Question and Answer 141-150

Question 150: i hope wermac continues on for many years more

Werner, I have visited your webpage since way back in 2007 when I was just cutting my teeth on the world of piping. It certainly has come a long way from the modest webpage I used to visit.

I am using this oportunity to thank you and commend you for the work you've done with Wermac. Thanks to the twist and turns of life I am once again involved with piping and has helped me once more.

I wish you success and I hope wermac continues on for many years more. Also, that it continues being profitale for you.

Kind regards

Answer from Werner Sölken

Hi, Paul
Your mail ended up in my spam box; do not ask me why.

Today, April 1, 2015, I have seen your email for the first time, while you have sent in December 2014. Sorry about that!

I'm not going to stop my website ... as long as I live, I will pass my knowledge to others.

greetings Werner


Question 149: how to calculate the acceptable leakage rate for mechanical seal?

Hi there,

I really appreciate your website and the effort you take in knowledge transfer. I am a Engineering student at a University in Canada and had a question:

API 682 std says max acceptable leakage rate for mechanical seals is 1000ppm (vol) vapor or 5.6 g/h for liquid per sealing face. It goes on to specify that when testing at 25 psi, the acceptable leakage rate should not be more than 2 psi in 5 minutes.

My question is how to calculate the acceptable leakage rate for mechanical seal at other psi, for example when testing at 5 or 10 psi?

Kiran Thomas

Answer from Werner Sölken

Hi Kiran Thomas,

Yes, you can calculate acceptable leakage for mechanical seals.

But, I can not give you an answer to your question; i do not know!

I hope you can appreciate my honest answer.

greetings Werner

Question 148: can we have multiple types of pipes in one pipeline?

Hi Werner,

I went through your website, and it's really great.

Well, I had a question to ask. Can we have multiple types of pipes in one pipeline? I've been asked by our client to use Seamless pipe for one portion of the pipeline, and ERW type for the other portion. Would that be technically ok from standards' viewpoint? The pipeline is 16" & 29KM long, and service is wet sour gas.

Can you respond to this question?

M. Asim Zakir
Pipeline Engineer

Answer from Werner Sölken

Hi Asim,

Yes it is possible and permissible to use more than one type of pipes.

The internal, calculated pressure for a pipe, determine the type of pipe.

With a pipeline of 29km you have for example 200bar at the beginning of the pipeline, and at the end 180bar.

Somewhere in the pipeline, for example, then ERW type can be used, because the type of that (welded) pipe is suitable for the lower pressure.

Below, two references, who also tell us something about your question.

pressure rating (question 143)

pipeline segmentation (scroll down}

greetings Werner

Question 147: what is the best connection? pipe nipple 1/2 (ANSI) to 1/2 tubing?

I want to make a connection with a pipe nipple 1/2 (ANSI 21.3mm OD, threaded one end) to 1/2 (tubing 12.7mm OD).
What is the best connection?

Principal work preparation
Robert D.

Answer from Werner Sölken


Hi Robert,

What is the best connection? Tell me...
The shortest connection that you can make is:
Use a connector as shown above
Female:1/2 inch NPT (pipe OD 21.3mm) with a possibility to connect to 1/2 tubing.

By the way, it is ASME, and not ANSI.

greetings Werner

Question 146: have you ever thought about selling your website?

I am contacting you because I am interested in purchasing advertising for a 1 year term on your website, "". I'm working with a small but reputable centrifugal pump company in Mississauga, ON.
What would be the cost of a small html 5 banner ad or textual ad on your
webpage for a 1 year term?
Also, I just want to throw this out there. Have you ever thought about selling your website?
If so may I ask the price?
You can connect with me through my email which is ...

Answer from Werner Sölken

Hi Sarah,

Currently you can only choose the position of an 728x90 advertising, top, middle (between text) and at the bottom.

Your question: Have you ever thought about selling your website?

My website is my profession!
I'm glad I could help a lot of people with my information.
I'm not doing this for money, but for the future of people who want to make the same buisness career, as I do.

greetings Werner

Question 145: why its always advised that reducer must be closer to the control valve?

Hi Werner,

Other doubt im having is, why its always advised that reducer must be closer to the control valve in control stations.

Robin Varghese

Answer from Werner Sölken

Hi Robin,

Control Valve Sizing

The line should be determined by an economic pipe sizing program.That will make the fluid velocity in the pipe stay within certain boundaries (not too slow or not too fast). If the flow is too slow, the pipe is probably larger than necessary which is more expensive to purchase and install. If the pipe is too small, the high fluid velocity will be noisy and probable erode the piping system.

The control valve needs to be sized using a pressure drop that is about equal to the system pressure drop (pipe friction + filters + heat exchangers ++). If the valve is sized with an arbitrary pressure drop of 10 pounds, it is a crap shoot as to it's ability to control. If the valve pressure drop is too low, the system will control the fluid flow, not the valve. If the pressure drop is too high, the valve may be much smaller than the pipe, noisy and probably wear out in a relatively short period of time. Also, the small valve, relative to the pipe size, may be under a great deal of stress when the pipe expands and contracts due to temperature changes.

So, in my vast experience as a valve sizer, they are usually smaller than the pipe. In order to get the valve to fit in a larger size pipe, you need 2 pipe reducers, one on each side.

If the valve and pipe are the same size, something is wrong. If the valve is larger than the pipe, everything is wrong and somebody spent a significant amount of money for a large valve and 2 reducers.


greetings Werner

Question 144: why 10" schedule 80 cs pipe has higher wall thickness, than 10" schedule 80s ss pipe?

Dear sir,

This is Robin Varghese from mumbai,India. Thanks for sharing detailed informations regarding piping engineering in your website. I have one doubt regarding pipe wall thickness.

Why 10" schedule 80 CS pipe has higher wall thickness, than 10" schedule 80s SS pipe?


Answer from Werner Sölken

Hi Robin,

I can not give you a clear answer to your question. I have searched in all the documentation available to me, but I could find an answer.

ASME says that there are differences, but why, that is not defined.

Short summary ASME B 36.19, Stainless Steel Pipe:

Pipes NPS 12 and smaller have outside diameters numerically larger than their corresponding sizes. In contrast, the outside diameters of tubes are numerically identical to the size number for all sizes.
The wall thicknesses for NPS 14 through 22 of Schedule 10S; NPS 12 of Schedule 40S; and NPS 10 and 12 of Schedule 80S are not the same as those of ASME B36.10M. The suffix "S" in the schedule number is used to differentiate B36.19M pipe from B36.10M pipe. ASME B36.10M includes other pipe thicknesses that are also commercially available with stainless steel material.
The size of all pipe is identified by the nominal pipe size.
The manufacture of pipe NPS 1/8 through NPS 12 is based on a standardized outside diameter (OD). This OD was originally selected so that pipe with a standard OD and having a wall thickness that was typical of the period would have an inside diameter (ID) approximately equal to the nominal size.
Although there is no such relation between the existing standard thicknesses - OD and nominal size - these nominal sizes and standard ODs continue in use as "standard."
The manufacture of pipe NPS 14 and larger proceeds on the basis of an OD corresponding to the nominal size.

greetings Werner

Question 143: what do we understand for pressure rating when...?

Hello Werner,

I want to ask you something that I have not been able to find in your great web page.

What do we understand for Pressure rating when talking about PIPES?

I understand that the Pressure rating of a Flange refers to how "robust" and "big" is the flange to withstand a certain pressure, so that the bigger pressure, the bigger is the Pressure class of the flange and the bigger is the flange (bigger dimensions, heavier, etc.)

However, I do not understand the concept of Pressure rating when talking about Pipes because the thickness of the pipe is specified by the SCHEDULE. How does it affect to the pipe having a Pressure rating 150# or 300#, for instance?

Thank you very much.
Kind regards,
Pedro Alberto Perez Puerta

Answer from Werner Sölken

Hi Pedro,

Only for flanges you can talk about pressure rating. This is based on ASME 16.5 Class 150, Class 300 etc..Pressure rating does not apply to pipes.

If you want to fabricate a pipeline, according to a pressure rating of class 150, then the maximum pressure for these flanges are based on the ASME pressure rating tables.

Pipes and fittings are calculated and tested for internal pressure and various other features. These tests determine the wall thickness (schedule) of a pipe.

Usually this will be documented in a pipe specification (Pipe Spec.), which tells you the wall thickness for a pipe or fitting.

greetings Werner

Question 142: what is the formula used to calculate thickness of...?


Have a nice day,what is the formula used to calculate thickness of hydro test blind flange?

Thanks & Regards
Sameer Moosa

Answer from Werner Sölken

Hi Sameer Moosa,

Take a look at: calculate thickness of spacer

greetings Werner

Question 141: i'd like to thank you for your brilliant website

Hi Werner,

I'd like to thank you for your brilliant website. I've been working in the gas industry as a technical writer for only a few years, so I often come across new and unfamiliar concepts. I seldom find that what I need is not on your site.

Great work!
Rob Napier

Answer from Werner Sölken

Hi Rob,

In the past, I have worked often with AMEC.

Drafters had no computer, but an ordinary drawing board.
Maybe I'm old-fashioned, but "those were people who could make real drawings", which were easy to read for everyone.

That time is over, I have to accept drawings that ask more questions than provide answers.

By the way, thanks for your compliments on my website.

greetings Werner

Questions & Answers


Top of Page