Hot tapping - bad experiences?

[Scipio]

I've got a project coming up involving a size-on-size tie in to a high pressure (ANSI 900# line class) natural gas pipeline. I'm looking at three or four ways of doing it, probably one of the cleanest would be hot-tapping - assuming I figure out a way to bring the operating pressure in the pipeline down during the actual tapping procedure. The biggest problem I have with hot tapping right now is the size-on-size (8" into 8&quot factor, and the fact a number of people who wouldn't have a problem tapping, say, a 4" leg into an 8" run, don't trust size-on-size. Just wondering if anyone out there has ever had a real problem doing this (assuming it's properly engineered in the first place) or if it's one of those "I know a guy who knew a guy" stories originating from an improperly engineered application.

 

[ColCol]

By all means, pick up the phone and call T.D. Williams. They will design and execute this tap using a split tee and a flange with a well completion plug. 900# SOS hot taps are specialized jobs. Call a specialist.

 

[MJCronin]

Scipio,

By all means, make sure that you contract with a "hot tapping" firm with HP natural gas experience!!!! Size-on-size is rhe most difficult tap

There is an API Standard that governs hot tapping of systems.....API-2201

TD Williams (and others) have websites to gain more information.

MJC

 

[Scipio]

Actually I have been in touch with TD Williams, plus a number of other firms supplying hot tapping equipment, and then other companies that actually perform the procedure. I know what they have to say, but I wouldn't have a job very long if I made engineering decisions based of the recommendations of one vendor. I've also read 2201 - it's more of a construction guideline than a design standard, plus CSA's hot tapping recommendations on pipeline systems. What I was hoping for was to find someone on the operator side who's had first hand knowledge of problems associated with it. My company has done the engineering for hot taps before for this client, just not a size-on-size tap, which was the question.

 

[ColCol]

Perhaps you spoke to the wrong department at TD Williams. While they do manufacture and sell equipment, they are also one of the few design/service contractors with experience in the type of tap you want to do.

As far as experienece, I have done two SOS taps like the one you wish to do. Both were done with a split tee, flange top and a completion plug. One was 8" the other 10", C.S. natural gas line. The reduced size taps you may have done before may have used a weldolet and a weld by flange ball valve. This will be different.

I have never had a "bad" experirnce with a hot tap, if I ever do you will see it on the evening news.

Basic warnings include pre heat and trying to reduce the pressure and the flow durng the proceedure. While reduced pressure is easy to understand, the reduced flow will aid in reducing the amount of heat that is carried away by the gas during the fillet welding processes used to secure the split tee to the carrier pipe.

 

[Scipio]

Ahh, thanks ColCol, that's the kind of feedback I was hoping for.

 

[hottapr]

Reducing pressure for hot tapping has been often a misleading attempt at preventing burn through situations. Internal surface temperature and welding techniques are the predominant factors. As well the type of fitting you are using is an important for long term integrity of your pipe. There have been significant advances in welding technology and Red Flame Hot Tap Services in Red Deer, AB. are the only true full service hot tap company with both mechanical and materials engineers with lots of high pressure Hot Tap experience.

 

[ColCol]

Hottapr, is that a commercial for Red Flame? Can you tell us about some of the significant advances in welding technology for carbon steel pipe?

Reducing the line pressure simply reduces hoop stress, it has little to do with burn through. As with most pipeline technologies, it's OK if the crews do the right things for the wrong reasons, as long as they do the right things.

 

[itchy]

I agree with hottapr's comments regarding size on size hot taps. Red Flame has the engineering expertise. They also have experts for buttering welding techniques. We haven't used Red Flame but are considering it. We have experts in our pipeline company that do the same work. We have used TD Williamson size on size split tees (30", 24", 16&quot using the buttering welding techniques to install the saddles at 80% MOP, with great success. The split with lock-o-ring flanges were purchased from TDW. They also included a flow-thru fitting to accomodate pigging the run pipe.

 

[hottapr]

Sorry for my enthusiasm, they have just completed alot of high profile work for our company. I agree that reducing pressure only reduces hoop stress, which is my point often people reduce line pressure thinking that they are reducing the chance of burn through and are in some instances making it worse for they reduce the flow( heat extraction) so the internal surface temperature increase. Burn through can occur at 100psi or 1,000psi. Red flame uses what they call a buttering technique to build wall thickness and temper their weld metals. they have a retired Nova individual who really knows his stuff.

 

[Scipio]

Just to wrap up the thread, hot tapping was eliminated as an option on this project for a variety of reasons (including tapping into a 1600 psig line) - actually I'm familiar with Red Flame, my company's used them before on a number of occasions, and I had reviewed their abilities prior to posting here. I was just looking for third party input specifically into experience with size-on-size hot taps, but it's irrelevant now. Thanks all the same!