19 replies to this topic

[Ajay S. Satpute]

Dear all, I have spent some time looking in different international standards (e.g. TOTAL, NORSOK & API)and copying line sizing criteria for gas, liquid and multiphase fluids. Please let me know if it is a good idea, if more standards (like SHELL DEP etc.) can be referred and line sizing criteria be incorporated in the same excel file. Someone with access to other standard can update the excel file or provide me the standards, so that I can do it myself. The idea is to have all the line sizing criteria in one file in our forum, so that all the working process engineers can benefit from it. Request you all to kindly provide feedback please. Thanks and regards. Ajay S. Satpute M. tech. (Chemical) IIT, Madras

Attached Files

•  Line sizing criteria as per different standards.xlsx   29.65KB   2159 downloads

[Santoshp9]

Dear Ajay,
Great,
I have one doubt ,which standard to be followed as universal to avoid the mismatching of calculated values of pipe size

[kkala]

Very good idea. Some line sizing criteria can be found in http://www.cheresour...id-line-sizing/ '> http://www.cheresour...id-line-sizing/ (after post No 6).

[Santoshp9]

Kkala Sir,
Thanks

[Bobby Strain]

Most major operating companies have their own standards, and they are quite different sometimes. If you follow Shell guides, you can be assured that the criteria is conservative. Good luck on reaching any agreement.

Bobby

[DB Shah]

Based on various standards and opt plant data, I prepared one for my ref. May be useful for you

Attached Files

•  Design Philosophy-Process Piping.doc   123.5KB   1187 downloads

[Ajay S. Satpute]

It so happened in one of my projects, where client was not very satisfied with my line sizing criteria, which were based on best engineering practice (followed by my employer for decades) and client needed some basis, such as international standards. I, then provided a couple of standards' sizing criteria. Now these three criteria were different from each other and client was confused and inquired us on which standard to follow.

I stick to our best engineering practice, because we know that it will work as it had worked for similar projects in past.

In my opinion, experience should outweigh any international standard, because there are many other factors which need to be considered by a process engineer, than just vmax, Vmin or pressure drop etc., for arriving to the decision of a line size. International standards are often silent about those variable (surge pressure, vibrations etc.) (However, I have utmost respect for people who prepared these documents from their experiences).

Thanks to Mr. Kkala and Mr Shah for their inputs, especially for the IPS document.

I intend to complete this excel sheet if I have sizing criteria only as per other standards (not as per best engineering practice).

Thanks.

Ajay

[kkala]

Pipe roughness values (for ΔP calculations) are mentioned sometimes in pipe sizing practices. If of interest, a collection of them can be found in http://www.cheresour...-starting-point '> http://www.cheresour...-starting-point .

[Art Montemayor]

Ajay:

I agree wholeheartedly with you. First, there are no such things as "international standards" for sizing piping. There are best practices as employed in each individual engineering department around the globe.

Secondly, an engineering firm or department can only backup or warrant that which it honestly feels it can justify - not someone else's opinion, "standard", or best practice. I am very familiar with Exxon's, Shell's, and BP's best global engineering practices and have used them many times in my projects with those companies. But I consider it foolish and a grave mistake to simply adopt those practices because you feel those organizations know more than you or can do it better. My recommendation is to use the practice, equations, friction factors, Overall "U"s, etc., etc. that you know work best for you and for your work. That, you should be able to defend and explain in a court of law. You, I, and many other engineers have no business trying to defend or explain Exxon, Shell, or BP best practices if we are not working on those projects or participated in their development. It is as simple and common sense as it sounds. And any legal system will back that up, I'll bet.

That is why I don't worry about engineering students being mesmerized with Shell DPs, Exxon GPs, and BP ETs. They honestly believe they are using the "best", most accurate, latest, and most stylish engineering practices. That is silly student thinking and not worthwhile debating. But as professional engineers we should all know from experience that hard-earned knowledge is far more applicable than someone else's guidelines. We simply don't have enought background in those systems to know what and why they were developed the way they are. NorSok "standards" are so full of conservativism that when I use them I know I am "safe" - but I also know these guidelines are not the optimum solution to a problem. They were put together for explicit reasons beyond workable and practical engineering. They involve some politics and backside protection - and we are aware of that when we use them.

[Ajay S. Satpute]

Thank you Mr. Art for your very useful feedback.

[kkala]

Beside the views expressed in post No 9 by Art Montemayor, I believe knowledge of several pipe sizing practices is useful for Chemical Engineers in the following cases. Those working in an Engineering company have to get fully familiar with its own pipe sizing practices too.
1. Project Clients can require modifications in company's pipe sizing practices during contract award, or even ask for specific examples like in post No 7. We should be able to negotiate Client requirements from technical viewpoint, or supply examples for the case.
2. Modifications in existing installations can result in some excess of values posed by "approved" practices. We should be able to judge whether excess is tolerable or e.g. pipe size shall change.
3. One practice may clarify or complete another. Let us specify Sch40 pipe diameter for 43 m3/h of mild water (ambient temperature) by using Norsok standard or "LS.xls", the latter from http://www.cheresources.com/invision/topic/11318-liquid-line-sizing/ - post No 9.
For 4" pipe: v=1.45 m/s, ΔP=0.20 Bar/100 m, both accepted by Norsok and LS.xls
For 3" pipe: v=2.50 m/s (accepted by Norsok, not by LS.xls), ΔP=0.78 Bar/100 m (not accepted by any of the two)
For 2" pipe: v=5.52 m/s (accepted by Norsok, not by LS.xls), ΔP=5.83 Bar/100 m (not accepted by any of the two).
Consequently both practices suggest 4" diameter pipe. But allowable velocities are based on different principle. Advice (if any) welcomed; a third practice could help on this point.
By the way http://www.cheresources.com/invision/topic/13563-supersonic-velocity-in-control-valve - post No 20 and above it - seems to indicate a case where Norsok standard is not the most conservative.
4. In brief broad critical knowledge on several pipe practices is a way to speed on judgement and "hard-earned knowledge" on the subject. Significant difference in results out of two practices usually indicates misunderstanding.

[Art Montemayor]

The main point that I want to make in this conversation is the following advice for engineers:

Do not take lightly any client requests on how calculations and engineering decisions are to made in a project. This is IMPORTANT LEGAL AND ENGINEERING requests that should be fully documented and explained to any client. Specifically, a client should be prepared to assume all engineering and legal repercussions should the engineering design that they insist be done on THEIR TERMS fail to produce the contracted results. If a client wants to have his project designed on his terms, then he/she should take 100% of the risk.

I cannot emphasize this important point enough. The engineering business is full of liabilities and legal ramifications that impact on the contractual agreeement between a client and an engineering firm. This is not about who is more right or who has access to more "standards". It is all about a contractual agreement to deliver a specified result. If you follow ANY ADVICE OR DEMANDS for doing an engineering job on the clients terms and conditions, you are well-advised to make sure that your contract with that client clearly defines that the resultant responsibility for the design is all his (the client's)!!

That is why all successful engineering firms have their own standards and guidelines for design. They - not the client - are considered the "experts" in a court of law and, as such, should know what they can guarantee and what they can't.

Quite frankly, I don't see any merit or profit in studying and mastering those guidelines and standards that you can't employ in a project simply because you are not the "owner" of the same. In fact, if you are working on a design for Shell Oil, why in the devil should you use Shell's DEPs? Certainly, you would be a fool to guarantee the results when you don't have access to all the information that went into making that DEP - assuming you are an independent contractor and not a Shell employee. That is how some engineers who have little business "sense" can get into some very deep legalistic and costly problems. Cases such as these are judged in courts all over the world every year.

[Bobby Strain]

Art,
Any project I did for Shell, they required that we use their guides and standards. Same with all the other majors. Use of these guides were usually stipulated in the contract.

Bobby

[asade abiodun]

Art,

What if you are handling a project that the client does not have their own in-house standards or design philosophy? What is the right approach to follow?

I have handled a project where I used Shell DEP guidelines to design a 2 phase separator and I checked the design with API 12J (Specification for Oil and Gas Separators). Am I wrong in using these guidelines?

Edited by asade abiodun, 17 December 2012 - 08:03 AM.

[Art Montemayor]

Bobby:

I am sorry; I made a typo mistake on my last post. I meant to write: "In fact, if you are NOT working on a design for Shell Oil, why in the devil should you use Shell's DEPs?"

I usually write my posts on Word for Windows and paste the result into the Forum Editor; this time, either I or Word, deleted the word "NOT". Sorry.

[Art Montemayor]

Asade:

In your case, you are taking on the responsibility for the results - regardless of whose guidelines and "standards" you use. As Bobby has stated, this should all be clearly stated and understood in your agreement with the client. If the client has not norms or guidelines, you surely can recommend any that you feel you can meet and back up. That is up to you to decide. But you must decide if you can GUARANTEE the expected results. If the client wants a guarantee, then that is another price higher than just doing calculations. The price is higher because you should have an insurance policy that covers you - if you can't insure yourself.

If you use Shell's DPs on a project without Shell's written approval and license and intend to profit from using them, then I believe Shell has a legal right to take you to court for using their intellectual property without permission. I don't know if that could happen in your country, but it is highly probable in countries such as the USA and the UK.

Bobby Strain, do you agree with the above paragraph?

[Neelakantan]

hi
@ART: again i find the words of experience and practicality;
without going into the technicalities of various practices (some of them are open and followed across the industry),possibly if i can put ART's statement with oriental / eastern way of learning: always go the basics and see what the project needs. I have done design for FPSO and early production systems where i have used "fit for purpose" values which are probably outside the ranges specified by TOTAL or Shell. and in one BP project for EPF i have used very conservative values as given by BP..

the bottom line is to see what the client wants, see whether their recommended in-house values are suitable for the project, what your engineering companies engineering practice is, whether these values are acceptable from the engineering basics, etc

I always tell my younger engineers: just dont look at the values spewed out from programs and excel sheet; just check with some basic data and see if it is matching with the basics. I have seen instances time and again where engineers tend to accept the values and i always like young engineers to question these values and look for reasons for acceptance or rejection of these values.

regards
neelakantan

[Bobby Strain]

Half the engineers in the world have major company guidelines, including Shell's. Any enforcement of their use probably wouldn't hold up in court, and they would not likely complain. Still, we should protect our client confidence. I have found some Shell guides on the web! But for those still practicing, they should encourage their employer to develop guides for use with clients who don't have their own.

Bobby

[Ajay S. Satpute]

Dear all, I have updated my excel file to make it more user-friendly. I'll request admin to save it in download section as well. Regards. Ajay

Attached Files

•  Line sizing criteria as per different international standards.xlsx   43.05KB   871 downloads

[kkala]

Thanking ajaysatpute for his presentatation on line sizing criteria (needed study from my part to get its whole usefulness), below you can find notes on several views expressed in this thread.
1. I believe broad knowledge of line sizing criteria are useful to Chemical Engineer, for reasons explained in post No 11 and other posts. Consider it as empirical knowledge showing the direction to the ball park. Some of us have no such guidelines in the beginning of career, others cannot master line sizing criteria of "Employer" because their rationale is not known. Both cases concern me and probably a lot of others.
2. Limiting the subject to line sizing, technical "negotiations" usually concern few unclear cases, where e.g. Client requests next more conservative line size in a lump sum contract. At any case Contractor will specify the relevant pump or fan accordingly to fulfill guarantees and is responsible for smooth operation of the line. In such cases "knowledge is power". This is also true in certain big projects, when Contractor proposes its pipe sizing criteria and Client has to assess them.
3. Using other companies' current pipe sizing criteria may be illegal, but any intellectual property has an expiration date, after which it gets public domain. Once I signed a secrecy agreement expiring after 10-20 (most probably 10) years. Cheresourses must be aware of this legal matter concerning expiration of companies' practices / standards and is kindly requested for advice. This would be welcomed from any other member too.

Edited by kkala, 30 December 2012 - 10:24 AM.