how tight is too tight? 2

[macmet]

I started a new job recently at a district energy centre. And one of the parts of my job is construction supervisor for all the various energy units. And part of that job is ensuring everything meets requirements based on various testing, notably pressure tests.

At my last job, in a different industry we would have to do pressure tests, but they weren't critical and if the system held pressure for a couple hours we were just gave them a pass. No trending of pressure, etc.

But at this new job, we test to the consultant's required specs. And I find most tests are technically failing, but I feel like the test results show the systems are good enough to a warrant a pass. But regardless, they didn't meet the spec, the test failed and they have to redo it. And of course I'm the one that gets to tell the contractors, with years of experience, to do it all over again because they dropped 1 or 2 psi outside the allowed range.

Does anyone else feel like specifications sometimes are a little too tight? I feel like if the consultants were on the site looking at the systems, they'd give them a passing grade, but they're not, and it's me who is obligated to say that the test failed or take on the responsibility myself.

How do you guys handle that situation? If I was in the contractors shoes I'd think my company is ridiculous for these tight specifications.

Maybe I'm just venting over my frustration with consultants who are sitting in an office 100 kms away (no offense to those who are consultants).

 

[IRstuff]

"just give them a pass on the whole system since it is a non critical leak" If a leak were a non-critical, then it shouldn't be in a critical test path. Either that, or there should be a looser requirement for the non-critical areas. The fact of the matter is that the supplier proposed, and the client ostensibly accepted, the test procedure as written, hence the ongoing testing.

While retesting without correction is often done, and the next time the test is run, the article often passes. This is usually an indication of a unreliable test, and raises the issue of whether a critical leak actually exists, but just was caught the testing. That would be a bad deal all around.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[macmet]

Well I feel like I should let everyone know that I had the crew redo the test. And it passed. Pressure held constant the entire length of the test.

I agree with many of the comments made. I feel this spec is somewhat flawed but at the same time the crew approached it in a flawed manner as well. this second time, they were more careful with conditions (temperature variations) and the results were better. Too bad they didn't take those precautions the first time.

Anyway, I hope the next time they're working on our equipment they keep in mind the fact I will only pass a test that meets the passing criteria and they'll do it properly the first time.

I appreciate the comments though. I like getting input from other engineers who have been in similar situations.

Cheers.

 

[rb1957]

remember too, some industries (mine for example) are notorious for over-specifying and sometimes without justification.

i remember a job awhile ago when we were testing a system (a whole airplane's load of systems). we took the prime's spec's and determined we needed a really special ground cart to create the conditions required by the specs. when this was presented back to the prime the reaction was "what, are we building a plane that can't use a standard Hobart ground cart?" "no, we need this to cover the spec requirements." "well that's just dumb ... we never had to do this before (when we tested ourselves)"

 

[SylvestreW]

From a guy who works on both design & post-installation issues, it's surprising how many times the specs do NOT pertain to the operation.

Your job is definitely NOT to turn a blind eye and pass things. If you feel the spec is too tight, pass your comments up/across the chain, with all your reasoning, and see what your feedback does.

You never know, you may have someone thank you. Odds are though, you'll be politely ignored.

 

[plasgears]

My earliest engineering work had to do with justifying small mfg defects to the customer. These were rocket cases with small weld offsets in the skirts. My analysis showed acceptability, but the customer wanted to run a test. They set up an axial test at Huntsville, which passed without undue distress. The test justified my analysis, but the customer was not thrilled to be coaxed by the mfr to accept less than specified details.

In another company I helped introduce fracture mechanics analysis for structural welds with defects. That got the attention of a lot of people in USAF. There is a place for debating the means of accepting less than specified results in mfg.

 

[SiliconeAurora]

I have seen specs put on things for extremely dubious reasons. As I am a a more industrial, hands-on engineer, this can be a large problem since, as you all know, the tighter the spec, the tougher it is to create product within spec. One of my jobs is to intentionally create parts out of spec (purely for experimental purposes, of course) and then test them in ways that best realistically simulate actual use conditions to see if the high specs are justified.

It's not that I'm combattative with the design team. It's that I have the luxury of being able to relatively quickly test things like this when the design team never comes within 50 miles of the parts. We are able to provide them with data about how the parts hold up when certain parameters are loosened. And sometimes things fail dramatically, and sometimes they fail undramatically, and sometimes they're just worringly enough out of spec to make me not want to question it. But sometimes there's no realistic change there at all.

None of this whatsoever says that you can justify ignoring or getting wiggle room specs. Follow the specs vigorously while they're the specs. But I think it's healthy to question them in ways that are valid both from a design as well as a use perspective. You might find some "well, it's always been like that" type situations that can be worked around to the benefit of all.