving after a slump, like we’ve had in the last few years, there is always a shortage of experienced people.

The trouble is that a lack of worthwhile practical training is and always has been difficult to find. Colleges and Universities may offer some pseudo piping courses but they are usually so far removed from the real world that they are largely ineffective in the short span. Learning institutes are profit centres and wish to fill every class with paying students and most young people from North America are not interested in pursuing careers in Engineering.

I teach several ASME short courses, however, these are between 3 and 5 days long whereas in the 1970’s we taught the same courses and they lasted for 260 hours. What is missing from today’s courses? The practical portion of the program where the students had to complete a ‘real live’ project using information they had covered in the course.

This months’ tips

CHECK LIST FOR PUMP PIPING

1.      Check maintenance clearances, (Removal of Motor, etc.)

a.  Valve heights – for operation and pump maintenance,

b.  Piping adjacent to pumps

c.   Adjacent equipment locations for clearances,

2.    Vertical pumps – assure clearance above pump for removal.

3.    Valve handwheels generally to extend over pumps (not motors) and not into walkways, etc.

4.    Provide spool pieces above vertical nozzles for removal of pump casing, etc.

(Check valve can sometimes be used for this purpose),

5.    Check pump nozzles – special thicknesses, integral studs, etc.

6.    Avoid pockets in suction lines

7.    Reducers in suction lines

Eccentric reducers to be flat side up at suction nozzle.

8.    ‘T’ and ‘Y’ type strainers – check clearance for removal of basket.

9.     Steam lines to drivers:
a. Check drainage of steam lines, valves etc.
b. Check turbine casing drains, whether they have to be piped up or plugged off.
c. Trap before control valve.

10.  Desurgers – locate as close as possible to pump discharge nozzle.

11.  Flexibility:

a. Suction lines generally to be short and rigid.

b. Check lines which are manifolded for flexibility and tolerance stack up.

12.  Pump starters – check size and location, show on key plan.

13.  Check that pump drains do not foul electrical gear, etc.

14.  Check position of cable trenches relative to drains, etc.

Bob’s Blog

Dundas, Ontario,

16 October 2011

After a busy year of travelling and teaching courses in Holland, Kuwait and South Africa I have finally got down to writing.

This months’ tip  rant.

3D CAD programs for plant design.

Ever since CAD programs appeared in the early 1980’s, management of engineering companies have been saying that 3D CAD will mean the demise of expensive piping designers as the programs will solve any and all of the piping layout and detail problems and route piping in a manner which is both efficient and cost effective.

This resulted in training programs, both in house and at the college level being watered down or shelved completely. Colleges produce CAD operators who, through no fault of their own, have a very basic understanding of what is involved in the piping discipline.

CAD programs will NOT route the piping efficiently when the operator is not familiar with all of the many ‘what if’ scenarios that must be considered. Computer programs cannot do Design Optimization, as I have said previously, if they did then we could stay in our beds in the morning and just press a button to design the plant. The computer will not make all required design decisions in a multi discipline environment. i.e. the common sense approach.

Subsequently, drawings are being issued for construction with incorrect or insufficient information to fabricate in the shop or field. Consideration is frequently not given to maintenance, process and safety procedures.

This will result in additional field construction costs and additional hours spent by maintenance personnel and operators once the plant is on stream.

Bob’s Blog

Dundas, Ontario,

16 July 2011

Things are on the up and up. Summer is here and the birds are chirping and things are a lot better on the job front.

The second edition of the book is now out and available through the Barnes and Noble website.

This months’ tip

SPRING HANGERS

The selection and sizing of spring hangers can be accomplished using whatever piping stress analysis software program. However, the selection should ALWAYS be checked using the manufacturers’ catalogue. The reason for this is that the stress program does not know what purpose the spring is being used for. For instance if you are trying to limit the loads on pump nozzles to a certain value and have located a spring on the piping close to the nozzle, the selected spring has been chosen by the program after completing a piping system moment calculation and distributing the loads amongst the restraints in order to achieve equilibrium.

The spring does not know that it is supposed to take more than its share of the load in order to reduce the pump nozzle load.

ACTION:    Once the program has selected a spring note the selected sizes and spring scales. Then change ‘hanger’ to a ‘user hanger’ and increase or decrease the selected spring size and/or spring scale. Several iterations will be required to come up with the appropriate nozzle loading.

Another reason for checking is to make sure that the selected spring agrees with the manufacturers’ catalogue and it gives you a better feel for the application.

Bob’s Blog

Dundas, Ontario, 18 November 2010

Well, the trees are now bare in Southern Ontario and people are gearing up for the winter once again. Things, project wise are quiet right now in the process and petrochemical disciplines and we seem to be in a holding pattern awaiting some big contracts. Whereas, the mining discipline is at last seeing a turnaround.

This months’ tip

STRESS CATEGORIES

The B31 codes provide design guidance for two stress categories, PRIMARY and SECONDARY STRESSES. Although the code reader will not find these terms listed or discussed in the code text, the understanding of these terms is very fundamental in applying the code equations to determine the stress levels in piping systems.

The definitions are:

A PRIMARY STRESS is a PRINCIPAL STRESS, SHEAR or BENDING generated by imposed loadings which are necessary to satisfy the simple laws of equilibrium of internal and external forces and moments. The basic characteristic of a PRIMARY STRESS is that it is not self limiting. As long as the load is applied, the stress will be present and will not diminish with time or as deformation takes place.

Examples of a PRIMARY STRESS are CIRCUMFERENTIAL STRESS due to internal pressure and LONGITUDINAL BENDING STRESSES due to gravity.

The failure mode of a PRIMARY STRESS is gross deformation due to rupture.

A SECONDARY STRESS is a PRINCIPAL STRESS, SHEAR or BENDING caused by structural restraints such as flexibility controls, or by self constraint of the pipe itself. The basic characteristic of a SECONDARY STRESS is that it is self-limiting. As this stress condition develops in a piping system, local yielding will occur, thus reducing these stresses.

An example of a SECONDARY STRESS would be the bending of an elbow the joins two lengths of pipe subjected to a temperature increase. The bending in the elbow will reach a maximum value as the temperature stabilizes at its new increased value. Thus, the condition causing the stress to increase now stops. The elbow, now in this new higher stress state, will experience local yielding or deformation which will reduce the stress in the elbow.

One can see from this example that SECODARY STRESSES are associated with cyclic conditions such as temperature increase or decrease in a piping system as the plant starts up or shuts down.

The failure mode of a SECONDARY STRESS is a crack initiation and propagation through the pressure boundary resulting in a leak.