2 replies to this topic

[jawbkk]

Hello All,

 

We have a situation where we need to replace a 24 year old DeZurik plug valve with a gate valve on a sewage treatment plant.

 

The 24 bolts are rusty particularly the lower half as the arrangement is located in a 1m deep pit which often has raw sewage in it due to drain down operations.

 

As an 'early works' plan, the construction team are looking to 'hot bolt' by taking one out and putting a bolt back in its place prior to the main shutdown.

 

I was challenged in the construction meeting yesterday for stating that the existing bolts must not be re-used.

 

My response was that the lubrication may not have been present at the time and that the torque ratings for such a rusty bolt cannot be relied upon. Despite this, there insistance was that 'it was only a temporary period'.

 

I am really not comfortable about this and wondered whether there are any guidelines around that I can use to confirm my request for new bolts?

 

In addition to this, as the bolts are hard to remove, they would like to grind off the head of the bolts (as there are no nuts on the other side of the Dezurik valve as the holes are blind into the valve body). By grinding, they will cause a certain amount of damage to the rear of the flange. This I think can affect the seating of the washer and the correct contact with the bolt.

 

I would be grateful if anyone who has had any experience in removing bolts such as these to offer some advice.

 

Unfortunately I am on my laptop and not my works computer so cannot attach a photograph. But hopefully I have made everything clear!!

 

Many thanks

John

UK

[Atttyub194]

Dear John

 

Good day!

 

After 24 years in service, it is very difficult to predict the health of the bolts. The safest approach is not to use these  bolts again

Generally speaking bolt fails due to following reasons

1. Overstress fatigue
2. Corrosion
3. Hydrogen Embrittlement
4. Stress Corrosion Cracking

Please do access the health with respect to Corrosion and embritlement when using existing bolts.Additionally, it would not be possible to remove the bolts easily and during dismentling there is a strong probability that your team may break the bolt and at the end they may  replace some of the bolts durin this exercise.

 

Your team might be aware of using a penetrant like PB Blaster, Liquid Wrench or WD-40 and probably they will not start the job with grinding as first option. They may have the option to apply heat via the blue flame of torch, which is really tricky, if they stuck up.

 

Regarding your query on replacement schedule , please note the following:

1.  To my knowledge there is no particular standard recommending such replacement and it is not mandatory to replace the bolts on each disassembly. This is not the case with the Gasket
2. If the bolts have been used in high-temperature applications, and there is no capability to test a representative few from the batch, it's a good idea to replace old with new  one since there may be a risk of hydrogen embrittlement.
3. If QA not employed periodically or other means of control when bolting critical flanges, then bolts should be replaced after every dis assembly. This should be done because there would be no idea whether the bolts had been tightened properly.
4. If the cost of failure isn't high and there is no hazard in case of failure, reuse the bolts may be considered.
5. Use of calibrated torque wrenches and following defined tightening patterns does not constitute QA or control. On the contrary, it often leads to unexpected failure because it provides a dangerous false sense of security.

Please do realize that probably in your case the failure would not result suddenly/ immediately, unless your maintenance team stuck up with removal. If I recall my memory,  a Fertilizer Unit had done similar exercise on a high pressure exchanger  down stream control valve ( 160 bar)  and abandoned the replacement plan in turnaround. Later on , probably after 5-6 months 2-4  bolt failed and on investigation hydrogen embrittlement was detected in the bolts.

 

Hope above will help you for taking the correct decision

 

Please do share your experience once you have carry out the exercise

 

Best regards and God Bless You

[jawbkk]

Many thank Attyub 194,

 

I will put some of these very important points to the construction team over this next week.

 

Tomorrow I will also attach a couple of pictures to show you why I was so concerned.

 

The fact that the joint could leak is an important safety concern as the whole pumping station drywell would flood.

 

We have 'HAZCON's in the UK where we discuss hazards in construction. I have already told them to buy new bolts and I have been over-ruled. At least they cannot say they were not warned if there is a problem.

 

Maybe they might get away with it, but it is very unprofessional approach to not listen to other people advice.

 

Will keep you posted on the progress so it will be nice for other members on this Forum to have the shared experience.

 

Best Regards

John