How do we define "sound engineering practice"

[AUSTER]

I have been asked to install a 50NB stainless steel pipeline to carry air at 7 bar. This is categorised as "Sound Engineering Practice" (here in South Africa) but what does this specifically mean?
My client wants me to weld without purging to reduce costs. The pipe would not leak but I would not be complying with B31.3 as far as welding standards are concerned. Any relevant comments would be appreciated.

 

[DSB123]

AUSTER,
I would consider "sound engineering practice" to mean that the system is designed, installed, inspected and tested to normal standards. For SS pipe for example welding is normally done with purge gas - to do otherwise is not "sound engineering practice". You must be able to stand in front of a court and "hand on heart" say that in your view/experience the system met what you consider to be "sound engineering practice". You need to be comfortable that you can defend your decisions as regards the installation (I mean the design-fabrication-inspection and testing )(for example - not to use purge gas when welding SS)

 

[BigInch]

Simple rule.

If there is a code that covers the issue and you don't follow it, that's the first indication that you've crossed the border from sound and to unsound engineering practice. Any return thereafter will be quite difficult. It is also one of the only things that lawyer's understand about codes and they do understand that part very well indeed.

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[rneill]

As mentioned by others, consider whether you could stand up in a courtroom and reasonably defend what you did as reasonable and prudent and consistent with established industry practice (as documented in established Codes and Standards, and typical industry specifications).

Myself, I default to written documents as my basis for sound engineering practice as often people who work without the benefit of written codes, standards and specifications have a tendency to adopt standards that are far less stringent than these. However, if you were to end up in a courtroom, it doesn't look good when your undocumented "established practices" are distinctly different from all the written industry standards that the Lawyer presents as evidence.

 

[AUSTER]

Thanks everyone. Your answers are so consistant that the way to go is extreemly clear.

 

[unclesyd]

As rneill states it has to come from a written page in some code or standard that pertains to the work at hand to get by. Some times you can get by with a recognised text book, tricky. I have seen cases where a lawyer holds up a code or standards book and ask the witness to show me, this is all it took. Lawyers can make it tough for any engineer if they so mind. The last case I saw was where an engineer used a reference on welding from the NBS standards for a land based storage tank and was blown out of the water, no pun intended.

Some information for your welding problem.

You could use Solar Flux.
For your application you could use a N2 purge.
An N2 purge along with Solar Flux works very well.

http://www.solarflux.com/

 

[AUSTER]

Thanks Uncle Syd. I'm actually a Matallurgical Engineer and I appreciate very much your ideas for lowering the cost of welding. It's not really the cost of consumables but the time taken in setting up the purging. I'm working on an overhead grid type system to supply air pick up points to some 3,600 m2 of workshop in a new factory installation.
Another problem that arises is that half the grid already exists and must be transferred to the new site. I'm not sure of the quality of the original construction so do you have any ideas of wording I can put on the C of C to cover my butt in case any of those welds should fail???
Again, I know that I could X-ray the welds but the client has very short arms and very deep pockets!!!

 

[unclesyd]

i don't envy you in your position.
In my humble opinion I would ask for some sort of inspection as would be required on existing process piping say under ASME 31.3 or under the banner of the fit for service approach. It sounds like you are not in an environment to accomplish this without getting someone upset, It appears that you are working against the philosophy of "Damn the torpedoes, full speed ahead.". This is going to a hard sell as all you will hear is that this line has been operation XX years. You best hope in getting management on board is to find some awful weld for a show and tell and sell.
If the line has to be cut in the process of moving, cut near a existing weld not in the weld where a visual if nothing else can be accomplished and where you maybe able to catch the old weld on an X-ray of new weld.

Do you have anyone in management on your side and?

Like it has been stated numerous time get you concerns on paper. Don't use too big of a distribution as you will quickly become the one that impeding progress.

Under the right circumstance you may be able to ask, "what code do we want to use on this project?"

Are there any company piping standards to fall back on?

If you have to do the job as you describe make sure that the closing reports states that the installation was not up to your requirements. Tempered of course.

On the use of Solar Flux the time of prep is minimal. Mix up a little, bruch on let dry and start welding.

 

[AUSTER]

Thanks again Uncle Syd

I'll be OK now. The ideas you and the others have given me and my understanding of the new Health and Safety laws in SA (I started life after University, nearly 40 years ago, developing early quality, health and safety systems for the British Government) will enable me to ensure my customer knows what he's doing (or committing!!) should he allow anyone to install his airline without purging. We'll also insist on an assessment of what's already installed and must be re-used.

 

[moltenmetal]

Be careful, as "sound engineering practice" has bitten my own hind end on more than one occasion. This is like one's watch: everyone has one, they all differ, and each engineer believes his own. It can be a code word for, "Do as you please-I don't care to specify what I want- but if I don't like something after the fact it's you that I'll blame, Mr. Engineer!". I would imagine that the same applies to any regulatory body who utters those words in statute.

When faced with a variety of watches that don't agree, you go to the international standard clock, right? The same with engineering judgment. That's where codes and standards come in very handy- in defining a minimum standard of care that at least a majority agree with. Useful, if not taken as if they were some religious text and used as an excuse not to do engineering.

Air at 7 barg is category D (low hazard) service per B31.3, is it not? If so, design fabricate and test in accordance with the requirements of that standard for that service. If it is category D, much of the testing becomes the owners' discretion. If you're doing butt welding, I don't remember off hand if radiography is a mandatory requirement in category D service, or not. Go look it up: if it isn't, some sugaring and discolouration on the root pass is probably not going to matter much to the soundness of the weld itself as long as the proper preparation between passes is done. If spot random radiography IS still required either by code or owner, then you've little choice but to purge the root, as costly and time-consuming as that may be.

Then again, the client is using stainless steel for some reason, and any sugaring and heat tint on the ID may or may not affect the cleanliness or chemical reasistance which was the reason stainless was selected- or was it merely selected to avoid external painting?

Sorry, I'm not familiar with your terminology. Does 50NB mean 2"NPS? If so, you'd be socket-welding and internal purging is NOT mandatory. If the service is truly air, consider using a non-welded system like Victaulic Press-Fit. Could save a huge amount of time and money, especially if the piping is long runs in a plant environment with few fittings.

 

[AUSTER]

Thanks moltenmetal, the main problem here reverts back to the client trying to get a high class job at cut price rates. It's a multinational (German based) company, one of the worlds largest, and they expect averything to be perfect and conforming to all relevant codes and specs. However, the local management is trying to impress the big guys by getting it cheap.
The management doesn't understand welding or pipeline applications and we are up against "backyard welders" who don't know either. We're small but very professional, understand and apply the codes, precedures, qualifications, controls etc, all of which are in place, but we don't want to loose this job because the client simply doesn't undersand the implications of going cheap.
By joining this forum I now understand far better the implications of our own (South African) health and safety regulations (which have only just been promulgated in the last couple of months). Being relatively new to pipe and pressure vesel design, I'm extremely grateful that forums such as this exist and I've been able to clarify my situation very quickly. Thanks again to all who have replied. Were all in different time zones but all seeing the same time!!!! It's been great.