Factory Acceptance Test for heat exchanger

[suraiya]

Hi,

Our company had awarded a contract to design and construct a gas-gas heat exchager (shell and tube)type for offshore natural gas field application. Gas tapped from high temp. wellhead will be utilized in the shell to transfer heat to low temp.gas which will be inside the tube. This is necessary, as with current temperature, the low temp. gas will form hydrate once pressure dropped acroos the choke valve if it is not heated.

I'm currently reviewing the inspection and testing plan submitted by the vendor. Could someone hilite to me major things that people tends to overlook when inspecting a shell and tube HX?

 

The basic test is the hydrotest. Depending on the tube material, mill tests such as eddy current and underwater may also be performed. Weld tests may also be important such as UT or Dyecheck of tubejoint welds.

Performance testing is a much more complicated question but may be performed according to ASME testing criteia.

 

[pmover]

suraiya,

in addition to HeatTransSpec, recommend that you review Section 7 in Standard API-660, Shell and Tube Heat Exchangers for General Refinery Service. This is a useful standard / guideline to use.
for a gas-gas shell-tube exchanger, it will be signficantly larger than plate-frame type. but since process conditions are not known, will have to assume the exchanger type fits the application.

 

[Shmulik]

Requirements of TEMA - Standards of the Tubular Exchanger Manufacturers Association:
RCB-1.31: Standard Test - The exchanger shall be hydrostatically tested with water. The test pressure shall be held for at least 30 min. The shell side and the tube side are to be tested separately in such a menner that leaks at the tube joints can be detected at least one side. when the tube siden design pressure is the higher pressure, the tube bundle shall be tested outsude of the shell only only if specified by the purchaser and the construction permits. welded joints joints are to be sufficiently cleand prior to testing the exchanger to permit proper inspection during the test. The minimum hydrostatic test pressure at the room temp. shall be 1.5 times the design pressure, corrected for the temp, except where where other Code requirements govern.
RCB-1.311: Liquids other than water may be used as a testing medium if agreed upon between the purchaser and manufacturer.
RCB-1.32 Pneumatic Test - When liquid cannot be tolerated as a test medium the exchanger maay be given a pneumatic test in accordance with the Code. It must be recognized that air or gas is hazardous when used as a pressure testing medium. The pneumatic test pressure at room temp. shall be 1.25 times the design pressure, corrected for temp, except where other Code requirements govern.

Hope it helps.

 

[hafiz]

Thanx Shmulik. It helps me too as I'm currently preparing specs for similar kind of heat exchanger.
What about tests performed to check functionality of the heat exchanger - normally what kind of tests are done, and what are familiar 'tricks' of manufacturers that I need to be wary of?

 

[TD2K]

What do you mean by 'functionality' Hafiz?

 

[hafiz]

What I meant was what are standard tests performed to check that the heat exchanger will work, ie desired temperature can be achieved within desired time. In another word , how to check if desired Q (rate of heat transferred, Btu/hr ) is achievable during factory test?

 

[TD2K]

Heat exchangers are rarely, if ever, factory tested for heat transfer performance. I've never heard of this being done though that isn't to say it can't or hasn't be done.

I have been involved in verifying the performance of some heat exchangers AFTER they have been involved in the operating plant.

First problem is simply having the fluids available that you expect in the field in the shop.

The heat exchanger the original poster was talking about was a high pressure natural gas exchanging heat with a low pressure natural gas stream, there is no way to practically mimic these fluids in the shop. I suppose you could 're-rate' the exchanger with water or air (or some common fluids) at some 'available' temperature(s) and pressures and then request a performance but this is not normal.

Inspection of heat exchangers in shops is more of a mechanical inspection. Checking of materials, weld procedures, sizes, QA records, etc versus the approved drawings.

If anyone has any other information, jump in here.

 

[Shmulik]

Hafiz,
I completely agree with TD2K opinion (from HE manufacturer’s point of view). I’m not familiar with any standard performance check. Our manufacture based on a pre-simulating by a reliable program of heat exchanger design and rating (HTRI is the best one for my opinion –

http://www.HTRI.net).

A real performance check requires a research facility that a manufacturer can’t effort. The best you may do is measuring of inlet and outlet temp, pressure and capacity in order to make sure that your design is satisfactory. Remember that fouling factors, over design etc can’t be checked.
Regards, Shmulik.

 

[MJCronin]

Hello...

TD2K, as usual, is correct and posts good advice.. It would be unusual for a shop to performance test a "custom built" heat exchanger. Standard HX designs, (such as would be used for example on a diesel oil coooler) are shop tested.

It should be pointed out here that the common practice for "shell and tube" heat exchangers is to provide extra surface area in the form of a specified "fouling factor".

It is probably cheaper for all concerned to provide extra area for the system than to go through any type of performance test.

hope that this helps.............................

MJC

 

[Graybeard]

TD2K and others are correct that heat exchangers are rarely performance tested, but there are exceptions. Most mfgs are not set up to do perfromance tests, which may limit available vendors. But some are. You need to weigh the risks vs the added cost involved.

We recently purchased 2 high high temp >1000F electric gas heaters to heat N2 and H2 gas. We paid over $5000 to test both with N2 prior to acceptance. This amounted to around a 20% premium for our heaters. Had we tested with H2 the mfg would have doubled cost as he would not test in his facility but subcontract test to another.

Although a 20% premium might seem excessive, it was peanuts compared to what it would cost to rip out and replace, loss of prduction, etc. had they not worked when installed. And in fact, problems were encountered during the test which required slight physical modifications. It took the vendor over a week to figure out problem and provide a fix.

This is not to say performance test should always be done. How different is this one from others of similar size, application.

Seldom can vendor do actual performance test, so you have to figure out what you can test to provide a datapoint that you can use to ensure that success is max at min cost.