Leaking Dryers and Scrubbers Located at Natural Gas Well Facilities

Introduction

In this article you will find the failure investigations of six 0.094 inch thick carbon steel vessels. These vessels were in service in natural gas well facilities; some functioned as dryers and were subjected to cyclic loads. Metallographic tests, hardness tests, and fracture surface scanning electron microscopy (SEM) examination results are presented for each of the vessels. The potential benefits of performing ultrasonic testing (UT) and radiographic testing (RT) while the vessels remained in service are discussed.

Design and Operating Conditions

The vessels were located at natural gas well facilities (see Figure 1); their design and operating conditions follow:

• The vessels do not require NDT during Manufacturing. With no NDT require- ments the vessels require a reduction in joint efficiency in accordance with Table UW-12 in ASME Section VIII, Div. 1.
• The vessels are fabricated for containing compressed air.
• The vessels have shell and head thickness values of 0.094 inch (3/32 inch).
• The vessels have a Minimum Design Metal Temperature (MDMT) of -20 °F.
• The vessels have a Maximum Allowable Working Pressure (MAWP) of 200 psi at 450 °F.
• The vessels have a diameter of 12 inch.

Their operating conditions are:

• Typical Operating Pressure: 120 psig.
• Operation Temperature: ~350 C.
• Service Life: 3 – 7 years.
• Leaks: Six vessels have leaked in six years.
• Operating Media: mainly natural gas; they may contain some produced water, some CO2 and some chlorides.
• Containing: desiccant.

Depending on their service, their pressure may or may not fluctuate. In one type of service:

• Two dryer towers operate in sequence.
• One is in service for several minutes at pressures such as 120 psig while the other is purged with dry gas at a lower pressure. This allows the desiccant to regenerate.
• The fluctuations are rapid.

However, vessels can be relocated to different wells where they are not subjected to pressure fluctuations.