Corrosion & Sch 40 Threaded Pipe

[CRG]

I am working on a design build and the customer's specifications require threaded 1-1/2” Sch 40 connections on a 12” steam main. The pressure is not a problem, 85 psi; however, I am concerned with corrosion. The majority of these 1-1/2” thread-o-lets are on the bottom of the line and blocked in. This creates a situation where condensate will form creating a liquid/vapor interface next to the thread line, and in my opinion this would be the first place corrosion problems would show up. I submitted a DCVR discussing the problem and asked the customer if they intended these taps to be welded or Sch 80 connections. I was instructed that it was their intent to have Sch 40 threaded pipe as per their specifications and there is no concern for corrosion.

What do you think? Could this be a major corrosion issue? Is it prudent to put so much faith in maintaining the chemistry of the boiler feed water where corrosion would not be an issue in places like this?

 

[MikeHalloran]

I know zip about boilers. I know that people who are eventually tasked with maintaining feedwater chemistry may be incautious, erroneous, or illiterate.

"I was instructed" makes it sound like you didn't get a response that you could use in court, and you wish you had.

It smells like one of those situations where something bad is going to happen, and the person who said there is "no concern for corrosion" is going to:
- Deny ever saying any such thing.
- Claim (s)he wasn't authorized to say it anyway.
- Assert that it's your fault, because you're the expert.

I think that _you_ know it's an issue, and that you know your customer (or your boss) is being imprudent.

I think you're struggling with what is really an ethics question, not a technical question.




Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[CRG]

Mike, thank you for your response. The customer is the U.S. government, and they are being represented by the United States Army Corps of Engineers. Correspondence is formal with questions submitted in writing and answers in writing as well. This project is 90% engineered by the USACE with the balance being engineered by the contractor. I am working for the contractor and submitted a DCVR (design clarification/verification request) discussing the potential problem. The contractor was instructed by the USACE to use the material as shown in contract drawings. The contractor agrees with me that using Sch 40 for this application is short sighted. It seems that the USACE is invested in their design and specifications and they do not want to issue a change order. I am not sure how to proceed. If I am overly concerned, this is not an ethics issue. I was hoping to get some responses or technical references that might help me decide how much I want to push this issue. Note: I have not and will not participate in the area of the design that calls for threaded Sch 40 pipe. I only noticed this in the contract drawings generated by the USACE. The contractor will install the pipe per USACE’s design unless the USACE can be motivated to write a change order for Sch 80 pipe.

 

[hacksaw]

you've raised the issue and done what you could, about all you can do is keep it in the file for future reference.

even corporations have such "rules" and it doesn't pay to fight them on your project.

 

[Montemayor]

CRG:

It's my opinion that you are technically correct in every engineering point you've brought out. That has been my personal experience and I would have done the same thing you've done. Furthermore, hacksaw reinforces your action: you've done the right thing which, although although unheeded, is still the correct (& only) thing to do from a professional and ethical point of view. You've given your customer the best of your knowledge and initiative - the ball's on his court.

If you haven't documented your advisement, I suggest you do so by sending a confirming memo or even an email to the effect that you appreciate their response to your suggestion and the issue will be followed according to their written specifications -- period. This puts you on record as trying to do your best but always subservient to your client's wishes - which is what is expected of all of us. These so-called minor items have a way of coming back to cause a lot of future grief and complaints. You've done the right and professional thing. It's not a matter of who's right; it's more of doing what's right.

Good Luck.

 

[waskillywabbit]

Follow the CYA principle and document, document, document that fact that you've told them that you don't think the SCH 40 pipe is adequate and state the reasons. If they choose to ignore the advice of the person they hired to engineer the project, then there is no more you can do.

Good luck.

Brian

 

[unclesyd]

Just remember to do your CMA in a professional way as some might take it as the Smart A__ approch. This happened to an acquaintance several years ago concerning Sch5 304 SS pipe on a local government job overseen by the same group. This fiasco cost the US taxpayers tons of money as the replacement line they went with a Sch80 316 SS where a properly designed Sch10 304 SS as initially suggested would have been adequate. He took the fall for his company in “ROF” where his ex-company could stay on the bid list.

Watch E-Mails as they tend to get erased in government circles. Be selective with who you copy in, but have at least one on your side that understands the situation.

They do kill the messenger.

 

[NozzleTwister]

I question whether your client contact has the engineering background or experience to address your concerns or if he reviewed them with someone who does. I would guess probably not.

Your concerns are on target, not just for corrosion, but also for mechanical strengh and robustness. Granted you may have some wall left for pressure after considering corrosion allowance, thread allowance and mill tolerance but it won't be much. Couple that with the SIF's for threaded connections and you going to have a hard time qualifying those joints if you do any kind of stress analysis. For vents, drains or branches, your asking for a failure if these connections get bumped.

For industrial installations, Sch. 80 is the norm for the MINIMUM wall on threaded connections and Sch. 160 is common for nipples at vents, drains and between the header and first block valve on small bore branches.

I would very tactfully approach your client again with your concerns spelled out with the reasons why and ask that the appropriate person in their organization review them if you can't talk to that person yourself one-on-one. From your post it seems your client is not a team player but rather wants to beat his chest and make sure you know who is calling the shots.

Engineering contractors that I have worked for in the past have had their own minimum standards that were used even when the clients minimum was less. If the client wouldn't pay for that we absorbed it. A well documented paper trail isn't the only way to CYA. Adhering to good design practices (whether they want it or not) is another.

Should a falure occur, your company's going to get the black eye whether it was their fault or not. People rarely hear the outcome of these kinds of lawsuits but they'll rember who engineered the system that failed. The best approach in my opinion is to do your best to insure it never comes to that.

Good luck,

NozzleTwister
Houston, Texas